Effects of Levamisole on Cocaine Self-Administration by Rats

Levamisole (LVM) is often added to illicit cocaine, but the reason for this is unclear. Previous research indicated that LVM sometimes increases the rewarding effects of cocaine, as measured by conditioned place preference. The present study examined the acute effects of LVM pretreatments on cocaine self-administration by rats. If LVM substantially increases the amount of cocaine self-administration in each bout, this effect could account for its use as an adulterant. Thirty-two catheterized rats were trained to self-administer cocaine (0.56 mg/kg/injection) and were subsequently tested after pretreatment with LVM (1 and 10 mg/kg) for self-administration of the training dose of cocaine and for self-administration of other doses (0–1.0 mg/kg/injection). Pretreatment with 10 mg/kg of LVM produced a statistically significant reduction in cocaine self-administration. Fewer cocaine-reinforced responses also occurred when 1 mg/kg of LVM was administered compared with control (no LVM) conditions, but the difference was not statistically significant. Because LVM never increased cocaine intake, the present data do not support the hypothesis that LVM is added to illicit cocaine to increase the amount of cocaine self-administered in each bout.