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Parkinson's disease (PD) is characterized by the degeneration of dopaminergic neurons. The gold standard therapy relies on dopamine (DA) replacement by the administration of levodopa ( l -DOPA). However, with time l -DOPA treatment induces severe motor side effects characterized by abnormal and involuntary movements, or dyskinesia. Although earlier studies point to a role of striatal cholinergic interneurons, also known as striatal tonically active neurons (TANs), in l -DOPA-induced dyskinesia (LID), the underlying mechanisms remain to be fully characterized. Here, we find that DA depletion is accompanied by increased expression of choline acetyltransferase (ChAT), the vesicular acetylcholine transporter (VAChT) as well as the atypical vesicular glutamate transporter type 3 (VGLUT3). TANs number and soma size are not changed. In dyskinetic mice, the VAChT levels remain high whereas the expression of VGLUT3 decreases. LID is attenuated in VGLUT3-deficient mice but not in mice bearing selective inactivation of VAChT in TANs. Finally, the absence of VGLUT3 is accompanied by a reduction of l -DOPA-induced phosphorylation of ERK1/2, ribosomal subunit (rpS6) and GluA1. Our results reveal that VGLUT3 plays an important role in the development of LID and should be considered as a potential and promising therapeutic target for prevention of LID. [ABSTRACT FROM AUTHOR]

• Mouse line generated to express hM3Dq selectively in microglia. • Microglial function was manipulated by specific activation of hM3Dq signaling. • Acute microglial hM3Dq signaling modulated expression of pro-inflammatory cytokines. • Chronic activation of hM3Dq increased tolerance to LPS-mediated cytokine expression. Microglia express muscarinic G protein-coupled receptors (GPCRs) that sense cholinergic activity and are activated by acetylcholine to potentially regulate microglial functions. Knowledge about how distinct types of muscarinic GPCR signaling regulate microglia function in vivo is still poor, partly due to the fact that some of these receptors are also present in astrocytes and neurons. We generated mice expressing the hM3Dq Designer Receptor Exclusively Activated by Designer Drugs (DREADD) selectively in microglia to investigate the role of muscarinic M3Gq-linked signaling. We show that activation of hM3Dq using clozapine N-oxide (CNO) elevated intracellular calcium levels and increased phagocytosis of FluoSpheres by microglia in vitro. Interestingly, whereas acute treatment with CNO increased synthesis of cytokine mRNA, chronic treatment attenuated LPS-induced cytokine mRNA changes in the brain. No effect of CNO on cytokine expression was observed in DREADD-negative mice. Interestingly, CNO activation of M3Dq in microglia was able to attenuate LPS-mediated decrease in social interactions. These results suggest that chronic activation of M3 muscarinic receptors (the hM3Dq progenitor) in microglia, and potentially other Gq-coupled GPCRs, can trigger an inflammatory-like response that preconditions microglia to decrease their response to further immunological challenges. Our results indicate that hM3Dq can be a useful tool to modulate neuroinflammation and study microglial immunological memory in vivo , which may be applicable for manipulations of neuroinflammation in neurodegenerative and psychiatric diseases. [ABSTRACT FROM AUTHOR]