Wheel Running Induced by Intermittent Self-Administration of Ethanol: A Proof of Concept

Previous attempts to induce behavior with intermittent administration of reinforcing drugs have met with several shortcomings, such as failure to replicate certain features of induced behavior under intermittent administration of food. It is argued that, aside from the difference in the nature of the reinforcer used, several characteristics of previous procedures functionally depart from research in which food is used as an inducer, such as the lack of a consummatory response. In this article we attempt to develop a more functionally equivalent procedure to induce behavior with intermittent administration of reinforcing drugs that might overcome these limitations. Wistar rats of both sexes were exposed to intermittent delivery of a 5% ethanol solution (v/v) using a fixed time schedule of 60 s while they had access to an activity wheel. Rats were also exposed to a massed-ethanol control condition. A progressive increase in wheel running was found during intermittent ethanol administration. Afterwards, and to dissociate the amount of running that would be function of mobility deprivation and induction, a wheel was also added to home cages. Under these circumstances, an approximately inverted U-shaped function was observed for the distribution of running within inter-reinforcement intervals. In addition, a decrease in wheel running was observed in a massed-control condition compared with intermittent ethanol administration. The developed procedure allows the study of behavior induced by the intermittent administration of reinforcing drugs, replicating core features of induced behavior not observed with previous arrangements.