MEASURING SEROTONIN DISTRIBUTION IN LIVE CELLS WITH 3-PHOTON EXCITATION

Tryptophan and serotonin were imaged with infrared illumination by thr ee-photon excitation (3PE) of their native ultraviolet (UV) fluorescen ce. This technique, established by 3PE cross section measurements of t ryptophan and the monoamines serotonin and dopamine, circumvents the l imitations imposed by photodamage, scattering, and indiscriminate back ground encountered in other UV microscopies. Three-dimensionally resol ved images are presented along with measurements of the serotonin conc entration (similar to 50 mM) and content (up to similar to 5 X 10(8) m olecules) of individual secretory granutes.