New and improved GRAB fluorescent sensors for monitoring dopaminergic activity in vivo

Abstract

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/F₀ 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.