Discriminative stimulus effects of N-allylnormetazocine in rats trained to discriminate a kappa from a sigma agonist.

Rats were trained to discriminate ethylketocyclazocine (EKC) from vehicle, phencyclidine (PCP) from vehicle, or ethylketocyclazocine from phencyclidine on a two-lever operant task with a fixed-ratio 30 schedule of food-reinforcement on the appropriate lever. The three groups were tested with the training drugs (i.e., EKC and PCP), N-allylnormetazocine (NANM), and the (+)- and (-)-isomers of N-allylnormetazocine. EKC produced EKC-appropriate responding in the EKC-vehicle group and in the EKC-PCP group; it produced vehicle-appropriate responding in the PCP-vehicle group. Similarly, PCP produced PCP-appropriate responding in the PCP-vehicle group and in the EKC-PCP group but vehicle-appropriate responding in the EKC-vehicle group. The (+)-isomer of NANM produced PCP-appropriate responding in both the PCP-VEH and EKC-PCP groups, whereas the (-)-isomer produced EKC appropriate responding in the EKC-VEH and EKC-PCP groups. The results of this study demonstrate that rats can be trained to discriminate a kappa-agonist from a PCP/sigma-agonist and can differentiate these discriminative stimulus properties of other test compounds. These results also indicate that the (-)-isomer of NANM has kappa-agonist discriminative stimulus properties, whereas PCP/sigma-like effects are produced by the (+)-isomer.