Unlocking opioid neuropeptide dynamics with genetically-encoded biosensors

Neuropeptides are ubiquitous in the nervous system. Research into neuropeptides has been limited by a lack of experimental tools that allow for the precise dissection of their complex and diverse dynamics in a circuit-specific manner. Opioid peptides comprise a clinically relevant family that modulates pain, reward, and aversion. To illuminate the spatiotemporal dynamics of endogenous opioid signaling in the brain, we developed a class of genetically-encoded fluorescent sensors based on kappa, delta, and mu opioid receptors: κLight, δLight, and µLight, respectively. We used κLight to identify electrical stimulation parameters that trigger endogenous opioid release and the spatiotemporal scale of dynorphin volume transmission ex vivo. Using in vivo fiber photometry, we characterized optogenetically-driven opioid release, and observed differential opioid signaling in response to fearful and rewarding conditions in the nucleus accumbens. These sensors reveal the dynamics of endogenous opioid neuropeptide release in vivo, in awake freely moving behavior.