Dissociation of experimentally induced drinking behavior by ibotenate injection into the median preoptic nucleus

Adult male Sprague-Dawley rats were injected with either ibotenic acid (5 μg/1 μl) or vehicle in the ventral median preoptic nucleus. The injections were given during either methoxyflurane or ketamine anesthesia. None of the rats injected with ibotenic acid were adipsic after surgery. After at least one week of recovery, all rats were tested for drinking responses to angiotensin II (1.5 and 3 mg/kg s.c.) and hypertonic saline (3% and 12% 1 ml/100 g b.wt.). Rats injected with ibotenic acid during methoxyflurane anesthesia drank significantly less than the vehicle injected control group in tests with both doses of angiotensin II and both concentrations of hypertonic saline. The rats that were injected with ibotenic acid during ketamine anesthesia drank significantly less than the control group when tested with 3% hypertonic saline but not when tested with angiotensin II. Histological examination of the injection sites indicated significant reductions in the volume of the median preoptic nucleus only in rats that had been injected with ibotenic acid during methoxyflurane anesthesia. The results are consistent with the interpretation that the drinking response to angiotensin II is dependent upon the integrity of neurons with postsynaptic N-methyl-D-aspartate receptors within the median preoptic nucleus.