Multiple variable interval schedule behaviour in humans: effects of ethanol, mood, and reinforcer size on responding maintained by monetary reinforcement

Ethanol is an effective reinforcer but, in common with other drugs of abuse , it may derive some of its reinforcing properties from the effects it has on behaviour maintained by other reinforcers. However, any assessment of et hanols hypothesized effect on behaviour maintained by other reinforcers mus t take into account the fact that ethanol may have multiple mechanisms of a ction. In order to address this problem the experiments reported herein use d a procedure based upon Herrnstein's Matching Law which allowed joint asse ssment of subjects' motor capacity and reinforcer sensitivity. The effect o f ethanol (0, 0.3, and 0.6 g/kg) on motor capacity and reinforcer sensitivi ty was assessed by studying behaviour maintained by monetary reinforcement. In the first experiment the procedure was validated by shoeing that the be haviour of subjects was sensitive to changes in reinforcer value and in the second experiment 0.6 g/kg ethanol reduced motor capacity but did not affe ct reinforcer sensitivity. As a secondary hypothesis we also studied the ef fect of mood on reinforcer sensitivity and motor capacity, It was found tha t lower mood scores (lower hedonic tone) were associated with reduced reinf orcer sensitivity and that male subjects showed higher motor capacity than females. However, there was also a mood by sex interaction, which indicated that higher motor capacity in males aas only found in the presence of lowe r mood scores. The results are discussed in relation to the mechanisms of e thanols dopaminergic effects, interactions between ethanol and other drugs of abuse, and the changes in reinforcer sensitivity which are thought to oc cur in depression. Behav Pharmacol 1998; 9:619-630 (C) 1998 Lippincott Will iams & Wilkins.