||Yulong Li（Peking University Professor）
Dopamine (DA) is a central monoamine neurotransmitter involved in many physiological and pathological processes. A longstanding yet largely unmet goal is to measure DA changes reliably and specifically with high spatiotemporal precision, particularly in animals executing complex behaviors. We very recently reported the development of genetically encoded GPCR-activation-based-DA (GRAB-DA) sensors that enable these measurements. In response to extracellular DA, GRAB-DA sensors exhibit large fluorescence increases with subcellular resolution, subsecond kinetics, nanomolar to submicromolar affinities, and excellent molecular specificity. GRAB-DA sensors can resolve a single-electrical-stimulus-evoked DA release in mouse brain slices and detect endogenous DA release in living flies, fish, and mice. In freely behaving mice, GRAB-DA sensors readily report optogenetically elicited nigrostriatal DA release and depict dynamic mesoaccumbens DA signaling during Pavlovian conditioning or during sexual behaviors. By tuning the residues in GFP and GPCRs, we now have developed a second generation of green GRAB-DA sensors, with over 2-4 fold larger fluorescence responses, 2-5 fold maximum brightness, up to 10-100 fold higher molecular selectivity (over norepinephrine), more affinity ranges and distinct pharmacological properties. In parallel, we also generated promising red GRAB-DA sensor candidates with similar affinity as green ones. The red sensors are capable of reporting DA dynamics in vivo in both flies and in rodents. The new generation dopamine sensors along with other GRAB sensors provide powerful tools to unravel the in-vivo dynamics of critical neuromodulators for diverse model systems in physiological and pathophysiological conditions.