title: Identification of the APUD endocrine cells of rat fundic mucosa by means of combined amine fluorescence and electron microscopy.
abstract: Rat fundic mucosa contains numerous APUD endocrine cells that can take up 5-hydroxytryptophan (5-HTP) and decarboxylate it to 5-hydroxytryptamine (serotonin), detectable by its formaldehyde-induced yellow fluorescence. To identify these cells by electron microscopy, pieces of rat gastric mucosa were incubated with DL-5-HTP. Some specimens were fixed in 4% formaldehyde-0.5% glutaraldehyde, while others were frozen, freeze-dried, and exposed to paraformaldehyde vapors. Thick sections of the Epon-embedded specimens were examined and photographed by fluorescence microscopy, and fluorescing and nonfluorescing cells were identified by electron microscopy in serial thin sections. Control specimens, not incubated with 5-HTP, revealed fluorescence of only the mast cells and EC cells, which were abundant in the pylorus, but rare in fundic mucosa. Specimens incubated with 5-HTP also exhibited numerous yellow fluorescent endocrine cells in fundic mucosa, which cells were found to be the ECL cells; the A-like cells did not fluoresce. In pyloric mucosa, many G and D (D1) cells also exhibited weak or moderate fluorescence after 5-HTP incubation. Thus, this study supports the contention of previous radioautographic studies that the ECL, but not the A-like, cells are the APUD endocrine cells of rat fundic mucosa, that G and D cells also possess some APUD activity, and that EC cells represent the enterochromaffin cells, which normally synthesize and store demonstrable quantities of serotonin.
mesh_terms: D006916:5-Hydroxytryptophan / Q000494:pharmacology; D001078:APUD Cells / Q000648:ultrastructure*; D000588:Amines; D000818:Animals; D002230:Carbidopa / Q000494:pharmacology; D005453:Fluorescence / Q000379:methods; D005753:Gastric Mucosa / Q000166:cytology*; D008297:Male; D008854:Microscopy, Electron; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D000588:Amines; D006916:5-Hydroxytryptophan; D002230:Carbidopa