Role of baroreceptor afferents on area postrema-induced inhibition of sympathetic activity.

Activation of the area postrema by either electrical stimulation or chemical application of L-glutamate has been shown to result in an enhancement of cardiovascular baroreflexes similar to that seen with systemic infusions of arginine vasopressin (AVP). In addition, it has been found that the effects of AVP on baroreflex inhibition of renal sympathetic nerve activity (RSNA) are similar to those observed with phenylephrine following lesions of the area postrema or after partial denervation of baroreceptor afferents. The present study was undertaken to determine the role of baroreceptor afferent input on area postrema stimulation-induced decreases in sympathetic activity. In anesthetized rabbits, the responses of arterial pressure, heart rate, and RSNA to area postrema electrical stimulation were obtained before and after progressive sinoaortic denervation and vagotomy. Stimulation of the area postrema in carotid sinus-denervated animals consistently decreased RSNA in a frequency-dependent manner. However, following bilateral removal of both the aortic nerves and the vagi, electrical stimulation of the area postrema had no effect on RSNA. These results suggest that the ability of area postrema stimulation to inhibit RSNA is dependent on the presence of baroreceptor afferent input.