Tachykinins and intestinal motility in different fish groups.

The presence and function of tachykinins were studied in the intestine of hagfish (Myxine glutinosa), lamprey (Lampetra fluviatilis), starry ray (Raja radiata), lungfish (Lepidosiren paradoxa), bichir (Polypterus senegalensis), and rainbow trout (Oncorhynchus mykiss), which represent different systematic groups of fish. Immunohistochemistry revealed cells containing substance P (SP)-like material in the intestine of lamprey and lungfish, and in the stomach of the ray. The intestinal motility was studied using isolated muscle strip preparations. SP had no effect on hagfish or lamprey intestine. In the other four species SP produced intestinal contractions. In ray, bichir, and lungfish the tachykinins may be released from endocrine cells and act, at least in the bichir and lungfish, directly onto the smooth muscle cells. In the rainbow trout intestine, where SP-like material may be released from both nerve fibres and endocrine cells, it is indicated that the contractile effect is in part direct upon the smooth muscle and in part via stimulation of cholinergic and serotonergic neurons.