The last decade has seen major advances in neuroscience tools allowing us to selectively modulate cellular pathways in freely moving animals. Chemogenetic approaches such as designer receptors exclusively activated by designer drugs (DREADDs) permit the remote control of neuronal function by systemic drug administration. These approaches have dramatically advanced our understanding of the neural control of behaviour. Here, we review the different techniques and genetic approaches available for the restriction of chemogenetic receptors to defined neuronal populations. We highlight the use of a dual virus approach to target specific circuitries and the effectiveness of different routes of administration of designer drugs. Finally, we discuss the potential caveats associated with DREADDs including off-target effects of designer drugs, the effects of chronic chemogenetic receptor activation and the issue of collateral projections associated with DREADD activation and inhibition.
AbbreviationsAAVs, adeno-associated viral vectors; BBB, blood-brain barrier; CAMKII, calmodulin-dependent protein kinase II; CAVs, canine adenoviruses; CNO, clozapine N-oxide; DREADDs, designer receptors exclusively activated by designer drugs; hM3D, human M 3 muscarinic DREADD; hM4D, human M 4 muscarinic DREADD; HSV, herpes simplex viral; hSyn, human synapsin; KORD, κ-opioid-based receptor designer receptor exclusively activated by designer drugs; LGICs, ligand-gated ion channels; NAc, nucleus accumbens; RASSL, receptor activated solely by a synthetic ligand; SalB, salvinorin B; VTA, ventral tegmental area
IntroductionDuring the last decade, there has been a revolution in neuroscience techniques that have resulted in increasingly precise methods to manipulate neural systems in awake, behaving animals. Understanding the relationship between brain function and behaviour is critical for the advancement of both neuroscience research and targeted medication development. Chemogenetics refers to the technique that allows for the reversible remote control of cell populations and neural circuitry via systemic injection or microinfusion of an activating ligand (Alexander et al., 2009;Armbruster et al., 2007). The chemogenetic technique uses engineered receptors and biologically inert ligands to achieve this aim. Unlike optogenetics, which has the ability to control cells and neural circuitry with light, the use of designer drugs makes chemogenetics simple to use, removing the need for optical fibre probes and tethers. While the temporal resolution of chemogenetics is lower than optogenetics, this relatively non-invasive technique is still effective for functional mapping, cell-type-specific manipulations and multiplexed control of neurons.In this review, we will evaluate the different strategies that have been used to restrict chemogenetic receptors to defined neuronal populations. We will also highlight the use of a dual virus approach at targeting projection neurons and the effectiveness of different routes of administration of designer drugs. Fin...