Method for direct induction of serotonin fluorescence in a carcinoid tumor after embedding in hydroxyethyl methacrylate.

Tissue slices from a carcinoid tumor were fixed in formalin and after dehydration embedded in hydroxyethyl methacrylate. Sections, 5 micrometers in thickness, were cut with a D-knife mounted on a serial microtome. Some sections were stained with either hematoxylin and eosin or by azo-coupling with fast garnet GBC, whereas others were reacted for catecholamines and indolamines either by exposing them to formaldehyde vapor for 1 hour at 80 degrees C. or by dipping them into a sucrose-phosphate buffer-glyoxylic acid solution followed by heating at 80 degrees C. for 15 minutes. Fluorescence intensities and the spectra of the fluorophores were recorded on 5-micrometers thick formaldehyde-reacted sections by microspectrofluorometry. With both the formaldehyde vapor method and the glyoxylic acid solution method, an intense yellow fluorescence was obtained from the carcinoid tumor cells, as well as from normal enterochromaffin cells. The excitation and emission maxima obtained by microspectrofluorometry from these cells indicated the presence of a fluorophore originating from serotonin.