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SUMMARY1. The effects of vagal efferent fibre stimulation on the smooth muscle of the lower oesophageal sphincter have been studied on the anaesthetized animal and on the isolated and perfumed organ.2. In both muscle layers (longitudinal and circular) vagal stimulation elicits two types of electromyographic (e.m.g.) potentials: (a) excitatory junction potentials (e.j.p.s) where there is a depolarization of the smooth muscle fibres. E.j.p.s can give rise to spike potentials inducing a contraction of the sphincter; (b) inhibitory junction potentials (i.j.p.s) where there is hyperpolarization of the smooth muscle fibres, often followed by a transient depolarization which may initiate spikes (postinhibitory rebound).3. Pure i.j.p.s are observed after atropine treatment which suppresses e.j.p.s. Under these conditions, a long lasting vagal stimulation induces a long duration hyperpolarization concomitant with an opening of the lower oesophageal sphincter followed after the cessation of stimulation by a powerful rebound leading to a strong contraction which closes the sphincter.4. Several arguments, pharmacological (action of acetylcholine (ACh), atropine and hexamethonium) and physiological (threshold and latency of responses) lead to the following conclusions.Preganglionic vagal fibres are cholinergic and they activate (a) intramural excitatory cholinergic neurones; (b) intramural non-adrenergic

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The autonomic nervous system is involved in the regulation of visceral function, including the regulation of digestive tract motility. One characteristic of this system is that the nervous regulatory structures are not localized exclusively in the cerebrospinal axis. From a classic point of view, it could be described as having an intrinsic level of regulation located in the viscera and an extrinsic level of regulation in the prevertebral ganglia and central nervous structures, with each level of regulation having its own integrative properties. The prevertebral ganglia, which are part of the sympathetic system, have long been considered as a simple relay on the efferent central pathway. During the last 20 years, numerous studies devoted to the prevertebral ganglia have shown that they behave as true integrative nervous structures able to organize intra-and interorgan regulation.Experiments performed on in vitro preparations consisting of prevertebral ganglia connected to part of the digestive tract have revealed the involvement of these ganglia in the organization of gastrointestinal reflexes. Kreulen & Szurszewski (1979) showed that an inhibitory reflex occurred between two segments of the colon connected only via the coeliac ganglion and the inferior mesenteric ganglion by the mesenteric nerves. This reflex disappeared after sectioning of the intermesenteric nerves. Inhibitory gastrointestinal reflexes organized by the coeliac plexus have also been demonstrated in in vitro models consisting of isolated stomach and duodenum connected only to the coeliac plexus by nervous rami (Kreulen et al. 1983;Mazet et al. 1993b). In a previous study (Mazet et al. 1993b), we demonstrated that a delayed and long-lasting gastrointestinal inhibitory reflex was organized by the coeliac plexus. This nervous Journal of Physiology (1999) 1. The coeliac plexus can organize a gastroduodenal inhibitory reflex without action potentials. The involvement of the nitric oxide-cGMP pathway in this reflex was investigated in the rabbit on an in vitro preparation of the coeliac plexus connected to the stomach and duodenum. Intraluminal duodenal pressures were measured with water-filled balloons. Gastric distension inhibited duodenal motility, thus characterizing a gastroduodenal inhibitory reflex organized by the coeliac plexus. 2. ¬_Arginine, superfused at the coeliac plexus level, enhanced this reflex, whereas N ù -nitro¬_arginine (¬-NOARG) or 2-(4-carboxyphenyl)-4,4,5,5tetramethylimidazoline-1-oxyl-3-oxide (carboxyPTIO) reduced or abolished it. Moreover, diethylamineÏnitric oxide complex superfused at the coeliac plexus level inhibited duodenal motility in the absence of gastric distension. 3. The effects of nitric oxide were mediated through the activation of guanylyl cyclase, as 1H_[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) reduced or abolished the gastroduodenal inhibitory reflex, whereas zaprinast enhanced it. Moreover, 8-bromo-cGMP and cGMP, superfused at the coeliac plexus level, inhibited duodenal motility in the absence of gas...