FM™ 2-10 Membrane Probe is an excellent reagent for identifying active stress neurons to study activity-dependent vesicle recycling mechanisms. This water-soluble dye is nontoxic to cells and barely fluoresces in aqueous media, but fluoresces brightly after inserting into the outer layer of the cell membrane. In neurons that actively release neurotransmitters, the dye is internalized in recyclable synaptic vesicles, resulting in bright staining of nerve terminals.