Figure 4. Initial cocaine sensitivity corresponds with differences in D₂ DA receptor sensitivity.

The area under the curve (AUC) was calculated for each rat’s cocaine-induced locomotor activity across both 5 and 15 mg/kg doses. Using this calculated score for initial cocaine-induced locomotor activity, rats were re-classified into a low cocaine responder group (LCR) and a high cocaine responder group (HCR). (A) HCR rats displayed significantly greater quinpirole-induced locomotor activity at the 0.3 and 1.0 mg/kg doses. *HCR significant from LCR, p<0.05. (B) An analysis of the entire cohort was conducted to determine the relationship between quinpirole AUC scores and cocaine AUC scores. A significant positive relationship was identified between initial quinpirole sensitivity and initial cocaine sensitivity.