Abstract
We here describe a technique to transiently activate specific neural pathways in vivo. It comprises the combined use of a CRE-recombinase expressing canine adenovirus-2 (CAV-2) and an adeno-associated virus (AAV-hSyn-DIO-hM3D(Gq)-mCherry) that contains the floxed inverted sequence of the designer receptor exclusively activated by designer drugs (DREADD) hM3D(Gq)-mCherry. CAV-2 retrogradely infects projection neurons, which allowed us to specifically express hM3D(Gq)-mCherry in neurons that project from the ventral tegmental area (VTA) to the nucleus accumbens (Acb), the majority of which were dopaminergic. Activation of hM3D(Gq)-mCherry by intraperitoneal (i.p.) injections of clozapine-N-oxide (CNO) leads to increases in neuronal activity, which enabled us to specifically activate VTA to Acb projection neurons. The VTA to Acb pathway is part of the mesolimbic dopamine system and has been implicated in behavioral activation and the exertion of effort. Injections of all doses of CNO led to increases in progressive ratio (PR) performance. The effect of the lowest dose of CNO was suppressed by administration of a DRD1-antagonist, suggesting that CNO-induced increases in PR-performance are at least in part mediated by DRD1-signaling. We hereby validate the combined use of CAV-2 and DREADD-technology to activate specific neural pathways and determine consequent changes in behaviorally relevant paradigms.
Highlights
While the existence of neuronal pathways has been appreciated since Ramon y Cajal’s time, techniques to activate them in vivo and study consequent changes in behavior have only been developed recently
We show that the effect of the lowest dose of CNO on progressive ratio (PR)-performance can be suppressed by administration of the dopamine receptor D1 (DRD1)-antagonist SCH23390, thereby underscoring the potential of the combined use of canine adenovirus-2 (CAV-2) and designer receptor exclusively activated by designer drugs (DREADD)-technology to provide means to bridge the gap that separates structure from function
Infusions of CAV-2 in the Acb led to expression of CRE in ventral tegmental area (VTA), as hM3D(Gq)-mCherry expression was restricted to this area, indicating that CAV-2 infected VTA to Acb projection neurons and expressed CRE, inducing hM3D(Gq)mCherry expression in the VTA only
Summary
While the existence of neuronal pathways has been appreciated since Ramon y Cajal’s time, techniques to activate them in vivo and study consequent changes in behavior have only been developed recently. The combination of optogenetic and designer receptor exclusively activated by designer drugs (DREADD) technologies with CRE-mediated homologous recombination enables specific targeting and manipulation of neural pathways and has improved our understanding of how the activity of specific neuronal pathways can act as determinants of behavior [1,2]. As suggested by Nair et al [3], the combination of these technologies with CRE-expressing viral vectors provides another means to target specific neural pathways on a cellular resolution. We test and validate the combined use of CAV-2 and DREADD-technology to pharmacogenetically activate specific neural pathways in vivo. The technique entails the infusion of two viral vectors (CAV-2 and AAV-hSyn-DIO-hM3D(Gq)-mCherry) into two sites that are connected through direct neuronal projections and represent a neuronal pathway. AAV-hSyn-DIO-hM3D(Gq)-mCherry is infused in the site where the cell bodies are located, while CAV-2 is infused in the area that is innervated by the corresponding axons.
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