Role for M5 muscarinic acetylcholine receptors in cocaine addiction

Abstract

Muscarinic cholinergic receptors of the M₅ subtype are expressed by dopamine‐containing neurons of the ventral tegmentum. These M₅ receptors modulate the activity of midbrain dopaminergic neurons, which play an important role in mediating reinforcing properties of abused psychostimulants like cocaine. The potential role of M₅ receptors in the reinforcing effects of cocaine was investigated using M₅ receptor‐deficient mice in a model of acute cocaine self‐administration. The M₅‐deficient mice self‐administered cocaine at a significantly lower rate than wild‐type controls. In the conditioned place preference procedure, a classic test for evaluating the rewarding properties of drugs, M₅‐deficient mice spent significantly less time in the cocaine‐paired compartment than control mice. Moreover, the severity of the cocaine withdrawal syndrome (withdrawal‐associated anxiety measured in the elevated plus‐maze) was significantly attenuated in mice lacking the M₅ receptor. These results demonstrate that M₅ receptors play an important role in mediating both cocaine‐associated reinforcement and withdrawal.