Attenuation of pentobarbital-elicited hypothermia in rats with a history of pentobarbital-LiCl pairings.

Rats were given five separate pairings (sequential IP injections) of pentobarbital and lithium chloride, both hypothermia-inducing agents. When the animals were subsequently tested with a single injection of pentobarbital alone, they exhibited an attenuated hypothermia relative to controls that had either (a) received pentobarbital-LiCl pairings spaced twenty-four hours apart, or (b) received only placebo injections of normal saline. This phenomenon provides further evidence that rats can learn an association between drug states and may help to explain why pentobarbital-LiCl pairings tend to eliminate pentobarbital's capacity to produce a conditioned flavor aversion.