Effects of phencyclidine-like drugs on punished behavior in rats

The effects of phencyclidine (PCP) and a number of PCP-like drugs on punished responding in rats were compared to those of chlordiazepoxide and morphine. Twenty rats, trained to lever-press for food reinforcement, were tested under a modified Geller-Seifter procedure using a multiple schedule with responding in one component reinforced under a fixed-interval 60-sec schedule while each response in the other component resulted in both food and brief electric shock presentation. Chlordiazepoxide, PCP, etoxadrol, (+)-N-allylnormetazocine and (-)-beta-cyclazocine all resulted in selective increases in rates of responding during the punishment component. Two drugs with predominant opiate-agonist actions in vivo, (-)-alpha-cyclazocine and morphine, did not increase punished responding at any dose tested. These results confirm previous research using pigeons that had shown antipunishment effects of PCP and provide further evidence for an overlap in the pharmacology of PCP-like drugs and depressant drugs such as barbiturates and benzodiazepines. The concordance between the discriminative stimulus properties and antipunishment effects of PCP-like drugs and actions at the PCP receptor suggests that the PCP receptor may play a role in both behavioral actions of this group of drugs.