Effects of variations of reinforcement magnitude on alcohol discrimination using intracranial stimulation as the reinforcer.

Male Wistar rats were trained to discriminate intraperitoneal injections of 2 g/kg of alcohol from 0.5 g/kg alcohol injections. Intracranial stimulation in the posterolateral area of the hypothalamus served as the reinforcer according to a FR 10 schedule of bar pressing. After discrimination between the two alcohol doses had been established, the response-reinforcement contingency was modified by progressively increasing the intensity of the intracranial stimulation. The results indicate that the generalization gradient varies with the number of reinforcements. The more the lever associated with a training dose was reinforced, the more the ED50 had the tendency to approach this dose. Our paradigm, by using electrical brain reinforcer, allowed to deliver in an equal manner the reinforcement schedule in order to obtain equal performances and equal number of reward received.