NUCLEUS-ACCUMBENS DOPAMINE DEPLETIONS IN RATS AFFECT RELATIVE RESPONSE ALLOCATION IN A NOVEL COST BENEFIT PROCEDURE/

Rats were tested on days 1, 3, and 5 of a 5-day test week in an operan t chamber in which they could either lever press on a fixed-ratio 5 (F R5) schedule to obtain food pellets (Bioserve) or approach and consume lab chow that was also available in the chamber (Teklad Premier). Rat s typically pressed at high rates to obtain the food pellets and ate l ittle of the lab chow. On days 2 and 4 of each week lab chow was not c oncurrently available, and rats could only lever press on the FR5 sche dule for pellets to obtain food. Dopamine depletions produced by intra accumbens injections of the neurotoxic agent 6-hydroxydopamine produce d a dramatic decrease in lever pressing and increase in chow consumpti on on days when lab chow was available. Lever pressing was not signifi cantly reduced in dopamine-depleted rats on days when chow was not ava ilable, although there was a significant correlation between lever pre ssing and accumbens dopamine levels. These results suggest that nucleu s accumbens dopamine depletions do not produce a general deficit in fo od motivation. Moreover, accumbens dopamine depletions do not appear t o produce severe deficits in fine motor control that impair the execut ion of individual motor acts involved in lever pressing. Rather, the p resent results are consistent with the notion that accumbens dopamine sets constraints upon which food-related response is selected in a par ticular situation, and that these depletions alter the relative alloca tion of food-related responses.