Differences in locomotor response to an inescapable novel environment predict sensitivity to aversive effects of amphetamine

Differences in locomotor response to an inescapable novel environment have previously been shown to predict sensitivity to amphetamine reward, where h igh responders (HR), compared to low responders (LR), showed greater initia l sensitivity to amphetamine self-administration, The present experiments s ought to extend these findings and assessed the relationship between locomo tor response to an inescapable novel environment and conditioned taste aver sion (CTA) with amphetamine and lithium chloride (LiCl). Male Sprague-Dawle y rats were tested for their locomotor response to an inescapable novel env ironment and divided into high (HR) or low (LR) responders, based on whethe r their locomotor scores were above or below the median activity level of t he subject sample. After several days, the animals were tested in a CTA pro cedure and conditioned with either amphetamine or lithium chloride, Compare d to HR rats, LR rats showed greater sensitivity to amphetamine CTA at the doses tested. In contrast, the results with LiCl showed no relationship bet ween locomotor response to an inescapable novel environment and CTA, Taken together, the present results suggest that LR, compared to HR, rats show le ss sensitivity to the rewarding effects of amphetamine because they are mor e sensitive to aversive effects of amphetamine, as reflected in CTA, In con trast, HR rats display less sensitivity to aversive effects of amphetamine, which may explain their greater propensity to self-administer amphetamine. (C) 2001 Lippincott Williams & Wilkins.