AREA POSTREMA AND AORTIC OR VAGAL AFFERENTS CONVERGE TO EXCITE CELLS IN NUCLEUS-TRACTUS-SOLITARIUS

Area postrema neurons enhance baroreflex function, perhaps by augmenting baroreceptor afferent processing in the nucleus tractus solitarius (NTS). If so, NTS neurons should receive convergent excitatory inputs from area postrema neurons and baroreceptors. The aims of this study were to record extracellular activity of NTS neurons to determine whether 1) area postrema and aortic baroreceptor afferents converged in NTS, 2) area postrema and vagal afferents converged in NTS, and 3) the convergent inputs were facilitative. Studies were performed in pentobarbital sodium- or alpha-chloralose-anesthetized rabbits. Forty-six of 194 NTS neurons received inputs from the area postrema and aortic depressor nerve. Twelve of the 23 inputs showed facilitative summation; unit response rate evoked by paired inputs (79%) doubled the predicted (calculated) response rate for simple addition (37%). Fifty-eight of 114 NTS neurons received excitatory inputs from the area postrema and vagus. Eleven of the 13 inputs showed facilitative summation; unit response to paired inputs (87%) doubled the predicted response (44%). Area postrema neurons may augment the processing of aortic and vagal inputs by NTS neurons and, hence, enhance the reflex output of these afferent pathways.