Cardiovascular and hypertonic NaCl and water intake effects induced by GABAC agonist injected into the lateral parabrachial nucleus (LPBN) in rats.

Abstract

The lateral parabrachial nucleus (LPBN), a pontine structure is an important area involved in the control of water and sodium intake. Previous studies showed inhibitory serotonergic and cholecystokinergic mechanisms in the LPBN in the control of water and sodium intake. Injections of methysergide, a serotonergic receptor antagonist or proglumide, a cholecystokinin antagonist, into the LPBN increase hypertonic NaCl intake induced by sodium depletion or combined treatment with furosemide and angiotensin converting enzyme inhibitor captopril and increases water intake induced by angiotensin II injected intracerebroventricular. However, methysergide or proglumide into the LPBN in satiated rats not submitted to any other dipsogenic treatment produces no intake of water or NaCl. GABA is an inhibitory neurotransmitter widely distributed in the central nervous system. Until recently, two receptor subtypes were known: bicuculline-sensitive GABAa and baclofen-sensitive GABAb receptors. Several lines of evidence now indicate the existence of a third class of GABA receptor; which is distinct pharmacologically from GABAa and GABAb receptors. These novel GABAc receptors are Cl- pores. They (GABAc receptors) are insensitive to drugs that modulate GABAa and GABAb receptors. Recent studies from our laboratory showed that injections of muscimol (a GABAa agonist) or baclofen (a GABAb agonist) into the LPBN induced hypertonic NaCl and water intake in satiated rats, induced by sodium depletion or hyperosmotic rats. Considering the involvement of central GABAergic mechanisms in the regulation of ingestive behavior, the existence of inhibitory mechanisms in the LPBN to control sodium intake, in the present study we pretend investigated the cardiovascular effects (arterial pressure and heart rate) of a third class of GABA receptors (GABAc receptors). In addition, the effects of the activation of GABAc receptors in the LPBN on water and hypertonic NaCl intake will also tested in satiated or depleted rats induced by injection of furosemide and captopril (FURO+CAP model).