Bombesin-, gastrin/CCK-, 5-hydroxytryptamine-, neurotensin-, somatostatin-, and VIP-like immunoreactivity and catecholamine fluorescence in the gut of the elasmobranch, Squalus acanthias.

The presence of peptides and 5-hydroxytryptamine (5-HT) in neurons and endocrine cells in the gastrointestinal tract of the spiny dogfish, Squalus acanthias, was investigated by means of immunohistochemistry, and the distribution of catecholamines by use of the Falck-Hillarp fluorescence-histochemical technique. Bombesin-like immunoreactivity was present in numerous nerves in all layers and all parts of the gut, and also in endocrine cells in the mucosa throughout the stomach, rectum and intestine. VIP-like immunoreactivity occurred in an abundance of nerve fibres and in nerve cell bodies in all parts of the gut except the oesophagus, while 5-HT-like immunoreactivity was found sparsely in nerve fibres and more frequently in endocrine cells throughout the gut. Gastrin/CCK-like immunoreactivity was present in numerous nerve fibres in the rectum, but only in scattered fibres in the other parts of the gut. Endocrine cells showing gastrin/CCK-like immunoreactivity were present in the intestine only. Somatostatin-like immunoreactivity occurred in both nerve fibres and endocrine cells of the stomach and intestine, but only in nerves in the rectum. Neurotensin-like immunoreactivity was confined to endocrine cells of the intestine. Falck-Hillarp fluorescence histochemistry revealed 5-HT in endocrine cells and catecholamines in nerve fibres (and possibly also in endocrine cells) throughout the gut. Bombesin-, VIP-, gastrin/CCK- and somatostatin-like immunoreactivities and catecholamine fluorescence were present in nerve fibres of the rectal gland and, with the exception of gastrin/CCK-like immunoreactivity, also in nerve bundles in the walls of the coeliac and mesenteric arteries. The findings of the present study form an anatomical basis for the assumption that several of the neuropeptides and amines could function as neurotransmitters or neuromodulators in the gut of Squalus.