In 30-min free-operant tests, the dopamine receptor blockers pimozide (.125, .25, and .50 mg/kg) and (-f-)-butaclamol (.1, .2, and .4 mg/kg) attenuated lever pressing for lateral hypothalamic brain stimulation. When discrete self-stimulation trials were offered in a straight alleyway, pimozide increased start box latencies, slowed running speeds, and reduced lever-pressing rates. However, performance early in both lever-pressing and runway sessions was normal; performance deteriorated as testing progressed, following patterns that paralleled those seen when animals were tested with reductions in the amplitude of stimulating current. Spontaneous recovery was obtained in both situations; experimenter-imposed 10-min time-outs caused renewed lever pressing and running. In contrast, a-noradrenergic receptor blockade by phenoxybenzamine (5,10, and 20 mg/kg) failed to produce extinction-like response patterns. These data support the view that central dopaminergic systems are important components of the neural mechanisms mediating reward.

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