CEREBRAL MICROGYRIA, THALAMIC CELL-SIZE AND AUDITORY TEMPORAL PROCESSING IN MALE AND FEMALE RATS

Induction of microgyria by freezing injury to the developing somatosen sory cortex of neonatal rats causes a defect in fast auditory processi ng in males, but not in females. It was speculated that early damage t o the cortex has sexually dimorphic cascading effects on other brain r egions mediating auditory processing, which can lead to the observed b ehavioral deficits. In the current series of experiments, bilateral mi crogyri were induced by placement of a freezing probe on the skulls of newborn male and female rats, and these animals were tested in adulth ood for auditory temporal processing. Control animals received sham su rgery, The brains from these animals were embedded in celloidin, cut i n the coronal plane and the following morphometric measures assessed: microgyric volume, medial geniculate nucleus (MGN) volume, cell number , and cell size, and, as a control, dorsal lateral geniculate nucleus (dLGN) volume, cell number and cell size. There were no sex difference s in the cortical pathology of lesioned animals. However, microgyric m ales had more small and fewer large neurons in the MGN than their sham -operated counterparts, whereas there was no difference between lesion ed and sham-operated females. There was no effect on dLGN cell size di stribution in either sex. Microgyric males were significantly impaired in fast auditory temporal processing when compared to control males, whereas lesioned females exhibited no behavioral deficits. These resul ts suggest that early injury to the cerebral cortex may have different effects on specific thalamic nuclei in males and females, with corres ponding differences in behavioral effects.