Discriminative stimulus properties of phencyclidine and five analogues in the squirrel monkey

Squirrel monkeys were trained to discriminate 0.16 mg/kg of 1-(1-phenylcyclohexyl) piperidine (PCP) from saline in a two-lever drug discrimination task on a fixed-ratio 32 schedule of food presentation. Intramuscular injections were given 5 min pre-session in a double alternation pattern. After reliable discriminative control of lever choice was established, dose-response determinations for generalization to the training dose of PCP was made with several doses of PCP, N-ethyl-1-phenylcyclohexylamine (PCE), 1-[1-(2-thienyl)cyclohexyl] piperidine (TCP), 1-(1-phenylcyclohexyl) morpholine (PCM), 1-(1-phenylcyclohexyl) pyrrolidine (PHP), and ketamine. All drugs produced dose-dependent PCP-appropriate responding. For each analogue, a dose was found which produced stimulus control of responding comparable to that of the PCP training dose. ED50 values were determined for each drug for percent drug-lever appropriate responding and for suppression of operant responding during test sessions. The relative potency for producing drug-lever appropriate responding was: TCP greater than PCP = PCE greater than PHP greater than PCM greater than ketamine. The relative potency for suppression of operant responding was: PCP = TCP greater than PHP greater than PCE greater than PCM greater than ketamine. In all cases, the dose necessary to suppress operant responding to fifty percent of vehicle rates was three to five times larger than the ED50 dose for drug-lever appropriate responding. The results of this study indicate marked similarities in the behavioral effects of these six arylcyclohexylamines.