Quantitative analysis of the human corpus callosum under light microscopy

In recent years many workers have studied the morphology of the adult corpus callosum and controversy exists regarding genderand ageassociated differences. Callosal size may vary due to differences in the number and size of nerve fibers, glial cells and blood vessels. However, very little is known about the fiber composition of the human corpus callosum and how this might affect the length and thickness. The aim of this study is to investigate the regional differences in the numbers and diameters of several components of the corpus callosum per unit area and to determine ageand sex-related differences in the fiber composition of the corpus callosum. Eight human brains, both male and female, ages ranging from 25 years to 67 years, were studied. Semithin sections taken from different regions of the corpus callosum were stained with toluidine blue, examined under a Leitz DMRHC research microscope at a magnification of 40 x, and viewed at larger magnification on a computer screen after zooming. The number, diameter and area occupied by myelinated nerve fibers, glial cells and blood vessels per 0.01mm were noted and analysed statistically. Thinly myelinated (diameter < 1.5 μm) nerve fibers were abundant in the genu and the lowest number was noted in the body per unit area. The area occupied by glial cells was more greater in the body of the corpus callosum. The splenium had a greater number of thick fibers (> 5 μm). The number of myelinated nerve fibers in the body of the corpus callosum was lower than in other regions. This may have been due to the presence of greater number of glial cells and large myelinated nerve fibers occupying a unit area. There was no statistically significant ageor sex-difference in the number of nerve fibers.