Continuous-access phencyclidine self-administration by rhesus monkeys leading to physical dependence

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Abstract
IV phencyclidine (PCP) self-administration was studied in five rhesus monkeys. The animals were given 23 h per day access with each response producing an injection. For the first seven sessions saline was made contingent on responding. For the next 30 sessions responses produced 0.01 mg/kg PCP and for the next 20 sessions responses produced 0.05 mg/kg PCP. Withdrawal signs and symptoms were evaluated every 4h during the subsequent saline-access period. All animals responded for 0.01 mg/kg injections at rates higher than their initial saline rates. Response rates decreased but total PCP intake increased during access to the higher dose. The levels of PCP self-administered resulted in severe intoxication. Evidence for physical dependence development was obtained. The symptoms emerged within 4–8h after access was terminated, peaked at 12–16h, and subsided by 24–48h. The syndrome could be reversed by IV PCP administration. The most common symptoms were vocalizations, hyperresponsivity, bruxism, oculomotor hyperactivity, and diarrhea. During withdrawal the animals refused preferred food. In some of the animals piloerection, tremors, ear and facial twitches, and priapism occurred. Rhythmic abdominal contractions and emesis were seen in one subject and convulsive activity was seen in one subject.