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 GPCR-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. Co-expressing red GRAB(DA) with either green GRAB(DA) or the calcium indicator GCaMP6s allows simultaneously tracking neuronal activity and dopaminergic signaling in distinct circuits in vivo.