The neurohypophyseal hormone vasopressin (AVP) is widely distributed throughout the central nervous system. It acts as an excitatory transmitter in the CNS and plays an important physiological role in water and electrolyte homeostasis. However, water deprivation has been shown to induce changes in the levels of monoamines, but there is little knowledge about the influence of AVP on monoamine levels after water deprivation. In this study, we investigated the effect of AVP and its receptor antagonists on alterations in dopamine (DA) release and cyclic adenosine 3′,5′ monophosphate (cAMP) efflux from rat brain slices following water deprivation. Striatal brain slices (500 µm thick) were incubated in a medium with or without AVP (0.1–1.0 µM) for 30 min. After 2 h of washout in normal medium, high KCl (40 mM)-evoked DA release and cAMP efflux from the rat brain slices were examined. In the brain slices of euhydrated animals, treatment with AVP slightly altered DA release and cAMP efflux from the brain. This increase in DA release and cAMP efflux was not significantly affected by the addition of a calcium/calmodulin-dependent protein phosphatase, calcineurin (20 µM), to the incubation medium or either by a V1 or V2 AVP receptor antagonist. In contrast, AVP significantly increased the DA release and enhanced the cAMP efflux from the brain slices of water-deprived animals. The AVP-induced increase of brain response in the water-deprived animals was significantly attenuated by a V2 receptor antagonist, partially by calcineurin, but not by a V1 receptor antagonist. The present results suggest that AVP may play a role in water-deprivation-induced DA release and cAMP efflux, which is possibly mediated through the activation of the V2 receptor. The V2 receptor action is attenuated by calcium/calmodulin-dependent dephosphorlyation of some cellular proteins critical for signal transduction.

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