Lesions in ventromedial hypothalamus or amygdala do not affect naloxone's suppression of water consumption.

Rats received lesions in the ventromedial hypothalamus (VMH) or amygdala, or were sham operated, and then were tested for two-hour intake of water after injections of naloxone (2 mg/kg), MIF-1 (2, 4, or 8 mg/kg), or diluent. There was a significant effect of test compound, with naloxone reducing consumption relative to the diluent control and the largest dose of MIF-1. Although MIF-1 tended to suppress drinking, the effect did not reach significance. There was no main effect for lesions, indicating that the amygdala and the VMH do not play a critical role in the effect of naloxone or MIF-1 on water consumption. A significant lesion by time interaction occurred, however, with amygdala-lesioned rats drinking the most in the first 30 min but much less after that. The VMH rats drank the most in the 30-60 min interval, but there were no differences in groups after 60 min. Thus, it appears that the intact VMH and basolateral amygdala are not necessary for naloxone's suppression of water consumption in the rat.