Microfluorimetric scanning of sympathetic nerve fibers. An improved method to quantitate formaldehyde induced fluorescence of biogenic amines.

A two dimensional scanning procedure was developed for studying quantitative aspects of formaldehyde induced fluorescence (FIF) from noradrenaline containing nerve fibers. A computer (PDP 12) controlled scanning device was equipped with a cooled photomultiplier, a 0.5 micron scanning stage and a 0.5 micron measuring spot. Photodecomposition was reduced by a high scanspeed (100/sec) and a small excitation field. Digitized images were obtained with a high resolution. Data (10,000/scan) of large scan areas (2500 micron2) in the iris of the rat were transformed into fluorescence histograms, which allowed statistical evaluation. Visible changes induced in the histochemical preparation by administration of drugs (reserpine, L-Dopa) were reflected in characteristic changes in the histograms. A minor reduction in noradrenaline content, which was too small to be detected by visual observation of the microscopical image and by classical microfluorimetric methods, did evoke a significant change in the histograms. It is concluded that microfluorimetric scanning is a very sensitive technique for detecting changes of formaldehyde induced fluorescence from neuronal networks.