Next-generation GRAB sensors for monitoring dopaminergic activity in vivo

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. 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.