Ethanol self-administration in rats: influence of (a) discriminative stimuli and conditioned reinforcers and (b)reinforcement delay

Abstract

The objective of this project is to characterize two important behavioral factors in alcohol dependence. Previous research indicate that environmental stimuli associated with the effects of ethanol may acquire discriminative or conditional reinforcing function related to the responses that precede these effects. The control of these stimuli over behavior is maintained even after long periods of drug abstinence, and is a major variable in the persistence of alcohol dependence. Another aspect often associated with drug abuse is the lack of control over the consumption of the substances, often identified as "impulsiveness". In the Experimental Analysis of Behavior, "self-control" and "impulsivity" are typically studied in situations of choice between two alternatives, one which is lower in quality or quantity, but more immediate than the other. The first objective of this research is to study the control of discriminative stimuli and conditioned reinforcement on self-administration of ethanol. The second goal is to characterize the effect of delay of reinforcement on choice of ethanol. Two experiments will be conducted. In the first experiment, rats previously trained to consume ethanol will be divided into two groups and subjected to discriminative training under a CRF schedule. Experimental sessions will be conducted in which responses in a lever will be reinforced by ethanol or water (ET group) and sucrose or water (SAC group). An odor A (SD+) will be present in sessions in which the response will be reinforced by ethanol or sucrose and each response will be followed by a conditioned reinforcer (Sr+) and the reinforcer. For both groups, an odor B (SD-) will be present in sessions when response will be reinforced by water and each response will be followed by a negative stimulus (Sr-) and water. Conditioning sessions will be followed by extinction sessions without SD or Sr presence. Then sessions of reinstatement will be carried out. At reinstatement sessions the stimuli arrangement presented at CRF will be reintroduced. Similar sessions with independent presentation of each stimulus will also be performed. In the second experiment, rats habituated to consume ethanol will be trained to bar press under a concurrent CRF CRF schedule. This training will be followed by discrete trials of choice between alternatives reinforced either by ethanol or sucrose. Then, delays in the availability of ethanol will be introduced, followed by delays in sucrose availability. Duration and order of delays will be: 0, 2, 4, 8, 16, 8, 4, 2, 0 s. The number of choices of each alternative relative to the total number of trials will be used as an index of preference. Both experiments should provide data on the role of stimulus control and reinforcement delay on the persistence of drug abuse. (AU)