numerous proton magnetic resonance spectroscopy ( 1h - mrs ) studies have linked cytosolic choline levels to the neuropathology of mood disorders ( 17 ) .
increases in choline in depressed subjects have been noted in adults ( 1,3 ) and in pediatric samples ( 4,5 ) .
auer and others ( 8) did not note any significant difference in choline levels in the cingulate in their study of mdd subjects and controls . the choline resonance derived by 1h - mrs arises mainly from phosphocholine and glycerophosphocholine ( 9,10 ) .
children and adolescents have been relatively understudied with regard to the neurobiology of mood disorders .
this is despite the fact that the prevalence of depression increases during adolescence , rising from 1% up to adult levels ( 68% ) .
mood disorders in youth are associated with impairment in social , family and academic functioning , are highly predictive of future episodes and are significantly related to suicide ( 11 ) . despite the prevalence and outcomes associated with the mood disorders , there is a paucity of information about the etiology .
hence , studies of children and adolescents are necessary in order to determine if abnormalities noted in adult populations occur across the life span , how early they present during development , and whether they can be used as predictors for future risk of developing depression .
studies early in the course of an illness also avoid the potential confounds of illness chronicity , hospitalization and long - term medication use .
this study endeavors to uncover neurobiological correlates of juvenile depression . based on the adult literature ( 13,6,7 ) and the reports on pediatric depression ( 4,5 )
, we hypothesized that youth with mdd and those without psychiatric illness will demonstrate differences with regard to cytosolic choline in the prefrontal cortex .
subjects were recruited through either of two methods : ( 1 ) advertisements , or ( 2 ) as participants in clinical treatment ( combined pharmacological and psychotherapy ) programs .
all subjects and one of their parents / guardians signed informed consents for the study after a full explanation of the procedures in accordance with the research ethics board approval provided by the iwk health centre .
each subject completed the children s depression rating scale ( cdrs ) ( mood disorder group mean = 66.083 + 14.042 ) at the time of scan .
diagnosis based on kiddie - schedule for affective disorders and schizophrenia - present and lifetime version ( k - sads - pl ) criteria were established by a board - certified psychiatrist ( primarily vk ) .
twelve subjects ( 5 males , 7 females ) aged 10 to 18 years old with mdd and twelve age and sex - matched healthy controls participated in this study .
exclusion criteria for participation in this study included a history of neurological illness , serious medical illness , claustrophobia , age greater than 18 years , or the presence of a ferrous implant or pacemaker .
scans were conducted at the queen elizabeth ii health sciences centre using a siemens magnetom vision 1.5 tesla scanner .
multi - slice scout images ( axial , coronal and sagittal planes ) were used for voxel orientation .
special care was taken to ensure adequate coverage of the right prefrontal gray matter by the voxel . a long echo proton magnetic resonance spectroscopic imaging ( 1h - mrs )
parameters were as follows : te = 135 ms , tr = 1500 ms , acquisitions 256 , voxel = 4cc , time = 8 minutes ( see figure 1 for sample spectra ) . a trained mrs analyst ( fpm ) analyzed data in a blind manner . mrs metabolites that can be visualized with this technique are n - acetyl - aspartate ( naa , 2.02ppm ) , creatine / phosphocreatine ( cr , 3.03ppm ) and choline compounds ( cho , 3.20ppm ) . following a convention that minimizes variations in the magnetic field homogeneity , metabolite concentrations are expressed as ratios of peak areas ( i.e. naa / cr , cho / cr ) .
a repeated measures anova was used to determine group differences in choline levels between mdd patients and healthy age and sex - matched controls .
we expected that close age and sex- matching allows for a reduction in the potential confounds of sex and age on the data set .
correlations ( two - tailed ) between metabolites and age and , in the psychiatric group , depressive symptom severity were also conducted .
subjects were recruited through either of two methods : ( 1 ) advertisements , or ( 2 ) as participants in clinical treatment ( combined pharmacological and psychotherapy ) programs .
all subjects and one of their parents / guardians signed informed consents for the study after a full explanation of the procedures in accordance with the research ethics board approval provided by the iwk health centre .
