Novelty Disruption of Amphetamine Self-Administration in High and LowResponder Rats

A recent study in our laboratory has demonstrated that novel stimuli presented during amphetamine self-administration decreases responding in rats that are highly active in a novel environment (high responders; HR) more than rats that are relatively inactive (low responders; LR). The specific aim of this project is to determine if individual differences in response to novelty predict the ability of novel stimuli presented prior to amphetamine self-administration to attenuate responding either during the acquisition or maintenance phases. Rats were screened for their response to novelty and classified as HR or LR. Prior to each session, rats in the handle condition were briefly handled and rats in the novelty condition were placed for 15 minutes in a chamber with 6 novel plastic objects. In Experiment 1, rats were trained on a fixed-ratio schedule to selfadminister amphetamine (0.03 mg/kg/infusion) following exposure to novelty or handling. In Experiment 2, rats were trained to self-administer amphetamine (0.1 mg/kg/infusion) and then the effect of novelty or handling was evaluated across a range of amphetamine doses (0.056, 0.03, 0.01, and 0.003 mg/kg/infusion). Novelty presented prior to the session during acquisition decreased amphetamine selfadministration. LR rats were more disrupted by the novelty than HR rats during the first thirty minutes of the session. Novelty presented prior to the session once animals have acquired amphetamine self-administration did not attenuate responding at any of the doses tested. These results suggest that novelty presented prior to amphetamine self-administration decreases responding only during acquisition