Search

Distension-evoked gastric reflexes were studied by intracellular recording from circular muscle cells in the gastric fundus, corpus and antrum in the isolated guinea-pig stomach. Localised electrical stimulation, 2 mm circumferential to the recording electrode, evoked inhibitory junctions potentials in all three gastric regions, sometimes followed by depolarisations in the antrum. In the mid corpus, the inhibitory responses were substantially reduced by Nw-nitro-L-arginine (100 microM), unmasking excitatory junction potentials. Residual hyperpolarisations were blocked by apamin (0.5 microM) which also enhanced the amplitude of excitatory junction potentials. These excitatory junction potentials were abolished by hyoscine (1 microM). Thus transmission from inhibitory motor neurons is mediated by both nitric oxide and an apamin-sensitive mechanism. Transmission from excitatory motor neurons to the circular muscle is mediated by acetylcholine via muscarinic receptors. Balloon distension of 10 s duration of the fundus or antrum elicited inhibitory junction potentials in circular muscle cells of the mid corpus. These inhibitory junction potentials were blocked by tetrodotoxin (0.6 microM) and were greatly reduced by Nw-nitro-L-arginine (100 microM). The residual hyperpolarisations were blocked by apamin (0.5 microM). This indicates the presence of ascending and descending inhibitory reflex pathways in the stomach. In 3 out of 7 experiments, following blockade of inhibitory transmission, small nerve-mediated excitatory junction potentials were evoked by antral distension indicating the presence of an additional ascending excitatory reflex pathway. Distension of the corpus elicited prominent inhibitory junction potentials, sometimes followed by large depolarisations, in circular muscle cells in the fundus, but not in the antrum. This suggests that there is also an ascending inhibitory reflex pathway from the corpus to the fundus but no distension-sensitive descending reflex pathway from the corpus to the antrum. These results demonstrate that within the stomach there are reflex pathways which can be activated by localised distension and project at some distance orally and aborally within the gastric wall. It is likely that the inhibitory reflex pathways are involved in gastric adaptive relaxation which occurs when the intact, isolated stomach is distended. The excitatory reflex pathways from the antrum to the corpus are likely to be involved in the intrinsic excitatory reflex responses observed in the isolated intact stomach to distension and thus be involved in the mixing and emptying of gastric contents.

The mechanisms involved at the prevertebral ganglionic level in a gastroduodenal inhibitory reflex were investigated in the rabbit on an in vitro preparation of the coeliac plexus connected to the stomach and duodenum. Intraluminal gastric and duodenal pressures were measured using water-filled balloons. Gastric distension inhibited duodenal motility via a nerve reflex which was abolished by section of the nerves connecting the coeliac plexus to the viscera. Superfusion of the coeliac plexus with a low Ca 2+ -high Mg 2+ solution abolished the gastroduodenal inhibitory reflex, indicating a synaptic link at the ganglion level. The reflex was unaffected by superfusion of the coeliac plexus with hexamethonium and tubocurarine, ruling out a nicotinic mechanism. The reflex persisted when the coeliac plexus was superfused with tetrodotoxin or when the nerves connecting the coeliac plexus to the viscera were superfused with a Na + -free solution; these results indicate that the reflex does not involve sodium-dependent action potentials. Moreover, superfusion of the nerves connecting the coeliac plexus to the viscera with a calcium blocker or with a Ca 2+ -free solution also failed to abolish the reflex, suggesting that calcium-dependent action potentials are not involved. Our study demonstrates that a gastrointestinal inhibitory reflex via the coeliac ganglion is not based on fast synaptic inputs or action potentials. These results provide new insights concerning the physiology of the sympathetic prevertebral ganglia.

Reflex responses of the lower oesophageal sphincter (l.o.s.) to distension of the stomach were studied by electromyographic and manometric techniques. Distension of the fundus and gastric antrum by inflation of a balloon elicited two types of reflex response of the l.o.s. Thus, whereas excitatory responses were recorded following slight distensions, larger distensions resulted in inhibitory responses. Splanchnic fibres and sympathetic fibres originating from the stellate ganglion, as well as vagal fibres served as the efferent pathways for the excitatory reflex response. The efferent pathways for the inhibitory response involved only vagal fibres.

Gastric responses to electrical stimulation of the vagus and splanchnic nerves and to esophageal distension were observed in studies of the reflex control of the gastric motility in anesthetized guinea pigs in vivo. The gastric motility was inhibited by both vago-vagal and splanchno-vagal reflexes through the activation of non-adrenergic inhibitory nerve fibers and by splanchno-splanchnic reflex through the inactivation of the intramural cholinergic excitatory neurons. Distension of the lower esophagus caused a relaxation of the stomach which was mediated by an intrinsic reflex via intramural non-adrenergic inhibitory neurons. Furthermore, stimulation of the splanchnic nerve innervating the stomach seems to activate adrenergic inhibitory, cholinergic excitatory and probably some non-adrenergic inhibitory fibers.