Brain oxytocin receptor antagonism disinhibits sodium appetite in preweanling rats

Previous studies have shown that preweanling rats do not express an endogenous sodium appetite until postnatal day 12. The present studies tested the hypothesis that prior to 12 days of age sodium appetite, induced by either central administration of angiotensin II (AngII) or adrenalectomy, is inhibited by endogenous oxytocin (OT). After 9- or 10-day old animals were given a central injection of either an OT receptor antagonist or vehicle, they were infused intraorally with 4% sodium chloride which the animals could either swallow or reject. Intake was measured as the increase from initial body weight. There was very little sodium consumption by vehicle-injected animals that received sham surgery or adrenalectomy; however, the OT receptor antagonist significantly elevated sodium consumption in adrenalectomized animals. The OT antagonist also potentiated sodium intake after AngII pretreatment. These results suggest that the neurochemical circuits necessary for the expression of sodium appetite are present and functional as early as postnatal day 9; however, until 12 days of age this behavior is suppressed by endogenous OT. (C) 1997 Elsevier Science B.V.