New and improved GRAB fluorescent sensors for monitoring dopaminergic activityin vivo

The monoamine neuromodulator 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 the first red fluorescent GPCR-activation–based DA (GRAB DA ) sensors and optimized versions of green fluorescent GRAB DA sensors following our previous studies. In response to extracellular DA, both the red and green GRAB DA sensors have a large increase in fluorescence (ΔF/F 0 values of 150% and 340%, respectively), with subcellular resolution, subsecond kinetics, and nanomolar to submicromolar affinity. Moreover, both the red and green GRAB DA sensors readily resolve evoked DA release in mouse brain slices, detect compartmental DA release in live flies with single-cell resolution, and report optogenetically elicited nigrostriatal DA release as well as mesoaccumbens dopaminergic activity during sexual behavior in freely behaving mice. Importantly, co-expressing red GRAB DA with either green GRAB DA or the calcium indicator GCaMP6s provides a robust tool for simultaneously tracking neuronal activity and dopaminergic signaling in distinct circuits in vivo .