Cardiovascular changes induced by the local application of glutamate-related drugs in the rat nucleus tractus solitarii.

The effects of the local application of drugs acting on glutamatergic receptors in the nucleus tractus solitarii (NTS) were investigated in anesthetized rats. Unilateral microinjection of agonists (L-glutamate, L-aspartate, N-methyl-D-aspartate (NMDA) and quisqualate) produced a dose-dependent hypotension and bradycardia. The effects of NMDA were prevented by low doses of the selective NMDA-receptor antagonist, 2-amino-5-phosphonovalerate (2-APV), or by the mixed NMDA/kainate antagonist, gamma-D-glutamylglycine. The response to all agonists and the bradycardia which was elicited in response to the intravenous administration of phenylephrine (vagal reflex response) could be prevented by the local microinjection of the glutamate antagonists kynurenic acid (3 nmol) and 2-APV (10 nmol) into the NTS. The present data suggest that in the NTS, NMDA and quisqualate receptors are implicated in blood pressure reflex regulation.