The effect of drugs on spontaneous motility and on response to stimulation of the extrinsic nerves of the gut of a teleostean fish.

Trout gut shows, in addition to changes in general muscle tone, longitudinal "pendular" rhythms, peristaltic waves, and longitudinal "colic" contractions. Both vagus and splanchnic nerves are motor and there is no evidence of antagonistic "sympathetic" and "parasympathetic" nervous control. A posterior autonomic nerve supplying the rectum stimulated or inhibited according to the duration and frequency of the electrical pulses applied. Acetylcholine increased the tone and amplitude of pendular movements in all regions of the gut, and produced strong contraction of the circular muscles. Both nicotine and hexamethonium antagonized the action of acetylcholine, suggesting that its principal site of action is the neurone. Adrenaline lowered the tone of the longitudinal muscle and abolished pendular activity in the intestine and rectum, but contracted the longitudinal and circular muscles of the stomach. Hexamethonium bromide abolished peristalsis but greatly increased the amplitude of pendular contractions.The reaction of the trout intestine to both histamine and pilocarpine was slight, but nicotine, 5-hydroxytryptamine, eserine, and barium caused strong contractions. The actions of atropine and piperoxan (933F) are discussed. Evidence is presented which suggests that the postganglionic vagus nerve fibres supplying the trout stomach may be adrenergic, while both the splanchnic nerve fibres to the stomach and intestine, and the preganglionic vagal fibres to the stomach, may be cholinergic. It is also suggested that there is a continuous release of acetylcholine by cholinergic neurones in the gut wall.