Cellular localization of monoamines in the area postrema of certain mammals

The area postrema was studied using a highly sensitive and specific fluorescence microscopical method for the demonstration of certain biogenic monoamines. In all the species studied (rat, guinea‐pig, rabbit, cat, dog, monkey) there occur small nerve cells containing a primary catecholamine. A varying number of catecholamine‐storing nerve terminals can be demonstrated in all species. Many — if not all — of these seem to derive from catecholamine axons running in abundance just outside the area postrema. Against the background of earlier findings (Vogt, '54; Amin, Crawford and Gaddum, '54) of high levels of noradrenaline and 5‐hydroxytryptamine thought to be present in glial cells in this organ it is concluded that these levels are not in accordance with the relatively small number of monoamine‐containing structures demonstrated in area postrema. The explanation for this is in all probability that the area postrema tissue taken for biochemical determinations have been contaminated with surrounding brain tissue, very rich in catecholamine and 5‐HT containing terminals. There is discussed in conclusion the possibility of adrenergic mechanisms being involved in the reflex path of central emesis.