Kidney and liver tumors in rats from 4,4'-methylene bis (2-carbomethoxyaniline).

4,4'-Methylene bis (2-carbomethoxyaniline), also known as methylene-bis methyl anthranilate (MBMA), was added to the diet of male and female ChR-CD rats for up to two years at levels of 0, 1500, and 15,000 ppm. Fifty rats of each sex were used at each dietary level. Female rats at both dietary levels of MBMA had a lower body weight gain and lower food efficiency values than did the controls. High-level males and females showed a slight anemia; all other clinical laboratory tests were within normal limits. MBMA caused slight degenerative histologic changes in the liver and kidney of both sexes at both dietary levels. High-level males developed a statistically significant increase in kidney and liver tumors when compared to controls (p less than 0.05, Fisher's Exact Test, one tail). High-level females had an elevated kidney tumor incidence compared with controls (p less than 0.10). There was a statistically significant lower incidence in pituitary tumors in high-level males (p less than 0.05) and in high-level females (p less than 0.10) than in controls. High-level females had a lower incidence of mammary tumors (p less than 0.05) compared to controls. MBMA was considered to be a carcinogen of moderate potency in rats, since tumors were not found until 18 months on test using a comparative large dose (1.5% of diet).


The production of hydroxamic acid metabolites of nitrosobenzene by Chlorella pyrenoidosa.

The ability of the green alga Chlorella pyrenoidosa to convert nitrosobenzene (I), phenylhydroxylamine (VI), aniline, and nitrobenzene to hydroxamic acid metabolites was investigated. Only nitrosobenzene and phenylhydroxylamine were partially converted to N-phenylacetohydroxamic acid (Va) and N-phenylglycolhydroxamic acid (Vb), with the latter compound being the major product. The possible mechanisms for the formation of these hydroxamic acid metabolites are discussed. The most plausible explanation for their production is through the interaction of the nitroso group with certain intermediates of thiamine-dependent enzymes. The conversion of phenylhydroxylamine to the hydroxamic acids probably is the result of initial oxidation to nitrosobenzene. Apparently, C. pyrenoidosa lacks nitroreductase and aniline hydroxylase activities, since no metabolic conversions of aniline or nitrobenzene were observed. The potential environmental significance of hydroxamic acid production from nitrosoaromatics is discussed.


Six month inhalation exposures of rats and guinea pigs to aluminum chlorhydrate.

Groups of rats and guinea pigs were exposed, by inhalation, to 0.25, 2.5, and 25 mg/m3 of aluminum chlorhydrate (ACH) for six months to study the effects of a common component of antiperspirants. Similar groups of animals of both species exposed to clean air served as controls. The ACH was generated as a particulate dust using a Wright dust feed mechanism. After six months of exposure, animals were sacrificed. Decreases in body weight were seen in rats exposed to 25 mg/m3 of ACH. Marked increases in lung weights and significant increases in lung to body weight ratios were seen in rats and guinea pigs exposed to 25 mg/m3 of ACH. The lungs of all rats and guinea pigs showed significant dose-related increases in aluminum accumulation when exposed to either 0.25, 2.5, or 25 mg/m3 of ACH. The lungs of all rats and guinea pigs exposed to either 2.5 or 25 mg/m3 of ACH contained exposure-related granulomatous reactions characterized by giant vacuoled macrophages containing basophilic material in association with eosinophilic cellular debris.


Pulmonary changes induced by low-level ozone: morphological observations.

This study defines the surface and ultrastructural changes which occur in mouse lungs during the early stages of continuous low-level ozone exposure. Swiss-Webster mice were exposed for 35 consecutive days to 0.5 ppm ozone, a level of oxidant gas which simulates levels occurring during an episode of severe smog in urban areas of the California south coast air basin. Groups of mice were killed on day 7, 21, or 35 of exposure and their lungs excised and examined by light microscopy, scanning electron microscopy, and transmission electron microscopy. Lung damage was most severe at the transition zone from terminal bronchiole to alveolar duct. This centriacinar lesion consisted of (1) increased numbers of macrophages within proximal alveoli of alveolar ducts, (2) clusters of type 2 pneumonocytes lining these proximal alveoli, (3) changes in surface characteristics of Clara cells, and (4) hyperplastic nodules of bronchiolar epithelium within terminal bronchioles. Inflammatory cell infiltrates were reduced in numbers at 35 days of exposure as compared to 7 days of exposure, but the hyperplastic bronchiolar epithelium persisted and, in fact, increased in severity as exposure length increased. Although inflammatory cell infiltrates were observed in proximal alveoli of alveolar ducts, the hyperplastic bronchiolar epithelial changes were observed throughout the lengths of terminal bronchioles examined. The variability in response to ozone insult of nonciliated cells in the terminal bronchiole of rats, mice, and monkeys is discussed.


Liver and urinary bladder tumors in dogs from 3,3'-dichlorobenzidine.

Six female beagle dogs were given, by capsule, a daily oral dose of 100 mg of 3,3'-dichlorobenzidine (DCB), 3 times per week for 6 weeks, then 5 times per week continuously for periods up to 7.1 years. The DCB test was terminated after 7.1 years. Six untreated female beagle dogs served as controls for several tests and were sacrificed after 8.3 to 9.0 years on test. All 6 DCB dogs had an elevated plasma glutamic-pyruvic transaminase activity during the first 3 years on test; two dogs showed persistent elevation throughout the test. One DCB dog, sacrificed in extremis after 3.5 years on test, had no tumors. Another DCB dog, sacrificed in extremis after 6.6 years on test, developed an undifferentiated carcinoma of the liver with metastases to many organs; this dog also had a papillary transitional cell carcinoma of the urinary bladder. Of the 4 remaining DCB dogs sacrificed after 7.1 years on test, 3 developed hepatocellular carcinomas and all 4 had papillary transitional cell carcinomas of the urinary bladder. No liver or urinary bladder tumors were found in the 6 control dogs. DCB was found to be carcinogenic for the liver and urinary bladder in dogs under the conditions employed (p less than .025, Fisher's Exact Test, one tail).


Inhalation studies with polyurethane foam dust in relation to respiratory tract carcinogenesis.

Male and female Sprague-Dawley rats were exposed to freshly generated polyurethane foam dusts, in concentrations averaging 8.65 mg/m3 air, for 6 hours daily 5 days a week over a period of 12 weeks. For comparison the same numbers of rats were exposed to titanium dioxide (TiO2) (15.95 mg/m3 air), which is a known inert dust, and to air alone, as controls for the same exposure period. This exposure caused no noticeable changes in appearance, behavior, or body weight. The average lifespan values were within the normal range. A high tumor rate was seen in all groups, with no significant differences among the groups. No indications of a carcinogenic effect of the inhaled dusts on the respiratory tract could be established. The numerous tumors found in the different organs and groups were of a spontaneous nature. The observed lung-reactions are discussed.


Liver and lung tumors in dogs from 4,4'-methylene-bis(2-methylaniline).

Six female beagle dogs were given, by capsule, a daily dose of 100 mg 4,4'-methylene-bis(2-methylaniline) (MeMDA), 3 times per week for 6 weeks, then 5 times per week for 5 weeks, at which time the dose was reduced to 50 mg 5 times per week, continuously for periods up to 7.0 years. Six female beagle dogs were kept as untreated controls for several studies and were sacrificed after 8.3 to 9 years test. MeMDA dogs developed renal atrophy with an elevated blood urea nitrogen during an approximate six-month period prior to death or being sacrificed in extremis. As three of three MeMDA dogs that survived for 5.2 years to 7.0 years developed hepatocellular carcinomas and two of the three dogs also developed primary lung tumors, with no liver or lung tumor in six control dogs, MeMDA was considered to be carcinogenic for the dog (liver tumors: p less than .05; lung tumors: p less than 10; Fisher's Exact Test, one tail).


Percutaneous absorption of radiolabeled TRIS from flame-retarded fabric.

Surface tris-(2,3-dibromopropyl) phosphate (TRIS) was removed from flame-retarded polyester fabric by benzene-hexane extraction and replaced with 14C-TRIS. Sections of the radiolabeled fabric (10 X 12 cm) were placed in contact with the clipped skins of rabbits, and urine and feces were collected over a 96 hr period. The cloths were allowed to remain dry or were moistened with either urine or simulated sweat. A similar collection of urine and feces was performed following i.v. injection of 14C-TRIS. From the results of these experiments, it can be calculated that up to 17 percent of the radiolabel on the cloth penetrated rabbit skin over the 96 hr period of exposure. Most of the excreted radiolabel appeared in the urine, with the kidney being the organ of highest specific radioactivity. The highest absorption of radiolabel occurred in the urine-moistened cloth group. Moistening the cloth with simulated sweat produced no increase in absorption over that seen with dry cloth.


The effects of discontinuing administration of high levels of 2-acetylaminofluorene on the transitional epithelium of the mouse urinary bladder.

The purpose of this study was to investigate the effects of discontinuing the administration of a high level of 2-acetylaminofluorene (2-AAF) on the transitional epithelium of the urinary bladder of BALB/c mice. Mice were fed 500 ppm of 2-AAF for 6 and 13 weeks and sacrificed at periodic intervals after discontinuing the compound. Urothelial hyperplasia regressed slower in the animals receiving the 2-AAF for 13 weeks than those receiving 2-AAF for only 6 weeks. A small number of bladder carcinomas were seen in the animals fed 2-AAF for 13 weeks and sacrificed at 26 and 39 weeks. Our results suggest that exposure to a high level of a carcinogen even for a relatively brief period may result in the development of carcinomas after the cessation of exposure.


Urine cytology as a medical surveillance tool: a study of variability in interpretation of urine cytology slides.

This study examines the value of urine cytology as a medical surveillance technique in the industrial setting through an evaluation of the variability in interpretation of urine cytology slides. Urine samples were collected from 259 individuals for cytological examination. The slides were read by pathologists and screeners at one large Army medical center and separately read again by an independent pathologist at another Army medical center. The two independent readings for each of the 259 cases were compared. The comparison indicated that overall agreement was fairly high in reporting the presence or absence of inflammatory cells, red blood cells, and atypical (including metaplastic) cells. However, considering positive findings of the presence of red blood cells or atypical cells only, significant differences between the two independent readings were noted when the sign test was applied. Implications of these findings are discussed in light of the use of urine cytology as a medical surveillance tool in occupational medicine.


