berrant oxidation products of indoleamines have been implicated in the etiology of neurodegenerative diseases such as Alzheimer's disease and psychotic diseases such as schizophrenia and major depression. They are formed after administration of amphetamines and may be involved in the neurodegenerative effects of prolonged usage of such drugs. Many of the initial abnormal oxidation products (typically dihydrotryptamines) undergo rapid dimerization resulting in autofluorescent products with absorption bands in the 320 to 360 nm range and strong fluorescence in the 420 nm region followed by trimerization to form fluorescent products that absorb in the 440 nm region with emission at 520 nm. Typical emission spectra of serotonin dimers and trimers are shown at right which were formed in vitro by the autooxidation of a concentrated serotonin solution for several hours (20 mM at 37C for 12 hours). Further polymerization of indoleamines results in indolic-melanin, a non-fluoresecent brown precipitate.

MPE microscopy allows for the measurement of the oxidative state of cellular indolamine pools within a cell by using 3PE of monomer indoleamine with simultaneous 2PE of the dimers and trimers.The image at right shows an example of MPE detection of serotonin dimers in vivo. RBL-2H3 cells were loaded with serotonin (A) and then exposed to 10 µM peroxide for 10 minutes (B). The emission filters used are those shown in panel 6-C and the color scale represents the ratio of the two emission channels (F₄₂₀/F₃₅₀). Excitation was at 720 nm, with ~8 mW at the sample. This technique could prove useful to in vivo studies of aberrant indoleamines and their relationship to the various pathologies with which they may be involved.




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