[The ventricular surface of the area postrema and the adjacent area subpostrema in the rabbit brain]

The ependymal surface of the area postrema (rabitt) was examined by scanning and transmission electron microscopy. The flattened ependymal cells show few microvilli. Towards the central canal, the ependymal cells change gradually to a columnar shape; the number of microvilli increases concomitantly. The area postrema ependymal cell surface mostly bears a single cilia. In contrast, a region immediately adjacent to the area postrema, which has been named area subpostrema (Gwyn and Wolstencroft 1968), shows cilia arranged in bunches. These cilia are regularly covered with colloid -- like droplets. A period-acid-bisulfit-aldehydthionine method (Specht 1970) permits to identify these droplets with glyproteids.it has been suggested that the droplets might derive from the area subpostrema ependymal cells. Above the ependymal surface of the area postrema, a great number of fine unmyelinated neuronal processes and thicker processes are observed. Some of them show bulb-like endings. These terminals contain small vesicles, dense cored vesicles (400...800 A), and mitochondria which are mostly characterized by a single central prismatic tubule. The plasmalemma of some bulbs is in a synaptic contact with the apical plasmalemma of the ependyma, while other bulbs see to end freely in the ventricle. Some neuronal processes penetrate between ependymal cells of the area postrema into the ventricular lumen.