Report of a workshop on urothelial lesions in mice.

Thirteen pathologists with a variety of backgrounds met at the National Center for Toxicological Research in Jefferson, Arkansas, to discuss and exchange views on urothelial lesions in mice. Fifteen slides of urothelial lesions from mice were distributed to the participants prior to the meeting. A consensus was reached on 11 of the lesions, 8 of which were neoplastic and 3 of which were non-neoplastic. The author encourages such workshops and feels that they are meaningful and beneficial in understanding the significance of such lesions.


Testicular atrophy and impaired spermatogenesis in rats fed high levels of the methylxanthines caffeine, theobromine, or theophylline.

Experiments were designed to determine the effects of feeding the methylxanthines caffeine, theobromine, or theophylline to 4- to 6-week-old male rats at a dietary level of 0.5 percent for periods ranging from 14 to 75 weeks. In the first two experiments, Osborne-Mendel rats were fed the test substances alone or in combination with sodium nitrite to test the hypothesis that these amines might nitrosate in vivo to produce toxic nitrosamine compounds. The compounds failed to produce neoplastic or preneoplastic lesions, but a significant positive finding was the occurrence of severe bilateral testicular atrophy with aspermatogenesis or oligospermatogenesis in 85-100 percent of the rats fed caffeine or theobromine. In a third experiment the methylxanthines were fed to Holtzman rats for 19 weeks to determine whether testicular atrophy would be induced in a second strain of rat. The testicular effects were similar to those in Experiments I and II but were more pronounced. Caffeine and theobromine induced testicular injury in nearly all rats. Theophylline induced severe testicular atrophy in 14 percent of the rats, mild to moderate atrophy in 71 percent, and had no effect in 15 percent. The relative testicular toxicity of the methylxanthines was caffeine, most potent; theobromine, slightly less potent; and theophylline, considerably less potent. Somewhat variable atrophic changes of the accessory sexual organs (epididymis, prostate, and seminal vesicles) accompanied the testicular changes. Cytogenetic analysis of testes from caffeine- or theophylline-treated rats revealed a significantly reduced number of mitotic cells in the caffeine-treated group. Plasma testosterone concentrations were significantly elevated in the theobromine group and somewhat elevated in the caffeine-treated group; this correlated morphologically with an apparent hyperplasia of interstitial cells in severely atrophied testes in these groups. Plasma cholesterol concentrations were significantly increased in the caffeine and theobromine groups. Possible sites and mechanisms of actions of the methylxanthines in the induction of testicular atrophy and impaired spermatogenesis are discussed.


NCTR computer systems designed for toxicologic experimentation. I. Overview.

Established in 1971 by the Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA), the National Center for Toxicological Research is committed to the study of long-term, low-dose effects of potentially toxic substances, including carcinogens. The Scientific Information Systems Division (SISD) facility provides logistic support for complex experiments involving large numbers of test animals. Animal population at the Center, including the breeding colony and animals on experiment, can be as high as 80,000. Each animal must be accounted for, fed and watered under strict control, and continually observed. From birth to final examination, an individual animal might have as many as 3,000 individual elements of information associated with it. This paper introduces a series of reports dealing with an integrated and comprehensive system of experiment planning and implementation (including information gathering, classification, analyses and reporting), employing state-of-the-art data processing techniques. This extensive use of computer technology has permitted the collection, proper classification, and rapid retrieval of virtually error-free data, resulting in cost-sensitive experiment planning.


Statistical analysis of urinary delta-aminolevulinic acid (ALAU) excretion in the white-footed mouse associated with lead smelting.

ALAU in white-footed mice trapped in the vicinity of a lead smelter has been measured to study the biological effect of lead smelting operations and the rate at which the ALAU level diminishes after removing animals from contaminated environments. The statistical method which has been developed for this purpose shows that the ALAU levels are initially higher among animals near the smelter and diminish to a common level after 5-6 weeks. The statistical method is generally applicable to a variety of physiological functions which exhibit a decay curve with respect to time.


NCTR computer systems designed for toxicological experimentation. II. Experiment start-up system.

The Experiment Start-Up System (ESS) developed and implemented at the National Center for Toxicological Research constructs models from information contained in experimental protocols. These models may then be used to project resource requirements and related schedules. Each experimental model provides information from which management can determine the raw resources such as quantity of food, water, bedding, cages, animals (sex, strain, species), chemical, facilities, and manpower needed for conducting the experiment. Based upon this information, management can determine if the required resources are available and determine the most feasible "start" date for the new experiment. In addition, the information provided by the experimental model assures the Principal Investigator that the protocol requirements are thoroughly understood by participating technical support groups and that quality control elements of the ESS and other integrated systems will provide a means for accurately monitoring the experiment.


Methylmercury induced biochemical and microsomal changes in the rat liver.

The change in the levels of DNA, RNA, protein, glucose-6-phosphatase, and microsomal enzymes in the rat liver following exposure to methylmercury was studied. The turnover rate of the membranes was also investigated by means of radioactive glycerol. A marked increase in microsomal enzyme levels, with no increase in smooth endoplasmic reticulum, was found one to four hours following administration. A delay in incorporation of radioactive glycerol and more rapid degradation of microsomal membranes were also detected as a result of mercury intoxication. These observations suggest an instability of the microsomal membranes which would be responsible for the early increase in microsomal enzymes upon homogenization. A general inhibition of the microsomal enzymes and proteins was found 1-2 days after mercury administration. The inhibition of glucose-6-phosphatase activity, however, was not noted until day 5. Most of the enzymatic activities returned to normal between days 5 and 8. A reduction of DNA and protein was found in the liver homogenate after 2 hours of intoxication. However, no change in the RNA level was detected.


A toxicity estimation model.

A statistical model has been developed for estimation of acute toxicity. The model, currently operational for rat oral LD50, permits the estimation of rat oral LD50 for untested chemical compounds. Only the chemical structure, partition coefficient, and molecular weight for a compound are needed for estimation purposes. The chemical structure is partitioned into substructural fragments using the CIDS fragment keys. A regression model is developed on the basis of 425 compounds. A test of the regression equation with 100 compounds not used in its design shows that 56 percent of the compounds are predicted with less than 0.4 log unit deviation between extimated and measured LD50. This toxicity estimation model can be readily adapted to other species and to other measures of toxicity by the use of suitable design data bases. The model also identifies the contribution to toxicity of the fragments and physical characteristics. The use of this model can materially reduce the amount of toxicological testing for new compounds. It also permits the ranking of potentially toxic compounds to allow the most likely candidates to be tested. The method may also prove applicable to the determination of optimum dosages for new drugs.


Hormonal carcinogenesis: a novel hypothesis for the role of hormones.

A testable hypothesis on the role of hormones in carcinogenic processes is presented. The hypothesis has been based on the findings that (1) hormones regulate cell division in normal cells, (2) successful neoplastic transformation requires hormonal stimulation of cells receiving carcinogenic insult, (3) normal cells have finite divisional capabilities, whereas neoplastic cells possess infinite divisional capabilities, and (4) normal cells, when present in high ratio, inhibit the growth of neoplastic cells. According to the hypothesis, hormones are considered to be neither mutagenic nor carcinogenic. (Carcinogen is defined as an agent which initiates normal-to-neoplastic transformation). Instead, they play a dual role in carcinogenesis. First, hormones are considered necessary for the fixation of the cell genome neoplastically transformed by carcinogens. Second, hormones, by enhancing the rate of cell division, shorten the life span of normal cells, thus causing a reduction of the normal- to tumor-cell ratio in the population--a condition which facilitates growth of tumor cells.


Utility of pharmacokinetics in designing toxicological protocols and improving interspecies extrapolation.

Key terms such as pharmacokinetics, pharmacodynamics, time course-concentration, and dosimetry and how they apply to predictive toxicology are defined and differentiated. The importance of utilizing pharmacokinetic techniques in teratology and developmental toxicology are discussed from the viewpoints that (1) agent's access to target tissue is modulated by the placenta, (2) interspecies sensitivities differ, (3) dose-response curves are steep, and (4) dosimetry information improves the validity of regulatory standards. We review the teratology literature where attempts were made to correlate embryonal/fetal exposure to teratogenic endpoints. The strengths and weaknesses of these papers are discussed as well as our suggested changes in their protocols, which would have improved interspecies extrapolation.


Liquid-tissue behavior and differential cohesiveness during chick limb budding.

Emerging chick limb-buds at first grow only in length, not width. The growth parameters of limb mesoderm--cell shapes, distributions, division patterns and cleavage orientations--are incompatible with representations of this tissue as an elongating solid composed of proliferating but immobile cells. We observe that samples of both early limb mesoderm and also surrounding flank mesoderm round up like liquid droplets in organ culture. Therefore, liquid-like tissue rearrangments, including cell shuffling movements and neighbor exchanges, may occur in limb and flank mesoderm during in vivo limb budding. If so, differences in limb-flank surface tension properties would have to be present to keep these two fluid cell populations segregated into distinct tissues and properly positioned underneath limb and flank ectoderm. Previous studies have shown that tissue surface tensions are reflected in the spreading behavior of fused pairs of cell aggregates. To determine whether or not they possess differing surface tension properties, we pair excised pieces of early leg-bud, wing-bud or intervening flank mesoderm with pieces of 5 3/4-day heart or liver in hanging drop cultures. For more rapid determinations of relative liquid-tissue cohesiveness than can be obtained in conventional, long-term experiments, aggregate pairs are fixed shortly after fusion. Since partial-envelopment configurations depend upon relative aggregate sizes as well as their tissue surface tensions, new procedures are used to deduce relative aggregate cohesiveness from cross-sections of these briefly fused aggregate pairs. The envelopment tendencies of aggregates fixed 6--9 h after fusion are similar to those fixed 15--19 h after fusion: heart tends to surround leg; heart and wing surround each other with similar frequencies, but flank tends to surround heart. Also, liver tends to surround leg and wing, but flank tends to surround liver. When the effects of relative aggregate size are taken into account, these non-random, tissue-specific patterns of aggregate envelopment indicate that the relative cohesiveness of these tissues falls into the sequence: leg greater than heart congruent to wing greater than liver greater than flank. The in vitro behavior of early limb-bud and neighboring flank mesoderm in these studies suggests that they are not simply mechanically identical portions of a single liquid tissue. We have previously proposed that early limb-bud mesoderm may act like a non-dispersing, cohesive liquid droplet which is embedded within a less cohesive fluid layer of flank tissue (and which is molded distally into paddle-shaped conformations by solid-like limb ectoderm and/or subjacent extracellular matrix). This proposal is not only compatible with the growth parameters of limb-bud mesoderm in vivo, but is also consistent with our observation that flank mesoderm surrounds tissues which surround limb mesoderm in these aggregate-fusion experiments. Our model suggests that differences in the surface tension properties of limb vs...


