Study The Involvement Of M4 Muscarinic Acetylcholine Receptor In Regulation Of CAMP Signaling And DARPP-32 Phosphorylation In MSNs

Both M1 and M4 are predominately muscarinic receptors in striatum, and play critical roles in the functional regulation of medium spiny neurons in the striatum.However, the muscarinic receptor signaling pathways are not fully elucidated.DARPP-32(dopamine- and c AMP-regulated phosphoprotein of Mr 32 k Da) plays an essential role in DA signaling transmission of striatum. In this study, we investigated the function of M1 and M4 receptors in regulating c AMP production and DARPP-32 phosphorylation in MSNs. Oxotremorine(OX,1μM), a non-selective acetylcholine muscarinic receptor agonist, increased c AMP production with dopamingeric dependent manner, but less potent when compared those induced by apomorphine(APO), a non-selective dopamine receptor agonist.Tetrodotoxin(TTX) can enhance the c AMP production by block presynaptic terminals. Interestingly, we then found OX and APO has different effect on DARPP-32 phosphorylation. OX phosphorylate DARPP-32 at Thr75 site rather than Thr34, whereas APO phosphorylate DARPP-32 at both Thr34 and Thr75.More important, either genetic knockdown of M4 or pharmacologic inhibition with MT3, trafficked DARPP-32 at Thr75 activation by OX. Our data show that M4 prom important role in the regulation of physiologic responses within the striatum and might be a potential novel therapeutic target for Parkinson’s disease.