Discriminative stimulus effects of direct‐ and indirect‐ acting dopamine receptor agonists in free‐feeding and food‐restricted mice.

Abstract

In rats, the discriminative stimulus effects of direct‐ (e.g., quinpirole) and indirect‐ (e.g., cocaine) acting dopamine receptor agonists are mediated by multiple dopamine receptor subtypes and the relative contribution of D2 and D3 receptors to these effects can be altered by manipulating feeding conditions (e.g., food restriction). In these studies two‐lever discriminations were trained with either 10.0 mg/kg cocaine or 0.032 mg/kg quinpirole in free‐fed and food‐restricted mice using a fixed ratio 10 schedule of reinforcement for 50% sweetened condensed milk. Although free‐fed mice responded at lower rates under training conditions and were more sensitive to the rate suppressant effects of their respective training drugs, feeding condition did not affect the acquisition of either discrimination and did not alter the potencies of cocaine or quinpirole to increase cocaine‐ and quinpirole‐appropriate responding, respectively. These novel discriminations will allow for the identification of the specific receptors that mediate the interoceptive effects of cocaine and quinpirole and will serve as the basis for future studies of the influence of diet on drug effects in mice. CPF is supported by a NIDA Senior Scientist Award (K05 DA017918).