Pimozide decreases the positive reinforcing effect of sham fed sucrose in the rat.

Rats with chronic gastric cannulas were intraperitoneally injected with the dopamine receptor antagonist pimozide (0.25 mg/kg) before sham feeding 5, 10, 20, or 40% (w/v) sucrose solutions. Amount of sham intake after control injections increased as a function of sucrose concentration. At each concentration, the rate of sham feeding was greatest during the initial 3 min of sham feeding and subsequently decelerated. Pimozide inhibited sham feeding rate, and the temporal pattern of decreases in sham feeding rate after pimozide were similar to those produced by decreasing the concentration of sucrose sham fed. These data extend previous reports of the inhibitory effect of pimozide on ingestion of sweet fluids by eliminating the possibility that the effect was the result of pimozide facilitating postingestional inhibitory mechanisms. Further, pimozide did not appear to produce fatigue or sedation, or to reduce the rats' motor capacity to sham feed. Therefore, these data are consistent with the hypothesis that central dopaminergic synaptic activity mediates the reinforcing effects of sweet taste that drive sham feeding.