Investigators publish new data in the report 'Self-administration of cocaine-pentobarbital mixtures by rhesus monkeys.' According to recent research from the United States, "A number of experiments have evaluated self-administration of the combination of a stimulant and an opioid. Less is known about the combination of a stimulant and a CNS depressant."

"The present experiment was designed to examine self-administration of the mixture of Cocaine and pentobarbital (PB). Rhesus monkeys (n=4) prepared with i.v. catheters were allowed to self-administer Cocaine or saline under a progressive-ratio schedule. When responding was stable, doses of Cocaine and PB, alone or in combination, were made available in test sessions. Cocaine functioned as a positive reinforcer in a dose-related manner in all monkeys. PB functioned as a relatively weaker reinforcer in one of four monkeys. Self-administration of intermediate doses of Cocaine (0.025-0.1mg/kg per injection) was decreased when mixed with PB (0.05-0.2mg/kg per injection); full maximum responding was re-established when Cocaine dose was increased. The magnitude of the shift to the right in the Cocaine dose-response function was directly related to PB dose. When PB was given as an i.v. pretreatment there was no effect on Cocaine self-administration up to a sedative dose of PB (5.6 mg/kg), suggesting that responding was not non-specifically suppressed by PB," wrote W.L. Woolverton and colleagues, University of Mississippi Medical Center (see also Life Sciences).

The researchers concluded: "Thus, simultaneous self-administration of PB diminished the potency but not the strength of Cocaine as a reinforcer, potentially encouraging self-administration of larger doses of cocaine."

Woolverton and colleagues published their study in Drug and Alcohol Dependence (Self-administration of cocaine-pentobarbital mixtures by rhesus monkeys. Drug and Alcohol Dependence, 2009;100(3):272-6).

For additional information, contact W.L. Woolverton, University of Mississippi Medical Center, University of Mississippi Medical Center, Dept. of Psychiatry and Human Behavior, 2500N State Street, Jackson, MS 39216 USA..