On the origin of the ciliary ganglion in birds studied by the method of interspecific transplantation of embryonic brain regions between quail and chick.

The development of the ciliary ganglion with reference to the site and cells of origin have been investigated by the method of quail-to-chick transplantation of embryonic fore-, mid-and hindbrain regions, and by the method of transplantation of cranial neural crest from specific brain levels. In chimaerical embryos, quail cells originating from the graft end up in the ciliary ganglion, only when the graft is from the midbrain level of quail embryo donors. In fore- and midbrain grafts the ciliary ganglia of chimaerical embryos are composed of chick cells only. The results indicate that the mesencephalon is the principal site for the precursor cells of the ciliary ganglia and clearly rules out any contribution to the ganglia from either the forebrain or hindbrain levels. In interspecific transplantation of cranial neural crest, quail cells originating from the graft are observed consistently in the ciliary ganglion of the operated side when the grafted neural crest material is derived from the mesencephalon of quail embryo donors. On the basis of the evidence provided, it is concluded that mesencephalon is the principal site and the cranial neural crest of this level the source from which the precursor neurons of the ciliary ganglia are derived.


Mutagenesis and cell transformation of mammalian cells in culture by chemical carcinogens.

In the process of in vitro cell transformation, normal cells, which have an oriented pattern of growth and a limited life span in vitro and which are not tumorigenic, are converted into cells that have a hereditary random pattern of growth, the ability to grow continuously in culture, and the ability to form tumors. Such heritable phenotypic changes may arise from alterations in gene expression due to somatic mutations after interaction of the carcinogen with due to somatic mutations after interaction of the carcinogen with cellular DNA. Our studies have indeed shown (a) that metabolically activated carcinogenic polycyclic hydrocarbons which have been shown to bind to cellular DNA induce somatic mutations in mammalian cells; (b) that there is a relationship between the degree of mutant induction and the degree of carcinogenicity of the different hydrocarbons tested; and (c) that the somatic mutations were induced by metabolites rather than by the hydrocarbons themselves. In the case of benzo(a)pyrene (BP), a very common carcinogenic polycyclic hydrocarbon, its 7,8-diol-9,10-oxide was identified as the major mutagenic and cell-transforming metabolite. Based on these studied, it was possible to estimate the genetic target size for cell transformation by comparing in the same cells the frequency of cell transformation and mutation for ouabain resistance (which is presumably due to a mutation at one locus) induced BP and by one of its major metabolites. The results indicated that the target size for transformation is 20 times larger than that determined for ouabain resistance. This suggests that cell transformation, as determined by a hereditary pattern of cell growth, may be due to a mutation and that this mutation can occur in one out of a small number of the same or different genes.


DNA synthesis inhibition in HeLa cells as a simple test for agents that damage human DNA.

Inhibition of HeLa cell DNA synthesis by DNA-damaging agents as a test for mutagenic carcinogens has been investigated further. Several mutagens and/or carcinogenic agents not previously assayed for DNA synthesis inhibition were tested and found to be positive. The effect of two DNA-damaging agents administered simultaneously was investigated: With ultraviolet light (UV) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) the effects were partly additive, whereas with MNNG and ICR-170 they were not. When UV was administered simultaneously with hydroxyurea (HU), a non-DNA-damaging inhibitor of DNA synthesis, the effects of the DNA-damaging agent were still evident after HU was removed and the HU-induced DNA synthesis inhibition reversed. Therefore, although the test probably cannot determine whethter there are one or more DNA-damaging agents in an unknown mixture, the presence of a powerful DNA synthesis inhibitor that is not a DNA-damaging agent will not mask the effects of a DNA-damaging agent in the same sample. Despite the fact that ICR-170 induces little DNA repair in xeroderma pigmentosum (XP) cells, which are deficient in excision repair, the inhibition of DNA synthesis induced by this agent was less in XP cells than in HeLa cells. The inhibition of DNA synthesis by MNNG was also less in XP than in HeLa cells. Therefore, contrary to expectations, the use of a repair-deficient cell did not increase the sensitivity of the test. Various in vitro mammalian cell tests are compared. Assays for unscheduled DNA synthesis are much less sensitive to intercalating agents, such as adriamycin, and to X-rays than are assays for inhibition of DNA synthesis but takes longer and requires more specialized skills than does measurement of DNA synthesis inhibition. Finally, the in vitro HeLa DNA synthesis inhibition test is compared with the in vivo DNA synthesis inhibition test with mouse testes.


Allophenic mice in cleft-palate investigations.

T1Wh (Rb (5;19)1Wh), an albino strain of mice not previously used in the investigation of cleft palate (CP), is homozygous for a (5;19) Robertsonian translocation which provides conspicuous chromosomal markers. Preliminary studies in this laboratory revealed that CP is induced in all the offspring of T1Wh females treated with 2.5 mg of cortisone acetate on days 11-14 of pregnancy and that palatal closure is accomplished at a later morphological and chronological age than in C57BL/6J strain mice. The latter strain had a CP frequency of 42% under similar experimental conditions. Eight- to 16-cell embryos were aggregated in the following combinations: T1Wh in equilibrium T1Wh, C57BL/6J in equilibrium C57BL/6J and T1Wh in equilibrium C57BL/6J. The resulting allophenic blastocysts were transferred to pseudopregnant C57BL/6J recipients which were given the above cortisone treatment and killed on the 18th day of pregnancy. CP was found in all of the 48 T1Wh in equilibrium T1Wh fetuses, 4 (20%) of of 20 C57BL/6J in equilibrium C57BL/6J fetuses and in 17 (26.2%) of 65 T1Wh in equilibrium C57BL/6J fetuses. Analysis of chromosome preparations from the palates of the T1Wh in equilibrium C57BL/6J fetuses demonstrated that there is a positive correlation between the presence of CP and the percentage of susceptible cells in the palate (P less than 0.02). Other data suggest a possible growth advantage in favor of C57BL/6J cells in the palates of T1Wh in equilibrium C57BL/6J allophenic mice.


Statistical analysis of teratologic data: problems and advancements.

A large scale replicated dose-response teratology study of 2,4,5-T was done in mice. Variability and variance of fecundity parameters and fetotoxicity endpoints are discussed. Another study on rats indicated less variation among teratologic endpoints than in mice. Calculations for the number of animals in strains of mice and rats needed to detect a 5 percent and 10 percent reduction in mean fetal weight or increase in resorptions are given. We concluded that at least 3 replicates with appropriate numbers of pregnant animals are needed to estimate variance for comparison among laboratories or among species. The utility of these calculations for standardizing teratologic studies is discussed.


Participation of neural crest-derived cells in the genesis of the skull in birds.

The differentiation of cephalic neural crest cells into skeletal tissue in birds has been observed using the quail-chick nuclear marking system, which is based on specific differences in the distribution of the nuclear DNA. Chimaeras were formed by replacing a fragment of cephalic neural primordium of a 2- to 12-somite chicken embryo by the corresponding fragment isolated from an equivalent quail embryo. The participation of the graft-derived cells in the formation of the skull of these embryos was studied on histological sections after Feulgen and Rossenbeck staining. Cells from the prosencephalic neural crest migrate into the frontal nasal process and mix with the mesencephalic neural crest cells in the lateral nasal processes, around the optic cupule and beneath the diencephalon. In addition, the mesencephalic neural crest cells form the bulk of the mesenchyme of the maxillary processes and mandibular arch, whereas the rhombencephalic neural crest cells become located in the branchial arches. The origin of cartilages of the chondrocranium and bones of the neurocranium and viscerocranium has been shown in the chimaeric embryos: the basal plate cartilages, occipital bones, sphenoid bones and the cranial vault are mainly of mesodermal origin. However some parts have a dual origin: rhombo-mesencephalic neural crest cells are found in the otic capsule, and the frontal bone, the rostrum of parasphenoid and the orbital cartilages contain diverse amounts of prosencephalo-mesencephalic neural crest cells. The squamosals and the columella auris are formed from mesectodermic cells as are the nasal skeleton, the palatines and the maxillar bones. The mesectodermal origin of mandibular and hyoid bones and cartilages was already known. From these results it appears that the cephalic neural crest is particularly important in the formation of the facial part of the skull, while the vault and dorsal part are mesodermal and cartilages and bones found in the intermediary region are of mixed origin. The presence of mixed structures implies that the mesoderm and the mesectoderm are equally competent towards the specific inducers of these bones and cartilages. This correlates with the equivalence in differentiation capacities already shown for cephalic mesodermal and mesectodermal mesenchymes.


Factors to consider when selecting animal models for postnatal teratology studies.

This presentation identifies some of the factors which should be considered when choosing a particular animal as a model to predict postnatal teratogenic hazards to man. The developmental pharmacologist-toxicologist must consider in concert the potential interactions of a xenobiotic on the mother, her placenta, her fetus, and her nursing young. Since the physiology of each of these components is in a state of dynamic flux during gestation and/or postnatal development, the critical time at which to expose the mother or her progeny to a chemical will vary widely from species to species and organ to organ. The identification of critical periods during the perinatal period may be quite difficult because the physiological or behavioral changes in the adult organism which signal that perinatal teratogenic effects have occurred are frequently subtle. Much research is still needed on the comparative aspects of maternal, placental, fetal, and neonatal pharmacokinetics and pharmacodynamics. We are not ready to intelligently evaluate large numbers of chemicals as potential postnatal teratogens for man.


