A comparison of some behavioural effects of amphetamine and electrical brain stimulation of the mesolimbic dopamine system in rats.

Separate groups of rats were trained to press a lever on either a fixed-ratio 40 or fixed-interval 1-min schedule of food reinforcement. Amphetamine increased low rates and decreased high rates of responding. In contrast, electrical stimulation of rewarding sites in the ventral tegmentum was effective only in decreasing high response rates. Stimulation of non-rewarding sites had little effect upon either low-or high-rate responding. Another group of rats was trained to discriminate between amphetamine (1.0 mg/kg) and saline in a standard two-lever procedure with food reinforcement. The internal stimulus produced by the stimulation of rewarding sites did not substitute readily for the discriminative stimulus produced by amphetamine. The results suggest that the operant response-rate decreasing property of amphetamine may be partially mediated through the mesolimbic dopamine system. However, this system may not play a prominent role in mediating either the operant response-rate increasing or discriminable properties of this drug. The idea that the abuse liability of amphetamine may be related to the ability of the drug to interact with one of the central reward systems is discussed.