PKD1 and type 2 diabetes mellitus: In contrast, the function of muscarinic receptor 3 (M3) has not been elucidated in the pathophysiology of schizophrenia other than probably related to the adverse effects of antipsychotics, such as type 2 diabetes [158], considering that M3 mediates insulin release from pancreatic β cells directly through Gq protein signaling [159] and indirectly through β-arrestin and polycystin 1 (PKD1) signaling [158].