Response of ependyma of the rat third ventricle to operative loss of cerebrospinal fluid: a transmission electron microscopical study.

The ependyma of the cerebral ventricles has been implicated in absorption and secretion of cerebrospinal fluid under resting and experimental conditions by various workers. To investigate the response of the ventricular ependyma to experimental leakage of the fluid, spinal transection was carried out in young adult Wistar rats in the lumbar region. The ependyma of the third ventricle was processed for transmission electron microscopy on the 7th post-operative day. The ependymal cells in the sham-operated control animal exhibited regional variations in respect of cilia, microvilli and in their relationship to the subjacent subependymal zone. However, most cells showed apical mitochondria and Golgi cisternae with few profiles of granular and smooth endoplasmic reticulum. Pinocytotic and dense-coated vesicles were not prominent features. In the operated rat, a few ultrastructural changes were noted. A profusion of microvilli and blebs with secondary surface modifications was characteristically seen on the ventricular face. Pinocytotic and dense-coated vesicles appeared to be consistent features. Proliferation of mitochondria, Golgi cisternae, polyribosomes and of smooth and granular endoplasmic reticulum was evident throughout the cytoplasm. The mitochondria, in many cases, presented a pleomorphic appearance with increased electron density. The above modifications in the fine structure, considered collectively, point to an increased ependymal activity. The evidences of both absorptive (presence of microvilli, pinocytotic and dense-coated vesicles) and secretory features (presence of blebs, proliferation in membrane components and in polyribosomes) within the same cell suggest its simultaneous involvement in both absorption and secretion. The observed changes may be interpreted as a compensatory attempt by the ependymal cell toward conservation and replenishment of cerebrospinal fluid.