An autoradiographic study of methyl-azoxy-methanol acetate-induced cortical malformation.

A completely disorganized pattern of neuronal migration was observed in intracortical neuronal nodules induced by the injection of methyl-azoxy-methanol acetate (MAM) in the rat on the day 14 of gestation. Labeled neurons were found at different cortical levels after a single injection of tritiated thymidine on days 14, 16, or 18 of gestation. Preservation of the ascending migratory progress of neuroblasts toward the cerebral cortex is, however, seen in the largest areas in which no intracortical nodules are found in spite of the abnormal structure of these areas. Neurons labeled on day 16 of gestation occupy deep regions of the cortex, while neurons labeled on day 18 are found at superficial levels. These results indicate variable degrees of disturbance in the migratory pattern in spite of the disorganization of the cortical structure in brains injured at an early stage before the cortical plate is formed.