Haloperidol induces a partial reinforcement extinction effect in rats: implications for a dopamine involvement in food reward.

The hypothesis that dopamine antagonist drugs attenuate the reinforcing properties of food was investigated in hungry rats trained to traverse a straight runway for food reward. Testing consisted of a single trial per day during which latencies to leave the start box and to traverse the alley were recorded. In each experiment, a reinforcement phase lasting 30 consecutive days was immediately followed by a 21 day extinction phase. The runway responses of animals that experienced intermittent food reward during the reinforcement phase of the experiments, was later found to be more resistant to extinction than those of continuously reinforced animals. This "partial reinforcement extinction effect" (PREE) was also observed in animals that experienced periodic reductions in the quantity, but not quality, of food reward. Intermittent pretreatment with 0.15 mg/kg of haloperidol during the reinforcement phase produced a PREE that was indistinguishable from that produced by reward omission on those same trials. Control groups for motor debilitation and for non-associative drug effects did not demonstrate a PREE. These results are consistent with the view that central dopamine substrates play a role in the neural basis of food reward.