Oral self-administration of ethanol, phencyclidine, methadone, pentobarbital and quinine in rhesus monkeys.

RATIONALE: Simultaneous and sequential drug use among clinical populations is the norm, whereas the pattern of self-administration of multiple drugs among non-human primate populations has not been thoroughly explored.

OBJECTIVES

To determine the relationship between the preferences and intakes of a large group of rhesus monkeys exposed to various orally available solutions.

METHODS

Thirteen male and eleven female young adult rhesus monkeys (Macaca mulatta) were exposed to orally available drug solutions using a concurrent choice (drug and water) procedure, where fluid delivery was made contingent upon single spout contacts (fixed ratio one).

RESULTS

Ethanol (0.25-16% w:v) produced biphasic effects on the number of fluid deliveries obtained, with peak ethanol preferences over water demonstrated at the 1-2% w:v concentrations. No preferences for the N-methyl-d-aspartate receptor antagonist phencyclidine or water were demonstrated at lower concentrations (0. 0078125-0.125 mg/ml) and, at higher concentrations (0.25, 0.5 mg/ml), a preference for water was demonstrated. The mu opioid receptor agonist methadone (0.001-0.3 mg/ml) and the prototypic bitter substance quinine (0.001-0.3 mg/ml) failed to produce preferences for drug or water. A large preference for water over the barbiturate pentobarbital (0.01-3 mg/ml) was also demonstrated. After rank-ordering the subjects based on their drug preferences or intakes, modest to no correlations across drugs were demonstrated.

CONCLUSIONS

These results reveal that a robust ethanol preference is not predictive of a preference for drugs of abuse from other classes and suggests that fluid intakes were correlated, irrespective of the presence or absence of drug in the solution.