 
 lead encephalopathy was induced in developing long - evans rats by adding lead carbonate ( 4% w / w ) to the diet of nursing mother immediately after delivery . 
 the morphological and biochemical features of cerebral ontogenesis were studied in 30-day - old rats . 
 by the 30th postnatal day , 
 the overall effect of lead intoxication was retardation of brain growth . 
 the mass of both the cerebral gray and white matter was appreciably reduced in the lead rats without any reduction in cell populations . while the neuronal population was preserved , the growth of neurons was reduced and their maturation retarded . 
 the retarded neuronal growth was characterized by the limited proliferation of processes in the neuropil and by the reduction in the number of synapses per neuron . 
 however , synaptogenesis was neither delayed nor perturbed but reduced by the limited development of neuronal dendritic fields . the myelination was altered and its cerebral content significantly reduced . 
 the effect of lead on myelination was one of hypomyelination . 
 the hypomyelination appears to be primarily related to retarded growth and maturation of the neuron and is not a reflection of a defect in the myelinating glia or a delay in the initiation of myelination . 
 
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