Autonomic nerve control of the swimbladder of the goldsinny wrasse, Ctenolabrus rupestris.

The autonomic nerve control of the swimbladder of the goldsinny wrasse has been studied by experiments with isolated strips from the muscularis mucosae, drug effects on gas secretion in vivo, fluorescent histochemistry and quantitative analysis of catecholamine content. Vagotomy, atropine and mecamylamine significantly inhibited induced gas secretion, suggesting a cholinergic vagal secretory innervation of the gas gland. The anterior part of the mucosa (secretory part) is contracted by acetylcholine and alpha-adrenoceptor agonists. These responses are competitively antagonized by atropine and phentolamine or yohimbine respectively. The posterior (resorbent) part of the mucosa is contracted by acetylcholine, but beta-adrenoceptor agonists relax the acetylcholine-precontracted preparations. These responses are competitively blocked by atropine and propranolol respectively. The pA2-values from all experiments with antagonists are well comparable with values obtained for the same drugs in other teleost or mammalian tissues. Tyramine, 5-hydroxytryptamine or phenylephrine had mixed effects on the posterior part. This effect is at least in part due to release of nervously stored catecholamines. Fluorescent histochemistry revealed a strong innervation by both smooth and varicose adrenergic fibres in all parts of the swimbladder, noradrenaline being the dominant catecholamine. Yellow fluorescent cells, which may contain 5-hydroxytryptamine, were also seen in the swimbladder mucosa. No conclusive evidence for a cholinergic innervation of the muscularis mucosae was obtained.