Effects of ethanol in an open field apparatus: modification by U50488H and WIN 44441-3.

The effects of U50488H, a kappa agonist, and WIN 44441-3, a kappa antagonist, and their modification of the effects of ethanol, on the behavior of rats in a modified open field apparatus, was examined. Crossover activity was increased by U50488H. Headpoke activity was decreased by WIN 44441-3 and increased by U50488H. Rearing activity was increased by WIN 44441-3 but was not affected by U50488H. The effect of both drugs was dose related, with the largest doses having no effect. Ethanol (0.5 g/kg) stimulated crossover activity while it depressed rearing, headpoke and corner activities; except for crossover activity the 2.0 g/kg dose of ethanol depressed these activities. Pretreatment with WIN 44441-3 (0.5 mg/kg) potentiated the stimulant effect of ethanol on crossover activity and partially reversed the depressant effect of ethanol on rearing and headpoke activities. U50488H potentiated the ethanol-induced depression of headpoke and reversed the depression of corner activity. Pretreatment with U50488H had no effect on ethanol's action on crossover and rearing behaviors. Our results indicate that kappa opiate receptors may mediate some behaviors exhibited by rats in a modified open field apparatus. Activation of these receptors increases locomotor and headpoke activity but had no effect on rearing activity. Furthermore, the 0.5 g/kg dose of ethanol has differential effects on different measures of open field behavior, while the 2.0 g/kg dose was largely depressant. Our data suggest that some of these effects of ethanol may be mediated via kappa opioid receptors.