Morphologic Changes of Intermediate Filaments of Ependymal Cells in Experimentally Induced Hydrocephalic Rats

Ependymal cells line the surface of cerebral ventricles. They do not regenerate after they are fully matured and have a limited response to injury. In hydrocephalus, the expansile force of the ventricular wall is applied to ependymal cells and causes cell deformity to some degree. As it is known that the intermediate filaments of a cell act as a framework that resists changes in cellular shape, there may be some detectable changes of intermediate filaments of ependymal cells in hydrocephalus. In developing ependymal cells, it is also unclear if there are any changes to intermediate filaments in hydrocephalus. Developing ependymal cells are known to lose their immunoreactivity to glial fibrillary acidic protein (GFAP), a kind of intermediate filaments which exist in some neuroglial cells. We experimentally induced congenital and postnatal hydrocephalus and investigated the changes of immunoreactivity against GFAP as well as the ultrastuctures of rat ependymal cells in both types of hydrocephalus. To induce congenital hydrocephalus, 40 mg/kg of ethylenethiourea (ETU) was orally administered to pregnant rats on the 15th day after conception. Tissues taken from fetuses on the 17th day, from newborn rats immediately after birth, and from rats of 1 week and 2 weeks after birth were obtained and processed for immunohistochemistry for GFAP and electron microscopy. Postnatal hydrocephalus was induced by injecting kaolin suspension into the subarachnoid space of 15-day-old rats. Ependymal tissues were obtained and processed for immunohistochemistry and electron microscopy after 1 and 2 weeks following injection. The results were as follows; 1. Congenital hydrocephalus was induced more consistently and extensively than postnatal hydrocephalus. 2. In congenital hydrocephalus, GFAP-reactive ependymal cells were found in lateral ventricles of 1-week and 2- week-old rats, while in control and postnatal hydrocephalic groups, GFAP-reactive ependymal cells were not found. GFAP-reactive cells tended to be found in clusters. 3. Electron microscopy showed ependymal cells in congenital hydrocephalus had a less marked flattening figure, scarce apical cilia, often widened regions in the intercellular gap, spaces in subependymal tissue, and different figures in mitochondria. Above all, intermediate filaments, including GFAP, increased and were irregularly arranged in ependymal cell cytoplasm in congenital hydrocephalus. Therefore, in congenitally-induced hydrocephalus, the ependymal cells appeared to have a greater responsiveness to expansile force and remained in a more premature state than postnatally-induced hydrocephalus.restrictio