Involvement of Cyclin Dependent Kinase 5 in M4 Muscarinic Acetylcholine Receptor-Mediated Cholinergic Transmission within the Mouse Dorsal Striatum

Abstract Background: An imbalance between dopamine (DA) and acetylcholine (ACh) within the striatum has reemerged as key to the pathophysiology of the neurodegenerative disorder, Parkinson's disease (PD). M4 is a prominent muscarinic ACh receptor subtype in the striatum and we have previously reported that M4 controls cyclin-dependent kinase 5 (Cdk5) / dopamine- and cAMP-regulated phosphoprotein of Mr 32 kDa (DARPP-32) activity in cultured medium spiny neurons (MSNs). However, the mechanism of this control remains unclear. Methods: Genetic, electrophysiological, and immunohistochemical approaches were used in conjunction with pharmacological methods to study isolated M4-deleted MSNs (M4-KD MSNs) and a dorsomedial striatum (DMS) M4 knockout mouse model. We examined the role of Cdk5 in M4-mediated neural cholinergic transmission and related behavior.Results: Oxotremorine M, a nonselective mAchR agonist, promoted Cdk5/P35 signaling activity in DSM MSNs both in vivo and in vitro. Either pharmacological inhibition or genetic knockdown of M4 decreased the amount of Cdk5 and DARPP-32 phosphorylation at Thr75 in dopamine 1 receptor-expressing MSNs. Furthermore, whole-cell patch-clamp recording confirmed Cdk5 is necessary for M4-mediated cholinergic inhibition of excitatory synaptic transmission in MSNs in vivo and in vitro. Concomitantly, deletion of M4 activity in the DMS caused Oxotremorine M-induced Cdk5 signaling and glutamatergic synaptic input to be altered in parallel with behavioral responses. Conclusions: We characterized a novel regulatory mechanism of Cdk5/DARPP-32 involved in M4-mediated cholinergic regulation on striatonigral neurons and on motor behavior. The findings indicate that inhibition of M4 mAChR could be a novel approach to correct the pathological conditions of PD.