Oral ethanol self-administration in rhesus monkeys: behavioral and neurochemical correlates

Previous research has revealed that orally administered ethanol serves as a reinforcer in nonhuman primates. The purposes of the present study were to examine the relationship between ethanol preferences and intakes in two distinct self-administration contexts and to reveal some of the behavioral and neurochemical correlates of oral ethanol self-administration in monkeys.

Three cohorts of 13 to 29 rhesus monkeys (Macaca mulatta) were socially housed and given daily, 1-hr, one-spout access to an ethanol solution (8.4%, w/v) sweetened with aspartame. Twelve of these monkeys were subsequently selected, individually housed, and given daily, 2-hr, two-spout access to a range of ethanol concentrations (0.25-16%, w/v) concurrently with water.

These monkeys (National Institute on Alcohol Abuse and Alcoholism group) showed a marked preference for ethanol (0.5-4%, w/v) over water, and ethanol preferences were 3-fold greater than those of a second group of 12 monkeys (University of Michigan group) purchased from a commercial vendor. Ethanol consumption was consistent across the self-administration paradigms. Monkeys that consumed large quantities of ethanol under the one-spout, social-housing conditions continued to drink large quantities of ethanol under the two-spout, individual-housing conditions (r = 0.86). An association between ethanol preferences and intakes was also demonstrated. Monkeys with the greatest preferences for ethanol over water under the two-spout choice conditions consumed the largest quantities of ethanol (r = 0.82). Finally, cerebrospinal fluid 5-hydroxyindoleacetic acid concentrations were inversely related to ethanol preference but not to ethanol intake.

These results indicate that ethanol consumption is stable across contexts and is positively correlated with the preference for ethanol over water.