Brain vasopressin involvement in behavioral sensitization to amphetamines and drinking hypertonic salt solutions.

Abstract

Sodium restriction cross-sensitizes rats to the psychomotor effects of amphetamines and activation of brain vasopressin pathways induce a psychomotor sensitization and facilitate salt intake in sodium-deficient rats. In Experiment 1, we tested the hypothesis that male rats previously sensitized to central VP injections would subsequently show enhanced psychomotor responses to amphetamine. Rats were administered either saline, intraventricular injections of VP (50 ng) or amphetamine (1 or 3 mg/kg, d-amphetamine sulfate, i.p.) on two consecutive days. All rats were administered amphetamine on day 3 and behavior was monitored. Amphetamine on day 3 elicited a significantly greater psychomotor response in rats that had two prior injections of amphetamine or VP, than in rats previously treated with saline or those receiving amphetamine for the first time on Day 3. In Experiment 2, the hypothesis that prior experience with central VP would cross-sensitize the rat to drinking hypertonic sodium (NaCl) solutions was tested. Naïve male rats were administered intraventricular injections of VP (50 ng) or isotonic saline for 3 days and on the fourth day non deprived rats were given access to 0.3 M NaCl and water for 1 h. Control (isotonic saline treated) rats only drank 1 ml of 0.3 M NaCl, but need-free rats previously exposed to central VP injections drank significantly more hypertonic saline (4 ml). These results show that prior experience with central VP cross-sensitizes rats to the psychomotor stimulant effects of amphetamine and the ingestion of concentrated NaCl solutions. Supported by NIH DK50586 and RR15640.