Influence of embryonic stage on the transdifferentiation of chick neural retina cells in culture.

Neural retina cells from chick embryos up to 15 days of incubation can transdifferentiate in culture into both lentoids and pigment cells. Some transdifferentiation into pigment cells but none into lentoids was found in cultures of 17-day embryonic neural retina. No transdifferentiation occurred in cultures of neural retina from embryos immediately before hatching. In general, lentoids and pigment cells develop more rapidly and in greater numbers in cultures of neural retina from the earlier embryonic stages, and lens-specific crystallins also appear earlier and accumulate in greater amounts in these cultures. Delta crystallin accumulation is much greater in transdifferentiating cultures of early embryonic neural retina, wheras alpha and beta crystallins become proportionately more prominent in cultures of late embryonic neural retina. Traces of alpha and beta but not delta crystallin are detectable in 60-day cultures of 17-day embryonic neural retina. Analogies between these results and the ontogeny of crystallin polypeptides in lens cells in vivo are discussed.


Gastrulation in the mouse: assessment of cell populations in the epiblast of tw18/tw18 embryos.

Homozygous tW18 embryos die prior to organogenesis. They develop gross abnormalities shortly after primitive streak formation. Anatomically, the lesion appears to be confined to the mesoderm with that tissue showing ultrastructural deficiencies and abnormal migration (Spiegelman & Bennett, 1974), and failing to develop in teratomas produced from mutant embryos (Artzt & Bennett, 1972). Analysis of growth rate by determining cell number increase, and by mapping mitotic activity and planes of cleavage in the epiblast shows that the mutant embryos are small but paradoxically show overall a very high mitotic activity, approximately double that of their normal litter mates. They also show a marked disorientation of the planes of cleavage in most of the epiblast. In pre-primitive streak embryos, before gross abnormality is detectable, two types of embryo can be found. One group constitutes the small embryos which also show the mitotic disturbances characteristic of the later stage mutants. The second group, larger embryos, do not show mitotic abnormalities. The tW18 allele thus seems to act several hours before primitive streak formation. Since there is no difference in the amount of cell between mutant and normal embryos until 6.75 days p.c. it seems that arrest in division is the cause of the elevated mitotic index in mutants. Significantly a small region of the epiblast in mutant embryos is free of the mitotic abnormalities characteristic of the tissue as a whole. This region is the so-called proliferative zone (Snow, 1977) and the data suggest that it may be from this region that some of the ectoderm of the later embryos is produced.


Intercalary regeneration around the circumference of the cockroach leg.

Epidermal cells from different circumferential positions around the femur of Blabera craniifer can interact to form an intercalary regenerate. Removal of a longitudinal strip of integument (cuticle plus epidermis) from any position around the circumference leads to the cut edges healing, localized growth and intercalary regeneration of the missing section of the circumference, so that the resulting femur is approximately normal in size and pattern of cuticular structures. Grafting a longitudinal strip of femur integument into a different circumferential position on the host femur confronts epidermal cells from different positions along both the inner and outer longitudinal graft/host junctions. In numerous different situations this results in local growth and intercalary regeneration of that section of the circumference normally separating graft and host positions, by the shorter route around the circumference. Confrontation of opposite positions results in the intercalation of either of the intervening half circumferences. In one opposite confrontation, between mid-anterior and mid-posterior, there was also a third result where graft and host healed together, provoking no intercalary regeneration. Grafts made with reversed proximal/distal polarity show that a confrontation between different circumferential positions gives the same result, regardless of the proximal/distal levels involved, hence circumferential position is an independent aspect of position on the femur. These results strongly suggest that epidermal position is not specified with respect to two transverse axes running through the epidermis and internal tissue of the leg, but that there is a continuous circular sequence of positional values running around the circumference, in the epidermis. This is analogous to but independent of the sequence previously shown by Bohn (1967) and Bullière (1971) to run proximal/distal along a leg segment. Hence epidermal position on the femur is specified in two dimensions and can be represented in terms of the French, Bryant & Bryant (1976) polar co-ordinate model. Interactions along the edges of the strip-grafts conform to the Shortest Intercalation Rule (French et al. 1976). At the proximal and distal ends of strip-grafts intercalation restores normal sequences of positional values where possible. However, where the graft, together with the intercalary regenerates formed at the longitudinal graft/host junctions and the adjacent host tissue formed a complete sequence of circular values, then a supernumerary distal regenerate was formed, in agreement with the Complete Circle Rule of French et al. (1976). The problem of generating a continuous circular sequence of positional values by one or more circumferential gradients, is briefly discussed.


Induced segmental reorganization in sabellid worms.

Processes of regeneration and reorganization are analyzed in two sabellid polychaetes. Abdominal pieces of Branchiomma nigromaculata, during head regeneration, ordinarily reorganize only a fraction of the number of segments typical of the thorax. In pieces transected in the vertical plane, but obliquely with regard to the main axis of the worm, the extent of reorganization is greatly enhanced. The same number of segments transform on the right and left sides, the surviving damaged segments transforming on one side and a corresponding number of more posterior, undamaged segments transforming on the other. Reorganization is shown, in abdominal pieces of Sabella melanostigma, to involve destruction and inversed dorso-ventral reconstitution of all parapodial structures in the segments affected, the conversion of intestine to thoracic stomach, and the invasion of previously abdominal segments by a pair of large nephridia which grow posteriorly after being formed in the basal portion of the head blastema. All three events exhibit a time-graded character, staring soonest at the anterior end and progressively later posteriorly, and apparently independently of one another. Abdominal type segments are formed only from the anterior region of the caudal, prepygidal zone of growth, successively, never by transformation. The dorso-ventrality of abdominal segments is the inverse of the thoracic, with the antero-posterior polarity unchanged, in all circumstances. Only during posterior regeneration from thoracic segments are thoracic segments produced from the posterior zone of growth, but only two or three are thus formed, the zone of growth then changing to the production of abdominal segments. It is concluded that the feature of sabellid-serpulid organization is the complete inversion of the dorso-ventrality of the posterior zone of growth as the result of emancipation from the generally dominating dorsal field emanating from the anterior end.


Transfilter induction of kidney tubules as a function of the extent and duration of intercellular contacts.

The kinetics of kidney tubule induction were examined in transfilter experiments by varying the time of transfilter apposition, the porosity and pore size of the filters, and the culture conditions. Transfilter contact between the interacting cells is established within an hour when cytoplasmic processes emerge through the interposed filter; then a further 16-24 h are needed for completion of induction. This lag is a function of thickness and pore size of the filter, and is not reduced by precultivation of the inductor on the filter. Material that accumulates on the far side of the filter during such cultivation displays no morphogenetic activity. The intensity of the mesenchymal response was roughly quantified and shown to be a function of pore size, pore density and duration of transfilter contact.


Surface properties of Entamoeba: increased rates of human erythrocyte phagocytosis in pathogenic strains.

The assertion that ingestion of human erythrocytes is restricted to invasive strains of Entamoeba histolytica has not been evaluated previously by comparative studies. In this report we describe the in vitro ingestion of human erythrocytes by pathogenic and nonpathogenic Entamoeba. Microscopic evaluation of erythrophagocytosis by eight different Entamoeba grown in culture revealed that strains of E. histolytica isolated from cases of human dysentery show a much higher rate of erythrocyte ingestion than nonpathogenic strains. However, all strains are able to phagocytize erythrocytes. The extremely high rate of phagocytic activity shown by pathogenic E. histolytica could be one of the properties related to the pathogenicity of this parasitic protozoan.


The origin and antigen-dependent distribution of IgA-containing cells in the intestine.

The aims of this paper were to establish the origin of cells producing IgA antibody to cholera toxoid in the lamina propria of the small intestine and to define the role of antigen in their distribution. The use of Thirty-Vella loops made it possible to restrict antigenic challenge to a defined segment of the intestine in rats which had been primed i.p. with toxoid in Freund's complete adjuvant. The anti-toxin-containing cells (ACC) which appeared in the draining thoracic duct lymph after challenge of a loop were almost all of IgA specificity and their numbers were proportional to the length of intestine exposed to antigen. The abolition of this cellular response which occurred when Peyer's patches (PP) were removed from a loop before challenge and the failure of mesenteric lymphadenectomy significantly to affect the response indicated that ACC originated exclusively from PP. Cell transfer studies showed that although nonrecirculating large lymphocytes gave rise to ACC in the lamina propria, some of the recirculating small lymphocytes also developed subsequently into ACC. Counts of ACC in the lamina propria of challenged loops were consistently greater than in nonchallenged loops although some ACC were always present in the latter. However, a time-course study on the appearance of ACC in the lamina propria of cannulated rats given a single dose of thoracic duct lymphocytes from immunized donors demonstrated that ACC continued to accumulate and persist in challenged loops but only appeared transiently in nonchallenged loops. These transients did not migrate from the lamina propria back into the lymph and they presumably died in situ. The increase in the number of ACC in loops which had been challenged with antigen was probably due both to cell division in the lamina propria and to the development of new ACC from recirculating lymphocytes which had been recruited into the loop. Thus, the cells which give rise to intestinal ACC can migrate into the lamina propria independently of antigen, but antigen has a profound effect on the location, magnitude, and persistence of the response.


Structural and functional differences between the H-2 controlled Ss and Slp proteins.

Based on functional and structural data, it is concluded that the Ss protein in the mouse expresses the activity of the fourth component of complement. Removal of the Ss, but not of Slp, antigen correlates with a high degree of significance (P less than 0.001) with decrease of C4 hemolytic activity. In phenotypically Slp negative mice the plasma/serum levels of Ss correlate with the C4 activity (P less than 0.001). Structurally, Ss is a 209,000-mol wt protein, consisting of three covalently linked polypeptide chains (alpha,beta,gamma). Treatment of Ss with C1 cleaves a 7,000-8,000-mol wt fragment from the alpha-chain. Slp is also a three chain covalently linked protein of 209,000 daltons, however its three chains differ in size from those of the Ss protein. Slp does not express hemolytic activity and its alpha-chain is not cleaved by C1.