each subject completed the children s depression rating scale ( cdrs ) ( mood disorder group mean = 66.083 + 14.042 ) at the time of scan .
diagnosis based on kiddie - schedule for affective disorders and schizophrenia - present and lifetime version ( k - sads - pl ) criteria were established by a board - certified psychiatrist ( primarily vk ) .
twelve subjects ( 5 males , 7 females ) aged 10 to 18 years old with mdd and twelve age and sex - matched healthy controls participated in this study .
exclusion criteria for participation in this study included a history of neurological illness , serious medical illness , claustrophobia , age greater than 18 years , or the presence of a ferrous implant or pacemaker .
scans were conducted at the queen elizabeth ii health sciences centre using a siemens magnetom vision 1.5 tesla scanner .
multi - slice scout images ( axial , coronal and sagittal planes ) were used for voxel orientation .
special care was taken to ensure adequate coverage of the right prefrontal gray matter by the voxel . a long echo proton magnetic resonance spectroscopic imaging ( 1h - mrs )
parameters were as follows : te = 135 ms , tr = 1500 ms , acquisitions 256 , voxel = 4cc , time = 8 minutes ( see figure 1 for sample spectra ) . a trained mrs analyst ( fpm ) analyzed data in a blind manner .
mrs metabolites that can be visualized with this technique are n - acetyl - aspartate ( naa , 2.02ppm ) , creatine / phosphocreatine ( cr , 3.03ppm ) and choline compounds ( cho , 3.20ppm ) . following a convention that minimizes variations in the magnetic field homogeneity ,
metabolite concentrations are expressed as ratios of peak areas ( i.e. naa / cr , cho / cr ) .
a repeated measures anova was used to determine group differences in choline levels between mdd patients and healthy age and sex - matched controls .
we expected that close age and sex- matching allows for a reduction in the potential confounds of sex and age on the data set .
correlations ( two - tailed ) between metabolites and age and , in the psychiatric group , depressive symptom severity were also conducted .
the two groups did not differ with regard to age ( control group mean = 14.917 years + 2.575 , mood disorder group mean = 14.750 years + 2.454 , t11 = 1.000 , p = 0.339 ) .
cho / cr ratios were increased ( 39% ) in right prefrontal cortex in the mdd group as compared to matched healthy controls ( control mean = 0.782 + 0.170 , mdd group mean = 1.088 + 0.368 , f1 , 11 = 10.741 , p = 0.007 ) .
right prefrontal naa / cr did not differ between the healthy controls and mdd subjects ( control mean = 2.135 + 0.378 , mdd group mean = 2.408 + 0.490 , f1 , 11 = 2.702 , p = 0.129 ) . in the control group ,
cho / cr demonstrated a trend for inverse correlation with age in years ( r = 0.516 , p = 0.087 ) but not in the mdd group ( r = 0.343 , p = 0.284 ) . in the mdd group , cho / cr demonstrated a weak trend for positive correlation with cdrs symptom severity score ( r = 0.480 , p = 0.117 )
we report a significant increase in cho / cr in youth with mdd as compared to age- and sex - matched healthy controls in a voxel located in the right prefrontal cortex .
this finding is consistent with previous reports of abnormalities in the choline resonance in mood disorders ( 17 ) .
choline acts as a precursor of the neurotransmitter acetylcholine and the membrane lipids , phosphatidylcholine and sphingomyelin . as these lipids are typically bound in the membrane , they contribute little to the mrs choline resonance , while the cytosolic choline compounds , such as glycerophosphocholine ( gpc ) and phosphocholine ( pc ) contribute as much as 50% to the choline signal .
free choline , acetylcholine , and cytidine diphosphate choline make smaller contributions to the resonance ( 1214 ) . based on this information ,
it has been postulated that changes in the choline resonance may be reflective of changes in local neuronal metabolism .
these changes in metabolism may be required for the incorporation of cytosolic choline compounds into phospholipids .
a previous study has shown changes in pet measures of metabolism to be inversely correlated with the 1h - mrs choline resonance ( 15 ) .
