Hedonic reactivity to sucrose in rats: modification by pimozide

Reward summation functions (RSFs) are an important way to dissociate and quantify hedonic and motor effects of neuroleptics. Previously used only with brain stimulation reinforcement, we demonstrate they will also work using sucrose solution reinforcement. Eighteen male rats were trained to lever press on a CRF schedule for 0.01 ml sucrose solution reinforcers of varying concentration (0.025, 0.05, 0.1, 0.3, 0.5, 0.7, 0.9, 1.1, 1.7, 2.3 M). Making the lever harder to press caused an increase in the asymptote of the function, demonstrating a motor effect. Quinine added to the solutions (0.05%) caused the function to shift right, demonstrating an hedonic effect. Rats injected with 0.2 mg/kg pimozide, a dopamine antagonist, then tested four hours later, showed a right shift in the function with no change in asymptote. Thus, at this dose pimozide affects hedonic and not motor substrates of the CNS. These data demonstrate the generalizability of the RSF method to reinforcers other than brain self-stimulation.