DOPAMINE DEPLETION IN NUCLEUS-ACCUMBENS INFLUENCES LOCOMOTION BUT NOTFORCE AND TIMING OF OPERANT RESPONDING

This experiment examined the role of dopamine (DA) in the nucleus accu mbens in regulating beam pressing and locomotor responses. Six rats we re rewarded with sucrose on a partial reinforcement schedule for press ing force-sensitive beams. Open-field locomotor activity, and the forc e and timing characteristics of operant motor responses were recorded. It is known that low doses of apomorphine decrease DA tone through ac tivating DA autoreceptors, resulting in suppression of both operant re sponses and locomotion. Our results showed that DA depletion in the nu cleus accumbens, induced by bilateral injection of 6-hydroxydopamine, did not affect the force and timing of operant responses; neither did it reverse the suppressive effects of low doses of apomorphine on the force and timing of operant responses. However, accumbens DA depletion did block the suppressive effect of apomorphine on open-field locomot ion. These results were interpreted as support for the hypothesis that the suppressive effects of low doses of apomorphine on locomotion, bu t not on operant beam pressing, are mediated mainly by DA autoreceptor s in the mesolimbic pathway. (C) 1998 Elsevier Science Inc.