Absence of reinforcement with low dose intravenous ethanol self-administration in rats

Male hooded rats were implanted with intravenous cannulas and housed in operant chambers supplied with 2 levers and enclosed in sound-attenuating cubicles. In Experiment 1, seven rats received a 1.0 mg/kg infusion of ethanol for each press on the previously determined non-preferred lever. The other lever served to count "activity lever presses." An additional 7 rats served as controls and were treated identically except that each press on the non-preferred lever led to an infusion of saline, isovolumetric to the ethanol infused in the experimental subjects. The rats were tested under these conditions of continuous reinforcement for 9 days. Throughout this period, self-infusions and "activity lever presses" did not differ between the groups, suggesting that ethanol was not reinforcing at a dose of 1.0 mg/kg. These results were replicated, and extended to other low doses of ethanol in Experiment 2. Here, we employed a design where depression of either lever, under conditions of continuous reinforcement, led to the infusion of a solution. Fifteen rats were randomly assigned to one of three groups (5 rats/group). In one group, depression of the previously determined non-preferred lever led to an infusion of 16.0 mg/kg of ethanol, while depression of the other lever led to an infusion of isocaloric glucose. For the other two groups, depression of the non-preferred level led to an infusion of 4.0 and 1.0 mg/kg ethanol respectively, and depression of the other lever led to a glucose infusion. The animals were tested for 9 days, and in each case, ethanol self-infusions did not differ significantly from glucose self-infusions.(ABSTRACT TRUNCATED AT 250 WORDS)