Muscarinic receptors acting at pre- and post-synaptic sites differentially regulate dopamine/DARPP-32 signaling in striatonigral and striatopallidal neurons

Muscarinic receptors, activated by acetylcholine, play critical roles in the functional regulation of medium spiny neurons in the striatum. However, the muscarinic receptor signaling pathways are not fully elucidated due to their complexity. In this study, we investigated the function of muscarinic receptors in the striatum by monitoring DARPP-32 (dopamine- and cAMP-regulated phosphoprotein of Mr 32 kDa) phosphorylation at Thr34 (the PKA-site) using mouse striatal slices. Treatment of slices with a non-selective muscarinic receptor agonist, oxotremorine (10 μM), rapidly and transiently increased DARPP-32 phosphorylation. The increase in DARPP-32 phosphorylation was completely abolished either by a dopamine D1 receptor antagonist (SCH23390), tetrodotoxin, genetic deletion of M5 receptors, muscarinic toxins for M1 and M4 receptors, or 6-hydroxydopamine lesioning of dopaminergic neurons, whereas it was enhanced by nicotine. Analysis in D1-DARPP-32-Flag/D2-DARPP-32-Myc transgenic mice revealed that oxotremorine increases DARPP-32 phosphorylation selectively in D1-type/striatonigral, but not in D2-type/striatopallidal, neurons. When D1 and D2 receptors were blocked by selective antagonists to exclude the effects of released dopamine, oxotremorine increased DARPP-32 Thr34 phosphorylation only in D2-type/striatopallidal neurons. This increase required activation of M1 receptors and was dependent upon adenosine A2A receptor activity. The results demonstrate that muscarinic receptors, especially M5 receptors, act at presynaptic dopaminergic terminals, regulate the release of dopamine in cooperation with nicotinic receptors, and activate D1 receptor/DARPP-32 signaling in the striatonigral neurons. Muscarinic M1 receptors expressed in striatopallidal neurons interact with adenosine A2A receptors and activate DARPP-32 signaling.

► The muscarinic agonist regulates DARPP-32 Thr34 phosphorylation in the striatum. ► Activation of M5 receptors at dopaminergic terminals stimulates dopamine release. ► The released dopamine activates D1 receptor/DARPP-32 signaling in D1-type neurons. ► M1 receptors activate A2A receptor-dependent DARPP-32 signaling in D2-type neurons.