The aim of this study was to demonstrate paraventricular hypothalamic nucleus (PVN) involvement in the cardiovascular changes induced by N-methyl-d-aspartic acid (NMDA) microinjections at the level of periaqueductal grey (PAG) matter. The study was carried out in anaesthetized rats and the arterial blood pressure monitored by a polygraph. NMDA injections (0.68-6.8 nmol/rat) into the PAG area induced a significant increase in blood pressure. After pretreatment by injection of the NMDA receptor antagonist dl-2-amino-5-phosphonovaleric acid (2-APV, 0.05-5 nmol/rat) into the PVN, administration of NMDA (0.68 nmol/rat) into the PAG area elicited a decrease, rather than an increase, of blood pressure. We observed a significant reduction of the pressor effect induced by 6.8 nmol/rat NMDA after 2-APV injection into the PVN. 2-APV injection into the dorsomedial hypothalamic nucleus, an area near the PVN, did not modify the increase in blood pressure induced by NMDA in the PAG area. We suggest the existence of a glutamatergic connection between the PAG area and the PVN in the cardiovascular effects of NMDA.