Microinjection of NMDA antagonist into the NTS of conscious rats blocks the Bezold-Jarisch reflex.

Abstract

The purpose of the present study was to evaluate whether or not cardiovagal excitatory and sympatho-inhibitory pathways of the Bezold-Jarischreflex at the NTS level were mediated by NMDA receptors. The Bezold-Jarischreflex was activated by intravenous (i.v.) injection of serotonin in consciousrats before and after microinjection of phosphonovaleric acid (AP-5), a selective NMDAantagonist, into the NTS. The Bezold-Jarischreflex was also activated before and after methyl-atropine (i.v.) in order to evaluate if the changes in mean arterial pressure were dependent on the bradycardic response. The data showed that AP-5 into the NTS produced a dose-dependent reduction in both bradycardic and hypotensive responses to activation of the Bezold-Jarischreflex. Methyl-atropine also blocked the bradycardic and hypotensive responses to Bezold-Jarischreflex activation. The data show that in consciousrats the cardiovagal component of the Bezold-Jarischreflex plays a major role in the cardiovascular changes produced by the activation of this reflex and suggest that the neurotransmission of the cardiovagal component of the Bezold-Jarischreflex is mediated by NMDA receptors.