INDIVIDUAL-DIFFERENCES IN THE FEEDING EFFECTS OF AMPHETAMINE - ROLE OF NUCLEUS-ACCUMBENS DOPAMINE AND CIRCADIAN FACTORS

Evidence indicates that amphetamine (AMP) affects feeding in a baselin e-dependent fashion and that the nucleus accumbens (Acc) is an importa nt site of action for AMP's effects on feeding. Experiment 1 examined the contribution of Acc-dopamine (DA) mechanisms to the baseline-depen dent feeding effects of a 0.125 mg/kg dose of AMP using intra-Acc admi nistrations of cis-flupenthixol (FLU). Results showed that there was a n inverse relation beetween baseline sugar intake and the feeding resp onse to AMP, such that AMP stimulated feeding in animals with low base line intake and inhibited feeding in animals with high baseline intake . Intra-Acc FLU administration reversed the stimulatory but not the in hibitory effect of AMP. Further, intra-Acc FLU attenuated baseline fee ding in high but not low baseline feeders. Experiment 2 sought to dete rmine whether AMP would affect feeding in a baseline-dependent manner when administered in the dark photoperiod of the rat circadian cycle, when rats do most of their feeding. To this end, rats were administere d three doses (0.05, 0. 1, and 0.25 mg/kg) of AMP in the dark photoper iod and the intake of sugar monitored. Results showed that in low base line feeders, AMP stimulated intake at lowest dose and had no effect a t higher doses. In high baseline feeders, AMP inhibited intake in a do se-dependent manner. Taken together, these results further establish t hat AMP affects feeding in a baseline-dependent fashion. Moreover, the similar effects of AMP across the light and dark photoperiods suggest that a straightforward rate-dependency interpretation is not adequate . Finally, it is speculated that Acc-DAergic activity may play a role in the observed differences in baseline intake levels and in the respo nse to AMP.