Time profile of eosinophilic neurons in the cortical layers and cortical atrophy

Eosinophilic neurons (ENs) appear in the post-ischemic cortex; however, whether there are differences in the time profile for different cortical layers and the fate of the cortex with ENs is largely unknown. We examined the time profile of ENs in different cortical layers and evolution of cortical atrophy after transient cerebral ischemia in Mongolian gerbils. Unilateral forebrain ischemia was induced twice by 10-minute unilateral common carotid artery occlusions. Brains at 24 hours, 4 days, and 2, 4, and 16 weeks post-ischemia were prepared for morphometric analysis. Quantitative analysis of ENs in regions of interest in the rostral and caudal cortex showed the highest number of ENs at 4 days post-ischemia in layers 3 and 6. Reduction in ENs after this peak was slower in layer 6 than in layer 3 in both rostral and caudal cortex, and this difference was significant in layer 6 of the caudal cortex. Infarcts with significant atrophy appeared in the rostral cortex. In the caudal cortex, only selective neuronal death with mild but distinct atrophy was observed. We observed a significant difference between cortical layers in the time profile of ENs in the post-ischemic cortex. Selective neuronal death without infarction was sufficient to induce cortical atrophy after transient cerebral ischemia.