Ethanol induces second-order aversive conditioning in adolescent and adult rats (original) (raw)

Alcohol abuse and dependence is considered a developmental disorder with etiological onset during late childhood and adolescence, and understanding age-related differences in ethanol sensitivity is important. Low to moderate ethanol doses (0.5 and 2.0 g/kg, i.g.) induce single-trial, appetitive second-order place conditioning (SOC) in adolescent, but not adult, rats. Recent studies have demonstrated that adolescents may be less sensitive than adults to the aversive properties of ethanol, reflected by conditioned taste aversion. The present study assessed the aversive motivational effects of high-dose ethanol (3.0 and 3.25 g/kg, i.g., for adolescent and adults, respectively) using SOC. These doses were derived from Experiment 1, which found similar blood and brain ethanol levels in adolescent and adult rats given 3.0 and 3.25 g/kg ethanol, respectively. In Experiment 2, animals received ethanol or vehicle paired with intraoral pulses of sucrose (conditioned stimulus 1 [CS1]). After one, two, or three conditioning trials, rats were presented with the CS1 while in a distinctive chamber (CS2). When tested for CS2 preference, ethanoltreated animals exhibited reduced preference for the CS2 compared with controls. This result, indicative of ethanol-mediated aversive place conditioning, was similar for adolescents and adults, for females and males, and after one, two, or three training trials. One finding, however, suggested that adolescents were less sensitive than adults to ethanol's aversive effects at the intermediate level of training. In conjunction with previous results, the present study showed that in adolescent rats subjected to SOC, ethanol's hedonic effects vary from appetitive to aversive as the ethanol dose increases. Adolescent and adult animals appear to perceive the post-ingestive effects of highdose ethanol as similarly aversive when assessed by SOC.