Maturation of bone marrow lymphocytes. II. Development of Fc and complement receptors and surface immunoglobulin studied by rosetting and radioautography.

Radioautographic DNA labeling and rosetting techniques were combined to study the development of surface IgM, Fc, and complement receptors (FcR, CR) on small lymphocyte populations in mouse bone marrow. [3H]thymidine was either infused continuously to label newly formed cells for periods up to 4 days, or injected daily, 21--35 days before use, to label a sample of long-lived cells. Bone marrow cells were incubated with sensitized sheep erythrocytes to detect surface IgM, FcR, and CR, respectively, and examined radioautographically after cytocentrifugation. During [3H]thymidine infusion, marrow small lymphocytes lacking surface markers were the first to show [3H]thymidine labeling. Most of these cells became labeled by 4 days (IgM--ve, 89%; FcR--ve, 92%; Cr--ve, 88%). Labeling of small lymphocytes bearing surface IgM, FcR, and Cr began after an initial lag and increased to high values by 4 days (IgM + ve, 73%; FcR + ve, 82%; CR + ve, 83%). Labeled IgM + ve small lymphocytes formed progressively larger rosettes as cell age increased. Some proliferating large lymphoid cells formed rosettes for IgM, FcR, and CR. Labeled long-lived small lymphocytes expressed surface IgM, FcR, and CR, the incidence of each receptor being uniformly high (38--43%) and the rosettes tending to be larger than those formed by newly formed lymphocytes. In double-surface marker studies, FcR and CR rosettes were formed by some IgM--ve small lymphocytes as well as IgM + ve cells in the marrow. After transfusion of marrow cells from donor mice infused with [3H]thymidine for 24 h, many labeled newly formed lymphocytes homed into the splenic red pulp of unlabeled syngeneic recipients. Subsequently, these cells showed a rapid increase in the incidence of rosettes for surface IgM, FcR, and CR, together with a progressive enlargement of each type of rosette. Although all the labeled small lymphocytes recovered from the spleen developed both surface IgM and FcR by 3 days, only approximately one-half developed CR. The results demonstrate that most of the small lymphocytes bearing FcR, CR, and surface IgM in mouse bone marrow are newly formed indigenous cells. Each receptor becomes detectable by rosetting soon after the small lymphocytes are first produced. The newly formed, marrow-derived small lymphocytes are able to continue their development of surface IgM, FcR, and CR after migrating into the spleen, consistent with a maturation of primary B lymphocytes. In addition, the data indicate the genesis in mouse marrow of a non-B lineage of lymphocytes (notably, IgM--ve FcR + ve cells.). A minority of small lymphocytes bearing IgM, FcR, and CR in mouse marrow are long-lived cells, presumptive recirculating immigrants, differing in receptor status from the newly formed cells. The results are discussed with regard to the heterogeneity of marrow lymphocytes and proposed models of primary B lymphocyte and null lymphocyte production.


Radiation leukemia in C57BL/6 mice. III. Correlation of altered expression of terminal deoxynucleotidyl transferase to induction of leukemia.

The expression of terminal deoxynucleotidyl transferase (TdT) in the thymus and bone marrow of irradiated mice has been examined. Mice given the leukemogenic regimen of irradiation of four weekly doses of 175 rads starting at 1 mo of age show a long-term elimination of TdT activity in the bone marrow and a reduction of TdT activity in thymocytes. In such mice, the reappearance of normal levels of TdT in the thymus appears to only be associated with the onset of overt leukemia. This effect on TdT expression was shown to be uniquely associated with the leukemogenic regimen of irradiation in that nonleukemogenic irradiation or variations such as bone marrow reconstitution or age which reduce leukemias did not show the same phenotypic effects on TdT expression. The basis for the loss of TdT-positive cells was shown not to be due to the lack of the requisite factors involved in differentiation, but rather to the ability of leukemogenic doses of irradiation to reduce or eliminate an inducible bone marrow stem cell. These results are discussed with respect to the possible mechanisms involved in radiation-induced leukemias in mice.


Role of phagocytosis in the activation of macrophages.

Macrophages were obtained by peritoneal lavage from untreated mice or from mice which had received either Brewer's thioglycollate broth or a suspension of streptococcus A cell walls intraperitoneally 4 days before. 3 h after harvesting, adherent cells from untreated mice were allowed to phagocytose zymosan, formaldehyde-treated sheep erythrocytes, or latex beads. Phagocytosis was stopped after 1 h and culture was continued for up to 10 days. Phagocytosis of zymosan or sheep erythrocytes triggered the immediate release of lysosomal glycosidases, stimulated the synthesis of cellular lactate dehydrogenase, and induced the delayed production and secretion of plasminogen activator . No such changes were observed upon phagocytosis of latex. Although all three particles used were phagocytosed, only zymosan and sheep erythrocytes stimulated glucose oxidation via the hexose monophosphate shunt. Similar findings were obtained in macrophages elicited with streptococcus A cell walls after zymosan phagocytosis. Thioglycollate-elicited macrophages, however, which were already secreting lysosomal hydrolases and plasminogen activator, could not be activated further by zymosan. The results of this study show that macrophages become activated after phagocytosis of particles that stimulate the activity of their hexose monophosphate shunt. The triggering event appears to be the burst of shunt activity itself or shunt-related biochemical reactions rather than phagocytic uptake per se or particle-dependent complement activation by the alternative pathway. Once initiated, macrophage activation proceeds independently of the intracellular fate of the ingested material .


Inheritance of antibody specificity V. Anti-2-phenyloxazolone in the mouse.

Antibodies to hapten 2-phenyloxazolone (phOx) of all BALB/c and DBA/2 mice have the same idiotype and the same major (public) isoelectric focusing pattern whose main spectrotype is called Ox-1. Neither of these characteristics could be readily demonstrated in anti-phOx antibodies of C57BL, C3H or LP mice; these antibodies were heterogeneous, and lacked public spectrotypes. Also, a fine specificty difference could be demonstrated between anti-phOx antibodies of BALB/c and C5MBL mice; the latter have a higher relative affinity than the former for a structural analogue of phOx (2-o-iodophenyloxazolone). The three BALB/c characteristics were inherited in congenic and recombinant inbred strains as an allotype-linked block, defining a new VH marker, VHphOx. Murine anti-phOx antibodies were found to exhibit three types of conservatism: (a) Every individual mouse of strains BALB/c, DBA/2 or BAB-14 had an almost indistinguishable IEF pattern. (b) These patterns (and the cross-reactive idiotype) remained virtually unchanged during an immunization course of 70 days. (c) An identical idiotype (and in some cases IEF pattern) was present in mouse strains of five different allogroups.


Assembly of the cytolytic alternative pathway of complement from 11 isolated plasma proteins.

The known cytolytic function of the alternative pathway in serum was quantitatively reproduced by combining 11 isolated plasma proteins at their respective serum concentrations. These proteins are: C3, Factor B, Factor D, C3b inactivator, beta1H, native properdin, C5, C6, C7, C8, and C9. In absence of activators of the alternative pathway, this mixture was stable at 37 degrees C as evidenced by lack of consumption of Factor B, C3, and C5. Upon addition of either rabbit erythrocytes or neuraminidase-treated sheep erythrocytes, cell lysis ensued and the extent of lysis was dependent on dose of the component mixture. The dose-response curves obtained with the isolated component mixture and with C4-depleted serum were virtually indistinguishable. Nonactivator erythrocytes (untreated sheep erythrocytes) were not lysed by the component mixture. Deletion of properdin resulted only in a twofold diminution of the hemolytic activity of the component mixture. No immunoglobulin requirement was apparent. These results indicate that the cytolytic systems studied are internally sufficient and capable of coupling the initiation and amplification sequence with the cytolytic membrane attack sequence.


Eye movements and integrating information across fixations.

A series of experiments was conducted in which a word or letter string initially appeared in parafoveal vision, followed by the subject's eye movement to the stimulus. During the saccade, the initially displayed stimulus was replaced by a word that the subject was asked to read. The results indicated that the types of prior parafoveal information studied facilitated the naming of the word. The effect was obtained when the subject made an eye movement and when the saccade was simulated. There was also evidence that attentional allocation was tied to the direction of the eye movement.


The effects of the reader's skill and the difficulty of the text on the perceptual span in reading.

Development of the perceptual span in reading was investigated by varying the availability of graphic information in the periphery of vision. Low-ability eighth-grade readers, high-ability eighth-grade readers, and skilled adult readers read texts presented in a normal prose format, with a single space between words, and texts typed with 13 letter spaces between words. It was found that removing peripheral information by wide spacing improved comprehension for low-ability eighth graders but did not affect their overall reading efficiency (the number of questions answered correctly per minute of reading time). Wide spacing decreased the reading efficiency of high-ability eighth-grade readers and skilled adult readers. In addition, the texts were of two levels of difficulty. It was hypothesized that subjects would employ a larger span of perception with the easy text. Surprisingly, the wide spacing of words did not produce greater decrement fo reading efficiency with the easy text. The findings thus suggest that the perceptual span may increase as reading skill develops but does not change under the influence of momentary task variables.


The seeing-more-than-is-there phenomenon: implications for the locus of iconic storage.

When a target figure is moved back and forth behind a window cut in an opaque screen, more of the figure is seen at a given instant than is physically present. This finding implies that the information presented at one instant is stored in iconic form so that it can be integrated with information presented at a slightly later instant. Two experiments explored the illusion and showed that it can be readily demonstrated under a variety of conditions. A third experiment indicated that it can occur in the absence of appreciable eye movements. This latter finding, together with various supporting argument, is taken as evidence against an explanation of the illusion in terms of the target image being painted across the retina. Rather, it appears that successive sections of the target item are projected onto the same retinal sector. It is difficult to understand how simple photoreceptors can simultaneously retain information presented at one instant and register information presented at a subsequent time without two pieces of information being fused. Therefore, it is concluded that the iconic storage implied by the illusion occurs at a level more central than that of the retinal receptors.


