Differential role for NMDA and non-nmda receptor subtypes in baroreceptor afferent integration in rat NTS

The role of NMDA and non-NMDA receptor subtypes in baroreccptor afferent integration in NTS was investigated in pentoharbital anesthetized, paralyzed and artificially ventilated rats. Aortic nerve (AN) evoked discharge was classified as monosynaptic (MS; second of two stimuli separated by 5 ms evoked discharge; minimal onset latency variability) or polysynaptic (PS). The effects of iontophoretic application of the NMDA antagonist AP-5 (lOmM) or the non-NMDA antagonists CNQX (5mM) or NBQX (4mM) on single pulse AN evoked discharge and spontaneous discharge were examined using ejecting currents of 20&40nA. Ai these "doses" AP-5 blocked NMDA induced excitation but not that induced by AMPA or kainic acid co-iontophoresis while CNQX and NBQX blocked AMPA and kainic acid induced excitation but not that induced by NMDA. AP-5 inhibited PS AN inputs (MANOVA, p<.(K)5, n=12), but not MS AN inputs (p=. 15, n=6). In contrast to AP-5, CNQX and NBQX inhibited both MS (p<.05 for both drugs, n=6&8 respectively) and PS (p<.fK)5 for both drugs, n=ll&13 respectively) evoked AN inputs. The spontaneous discharge of AN evoked cells was significantly inhibited by AP-5 (p<. 01. n=2 MS & 7 PS), CNQX (p<.01, n=2 MS & 10 PS) and NBQX (p<.(X)l. n=5 MS & 9 PS). The data suggest that excitatory amino acid receptor subtypes are differentially involved in the integration of MS and PS baroreceptor inputs by NTS neurons.