Naloxone's effects on intake of sequentially presented fluids.

Fluid-deprived rats were presented with one of three types of palatable solutions for 15 min, followed by access to either the same solution or one of the other types for 15 min. The solutions were 5.3% sucrose, 0.9% salt solution, and tap water. Naloxone reduced intake of all solutions, as compared to placebo, regardless of type of fluid or order of presentation. Rats receiving water followed by sucrose solution reduced their intake of water under naloxone, but did subsequently take a considerable amount of sucrose solution showing that they were capable of drinking more. These findings indicate that naloxone's effects closely track ordinary satiation-effects, merely enhancing satiation-like functions at each instance of opportunity to take fluids.