Cognitive determinants of fixation location during picture viewing.

This experiment involved the question of where human observers look in a picture. The results indicated that observers fixate earlier, more often, and with longer durations on objects that have a low probability of appearing in a scene (e.g., an octopus in a farm scene) than on objects that have a high probability of appearing (e.g., a tractor in a farm scene). These findings (a) imply a role of cognitive factors in peripheral visual processing and (b) suggest a possible relationship between the nature of information initially acquired from a picture and subsequent recognition memory for that picture.


Retinal image smear as a source of information about magnitude of eye movement.

A number of experiments were conducted to determine to what extent retinal image smearing during saccades provides information about the eye movement magnitude to the perceptual system. The technique involved obtaining measures of perceived movement when the total visual field was displaced in conjunction with saccadic eye movements. Trials with normal retinal smear were compared with trials on which smearing was greatly reduced or eliminated. The results are interpreted as showing that the absence of normal retinal smear during a saccade increases the uncertainty in the information available to the perceptual system and that this uncertainty results in a tendency to perceive smaller than veridical amounts of movement.


Contrast effects on stop consonant identification.

Changes in the identification of speech sounds following selective adaptation are usually attributed to a reduction in sensitivity of auditory feature detectors. An alternative explanation of these effects is based on the notion of response contrast. In several experiments, subjects identified the initial segment of synthetic consonant-vowel syllables as either the voiced stop [b] or the voiceless stop [ph]. Each test syllable had a value of voice onset time (VOT) that placed it near the English voiced-voiceless boundary. When the test syllables were preceded by a single clear [b] (VOT = -100 msec), subjects tended to identify them as [ph], whereas when they were preceded by an unambiguous [ph] (VOT = 100 msec), the syllables were predominantly labeled [b]. This contrast effect occurred even when the contextual stimuli were velar and the test stimuli were bilabial, which suggests a featural rather than a phonemic basis for the effect. To discount the possibility that these might be instances of single-trial sensory adaptation, we conducted a similar experiment in which the contextual stimuli followed the test items. Reliable contrast effects were still obtained. In view of these results, it appears likely that response contrast accounts for at least some component of the adaptation effects reported in the literature.


Feature detection process in speech perception.

One current view of speech perception is that speech is initially processed by the extraction of independent features which are then integrated over time by a synthesis process into a phonetic or syllabic percept. This feature synthesis model was contrasted with the alternative view that speech is initially processed as a continuous multidimensional whole. Two selective adaptation experiments were carried out to provide a test between these views. In the first experiment, the feature synthesis model predicted an increase in adaptation with an increase in adaptor processing time. The alternative view can also explain this result based on the perceptual simiiarity of the adaptation sequence and the test items. In the second experiment, the alternative view predicted an increase in adaptation with a decrease in adaptor processing time in a case in which the short adaptation sequence was more perceptually similar to the test items than the long sequence. The feature synthesis model cannot readily handle this reversal of the effect found in the first experiment. Some problems with the current view of the feature detection process in speech perception are discussed.


Perceptual integration of acoustic cues for stop, fricative, and affricate manner.

Introducing a short interval of silence between the words SAY and SHOP causes listeners to hear SAY CHOP. Another cue for the fricative-affricate distinction is the duration of the fricative noise in SHOP (CHOP). Now, varying both these temporal cues orthogonally in a sentence context, we find that, within limits, they are perceived in relation to each other: The shorter the duration of the noise, the shorter the silence necessary to convert the fricative into an affricate. On the other hand, when the rate of articulation of the sentence frame is increased while holding noise duration constant, a longer silent interval is needed to hear an affricate, as if the noise duration, but not the silence duration, were effectively longer in the faster sentence. In a second experiment, varying noise and silence durations in GRAY SHIP, we find that given sufficient silence, listeners report GRAY CHIP when the noise is short but GREAT SHIP when it is long. Thus, the long noise in the second syllable disposes listeners to displace the stop to the first syllable, so that they hear not a syllable-initial affricate (i.e., stop-initiated fricative) but a syllable-final stop (followed by a syllable-initial fricative). Repeating the experiment with GREAT SHIP as the original utterance, we obtain the same pattern of results, together with only a moderate increase in GREAT responses. In all such cases, the listeners integrate a numerous, diverse, and temporally distributed set of acoustic cues into a unitary phonetic percept. These several cues have in common only that they are the products of a unitary articulatory act. In effect, then, it is the articulatory act that is perceived.


The role of spatial redundancy in grapheme recognition: perception or inference?

The question under investigation is whether spatial redundancy operates by restricting the number of valid alternatives at each serial position or whether it serves a perceptual function by keeping visually confusable graphemes from appearing in the same array and/or maximizing the distance between such graphemes when they do occur in the same array. The first experiment used the same-different task to establish a confusion matrix for 12 non-linguistic symbols. The spatial relation between the members of two pairs of confusable symbols was manipulated in a second experiment, which had subjects look for the presence or absence of a predetermined target symbol in single six-symbol linear arrays. Facilitation was found to be dependent upon the perceptual consequences of serial position constraint rather than upon the constraint per se. The constraint was most effective when it served to prevent members of visually confusable pairs from occurring in the same array. Since spatial redundancy may operate at the feature extraction stage by minimizing competition for the same sets of feature detectors and since words are likely to be high in spatial redundancy, the possibility is raised that part of the word superiority effect may be due to visual factors rather than to linguistic context.


Perceptual flexibility in word recognition: strategies affect orthographic computation but not lexical access.

Four tachistoscopic forced-choice recognition experiments explored the flexibility of processes underlying word perception. Stimuli were words, orthographically regular but unfamiliar pseudowords, and orthographically irregular nonsense strings. In the first two experiments, subjects knew that several different kinds of stimuli would occur in each block of trials and that one kind would occur much more often than the others. No matter which stimulus subjects expected to see most often, accuracy on words and pseudowords differed little, and both were identified considerably better than nonsense. In the third and fourth experiments, subjects were led to believe that only on stimulus type would occur but were surreptitiously shown another type on a small number of trials. Words were again identified more accurately than nonsense, and the size of the effect was independent of expectations. However, when either words or nonsense strings were expected exclusively, pseudoword accuracy did not differ from nonsense accuracy. Only when subjects knew that pseudowords would occur did they identify pseudowords more accurately than nonsense. This dissociation between word and pseudoword identification indicates the operation of two independent encoding mechanisms during tachistoscopic recognition, a stimulus-specific or logogenlike system sensitive to particular familiar strings and an orthographic mechanism sensitive to generally applicable constraints on letter sequencing. The stimulus-specific mechanism appears to be utilized automatically, but use of the orthographic mechanism is under strategic control. As shown in the first two experiments, however, rather extraordinary measures were required to demonstrate the flexibility of the orthographic processes used in this task.


Orientation and symmetry: effects of multiple, rotational, and near symmetries.

Time to detect bilateral symmetry in different orientations was studied for closed polygons with single, double, quadruple, rotational, and near symmetry. In Experiment 1, the orientation of the axis of symmetry was varied. Detection was fastest for vertical symmetry, next fastest for horizontal, and slowest for left- and right-diagonal symmetries. For corresponding orientations, responses were faster to quadruple than double symmetries, and faster to double than single symmetries. Negative responses to nearly symmetric figures produced an orientation effect similar to that for single symmetries. Rotational symmetries showed no orientation effect and took longer to reject than near symmetries. In Experiment 2, subjects looked only for vertical symmetry. Responses were twice as fast as in comparable conditions of Experiment 1. The effect of multiple symmetries was still present, but rotational symmetries were rejected faster than near symmetries. The results are interpreted as supporting a dual process model for detecting symmetry in multiple orientation channels: Observers first select potential axes of symmetry defined by mirror-similar parts and then evaluate specific axes sequentially in a detailed comparison for mirror-identity.


Cost analysis of laboratory tests in ambulatory primary care.

The cost of laboratory tests in the ambulatory primary care setting was analyzed to study relationships among cost to the patient, degree of abnormality of results, and physician follow-up of abnormal results. Laboratory fees constituted 32 cents of the total dollar for office charges. Considering only that portion of patient money spent for laboratory blood tests, 20 cents of the dollar went for tests with normal results, 25 cent for abnormals that were followed up by physicians, and 55 cents for abnormals that were not followed up. Separate analysis including only the abnormals was performed using two methods that differed as to whether or not low degree abnormals were considered worthy follow-up. Even when considering follow-up of this group unnecessary, 30 cents of the patient's dollar for abnormals was spent on appreciably high abnormal tests that were not followed up. This represents a substantial cost to the patient, from which no benefit can be envisioned.


Tricyclic antidepressant prescribing habits: a comparison of family physicians and psychiatrists.

Because of persistent evidence that tricyclic antidepressants are generally underprescribed in respect to dosage and duration of treatment, a large group of family physicians attending a postgraduate course were asked specifically about their prescribing habits for these drugs. Their responses were compared to a group of psychiatrists. This study documented a tendency among family physicians, when compared to psychiatrists, to prescribe too low a dosage of tricyclics for treatment, to be hesitant to increase the dosage, and to discontinue maintenance prematurely. The family physicians overwhelmingly expressed the belief that 75 mg per day of imipramine or amitriptyline was sufficient for treatment maintenance, whereas 150 mg per day is ordinarily considered the minimum effective dosage. Proper use of tricyclic medication with a discussion of side effects and potential hazards is presented.


Ethical and legal issues in family practice.

The unique goal of family practice, that of caring for the entire family's broadly defined health needs, places the family physician in an especially uncomfortable position when there is intrafamily conflict. In particular, the question of "whose agent (physician) are you?" when a family is in conflict often creates a serious ethical dilemma for the family physician. The roles of three experts who deal with family conflict, the psychotherapist, the lawyer, and the family physician, are compared and contrasted. The physician as expert is a useful approach only insofar as there are clearcut answers to a particular problem. But the ambiguity inherent in ethical problems makes this approach less than satisfactory. The role of the physician as teacher/facilitator is explored as an alternative to resolving the ethical dilemmas of intrafamily conflict.


