Effects of the selective delta opioid agonist SNC80 on cocaine‐ and food‐maintained responding in rhesus monkeys

Abstract

Delta agonists such as SNC80 produce some cocaine-like behavioral effects and warrant evaluation as candidate “agonist” medications for cocaine abuse. The present study examined acute and chronic effects of SNC80 on cocaine- and food-maintained responding in rhesus monkeys. In acute studies, SNC80 (0.32–3.2 mg/kg, i.m.) was administered i.m. 15 min before 2 hr, multiple-component sessions during which food or cocaine was available under a FR30 schedule. SNC80 dose-dependently decreased cocaine self-administration, but doses of SNC80 that decreased cocaine self-administration also decreased food-maintained responding. In chronic studies, SNC80 (0.32–3.2 mg/kg/hr) was delivered by continuous i.v. infusion for 7 days, and food or cocaine (0.01 mg/kg/inj) were available during four daily 1hr food components and four 1hr drug components under a FR4(VR16:S) schedule. SNC80 doses up to 1.8 mg/kg/hr had little effect on cocaine self-administration, although 1.8 mg/kg/hr SNC80 transiently decreased food-maintained responding. A higher dose of 3.2 mg/kg/hr SNC80 eliminated all responding and produced profound sedation for 2 days in the first monkey tested. Further treatment was terminated in this monkey, and other monkeys were not tested. These findings indicate that SNC80 produced a dose-dependent and non-selective reduction in cocaine self-administration. These results contrast with the selective reductions in cocaine self-administration produced by other compounds (e.g. amphetamine, low-efficacy mu agonists) and suggest that SNC80 is unlikely to be useful as a treatment for cocaine dependence. Support: RO1-DA11460, RO1-DA02519 and K05-DA000101.