Sex differences in the development of the splenium of the rat corpus callosum
Kim, Jan Haeyoung
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Permalink
https://hdl.handle.net/2142/21408
Description
Title
Sex differences in the development of the splenium of the rat corpus callosum
Author(s)
Kim, Jan Haeyoung
Issue Date
1995
Doctoral Committee Chair(s)
Juraska, Janice M.
Department of Study
Neuroscience
Discipline
Neuroscience
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Neuroscience
Psychology, Psychobiology
Language
eng
Abstract
This series of studies examines sex differences in the development of the splenium of the rat corpus callosum. An HRP study, in which the trajectory in the splenium of axons with different cortical origins was mapped, revealed a rostrocaudal organization of axons in the splenium that corresponds to the rostrocaudal topography of the cortex. At postnatal days 15, 25 and 60, axons originating from visual areas are located in the posterior fifth (relative to the overall length) of the corpus callosum. There were no sex differences in the topography of the splenium, or in the location of visual fibers. An electron microscopy study, in which the posterior fifth of the corpus callosum was extensively sampled, revealed significant dorsoventral and rostrocaudal variation in axon density in the rat splenium. While there were no sex differences in total axon number in the rat splenium at day 15 or 60, there was a sex difference (female $>$ male) at day 25. There was also a sex difference in myelinated axon number in adults (male $>$ female). Axon number decreased after day 15 both sexes, and a further decrease in axon number after day 25 in females only. Thus, axon withdrawal occurs after the adult pattern of callosal projections in the visual cortex is present. Furthermore, there is a sex difference in the time course of axon withdrawal. Phosphorylated MAP1b, which has been associated with axonal outgrowth, was present in the splenium at postnatal days 9 and 11, but not at day 17. This suggests that axonal outgrowth in the rat splenium ceases by the end of the second postnatal week. Embryonic NCAM was present in the splenium from postnatal day 9 through young adulthood. Because the persistent expression of e-NCAM in adult animals has been associated with brain regions capable of structural plasticity, the splenium of the rat corpus callosum may remain plastic into adulthood.
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