DREADDs, designer receptors exclusively activated by designer drugs, are engineered G proteincoupled receptors (GPCR) which can precisely control GPCR signaling pathways (for example, Gq, Gs and Gi). This chemogenetic technology for control of GPCR signaling has been successfully applied in a variety of in vivo studies, including in mice, to remotely control GPCR signaling, for example, in neurons, glia cells, pancreatic beta-cells, or cancer cells. In order to fully explore the in vivo

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... ions of the DREADD technology we generated hM3Dq and hM4Di strains of mice which allow for Cre recombinase-mediated restricted expression of these pathwayselective DREADDs. With the many Cre driver lines now available, these DREADD lines will be applicable to studying a wide array of research and preclinical questions. RESULTS AND DISCUSSION Using directed evolution in a yeast mutagenesis system mutant G protein coupled muscarinic receptors were isolated which lost the ability to respond to the natural ligand acetylcholine, but gained the ability to respond to an inert compound (clozapine-N-oxide; CNO) with nanomolar potencies (Armbruster et al. 2007). We also demonstrated that CNO is both pharmacologically inert and metabolically stable in C57Bl6 mice (Alexander et al. 2009). Importantly, mutant receptors were selected to have low basal activity thereby providing a maximal dynamic range in agonist-induced responses (Armbruster et al. 2007). Currently, the existing DREADDs include the Gq, Gi and Gs (e.g. hM3Dq, hM4Di, and GsD respectively) signaling pathways, allowing for remote and non-invasive activation, inhibition and modulation of GPCR signaling pathways and neurotransmission in a variety of cells in