Congenital Anomalies of Central Nervous System and Neuronal Plasticity *

Pathological studies on autopsied brains of mentally and physically handicapped children disclose not infrequently various abnormalities at the histological and cytological levels, such as the abnormal cytoarchitecture, heterotopic neuronal nests, abnormal orientation of neurons and tortuous dendrites. These abnormalities have generally been considered to result from the disorders of neuron production and/or mechanical obstruction of neuronal migration including abnormal radial fibers. Our experimental studies on the microcephalic mouse, which was induced either by prenatal or by postnatal administration of cytosine arabinoside, indicated that the following factors play important roles for above mentioned histological and cytological changes: (1) Disturbance of the neuron production following the destruction of the matrix layer. (2) Regional and incomplete regeneration of the matrix layer and delayed neuron production in the regenerated matrix layer. (3) Unbalanced and plastic synaptogenesis between the remaining neurons which have been produced prior to the destruction of the matrix layer, migrating young neurons produced in the regenerated matrix layer and the afferent fiber terminals which originate from subcortical neurons.