Cerebral microgyria, thalamic cell size and auditory temporal processing in male and female rats

Induction of microgyria by freezing injury to the developing somatosensorycortex of neonatal rats causes a defect in fast auditory processing inmales, but not in females. It was speculated that early damage to thecortex has sexually dimorphic cascading effects on other brain regionsmediating auditory processing, which can lead to the observed behavioraldeficits. In the current series of experiments, bilateral microgyri wereinduced by placement of a freezing probe on the skulls of newborn male andfemale rats, and these animals were tested in adulthood for auditorytemporal processing. Control animals received sham surgery. The brains fromthese animals were embedded in celloidin, cut in the coronal plane and thefollowing morphometric measures assessed: microgyric volume, medialgeniculate nucleus (MGN) volume, cell number, and cell size, and, as acontrol, dorsal lateral geniculate nucleus (dLGN) volume, cell number andcell size. There were no sex differences in the cortical pathology oflesioned animals. However, microgyric males had more small and fewer largeneurons in the MGN than their sham-operated counterparts, whereas there wasno difference between lesioned and sham-operated females. There was noeffect on dLGN cell size distribution in either sex. Microgyric males weresignificantly impaired in fast auditory temporal processing when comparedto control males, whereas lesioned females exhibited no behavioraldeficits. These results suggest that early injury to the cerebral cortexmay have different effects on specific thalamic nuclei in males andfemales, with corresponding differences in behavioral effects.