Pituitary adenylate cyclase-activating polypeptide (PACAP)-deficient mice display remarkable behavioral changes including increased novelty-seeking behavior and reduced hypothermia induced by either serotonin (5-HT)(1A) receptor agonists or ethanol. Because 5-HT(1A) receptors have been implicated in the development of alcohol dependence, we have examined ethanol preference in PACAP-deficient mice using a two-bottle choice and a conditioned place preference test, as well as additive effects of ethanol and 5-HT(1A) receptor agents on hypothermia. PACAP-deficient mice showed an increased preference towards ethanol compared with wild-type mice. However, they showed no preference for the ethanol compartment after conditioning and neither preference nor aversion to sucrose or quinine. The 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) restored the attenuated hypothermic response to ethanol in the mutants to similar levels in wild-type mice, with no effect in wild-types. In contrast, the 5-HT(1A) receptor antagonist WAY-100635 attenuated the ethanol-induced hypothermia in wild-type mice, with no effect in the mutants. These results demonstrate increased ethanol preference in PACAP-deficient mice that may be mediated by 5-HT(1A) receptor-dependent attenuation of ethanol-induced central inhibition.
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