The purpose of these studies was to determine the relative role of N-methyl-D-aspartic acid (NMDA) receptors and non-NMDA receptors in the nucleus of the tractus solitarius (NTS) in mediating arterial baroreceptor reflexes evoked by electrical stimulation of the aortic nerve. Selective blockade of NMDA receptors in the NTS had little effect on aortic baroreflexes except at high frequencies of aortic nerve stimulation. In contrast, blockade of non-NMDA receptors in the NTS abolished aortic baroreceptor reflexes. These results suggest that although NMDA receptors may modulate baroreflex responses, synaptic activation of non-NMDA receptors in the NTS plays the predominant role in mediating aortic baroreceptor reflexes.