Photoactivatable Neuropeptides for Spatiotemporally Precise Delivery of Opioids in Neural Tissue

Neuropeptides activate G protein-coupled receptors to acutely modulate cellular excitability and synaptic transmission. However, due to the lack of reagents for precise delivery of peptides within dense brain tissue, the spatiotemporal scale over which neuropeptides act is unknown. To achieve rapid and spatially delimited delivery of neuropeptides in mammalian brain tissue, we developed photoactivatable analogs of two opioids: [Leu5]-enkephalin (LE) and the 8 amino acid form of Dynorphin A (Dyn-8). These peptides are functionally inactive prior to photolysis, and exposure to ultraviolet (UV) light causes clean release of LE and Dyn-8. Recordings from acute slices of rat locus coeruleus (LC) demonstrated that photorelease of LE activates mu opioid receptor-coupled K+ channels with kinetics that approach the limits imposed by G protein-mediated signaling. Temporally precise and spatially delimited photorelease revealed the kinetics and ionic nature of the mu opioid response and the mechanisms that determine the spatial profile of enkephalinergic volume transmission in LC. ► Development of photoactivatable neuropeptides ► Activation of opioid signaling in tissue is limited by receptor kinetics ► Mu opioid response in LC is mainly mediated by GIRK channels ► Peptidases spatially confine Enkephalinergic signaling The actions of neuropeptides in the brain as well as the time and space scales over which they signal have been difficult to determine. Now, Banghart and Sabatini have developed photoactivatable opioid peptides and used them to study the spatiotemporal dynamics of opioid signaling.