Ultrastructure of the paraphysis cerebri of the water snake Natrix maura L.

Paraphyseal epithelial cells of Natrix maura have been studied with light and electron microscopy. They showed a clear polarity apically related to the third ventricle and, basally, to a connective tissue layer which surrounded the whole organ. The apical surface of the cells, attached by junctional complexes, showed many microvilli, scarce cilia, and some pinocytotic coated vesicles. In their apical cytoplasm many mitochondria and a well-developed golgi apparatus and endoplasmic reticulum were observed. Whereas lamellar bodies were abundant and closely related with mitochondria, glycogen particles were absent. Basal cell membrane showed infoldings where pinocytotic coated vesicles were detected. In the connective tissue layer, fenestrated sinusoids and fibrocytes, as well as rare unmyelinated nerve fibers engulfed by Schwann cells, were present. The possible active role of paraphyseal cells in exchanging substances between cerebrospinal fluid and blood is discussed.