A HISTORY OF POSTPONING SHOCK DOES NOT APPEAR TO ALTER THE DISCRIMINATIVE STIMULUS EFFECTS OF COCAINE

Previous research has shown that the rate of punished lever pressing o f monkeys is typically decreased by cocaine administration. However, c ocaine increases punished responding in monkeys with a history of resp onding maintained by the postponement of shock presentation. This rais es the question of whether other behavioral effects of cocaine differ following a history of postponing shock. The present experiment examin ed whether a history of postponing shock alters the discriminative sti mulus effects of cocaine. Three squirrel monkeys were trained to discr iminate cocaine (0.56 mg/kg, intramuscular) from saline. Presses on th e left lever produced food following saline injections whereas presses on the right lever were reinforced following administration of cocain e. Occasional test sessions were conducted in which cocaine (0.1-0.56 mg/kg), midazolam (0.03-0.56 mg/kg) or pentobarbital (0.3-5.6 mg/kg) w as injected prior to the session and responding on either lever was re inforced. Discrimination training was discontinued during a second exp erimental phase in which responding was maintained by shock postponeme nt. Pulling a chain postponed mild shocks for 25 s, whereas shocks occ urred every 5 s in the absence of responding. Next, the drug discrimin ation dose-response curves were redetermined. The dose-response curves for all drugs before and after the shock postponement history were si milar. This outcome suggests that the influence of a history of shock postponement is specific to punished responding, Behav Pharmacol 1998; 9:437-444 (C) 1998 Lippincott Williams & Wilkins.