Next-generation GRAB sensors for monitoring dopaminergic activity in vivo

Red and improved green versions of the genetically encoded dopamine sensor GRAB(DA)have been developed. These neurotransmitter sensors are used alone or in combination with, for example, calcium sensors in behaving fruit flies and rodents. Dopamine (DA) plays a critical role in the brain, and the ability to directly measure dopaminergic activity is essential for understanding its physiological functions. We therefore developed red fluorescent G-protein-coupled receptor-activation-based DA (GRAB(DA)) sensors and optimized versions of green fluorescent GRAB(DA)sensors. In response to extracellular DA, both the red and green GRAB(DA)sensors exhibit a large increase in fluorescence, with subcellular resolution, subsecond kinetics and nanomolar-to-submicromolar affinity. Moreover, the GRAB(DA)sensors resolve evoked DA release in mouse brain slices, detect evoked compartmental DA release from a single neuron in live flies and report optogenetically elicited nigrostriatal DA release as well as mesoaccumbens dopaminergic activity during sexual behavior in freely behaving mice. Coexpressing red GRAB(DA)with either green GRAB(DA)or the calcium indicator GCaMP6s allows tracking of dopaminergic signaling and neuronal activity in distinct circuits in vivo.