Oral ethanol self-administration in free-feeding rhesus monkeys

The ability of a conditioning procedure to establish oral ethanol self-administration in free-feeding rhesus monkeys was assessed. The conditioning procedure required the monkey to drink an ethanol solution in order to have access to a sweet orange-flavored solution. Following an average of 14 sessions under these conditions, the orange solution was no longer delivered and ethanol solution alone was made available in the sessions. During both the conditioning and the ethanol self-administration portions of the experiment each monkey was required to drink an average of 0.5 g/kg ethanol per session in order to continue in the experiment. Of the nine monkeys exposed to these contingencies, five monkeys continued to self-administer ethanol after the presentation of the orange drink was discontinued. However, two of these five monkeys decreased their ethanol solution intake below 0.5 g/kg within 3 weeks after the conditioning sessions had terminated. The three monkeys that sustained high ethanol intake were male and had histories of drug self-administration, suggesting that gender and drug history may influence the initiation of ethanol self-administration. Once ethanol self-administration was established, concentrations of ethanol from 4 to 15% (v/v) were made available. The monkeys consumed intoxicating amounts of ethanol, as indicated by average intakes ranging from 0.5 to 0.9 g/kg and blood ethanol levels over 100 mg/dl. These results demonstrate that ethanol self-administration can be established and maintained through the initial reinforcement of ethanol consumption by the contingent presentation of another reinforcing stimulus. However, the results of this study also indicate that individual differences may be an important determinant of animals initiating ethanol self-administration.