Effects of naloxone and its quaternary analogue on fluid consumption in water-deprived rats.

The effects of subcutaneous administration of naloxone and its quaternary analogue on the consumption of water, saline and saccharin solution were investigated in the water-deprived rat. Quaternary naloxone (0.01-10 mg . kg-1), effective in blocking peripheral opiate receptors, had no effect on fluid intake. In contrast, naloxone (0.01-10 mg . kg-1), produced dose-dependent attenuation of intake for each of the three fluids, indicating a central location of the relevant opiate receptors. Access to saline induced additional drinking, compared with water intake, due to an extension of the initial avid consumption which follows the period of water-deprivation. This enhancement of drinking was blocked by naloxone, but not by its quaternary analogue. Interactions between naloxone and taste factors in drinking may, therefore, depend on blockade of central opiate receptors.