Effects of corticosterone on place conditioning to ethanol.

RATIONALE AND OBJECTIVE: Effects of corticosterone on place conditioning to ethanol were investigated in mice using two conditioning schedules; the conventional method and a rapid conditioning schedule in which exposure to the CS+ followed immediately on exposure to the CS-. METHODS: Effects of administration of corticosterone, 10 mg/kg, on the acquisition of place conditioning produced by ethanol, 1-2.5 g/kg, were investigated using the conventional method of conditioning, with exposure to the CS+ and the CS- on alternate days, and also using the rapid conditioning method. Total and free blood corticosterone concentrations were measured after administration of ethanol and corticosterone. RESULTS: In the conventional, alternate day, conditioning schedule, ethanol produced significant place preference at 2 and at 2.5 g/kg, but when these alcohol doses were given with corticosterone 10 mg/kg, significant place conditioning was not seen. In contrast, in the rapid, same day, conditioning schedule corticosterone significantly decreased the dose at which ethanol produced an apparent place preference, with significant place conditioning being seen with ethanol at 1 and 1.5 g/kg in combination with corticosterone, 10 mg/kg. Total and free corticosterone concentrations were increased after ethanol, 1.5 g/kg, compared with controls, and administration of corticosterone, 10 mg/kg, caused a significantly greater increase. There were no significant differences in spontaneous locomotor activity or brain alcohol concentrations between any of the treatment groups. CONCLUSIONS: The effects of corticosterone on ethanol-induced place conditioning are substantially affected by the conditioning schedule used.