ADCY1 and Parkinson disease: On the other hand, the M2 and M4 subtypes primarily couple toGi/o proteins, resulting in the inhibition of adenylate cyclase and a reductionin intracellular cyclic adenosine monophosphate (cAMP) levels.28 Theabnormal activity of mAChRs has been linked to the development of several pathologicalconditions, including cancer, as well as psychiatric and neurological disorders such as AD,schizophrenia, Parkinson’s disease (PD), and drug abuse.