Selective inhibition of M5 muscarinic acetylcholine receptors attenuates cocaine self‐administration in rats

Cocaine use disorder (CUD) remains a debilitating health problem in the United States for which there are no FDA-approved treatment options. Accumulating anatomical and electrophysiological evidence indicates that the muscarinic acetylcholine receptor (mAChR) subtype 5 (M5) plays a critical role in the regulation of the mesolimbic dopaminergic reward circuitry, a major site of action for cocaine and other psychostimulants. In addition, M5 KO mice exhibit reduced cocaine self-administration behaviors with no differences in sugar pellet-maintained responding relative to wildtype mice. These findings suggest that selective inhibition of M5 mAChR may provide a novel pharmacological approach for targeting CUD. Recently, we reported the synthesis and characterization of ML375, a selective negative allosteric modulator (NAM) for the rat and human M5 mAChR with optimized pharmacokinetic properties for systemic dosing in rodents. In the present study, male Sprague-Dawley rats were trained to self-administer intravenous cocaine (0.1–0.75 mg/kg/injection) under a 10-response, fixed ratio (FR10) or a progressive ratio (PR) schedule of reinforcement. Under both schedules of reinforcement, ML375 produced dose-related reductions in cocaine self-administration. ML375 also modestly reduced sugar pellet-maintained responding on the FR10 schedule, but had no effect under a PR schedule of reinforcement. Further, ML375 did not affect general motor output as assessed by a rotarod test. Collectively, these results provide the first demonstration that selective inhibition of M5 using the M5 NAM ML375 can attenuate both the reinforcing effects and the relative strength of cocaine and suggest that M5 NAMs may represent a promising, novel treatment approach for CUD.