INDIVIDUAL-DIFFERENCES IN SUGAR INTAKE PREDICT THE LOCOMOTOR RESPONSETO ACUTE AND REPEATED AMPHETAMINE ADMINISTRATION

Rats exhibit profound individual differences in their propensity to in gest sugar and in their locomotor response to AMP. Intrinsic variation in the responsiveness of mesolimbic dopamine mechanisms has been sugg ested to account for these individual differences. In light of this ov erlap, it might be expected that individual differences in one behavio r would predict individual differences in the other. The present study determined whether individual differences in sugar intake would predi ct individual differences in the locomotor response to AMP; Male Wista r rats were divided into low and high feeders based on a median split of their sugar intake in response to saline administration and were su bsequently tested for their locomotor response to either 1.0 or 1.75 m g/kg AMP in experiment 1. High sugar feeders exhibited significantly m ore locomotion than low sugar feeders in response to 1.75 mg/kg AMP. T his difference was observed immediately after injection and continued for approximately 90 min. There was no difference between the two grou ps in their locomotor response to 1.0 mg/kg AMP. In experiment 2, rats receiving 1.0 mg/kg AMP in experiment 1 were tested for the developme nt of behavioral sensitization with repeated AMP administrations. Rats were administered 1.0 mg/kg AMP across 5 test days, interspersed with days in which they received AMP treatment in their home cages to mini mize conditioning effects. High sugar feeders exhibited greater behavi oral sensitization than low sugar feeders with repeated AMP administra tion. Starting on test day 3, high sugar feeders exhibited significant ly greater AMP-induced locomotor activity than low sugar feeders. Take n together, these findings support the notion that there is overlap in the neurobiological substrates regulating sugar intake and responsivi ty to the locomotor activating effect of AMP. Furthermore, these resul ts establish that the propensity to ingest sugar is a predictor of the susceptibility to the locomotor enhancing properties of AMP.