Dissecting Intracellular Signaling and Affective Behavior Using Optically Active GPCRs

Optogenetics has provided a revolutionary approach to dissecting biological phenomena. Traditional techniques however use binary control schemes to selectively turn on/off neurons in the presence of light. While useful in helping to understand aspects of the cell biology and neural circuitry in healthy and diseased states, these approaches are limited in their ability to mirror endogenous neuromodulator receptor signaling. For this reason, the development of optically active G-protein coupled receptors (GPCRs) allows for more fine tuned modulation of cellular activity. This, in combination with the spatiotemporal control offered through optogenetics, provides more refined in vitro and in vivo GPCR toolkits. Here we generated, and characterized two optically active GPCRs. A Gαs- coupled chimera of rhodopsin and the β2-adrenergic receptor (opto-β2AR) and a Gαi- coupled chimera of rhodopsin and the mu-opioid receptor (opto-MOR). We first fully compare these receptors to their wild type counterparts using canonical in vitro readouts of GPCR activity and demonstrate that our chimeric receptors indeed behave as their biological complements. We then package these receptors into viral hosts and transfect them into various brain regions of interest. Utilizing electrophysiological and behavioral measurements we demonstrate that optical activation of opto-β2AR mimics noradrenergic activity, producing an anxiety-like behavioral phenotype, while optical activation of opto-MOR shows robust effects on motivational behavioral, similar to endogenous mu-opioid receptor activity. Taken together, we show that these optically active GPCR approaches enhance the utility of optogenetics and allow for discrete spatiotemporal control of GPCR signaling in vitro and in vivo, thus expanding the toolbox for understanding both neurotransmitter and neuropeptide signaling within neural circuits