Kim J H, Ellman A, Juraska J M
Department of Psychology, University of Illinois, Champaign 61820, USA.
Brain Res. 1996 Nov 18;740(1-2):47-56. doi: 10.1016/s0006-8993(96)00637-3.
Previous work from our laboratory reported a sex difference in axon number in the splenium of the adult rat corpus callosum. However, the cortical origin of the axons that were sampled is unknown and sex differences may exist in the topography of axons in this area. The present study revisits the issue of sex differences in axon number in the splenium. First, the topographical organization of axons in the splenium was investigated. Rats each received single intracortical injections of horseradish peroxidase (HRP). The location of HRP labelled fibers in the corpus callosum was compared across the various injection sites. There is a rostrocaudal organization of axons in the splenium based on rostral to caudal cortical location that does not vary by sex. Second, visual axons, which comprise the posterior fifth (relative to overall length) of the corpus callosum in both sexes, were thoroughly sampled with electron microscopy. Significant dorsoventral and rostrocaudal variation in myelinated and unmyelinated axon density was found. While axon density varied to some extent depending on the sex of the animal, axon number calculations revealed no sex differences in total axon number. Males, however, had significantly more myelinated axons than females. Thus, sex differences in axon density in the adult rat splenium were regional and did not result in overall sex differences in axon number.
我们实验室之前的研究报告称，成年大鼠胼胝体压部的轴突数量存在性别差异。然而，所采样轴突的皮质起源尚不清楚，且该区域轴突的拓扑结构可能存在性别差异。本研究重新探讨了胼胝体压部轴突数量的性别差异问题。首先，研究了胼胝体压部轴突的拓扑组织。给大鼠分别进行单次皮质内辣根过氧化物酶（HRP）注射。比较了不同注射部位在胼胝体中HRP标记纤维的位置。基于从吻侧到尾侧的皮质位置，胼胝体压部的轴突存在从吻侧到尾侧的组织排列，且不随性别而变化。其次，用电子显微镜对视觉轴突进行了全面采样，视觉轴突在两性中均占胼胝体后五分之一（相对于总长度）。发现有髓和无髓轴突密度在背腹侧和吻尾侧存在显著差异。虽然轴突密度在一定程度上因动物性别而异，但轴突数量计算显示总轴突数量不存在性别差异。然而，雄性的有髓轴突比雌性明显更多。因此，成年大鼠胼胝体压部轴突密度的性别差异是区域性的，并未导致轴突数量的整体性别差异。
