FM 1-43 Membrane Probe is an excellent reagent for identifying active stimulate 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. Nonspecific staining of cell surface membranes can be easily removed by washing prior to imaging. FM 1-43 membrane probe is also available in 1 mg packaged in single vials (T-3163). Also available is the FM 1-43FX Membrane Probe (F-35355), a mimic of the FM 1-43 Membrane Probe that can be immobilized with aldehyde fixatives.