The contribution of environmental cues to cross-tolerance between ethanol and pentobarbital.

The contribution of Pavlovian conditioning of environmental cues has been studied in relation to tolerance to ethanol-induced hypothermia and cross-tolerance to pentobarbital. Two groups of 12 male Sprague-Dawley rats were exposed every other day to a distinctive set of environmental cues paired with an IP injection of either ethanol 2.5 g/kg or an equivalent volume of isotonic saline. On alternating non-drug days, both groups received saline in the animal room. When they were tested for tolerance to the hypothermic effect of ethanol 2.5 g/kg and cross-tolerance to pentobarbital 25 mg/kg in each environment, tolerance and cross-tolerance in the ethanol-treated group were significantly more pronounced in the ethanol-paired environment than in the saline-paired environment. This indicates the importance of a conditional factor in tolerance and cross-tolerance in this paradigm. Determination of blood levels of ethanol and pentobarbital at various times after injection indicated that conditioned tolerance and cross-tolerance can be explained in part by dispositional factors.