Sigmoidoscopy as a periodic screening test.

Available data suggest that routine screening procedures and removal of benign adenomatous polyps in all asymptomatic patients over the age of 40 to 50 years may significantly reduce both mortality and morbidity rates for colorectal carcinoma. Such data show that sigmoidoscopy is a valuable part of any screening program and can be performed at low cost and with minimal risk to the patient. It is concluded that an adequate routine screening program can be achieved with annual stool guaiac examination and sigmoidoscopy every five years between ages 40 and 50, and every three years over the age of 50 in asymptomatic patients. All patients with a history of colonic lesions must be seen more frequently because of the higher risk of recurrence.


Urinary tract infections in children: a review.

Urinary tract infections (UTIs) in children are a common and challenging problem for the primary care physician and continue to be a cause of significant morbidity. Except for the neonatal period, UTIs occur most frequently in girls. The symptoms of UTI in the child may be obscure, and often a high index of suspicion is required. Diagnosis ultimately depends on the urine culture. Current concepts in the diagnosis and therapy of UTIs in children include the use of urine culture for initial diagnosis and home cultures for follow-up. Evidence fully supports the concept that even a single episode of documented bacteriuria, symptomatic or asymptomatic, should be investigated with an intravenous pyelogram (IVP) and voiding cystourethrogram (VCUG).


Long Q-T syndrome: a preventable form of sudden death.

The long Q-T syndrome, with or without congenital deafness, is characterized by syncopal attacks and prolongation of Q-T interval on the electrocardiogram. Untreated cases with syncope are usually fatal, but if diagnosed and treated appropriately with beta adrenergic blockers or surgical left stellate ganglionectomy, prognosis is markedly improved. This report describes an 11-year follow-up of a child with the long Q-T syndrome, in whom frequent syncopal attacks were successfully treated with propranolol.


Acetaminophen poisoning.

A case of suspected acetaminophen poisoning is reported in a child who ingested 19 gm of acetaminophen over a seven-day period. She exhibited evidence of severe renal and hepatic damage which resolved with supportive therapy. Serum levels of acetaminophen were not in the toxic range; hence, proof of the etiology was not possible. It is probable that a delay in suspecting acetaminophen toxicity allowed time for the serum acetaminophen level to return to normal. Acetaminophen is a safe drug when used properly, but overdosage can cause severe toxicity. With increased use in this country, increasing episodes of overdosages should be anticipated. Blood levels should be obtained early in acutely ill patients when acetaminophen toxicity is suspected.


Contraceptive compliance in family medicine: a comparison of the family physician and the family planning clinics.

A longitudinal, controlled study of contraceptive compliance was undertaken in a solo family practice in which 240 high-risk women were allocated alternatively to Practice and Clinic Groups. The effectiveness of the two services was evaluated at six-month intervals. Women in the family practice demonstrated better contraceptive compliance than those referred to the family planning clinics. There was a significantly lower number of pregnancies and fewer women experiencing unprotected intercourse in the Practice Group. The study demonstrates the potential of the family physician to achieve better compliance than the clinics of a well-resourced, successful family planning association. The need for the physician to accept his/her role as a family planning counselor and to be trained to offer a comprehensive contraceptive service is discussed.


Life change and illness onset: importance of concepts for family physicians.

The questions of illness susceptibility and the how and why of the onset of illness are of great concern to family physicians, who are constantly presented with a bewildering array of maladies. This paper presents a model of illness onset as related to life change which is felt to be a highly relevant and useful concept for family physicians. This model has been developed over many years and proposes that illness onset is predictably related to life change, which in turn is a reflection of the amount of coping required. The specific development of these concepts is presented in detail including the development and quantitation of the social readjustment rating scale which quantifies life changes.


The teaching of human sexuality in a family medicine training program.

Sexual health is an important component of the individual's total health picture. The primary physician, however, is often ill-prepared to deal with issues around sexuality and sexual dysfunction, and family medicine units need to structure programs for teaching in this area. This article describes a teaching program on human sexuality in a family medicine setting. Its major goals were the transmission of information, the teaching of skills, and the desensitization of the health care professional in this area. The program consisted of a series of four seminars and ongoing teaching. The seminars focused on the human sexual response, sexual myths, sexual history taking, and sexual dysfunction and treatment. Ongoing teaching included case discussion, consultation, and joint interviews. It is hoped that the description of this program will serve as a model and/or impetus to other family medicine training programs.


Genetic variation, cellular distribution and ontogeny of sorbitol dehydrogenase and alcohol dehydrogenase isozymes in male reproductive tissues of the mouse.

Cellulose acetate zymograms of alcohol dehydrogenase (ADH) and sorbitol dehydrogenase (SDH) extracted from male reproductive tissues of inbred mice were examined. ADH isozymes were differentially distributed in these tissues of C3H/He mice; ADH-B2 was observed in all tissues and testis cellular preparations examined; ADH-C2 was localized predominantly in the epididymis but was also present in the seminal vesicles, coagulating gland, and prostate gland. SDH was broadly distributed in these tissues but exhibited highest activities in the seminal vesicles, coagulating glands, and germinal cells of mature testes. Genetic variants for ADH-C2 and SDH provided evidence for (1) the identity of a second form of SDH in epididymis with ADH-C2; (2) the genetic identity of kidney, seminal vesicle, and testis SDH; and (3) the gentic identity of stomach and epididymal ADH-C2. Developmental changes in testis and epididymal ADH isozymes during maturation were examined. ADH-C2 appeared in the mature epididymis whereas ADH-B2 exhibited no major changes in activity in testis and epididymis during development.


Potassium channels as multi-ion single-file pores.

A literature review reveals many lines of evidence that both delayed rectifier and inward rectifier potassium channels are multi-ion pores. These include unidirectional flux ratios given by the 2--2.5 power of the electrochemical activity ratio, very steeply voltage-dependent block with monovalent blocking ions, relief of block by permeant ions added to the side opposite from the blocking ion, rectification depending on E--EK, and a minimum in the reversal potential or conductance as external K+ ions are replaced by an equivalent concentration of T1+ ions. We consider a channel with a linear sequence of energy barriers and binding sites. The channel can be occupied by more than one ion at a time, and ions hop in single file into vacant sites with rate constants that depend on barrier heights, membrane potential, and interionic repulsion. Such multi-ion models reproduce qualitatively the special flux properties of potassium channels when the barriers for hopping out of the pore are larger than for hopping between sites within the pore and when there is repulsion between ions. These conditions also produce multiple maxima in the conductance-ion activity relationship. In agreement with Armstrong's hypothesis (1969. J. Gen. Physiol. 54:553--575), inward rectification may be understood in terms of block by an internal blocking cation. Potassium channels must have at least three sites and often contain at least two ions at a time.


Calcium efflux from squid axons under constant sodium electrochemical gradient.

The effect of varying Nao and Nai on Ca efflux while maintaining the ratio Nao/Nai constant was explored in squid giant axons dialyzed with and without ATP. In the absence of ATP, the Ca efflux increased 3.4 +/- 0.2-fold when the Nao/Nai concentrations were reduced from 440/80 to 110/20 mM. In the presence of ATP a similar change did not have an appreciable effect. The inhibition of Ca efflux produced by Nai was studied in the presence and in the absence of ATP. In the absence of ATP, inhibition is very marked and is reminiscent of a unimolecular noncompetitive reaction (inactivation constant [KI] of 34 +/- 5 mM of Nai) whereas in the presence of ATP, the slight inhibition observed indicates that ATP probably increases the KI to 200mM. From the inhibition of the Ca efflux produced by Nai in the presence or absence of ATP a curve describing the dependence of Nai of the ATP-promoted fraction of Ca efflux was constructed. The effect of Nao on the Ca efflux was studied as a function of [Na]i: at low Nai, an activation constant (KA) of 41 mM for Nao was obtained either in the presence of in the absence of ATP. As the intracellular Na is increased in the presence of ATP, Nai seems to have no effect on the apparent half-activation constant. However, in the absence of ATP, the KA for activation increases along a sigmoid curve reaching a value of 112 mM at 100 mM Nai. It is concluded that the Ca efflux system uses the energy of the Na electrochemical gradient. The action of Nai appears to be such that the interaction of a single Na+ is sufficient to block Ca extrusion whereas several Naps externally are necessary to activate Ca extrusion.


Diffusion of water in cat ventricular myocardium.

The rates of diffusion of tritiated water (THO) and [14C]sucrose across cat right ventricular myocardium were studied at 23 degrees C in an Ussing-type diffusion cell, recording the time-course of increase in concentration of tracer in one chamber over 4--6 h after adding tracers to the other. Sucrose data were fitted with a model for a homogeneous sheet of uneven thickness in which the tissue is considered to be an array of parallel independent pathways (parallel pathway model) of varying length. The volume of the sucrose diffusion space, presumably a wholly extracellular pathway, was 23% of the tissue or 27.4 +/-1.7% (mean +/- SEM; n=11) of the tissue water. The effective intramyocardial sucrose diffusion coefficient, D8, was 1.51 +/- 0.19 X 10(-6)cm2.s-1 (n=11). Combining these data with earlier data, D8 was 22.6 +/- 1.1% (n=95) of the free diffusion coefficient in aqueous solution D degrees 8. The parallel pathway model and a dead-end pore model, which might have accounted for intracellular sequestration of water, gave estimates of DW/D degrees W (observed/free) of 15%. Because hindrance to water diffusion must be less than for sucrose (where D8/D degrees 8=22.6%), this showed the inadequacy of these models to account simultaneously for the diffusional resistance and the tissue water content. The third or cell-matrix model, a heterogeneous system of permeable cells arrayed in the extracellular matrix, allowed logical and geometrically reasonable interpretations of the steady-state data and implied estimates of DW in the cellular and extracellular fluid of approximately 25% of the aqueous diffusion coefficient.


Limulus ventral eye. Physiological properties of photoreceptor cells in an organ culture medium.

