The effect of US-preexposure on METH-induced CTA in periadolescent and young adult rats.

摘要

The age at which drug use begins is a critical factor in predicting future drug use liability. It is uncommon for individuals older than 25 to initiate drug use and progress to drug abuse. Thus, adolescence is a developmental period of considerable importance for investigating drug abuse vulnerability. It has been shown that adolescents learn less about the aversive effects of abused drugs than adults. Therefore, the present study utilized the conditioned taste aversion procedure (CTA) to investigate the aversive effects of the highly addictive drug methamphetamine (METH). Specifically, the experiment investigated the impact of US-preexposures on METH-induced CTA, in periadolescent (PND 30 - 40) and young adult (PND 60 - 70) rats with two preexposure-to-conditioning delays; either 3 or 9 days.;Animals were preexposed for 5 consecutive days to METH (1.0 mg/kg), prior to conditioning trials. After the preexposure phase, METH-saccharin pairings occurred for 3 consecutive days. Following conditioning trials, animals were administered a 2-bottle saccharin preference test. And for 7 days following the 2-bottle test, 1-bottle saccharin extinction trials occurred. It was hypothesized that, overall, periadolescent animals would exhibit a greater unconditional stimulus preexposure effect (USPEE) than young adult animals. Furthermore, the USPEE would be graded as a function of preexposureto- conditioning delay; 3-day delay groups would show less saccharin avoidance than those in the 9-day delay.;Analyses revealed no significant USPEE in the periadolescent or young adult animals, regardless of delay, during the conditioning phase. There was however, a significant effect of age; young adult animals demonstrated more saccharin avoidance than periadolescents, replicating previous findings. Two-bottle preference data showed higher saccharin preferences in periadolescents compared to young adults; furthermore, all 9-day delay groups exhibited lower saccharin preferences than 3-day delay animals. Extinction data revealed a USPEE in the young adult animals but not in the periadolescents, which showed no sign of aversion during extinction trials. The lack of a USPEE is directly related to the dose of the US-preexposures, a larger dose would be necessary to produce a robust USPEE. These results have implications on the factors which impact drug initiation during adolescence.