Role of vasopressin on excitatory amino acids mediated pressor responses in the periaqueductal gray area

Abstract

In order to evaluate the role played by vasopressin on pressor responses elicited by stimulation of the periaqueductal gray (PAG) area by excitatory amino acids we carried out in vivo studies in genetically vasopressin deficient rats (Brattleboro). Microinjections of 1-glutamic acid (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 rats induced increases of arterial blood pressure values significantly lower than those obtained in Long Evans rats (control) (glutamate in Brattleboro rats: from +2+/-1 mmHg to 16+/-3 mmHg; glutamate in Long Evans 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 Brattleboro rats (urethane 1.2 g/kg i.p.) pressor responses to NMDA microinjections (0.7 nmol/rat) into the PAG area were significantly lower than in Long Evans rats (controls) (+15+/-3 mmHg vs +24+/-4 mmHg). In Long Evans rats NMDA injection also reversed blood pressure decrease induced by ganglionic blocker, hexamethonium and/or losartan (3 mg/kg i.v.), an AT1 receptor antagonist. In Brattleboro rats, NMDA injection did not reverse blood pressure decreases induced by hexamethonium (5 mg/kg i.v.). Moreover, hexamethonium induced blood pressure decrease was not reversed by acetylcholine injection (137 nmol/rat) into the PAG area of anaesthetized Long Evans rats, but if injected before hexamethonium, acetylcholine was able to increase blood pressure (+25+/-3 mmHg). Our results document: i) the importance of the PAG area in the control of cardiovascular system; ii) the involvement of excitatory amino acids in the neural control of vasopressin release; iii) the close relationship between glutamate and vasopressin in the central blood pressure regulation.

Vasopressin V1a receptors mediate the hypertensive effects of [Pyr1]apelin‐13 in the rat rostral ventrolateral medulla

“…), whereas VP is a potent vasoconstrictor and the pressor responses of excitatory amino acids injected into the brain have been shown to be mediated via VP release (Pizzirusso et al . ). Additionally l ‐glutamate and GABA receptors play important roles in the synaptic regulation of RVLM central pressor responses (Dampney ).…”

“…We evaluated the role of Ang II, VP, glutamate and GABA neurotransmission on the cardiovascular effects mediated by bilateral RVLM [Pyr 1 ]apelin-13 microinjection. Ang II, acting via the AT1 receptor expressed in the RVLM, is known to function as an excitatory modulator increasing BP and sympathetic outflow (Mayorov & Head 2003a), as well as increasing the excitability of spinally projecting PVN neurons by attenuation of GABAergic synaptic inputs (Li et al 2003), whereas VP is a potent vasoconstrictor and the pressor responses of excitatory amino acids injected into the brain have been shown to be mediated via VP release (Pizzirusso et al 1998). Additionally L-glutamate and GABA receptors play important roles in the synaptic regulation of RVLM central pressor responses (Dampney 1994).…”

Cardiovascular effects of noradrenaline microinjected into the dorsal periaqueductal gray area of unanaesthetized rats

“…There is evidence pointing to the involvement of systemically released vasopressin in the mediation of pressor responses evoked by the injection of excitatory amino acid into the PAG of unanaesthetized rats (Maione et al ., 1992). This idea is further reinforced by the observation that, after blockade of the paraventricular hypothalamic nucleus, the pressor response to the injection of NMDA in the PAG of anaesthetized rats was reversed into a depressor response (Berrino et al ., 1996) and that significantly lower pressor responses were observed after the injection of NMDA into the PAG of unanaesthetized Brattleboro rats, which are genetically vasopressin‐deficient (Pizzirusso et al ., 1998).…”

The diagonal band of Broca is involved in the pressor pathway activated by noradrenaline microinjected into the periaqueductal gray area of rats

“…Both electrical and chemical PAG stimulations evoke cardiovascular changes Pizzirusso et al 1998;Lovick 1985;Krieger and Graeff 1985). Previously, we have reported that noradrenaline (NA) microinjection into the dorsal PAG (dPAG) caused dose-related responses associated with bradycardia (Pelosi and Corrêa 2005).…”