Neurotransmission of autonomic components of aortic baroreceptor afferentsin the NTS of awake rats

The effect of sequential blockade of N-methyl- D-aspartic acid (NMDA) recep tors with DL-2-amino-5-phosphonopentanoic acid (AP-5) and non-NMDA receptor s with 6,7-dinitroquinoxaline-2,3 dione (DNQX) in the nucleus tractus solit arii (NTS) on the cardiovascular responses to electrical stimulation (ES) o f the aortic depressor nerve (ADN) was evaluated in awake rats. Two protoco ls were used. In protocol 1, bilateral microinjection of AP-5 into the NTS (n = 7) reduced the hypotensive response to ES of the ADN; subsequent micro injection of DNQX produced additional reduction in this response. AP-5 redu ced the bradycardic response, and DNQX almost abolished this response. In p rotocol 2, bilateral microinjection of DNQX into the NTS (n = 6) reduced th e hypotensive response, and subsequent microinjection of AP-5 significantly reduced this response. DNQX produced a significant reduction in bradycardi c response, and AP-5 abolished this response. The data indicate that proces sing of the parasympathetic component of the NTS aortic baroreceptor affere nts is mediated by both NMDA and non-NMDA receptors, whereas processing of the sympathoinhibitory component seems to be only partially mediated by ion otropic receptors.