Immunolocalisation of leptin in the digestive system of juvenile European sea bass (Dicentrarchus labrax)

Leptin is a hormone that is mainly produced by adipocytes; it is connected with metabolism regulation, but knowledge about its effect on teleosts, particularly in juvenile specimens, is still scarce. This study is the first to investigate the presence of leptin immunoreactivity in juvenile European sea bass (Dicentrarchus labrax) and its distribution in the digestive system. Leptin immunoreactivity was detected by Western blot analysis, while its distribution was obtained using immunohistochemical methods with a human leptin-specific antibody. The homogenate of the body of a whole European sea bass contains a leptin-like protein with an estimated molecular weight of approximately 16 kDa. Leptin immunoreactivity was distributed along the digestive system, especially in the oesophageal mucous cells, neuroendocrine gastrointestinal cells and eosinophilic granular cells of the gastrointestinal lamina propria. This is the first report on leptin immunoreactivity in juvenile sea bass and our data can provide a good morphological basis for further investigation into food, metabolism and immunoresponse regulation in aquacultured fish.