Distribution of two types of monoamine oxidase-containing neurons in the cat medulla oblongata demonstrated by an improved histochemical method.

The topographic distribution of cells containing monoamine oxidase, the enzyme which deaminates amines, was studied in the cat medulla oblongata. By means of enzyme histochemistry using a new coupled peroxidation method, monoamine oxidase activity was demonstrated in the somata, dendrites and fibers. Type A monoamine oxidase, inhibited by clorgyline but not deprenyl, were localized in the cells distributed in the ventrolateral and dorsomedial medulla where catecholaminergic neurons are present. Type B monoamine oxidase-positive cell bodies were identified in the regions containing serotonergic neurons. Furthermore, we found an intense activity of type A monoamine oxidase in many cells of the dorsal motor nucleus of the vagus of the rostrocaudal extent, and more rostrally in the nucleus parvocellularis where few or no aminergic neurons have been described.