Autofluorescent vesicular structures in hematoxylin and eosin stained duodenal mucosa of the domestic cat

Sections of formaldehyde-fixed, paraffin-embedded and routinely haematoxylin and eosin stained duodenal tissue of the domestic cat were inadvertently observed under blue excitation visible light of a fluorescence microscope, while undertaking histological studies on normal mammalian gastrointestinal tract. The sections revealed yellow fluorescing vesicular droplets in basally located cells within mucosal epithelium of the villi and the intestinal glands. The droplets had pink coloration under light microscopy, while with non-routine staining methods of Periodic acid – Schiff reagent and silver (Fontana method), they were negatively stained. An evaluation for similar structures in duodenal tissue of dogs, cattle and rats proved negative. A review of the literature indicates that these structures may be unique to the cat’s duodenum, and that they may represent serotonin secretory product of cells that can be classified as a member of the diffuse neuroendocrine system.