Cortical Oligodendrocytes in Kaolin-Induced Hydrocephalus in Wistar Rat: Impact of Degree and Duration of Ventriculomegaly

Abstract

Background: Oligodendrocytes are critical to the function of the brain. They generate the myelin sheath which ensures saltatory conduction, which is a more energy saving and efficient means of axonal impulse transmission. Ventriculomegaly results in neuronal degeneration and astrogliosis. Purpose: The effect of the degree of ventriculomegaly on oligodendrocyte in kaolin-induced hydrocephalus and the timeline have not been extensively documented, hence this study. Methods: A total of 81 rats that were 3 weeks old were divided into 4 groups each consisting of control and experimental subgroups. Kaolin suspension was intracisternally injected to induce hydrocephalus and the animal sacrificed post-induction at 1, 2, 3, and 4 weeks. Two 1-mm-thick coronal slices at optic chiasma level were fixed in 10% buffered formal-saline and Karnovsky's fixative for light and transmission electron microscopy (TEM), respectively. The former slices were processed and stained with hematoxylin and eosin for glial density, cortical thickness, and oligodendrocyte evaluations. Subcortical white matter region of the latter were processed by conventional techniques for TEM. Results: Compared with their corresponding control rats, thickness of the dorsolateral cortex was significantly reduced across the 2-4 week post-induction (WPI), glial density was significantly increased in the mild and moderate ventriculomegaly subgroups 1 WPI but only in mild ventriculomegaly subset 2 WPI. In the 4 WPI group, there was significant increase in glial density across the 3 ventriculomegaly subsets. Early hydropic changes of oligodendrocytes were noted in the inner pyramidal layer mostly in the 4 WPI experimental rats. Dilation of the endoplasmic reticulum precedes that of mitochondria, while mitochondrial crista disruption was noted in the 3 and 4 WPI rats. The nuclear membrane of the oligodendrocytes was progressively deformed from the 2nd to 4th WPI. Conclusion: This study reported degenerative changes of oligodendrocytes and its organelles in kaolin-induced hydrocephalus. Degeneration was worse with duration and in the deep cortical layers.