steingard and others ( 4 ) have also found increases in prefrontal choline in adolescent depression .
this is an interesting finding given that the prefrontal cortex has been repeatedly implicated in metabolic neuroimaging studies in mood disorders ( 16,17 ) .
it is also a possibility that the choline increase demonstrated in the prefrontal cortex of mdd subjects as compared to the controls in this study may reflect differences in glucocorticoid activity
. one of the most - replicated findings in biological psychiatry has been the alteration in the endocrine system in mood disorders .
many mood disorder patients demonstrate hypothalamic - pituitary - adrenal ( hpa ) axis over activation ( 18 ) . in conditions that result in excess glucocorticoids , such as graves disease , bhatara and others ( 19 )
glucocorticoids likely adversely affect phosphatidylcholine ( ptd - cho ) metabolism in the brain by inhibiting the activity of enzymes such as phospholipase a2 and c ( 21 ) .
ptd - cho plays a role in the second messenger system and signal transduction , as it is a source for diaglycerol ( 2225 ) .
as an increase in choline has been shown in this report , a primary role for glucocorticoids in this instance may be unlikely . in emotional processing ,
tone  to a stimulus while the prefrontal cortex provides inhibitory modulation ( 26 ) .
prefrontal cortex modulation of amygdala function may be diminished in mood disorders , and hence a lack of control over negative cognition may result . should critical prefrontal inputs to the amygdala be rendered impotent , the inhibitory control of the prefrontal cortex would be lost .
most likely , however , is that the emotional homeostatic mechanisms of both the prefrontal and limbic regions are dysfunctional in mood disorders ( 27 ) .
previous work has demonstrated that the prefrontal choline resonance decreases with increasing age in healthy children and adults ( 28 ) . in our study ,
only the cho / cr levels in controls were inversely correlated with age in years .
as changes in the choline resonance during childhood and adolescence are typically thought to reflect changes in brain development , the lack of a correlation in the mood disorder sample may be indicative of a differential developmental trajectory for these subjects .
alternatively , the change in choline may be wrought by changes in metabolism , signal transduction , or glucocorticoids .
the principle limitations of this study are the small sample size and the heterogeneity of clinical presentation of the mdd group .
a further limitation of this study is the lack of absolute quantification of the prefrontal metabolites .
however , absolute quantifications are themselves subject to magnetic inhomogeneities and partial volume effects within the region of interest .
the use of ratios minimizes the error introduced by variable tissue composition and instrumental instability while allowing the evaluation of relative alterations in metabolites .
further experiments are required to elucidate the exact mechanism of the increase in the cho / cr peaks and its relation to depressive symptomotology .
we report a significant increase in cho / cr in youth with mdd as compared to age- and sex - matched healthy controls in a voxel located in the right prefrontal cortex .
this increase in the cho / cr ratio may be the result of reductions in metabolism in the prefrontal cortex .
 purpose of study : the prefrontal cortex has been previously implicated in the neuropathology of major depressive disorder ( mdd ) . 
 hence , we used proton magnetic resonance spectroscopy ( 1h - mrs ) to examine choline levels in the prefrontal cortex of youth with major depression . 
 basic procedures : twelve age- and sex - matched case - control pairs were examined ( age range 10 to 18 years , 7 females and 5 males in each group ) . 
 all subjects were treatment naive at the time of the scan . 
 a long echo 1h - mrs scan was acquired from the right prefrontal cortex ( 4cc ) in all subjects . 
 main findings : right prefrontal choline / creatine ratios were elevated in the youth with mood disorders ( f1 , 11 = 10.741 , p = 0.007 ) as compared with healthy controls . 
 principal conclusions : these findings suggest that prefrontal cytosolic choline may be increased in youth with mdd in comparison with healthy controls . 
 this is consistent with reported findings in both adults and adolescents and suggests that mdd in youth is associated with alterations in choline metabolism in the prefrontal cortex . 
INTRODUCTION
METHODS
Subjects
Magnetic Resonance Spectroscopy Procedures
Statistical Analysis
RESULTS
DISCUSSION