A sympathoinhibitory area in cat rostral medulla: its role in cardiovascular tone regulation and baroreflex

Abstract

We have found a medullary vasodepressor area in cat centered 3 mm rostral to the obex and just lateral to the compact division of the ambiguus nucleus. The area is compact, extending at most 1 mm in any direction. Microinjection of l-glutamate into this rostral depressor area (RDA) elicited acute hypotenssion and bradycardia. These response were not reduced by either peripheral atropine blockade or bilateral vagotomy, but they were nearly abolished by peripheral phentolamine/propranolol blockade or high cervical cord transection. Bilateral reversible blockade of the RDA by local microinjection of the neuronal hyperpolarizing agent muscimol yielded chronic hypertension and tachycardia. Sympathetically mediated baroreflex, observed as a bradycardic response to a peripherally administered phenylephrine bolus in atropinized animal, was partially (50%) abolished during this same blockade. We conclude that the RDA contains sympathoinhibitory cells which are involved in the regulation of cardiovascular tone and in the expression of the sympathetic component of baroreflex.