ADHESION AND FUSION OF EPENDYMA IN RAT-BRAIN

Changes of the ependyma of the rat brain from 2 days after birth to 1 year were studied. In neonatal rats, the ependyma of the lateral ventr icle extended medially to cover the hippocampus. The ependyma above th e hippocampus disappeared with age in two ways: (1) a zipper-like with drawal of the medial portion of the ventricle towards the lateral dire ction, and (2) adhesion and fusion of the ependyma in the lateral regi on. The zipper-like closure and fusion, which resulted in disappearanc e of the ependyma, took place in almost all rats within 2 or 3 weeks a fter birth. Initially, ependymal cells retained their cell polarity wi th regular organization at adhesion sites as a two-cell-layer seam. Su bsequently, their polarity became disorganized in the fusion areas wit h convergence of the two-cell-layer seam into a one-cell-layer seam, f ollowed by disruption. The ciliary bundle of individual ependymal cell s became randomly oriented, sometimes in two or more directions. At th e sites where fusion had occurred, fragmentary ependymal seams remaine d detectable (more than 50%) among the neuropil even in adults. These ectopic seams often contained cystic ependymal cells. In the third ven tricle, adhesion was observed but fusion was not. The results indicate that adhesion and fusion of the ependyma occur in select areas during brain development, during which ependymal cells lose their cell polar ity.