Potentiation of non-N-methyl-D-aspartate receptor-induced changes in bloodpressure by substance P in rats

Central release of substance P (SP) in the nucleus tractus solitarius (NTS) may potentiate the reflex responses evoked by baroreceptor afferent input to this medullary nucleus. The mechanism is not known but may involve modul ation of responses produced by release of glutamate, the putative primary b aroreceptor transmitter, at neurons within the NTS. The principal glutamate receptor subtype proposed to transmit baroreceptor afferent input at secon d-order neurons is the non-N-methyl-D-aspartate (NMDA) receptor. The presen t study examined the effects of microinjection of SP into barosensitive reg ions of the NTS on the depressor and bradycardic response induced by activa tion of non-NMDA receptors in the NTS by subsequent microinjection of (+/-) -alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), a non-NMD A receptor agonist. Substance P potentiated the non-NMDA receptor-induced d epressor response to AMPA in the NTS, evoking a significantly larger change in blood pressure over the same time period. These data suggest that SP ma y modulate a non-NMDA-mediated component of the baroreflex to influence the control of arterial blood pressure by increasing the sensitivity of the ba roreceptor reflex. (C) 2000 Elsevier Science Ireland Ltd. All rights reserv ed.