Orexins and receptor OX2R in the gastroenteric apparatus of two teleostean species: Dicentrarchus labrax and Carassius auratus

Orexin A and B peptides and the receptor OX2R were studied in sea bass and goldfish gastroenteric tract by immunoblotting combined with densitometric analysis using NIH Image J software and immunohistochemical techniques. These teleost species present a different gut organization and diverse feeding habits. Immunoblotting experiments showed one band of 16 kDa corresponding to prepro-orexin, and one band of 38 kDa corresponding to the OX2R receptor. Immunohistochemical localization of OXA and OXB was observed in the enteric nervous system throughout the gastroenteric tract of both species. OXA and OXB immunoreactive cells were found in the gastric and intestinal regions of sea bass, and were mainly found in the basal region of folds in intestinal bulb, and in the midgut and hindgut of goldfish. The distribution of OX2R was mainly detected in the mucosa of the gastroenteric tract of sea bass and goldfish. This distribution suggests an endocrine action of OXA and OXB in the gastrointestinal tract as well as involvement in the peripheral control of food intake and digestive processes in both species. This study might also serve to determine the productive factors in breeding and as a baseline for future experimental studies on the regulation of the gastroenteric functions in non-mammalian vertebrates.