Supraependymal neuronal elements of the floor of the fourth ventricle in adult rat: a scanning electron microscopic study.

Scanning electron microscopic studies of the floor of the fourth ventricle revealed the presence of a cluster of neuron-like structures and an extensive network of fibers on the ependymal surface. These supraependymal cell clusters are found on the sparsely ciliated regions of the fourth ventricle. The surface of these cells is richly covered with nerve ending-like structures of varying size and shape. Long cables of intertwined fibers are present all over the surface of the fourth ventricular floor. Majority of these fibers are varicose in nature. Some of these fibers end blindly as round or ellipsoid thickening in the ventricular cavity. The widespread occurrence of supraependymal structures of the third and fourth ventricles, which are presumed to be neurons, nerve fibers and free floating nerve endings in the cerebrospinal fluid (CSF), suggest that they potentially function as an additional of intraventricular communication.