[Light and electron-cytochemical analysis of acetylcholin-positive esterase-structures in the area postrema and...

Localization of acetylcholinesterase (AChE) in the area postrema and area subpostrema of the rat was investigated by light- and electronmicroscopic histochemical methods. AChE-positive small cells probably identical with parenchyma cells are spread evenly in the area postrema. Since axosomatic synapses and axons could not be identified, the neuronal character of these cells could not be unequivocally proved. AChE-positive suggests, however that the parenchyma cells of the area postrema of the rat are more closely related to neurons than to glial cells. Capillaries possessing fenestrated endothelium of the area postrema and various types of glial cells do not exert any AChE-positivity. The area postrema is surrounded by a meshwork of AChE-positive capillaries, constituting the area subpostrema. Since we found no signs of AChE synthesis in the endothelial cells of these capillaries, the possibility of dendritic secretion as the source of AChE activity of the basement membrane and pinocytotic vesicles, cannot be excluded. On the basis of the results it seems possible that the AChE activity is related to the specific structure of the basement membrane; participation of enzyme activity in the presumed function of the area postrema and area subpostrema is suggested.