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The presence and distribution patterns of ghrelin, a gastric acylated peptide, were studied in the entire gastrointestinal tract of the chicken (Gallus domesticus) using the peroxidase-antiperoxidase immunohistochemical method, western blot analysis and a specific antibody against the C-terminal region of rat ghrelin. Ghrelin-immunopositive cells were observed in the mucosal layer of all segments examined. The largest numbers of ghrelin-positive cells were located at the base of lobuli of the proventriculus gland, along villi of the intestines and in crypts of the duodenum. Lower numbers of ghrelin-immunostained cells were located in crypts of jejunum and ileum and only few ghrelin-immunostained cells were detected at the base of crypts of the large intestine. Closed and open types of cells were observed in all segments. Western blot analysis confirmed the presence of ghrelin-like protein in the entire chicken gastrointestinal tract. The anatomical distribution patterns and the morphological characteristics of chicken ghrelin-positive cells suggest that they are endocrine cells. Furthermore, it is concluded that ghrelin shows a high degree of preservation during evolution from non-mammalian vertebrates to mammals.

The localization of vasoactive intestinal polypeptide (VIP)-immunoreactive (ir) nerve cell bodies and fibers has been studied in the gill arches of goldfish (Carassius auratus, L.) using the peroxidase-antiperoxidase (PAP) immunohistochemical method. It was found that VIP-ir nerve cell bodies are localized in connective tissue on the oral side of the gill arch; these cells were present as single cells, in couples or as small clusters. Moreover, a dense network of VIP-ir fibers was observed beneath the lining epithelium of the raker cushion. The possible involvement of this peptide in mucus secretion in the gill arches of teleost is discussed.