Expression and Immunohistochemical Detection of Leptin-Like Peptide in the Gastrointestinal Tract of the South American Sea Lion (Otaria flavescens) and the Bottlenose Dolphin (Tursiops truncatus).

This study provides an immunohistochemical approach to the expression of leptin in the gastrointestinal tract of the monogastric South American sea lion (Otaria flavescens), and the poligastric bottlenose dolphin (Tursiops truncatus). The specific organization of the gastrointestinal tract is examined in relation to the neuroendocrine regulation of the gut exerted by leptin. In the South American sea lion some leptin-like-immunoreactive (ir) cells, and endocrine type cells, were found in the pit of gastric mucosal folds and in the epithelium of duodenum as well as numerous neurons were detected in the submucosal and myenteric plexuses of the stomach. In the bottlenose dolphin, many leptin-like-ir cells, and exocrine type cells, were identified in the mucosal layer of the main stomach as well as several neurons and nervous fibers were detected in nervous plexuses of main stomach, pyloric stomach, proximal, and middle intestine. Our data suggest that the distribution of leptin-like peptides is similar in the two species, notwithstanding the different anatomical organization of the gastrointestinal apparatus of South American sea lion and bottlenose dolphin. These findings "suggest" the presence of a basal plan in the regulation of food intake, body weight, energy balance and of the gastrointestinal functions in general also in marine mammals with different and specific feeding habits.