Cholinesterases in the area subpostremas. A region adjacent to the area postrema in the cat

A region in the medulla oblongata of the cat, which has been named the area subpostrema, has been described. This area is unique in demonstrating strong staining for both specific and pseudocholinesterase in the walls of capillaries and also in an arc of neuropil which partly surrounds these capillaries. Over most of its length the area subpostrema lies immediately ventral or ventrolateral to the area postrema, dorsal to the dorsal motor nucleus of the vagus and dorsomedial to the tractus solitarius. The area subpostrema, unlike the area postrema, is not stained by the vital dye trypan blue. A group of capillaries in the inferior olivary nucleus which demonstrate specific but not pseudocholinesterase activity have also been described. Using Nissl stains and silver impregnation techniques the area subpostrema has been found to contain a few small neurones and many unmyelinated nerve fibers. Some nerve fibers within the area subpostrema demonstrate specific cholinesterase activity. The relation of the area subpostrema to the nucleus of the tractus solitarius has been discussed. It has been suggested that the area subpostrema might have receptor functions related to autonomic control.