NMDA receptor antagonist blocks the bradycardic but not the pressor response to l-glutamate microinjected into the nucleus tractus solitarius (NTS) of unanesthetized rats

Abstract

In the present study we evaluated the role of NMDA receptors on the pressor and bradycardic responses to l-Glutamate ( l-G1u) microinjected into the nucleus tractus solitarius (NTS) of unanesthetized rats. l-Glu (1 nmol/100 nl) was microinjected into the NTS before and 10 min after microinjection of phosponovaleric acid (AP-5), a selective NMDA receptor antagonist, into the NTS of three different groups of rats (0.5, 2.0 and 10.0 nmol/100 nl). Microinjection of AP-5 into the NTS produced a dose-dependent reduction in the bradycardic response to l-Glu. However, no significant change in the pressor response to l-Glu was observed. These results indicate that the activation of the cardiovagal component (bradycardia) by l-Glu involves NMDA receptors and suggest that the activation of the sympatho-excitatory component (pressor response) by l-Glu in the commissural NTS is mediated by non-NMDA receptors.