Ventral photoreceptor cells bathed in an organ culture medium typically have resting potentials of -85 mV and membrane resistances of 35 Momega and, when dark-adapted, exhibit large potential fluctuations (LPFs) of 60 mV and small potential fluctuations (SPFs) of less than 30 mV. LPFs appear to be regenerative events triggered by SPFs, the well-known quantum bumps. In the dark, SPFs and LPFs occur spontaneously. At intensities near threshold, the rate of occurrence is directly proportional to light intensity, indicating that SPFs and LPFs are elicited by single photon events. At higher intensities, SPFs and LPFs sum to produce a receptor potential that is graded over approximately a 9-log-unit range of light intensity. Amplitude histograms of the discrete potential waves are bimodal, reflecting the SPF and LPF populations. Histograms of current waves are unimodal. SPFs and LPFs are insensitive to 1 microgram tetrodotoxin. I-V characteristics show initial inward currents of approximately 15 nA for voltage clamps to -40 mV and steady-state outward currents for all clamp potentials. Photoreceptor cells bathed in organ culture medium retain these properties for periods of at least 75 days.


The effects of some different metabolic inhibitors on interferon superinduction.

Three different inhibitors of RNA synthesis, actinomycin, alpha-amanitin and camptothecin, and five different inhibitors of protein synthesis were able to superinduce interferon production in human diploid fibroblasts treated with poly(rI).poly(rC). Camptothecin was shown to be a reversible inhibitor of virus induced interferon formation. It also substantially reduced the interferon yield from human diploid fibroblasts which had been superinduced with actinomycin D and cycloheximide. This suggests that the previously reported failure of camptothecin to inhibit interferon production in human diploid cells after induction with poly(rI).poly(rC) is the result of two mutually opposing effects: a marked inhibition of interferon messenger RNA synthesis, but a stimulation of the activity of the interferon messenger RNA that is formed.


Isolation and characterization of polysheaths, phage tail-like defective bacteriophages of Alcaligenes eutrophus H 16.

Polysheaths were spontaneously formed inside cells of the hydrogen bacterium Alcaligenes eutrophus H 16. These particles are long tube-like structures of 24 nm diam. belonging to the phage tail-like defective bacteriophages (Lotz, 1976). In mid log-phase fermenter-grown cells, polysheaths were observed in about 20% of all cells sectioned. Evidence is provided for an inhibition of cell fission by polysheaths. Polysheaths were isolated by differential centrifugation and precipitation techniques using PEG and antibodies. The morphology of polysheaths was investigated electron microscopically by negative staining, ultrathin sectioning and metal shadowing. A surface lattice of the polysheath was derived from light optical diffraction data. The particles were also characterized by their biochemical and biophysical features: mol. wt. of the subunit determined by SDS-gel electrophoresis (58 000), amino acid composition, isoelectric point (4.4), u.v. absorbance spectrum indicating the absence of nucleic acid, buoyant density (1.258), and stability against denaturants and proteolytic enzymes.


Phage growth characteristics on stationary phase Achromobacter cells.

The growth characteristics of alpha3a bacteriophage on stationary phase Achromobacter strain 14 are described. Phage alpha3a growth on stationary phase cells is characterized by a long and variable latent period of 6 to 9 h and an increased burst size of 710 p.f.u./cell as compared with 153 p.f.u./cell in exponential wild type cells. During the latent period the infected cells are very sensitive to changes in growth conditions and in particular, dilution. Pre-conditioning of the bacterial cells by allowing them to stand for 24 h after shaking for 3 days is an important aspect of the stationary phase phage growth system. Cells which have been allowed to stand retain the ability to be infected and to support phage growth for at least 16 days. Shaking cultures gradually lose the ability to support phage growth but the phage can persist in the host cell for 10 days until removal from shaking when the lytic cycle can proceed after allowing the cultures to stand.


Isolation and phenotypic characterization of human adenovirus type 2 temperature-sensitive mutants.

Thirty-nine temperature-sensitive (ts) mutants that fail to grow at 39.5 degrees C but develop normally at 33 degrees C have been isolated from a nitrous-acid-treated stock of a wild-type strain of type 2 human adenovirus. The frequency of ts mutants among the surviving viruses was about 10%. Complementation tests in doubly infected cell cultures at restrictive temperature permitted the assignment of 19 of these mutants to 11 complementation groups. They are characterized phenotypically according to their soluble capsid antigen production quantified by two-dimensional immunoelectrophoresis, virus DNA synthesis, as measured by alkaline sucrose gradient sedimentation of 34S DNA, and virion morphogenesis, as analysed by electron microscopy os cell sections. Two complementation groups were defective for DNA synthesis, four for soluble hexon production and two groups for total penton (penton base + fibre), while one group revealed no fibre production. Two complementation groups presented a normal antigen pattern, but the particles exhibited altered morphology as observed in cell sections.


The isolation of recombinants between related orbiviruses.

Temperature-sensitive mutants of the related orbiviruses, Wallal and Mudjinbarry, recombine with high frequency when grown in pairs in cell culture. The genome of each virus consists of discrete segments of double-stranded RNA and high frequency recombination suggests that reassortment of genome segments occurs rather than classical recombination. Electrophoresis in acrylamide gels of RNA extracted from the progeny of a cross between Wallal ts 101 and Mudjinbarry ts 3 mutants, revealed that three plaque isolates of 60 tested differed in RNA pattern from each of the parent viruses and from each other. Further analysis of the electrophoretic profiles suggested that the isolates were recombinants with RNA segments derived from each of the parent viruses.


Assembly of Semliki Forest virus nucleocapsid: detection of a precursor in infected cells.

The synthesis of Semliki Forest virus nucleocapsid in infected cells was studied by labelling the virus RNAs with 3H-uridine for different periods at various phases of infection. Short pulses (10 to 20 min) revealed the accumulation of 42S RNA in a ribonucleoprotein which sedimented at about 90S (90S RNP) and contained only small amounts of capsid protein. Only after longer pulses was the labelled 42S RNA found in the virus nucleocapsid, suggesting that the 90S RNP may be its precursor. The life time of the 90S RNP was long in the early phases of infection and short in the late phases, reflecting the increased rate of assembly of the nucleocapsid during infection. The 90S RNP was the only 42S RNA containing RNP found in cells infected with temperature sensitive mutants deficient in nucleocapsid formation or wild type infected cells treated with cycloheximide to inhibit nucleocapsid assembly.


An improved method for determining neutralizing antibody against lymphocytic choriomeningitis virus in human sera.

Human antibody neutralizing lymphocytic choriomeningitis virus is most reliably determined in mice as assay hosts. Whereas the previously recommended procedure yielding a neutralization index requires much serum, the method described here uses only 0.1 ml. An equal mixture of virus and serum is incubated and residual infectivity is titrated intracerebrally in mice. The neutralizing activity is given by the ratio of virus surviving after incubation with control serum and with the test serum respectively. This ratio is called the neutralization factor.


Exposure to onion taste in mother's milk leads to enhanced preference for onion diet among weanling rats.

Five mothers of 50 newborn rat pups were maintained on either standard lab chow or a diet composed of the same chow with onion powder added. Taste preference tests administered during weaning indicated that the pups whose mother was fed the onion chow showed a preference for onion diet, but that such preference dissipated across the five day testing period. A control group of pups who were exposed to any onion diet cues available through channels other than the mother's milk did not show a preference for onion diet. It was concluded that exposure to onion taste in mother's milk was responsible for an initial preference for onion diet.


Failure to observe visual discrimination in old gerbils: replication report.

A recent study showed that while young gerbils can learn a visual line discrimination task, old gerbils cannot. That study has been criticized for not equating the motivational levels of the two age groups. The present study attempted to answer that criticism. Accordingly, two groups of old gerbils (total N = 10) were motivated either by a 22 hour food deprivation schedule or an 80% reduction in their ad lib weight. All animals were tested in a T-maze with sunflower seed reinforcers (highly prized by gerbils) being associated with horizontal or vertical stripes. As in the earlier study, these old gerbils did not acquire the visual discrimination.


Effect of familiarity on primacy performance of normal and retarded children.

On the assumption that serial recall tasks reflect spatial memory rather than verbal rehearsal, the purpose of this experiment was to determine what effect stimulus familiarity had on the spatial primacy performance of 20 retarded and 20 normal boys and girls. Linear presentation effects of familiar and nonfamiliar pictures upon serial position curve performance when overt verbalization was suppressed were investigated. Results indicated that an interaction of stimulus familiarity and spatial memory is responsible for the primacy effect found in serial position curves. No primacy effect for either the normal or retardate group was found in the nonfamiliar stimulus condition. No overall developmental effects were found between groups of children on serial position performance. Consistent with Craik and Lockhart's memory processing model, the present results indicated stimulus familiarity provided deeper levels of processing, thereby facilitating primacy effects.


Approach-withdrawal response competition (AW-RC), displacement, and behavior modification.

This paper reviews displacement theory and animal research as derived from approach-withdrawal response competition (AW-RC), with a selected emphasis on clinical implications. AW-RC displacement is seen as part of the larger area of behavior modification while nevertheless distinguished from the larger area by a singular model and methodology. It is suggested that a lack of operational analysis of AW-RC displacement and behavior modification is responsible for some confusion about the two areas, has retarded developments and conclusions about behavior modification, and has contributed to, or produced, termination of research on AW-RC displacement. This review uncovers two major sets of results and one interesting observation. First, the displacement effect and the extinction effect of displacement are strongly supported, but the therapeutic effect of displacement is not supported. Second, time-delay that is characterized by eating under deprivation in an irrelevant situation does appear to produce true therapeutic effects of large magnitude. Berkun's observation, opening to other nondisplacement but AW-RC related observations and findings, suggests separable aspects of AW-RC behavior that are not correspondingly observable with other methodologies.


Color context as a factor in encoding and as an organization device for retrieval of word lists.

One hundred twenty female undergraduates were presented hierarchically organized or randomly arranged word lists within a context of hierarchically organized or randomly arranged color patterns. Recall scores were significantly higher with a hierarchic color pattern than with a random color pattern; this facilitating effect occurred for both hierarchic organizations and random arrangements of the word lists. The results suggest that Ss may use context as both a cueing of differentiating factor in encoding and as an organizational device for retrieval.