Chronic haloperidol treatment: effects on operant responding and inter-response time.

Three groups (n = 6) of male Sprague-Dawley rats were trained to barpress for food reinforcement on a fixed ratio-40 schedule. Each group then received one of three doses of haloperidol (0.125, 0.25, or 0.5 mg/kg, i.p.) according to the following treatment regimen: Baseline, Presession, Postsession, Presession, Postsession, Baseline, Extinction. Each treatment lasted six days each. Only the Presession and Extinction conditions resulted in a significant decrease in the number of reinforcements earned. The number of inter-response times greater than ten sec was inversely related to the number of reinforcements earned. The fact that chronic presession, but not postsession treatment, significantly decreased the number of reinforcements earned would favor an anhedonia interpretation over one postulating cumulative motor deficits. In any event, prior concurrent experience with the drug effect and the operant behavior appears to be critical to the decrement induced by haloperidol.