ROLE OF VASOPRESSIN ON EXCITATORY AMINO-ACIDS MEDIATED PRESSOR-RESPONSES IN THE PERIAQUEDUCTAL GRAY AREA

In order to evaluate the role played by vasopressin on presser respons es elicited by stimulation of the periaqueductal gray (PAG) area by ex citatory amino acids we carried out in vivo studies in genetically vas opressin deficient rats (Brattleboro). Microinjections of 1-glutamic a cid (glutamate. 0.6 to 60 nmol/rat) or N-methyl-d-aspartic acid (NMDA, 0.07 to 7 nmol/rat) into the PAG area of freely moving Brattleboro ra ts induced increases of arterial blood pressure values significantly l ower than those obtained in Long Evans rats (control) (glutamate in Br attlebore rats: from +2+/-1 mmHg to 16+/-3 mmHg; glutamate in Long Eva ns rats: from +16+/-2 mmHg to +36+/-4 mmHg; NMDA in Brattleboro rats: from +5+/-2 mmHg to +34+/-8 mmHg; NMDA in Long Evans rats: from +18+/- 7 mmHg to 80+/-9 mmHg; n=5). Similarly, in anaesthetized Brattlebore r ats (urethane 1.2 g/kg i.p.) pressor responses to NMDA microinjections (0.7 nmol/rat) into the FAG area were significantly lower than in Lon g Evans rats (controls) (+15+/-3 mmHg vs +24+/-1-mmHg). In Long Evans rats NMDA injection also reversed blood pressure decrease induced by g anglionic blocker, hexamethonium and/or losartan (3 mg/kg i.v.), an AT 1 receptor antagonist. In Brattleboro rats, NMDA injection did not rev erse blood pressure decreases induced by hexamethonium (5 mg/kg i.v.). Moreover, hexamethonium induced blood pressure decrease was not rever sed by acetylcholine injection (137 nmol/rat) into the FAG area of ana esthetized Long Evans rats, but if injected before hexamethonium, acet ylcholine was able to increase blood pressure (+25+/-3 mmHg). Our resu lts document: i) the importance of the FAG area in the control of card iovascular system; ii) the involvement of excitatory amino acids in th e neural control of vasopressin release; iii) the close relationship b etween glutamate and vasopressin in the central blood pressure regulat ion.