Acute corticosterone increases conditioned spontaneous orofacial behaviors but fails to influence dose related LiCl-induced conditioned "gaping" responses in a rodent model of anticipatory nausea.

Acute administration of corticosterone has been shown to facilitate learning in a number of associative paradigms, including LiCl-induced conditioned taste aversion learning. The present study examined the effects of acute corticosterone on LiCl-induced conditioned anticipatory nausea in male rats. Anticipatory nausea is produced by pairing a novel distinctive context with the nausea-inducing effects of a toxin, such as LiCl. Following a number of pairings of the context with the effects of the toxin, rats will display a distinctive conditioned "gaping" response when placed into the context in a drug free state. Adult male Long-Evans rats were injected (intraperitoneal, ip) with a LiCl solution (32, 64, or 128 mg/kg, 0.15M) or saline (NaCl, 0.15 M) followed 10 min later by either corticosterone (5 mg/kg) or β-cyclodextrin vehicle (45%) prior to placement in a distinctive context on four conditioning days (72 h apart) for 30 min. On the conditioning test day rats were placed in the distinctive context in a drug-free state and orofacial and somatic responses were video-recorded for 10 min. Gaping responses increased with increasing doses of LiCl in a linear fashion (P<0.01) but were not significantly influenced by the corticosterone treatment. In contrast, significant increases in the frequency of conditioned spontaneous orofacial behaviors on the drug free test day were produced by the corticosterone treatment during the acquisition phase, whereas LiCl treatment during acquisition had no significant effect on these behaviors. Thus, acute corticosterone did not alter the strength of conditioning of anticipatory nausea in rats.