| Adolescence is a developmental period characterized by elevations in the consumption of natural reinforcements. We hypothesize that these age-related increases in consumption of reinforcers are due to developmental changes in hedonic sensitivity. The present series of experiments investigated the cannabinoid (CB) and opioid modulation of hedonic sensitivity in both adult and adolescent rats using the taste reactivity (TR) test. Experiments 1-4 consisted of four separate dose response experiments, each with a 2 age (adolescent and adult) x 4 dose (vehicle, low, medium and high) repeated measures design. Drugs used in Experiment 1-4 were as follows: a cannabinoid agonist (ACEA), a cannabinoid antagonist (SR-141716), a mu opioid antagonist (CTAP), and a kappa opioid antagonist (Nor BNI) respectively. ACEA and nor-BNI failed to produce any significant effects on total positive or negative TR, whereas SR-141716 eliminated positive taste responses to water and dose-dependently suppressed positive responses to sucrose at both ages. SR also increased expression of negative TR to sucrose, but had no effect on responding to quinine. CTAP failed to alter TR to sucrose or quinine, although it dose-dependently suppressed positive responding to water. The current results suggest that the CB antagonist, SR-141716, reduces hedonic sensitivity in both adult and adolescent rats to positive tastants without altering negative taste reactivity. The lack of impact of the CB agonist and the mu and kappa antagonists on TR was surprising, as was the absence of age differences. Clearly more work is needed to characterize the opioid and CB system's role in modulation of the hedonic and incentive properties of reward. |
