D1 or D2 antagonism in nucleus accumbens core or dorsomedial shell suppresses lever pressing for food but leads to compensatory increases in chow consumption

Although interference with dopamine (DA) systems can suppress lever pressin g for food reinforcement, it is not clear whether this effect occurs becaus e of a general disruption of food motivation. One way of assessing this has been a choice procedure in which a rat responds on an fixed ratio 5 (FR5) schedule for preferred Bioserve pellets while a less preferred lab chow is concurrently available in the operant chamber. Untreated rats consume littl e of the chow, preferring to respond for the Bioserve pellets. Previous stu dies have shown that depleting DA in the accumbens substantially decreased lever pressing while increasing chow consumption. In the present study, low doses (0.0625- 1.0 mug) of the D1 antagonist SCH 23390 or the D2 antagonis t raclopride were injected into the either the core or shell subregions of nucleus accumbens, and rats were tested on the concurrent lever pressing/fe eding task. Analysis of the dose response curves showed that injections of SCH 23390 into the core were more potent than injections into the shell for suppressing lever pressing (i.e., the ED50 was lower in the core). Neverth eless, injections of either drug into either site suppressed lever pressing and increased intake of the concurrently available chow. Across both drugs and at both sites, the amount of chow consumed was negatively correlated w ith the total number of responses. Neither drug significantly increased res ponse duration, suggesting that accumbens DA antagonism did not produce the type of motor impairment that leads to severe alterations in the form of l ever pressing. In summary, the blockade of D1 or D2 receptors in nucleus ac cumbens core or shell decreased lever pressing for food reinforcers, but ra ts remained directed toward the acquisition and consumption of food. These results indicate that accumbens D1 antagonism does not decrease lever press ing because of a general reduction in food motivation. Nevertheless, interf erence with accumbens DA does appear to set constraints upon which response s are selected for obtaining food, and may impair the ability of animals to overcome work-related response costs in order to obtain food. (C) 2001 Els evier Science Inc. All rights reserved.