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

Area postrema neurons enhance baroreflex function, perhaps by augmenti ng 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 w ere to record extracellular activity of NTS neurons to determine wheth er 1) area postrema and aortic baroreceptor afferents converged in NTS , 2) area postrema and vagal afferents converged in NTS, and 3) the co nvergent inputs were facilitative. Studies were performed in pentobarb ital sodium- or alpha-chloralose-anesthetized rabbits. Forty-six of 19 4 NTS neurons received inputs from the area postrema and aortic depres sor nerve. Twelve of the 23 inputs showed facilitative summation; unit response rate evoked by paired inputs (79%) doubled the predicted (ca lculated) response rate for simple addition (37%). Fifty-eight of 114 NTS neurons received excitatory inputs from the area postrema and vagu s. Eleven of the 13 inputs showed facilitative summation; unit respons e to paired inputs (87%) doubled the predicted response (44%). Area po strema neurons may augment the processing of aortic and vagal inputs b y NTS neurons and, hence, enhance the reflex output of these afferent pathways.