Sex differences in the cortex of the rat: The cellular basis
Anatomical sex differences were examined in the cortex of socially housed Long-Evans hooded rats at 90 days of age. Sex differences in cortical size were found to be widespread across the cortical mantle; however, the expression of sex differences was specific to region and lamina. Asymmetries in cortical thickness were found in a few areas but did not vary with the sex. The binocular area of the primary visual cortex (Oc1B) was among the areas showing sex differences in the cortical thickness. This area was identified by cytoarchitectonic criteria on Nissl stained sections and it had a greater volume in male than female rats. Much of the difference in the volume was due to the greater numbers of neurons and glial cells in male than female rats. This finding is consistent with other areas of the nervous system where sex differences in the gross size have been found. It was found that male rats not only had more neurons, but also had more synapses in layers II-III of Oc1B. However, individual neurons in these layers did not receive a different number of synapses between the sexes. Data from this thesis indicate that sex differences may occur at the gross anatomical level of the cortex but the organization of the basic units (neurons) of the cortex may be similar in both sexes. This thesis also shows that studies of sex differences can aid our understanding of cortical organization and neural circuitry.
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign