Discriminative stimulus effects of cocaine in squirrel monkeys: lack of antagonism by the dopamine D2 partial agonists terguride, SDZ 208-911, and SDZ 208-912.

The effects of cocaine alone and after pretreatment with the dopamine D2 partial agonists terguride, SDZ 208-911, and SDZ 208-912 were determined in squirrel monkeys trained to discriminate cocaine from saline using a two-lever drug discrimination procedure. When tested alone, cocaine engendered dose-related increases in the percentage of responses on the cocaine-associated lever, reaching virtually exclusive cocaine-appropriate responding after a dose of 1.0 mg/kg. Pretreatment with terguride (0.003-0.03 mg/kg), SDZ 208-911 (0.001-0.01), and SDZ 208-912 (0.003-0.018 mg/kg) did not consistently alter the discriminative stimulus effects of cocaine. Although some doses of each D2 partial agonist either increased (notably SDZ 208-911) or decreased (notably SDZ 208-912) the level of cocaine-appropriate responding engendered by low to intermediate doses of cocaine, none of the drugs reduced the percentage of cocaine-appropriate responding engendered by low to intermediate doses of cocaine, none of the drugs reduced the percentage of cocaine-appropriate responses engendered by 1.0 mg/kg cocaine. The results do not support the view that terguride, SDZ 208-911, or SDZ 208-912 would serve as functional antagonists of the subjective effects of cocaine.