Metabotropic glutamate group II receptor activation in the dorsal striatum suppresses the motivation for cocaine in rats

Abstract

After a history of intermittent cocaine intake, rats develop patterns of drug use characteristic of addiction. The dorsal striatum is involved in the increased pursuit of cocaine after intermittent drug self-administration experience. Within the dorsal striatum, chronic cocaine use changes metabotropic glutamate type II receptor (mGlu2/3) density and function. We examined the extent to which activity at these receptors mediates responding for cocaine after intermittent cocaine use. In Experiment 1, male Wistar rats (n = 11) self-administered 0.25 mg/kg/infusion cocaine during 10 daily intermittent access (IntA) sessions (5 min ON/25 min OFF, for 5 h/session). We then examined the effects of intra-dorsal striatum infusions of the mGlu2/3 receptor agonist LY379268 (0, 1, and 3 g/hemisphere) on cocaine self-administration under a progressive ratio schedule of reinforcement. We observed a non-significant tendency for LY379268 to reduce responding for cocaine. In Experiment 2, we used a larger sample of male (n = 11) and female (n = 10) rats. Across 10 IntA sessions, the sexes showed similar levels of cocaine intake. Across the sexes, locomotion significantly increased over sessions, suggesting that rats developed psychomotor sensitization to self-administered cocaine. After 10 IntA sessions, intra-dorsal striatum LY379268 significantly reduced breakpoints achieved for cocaine, active lever presses, and cocaine infusions earned under progressive ratio. LY379268 had no effects on locomotion or inactive lever presses, indicating no motor effects. These results suggest that mGlu2/3 receptor activation in the dorsal striatum suppresses incentive motivation for cocaine, and this holds promise for anti-addiction therapeutics.