Discriminative stimulus effects of inhaled cocaine in squirrel monkeys

Abstract

Squirrel monkeys (N=4) were trained with food reinforcement to press one of two levers after administration of IV cocaine (0.3 or 1.0 mg/kg) or the other lever after saline. After training, IV cocaine (0.03–3.0 mg/kg) produced dose-related increases in the percentage of responses on the cocaine lever (ED₅₀=0.15 mg/kg). Cocaine delivered IM also produced dose-related increases in cocaine-appropriate responding (ED₅₀=0.32 mg/kg), but was approximately half as potent as IV cocaine. Similar relative potency relations were obtained for decreases in response rates produced by cocaine. Prior to some sessions subjects were placed in a Plexiglas^® chamber and exposed for 60 s to cocaine vapor created with an ultrasonic nebulizer. Exposure to vapor from cocaine solutions (1.0–30.0 mg/ml) produced concentration-dependent increases in cocaine-appropriate responding and decreases in response rates. Exposure to vapor from a 30 mg/ml concentration produced virtually exclusive cocaine-appropriate responding. Concentration-effect curves for inhaled cocaine were similar to dose-effect curves obtained when cocaine was administered by the other routes. The time course of the minimally effective concentration of inhaled cocaine was compared to that of the minimally effective doses of systemically administered cocaine. Inhaled cocaine had a duration of action longer than IV cocaine. The results indicate that inhaled cocaine vapor has effects qualitatively similar to those of IV cocaine, and may have a duration of action longer than that of an IV cocaine dose producing a similar degree of drug-appropriate responding.