Localization of the orexin system in the gastrointestinal tract of fallow deer

The aim of the present study was to investigate by immunohistochemistry the presence and distribution of the orexin system in the stomach and gut of fallow deer. Abundant orexin A-positive cells were localized in the middle and basal portions of the mucosal glands of the cardial and fundic regions of the stomach. In the same gastric areas, orexin B-positive cells were also found, mainly localized in the basal portion of glands. In the intestinal tract, orexin-containing cells were occasionally found in the duodenal epithelium and in the rectal intestinal glands. Immunoreactivity for orexin receptors, type 1 and 2 (OX1R and OX2R), was not detected in the same stomach regions. OX1R-immunopositivity was observed in the enteric neuron ganglia localized in the submucosal and muscular intestinal layers, while OX2R-immunopositivity was found close in contact with the cytoplasmic membrane of epithelial cells in the small intestine.