Effect of lead intoxication on the postnatal growth of the rat nervous system.

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.