DIFFERENT EFFECTS OF NUCLEUS-ACCUMBENS AND VENTROLATERAL STRIATAL DOPAMINE DEPLETIONS ON INSTRUMENTAL RESPONSE SELECTION IN THE RAT

This experiment was undertaken to investigate dopaminergic involvement in food-related instrumental behavior. Rats were tested in an operant chamber in which there was a choice between pressing a lever to recei ve a preferred food (Bioserve pellets) or feeding upon a less preferre d food (lab chow). The lever-pressing schedule was a fixed ratio 5 (FR 5). Rats usually pressed the lever at high rates to obtain the preferr ed food, and typically ate little of the lab chow even though it was f reely available in the chamber concurrently with the lever-pressing sc hedule. The neurotoxic agent 6-hydroxydopamine was injected directly i nto the nucleus accumbens, medial striatum, or ventrolateral striatum to determine the effects of dopamine depletion on the performance of t his task. Depletion of dopamine in the nucleus accumbens led to a dram atic shift in behavior in which there was a significant decrease in le ver pressing but a significant increase in consumption of lab chow. Th e shift away from lever pressing and towards chow consumption in rats with accumbens DA depletions was significantly correlated with a decre ase in spontaneous locomotor activity. Dopamine depletions in the medi al striatum did not significantly affect lever pressing or chow consum ption. Ventrolateral striatal dopamine depletions decreased lever pres sing but also tended to reduce consumption of lab chow. Rats with vent rolateral striatal dopamine depletions also showed profound deficits i n home-cage feeding, and these rats had to receive wet mash or tube fe eding to maintain body weight. These data indicate that depletions of dopamine in the nucleus accumbens do not produce a general reduction i n food motivation, although accumbens dopamine depletion does decrease instrumental lever pressing for food. In contrast, depletions of dopa mine in the ventrolateral striatum produce a profound motor deficit th at interferes with both lever pressing for food and food consumption.