5‐Hydroxytryptamine participation in the vagal inhibitory innervation of the stomach

Abstract

1. Intraluminal pressure was recorded from the isolated guinea-pig and mouse stomach with the vagus and sympathetic nerves attached.2. The response to vagal stimulation, which consists of an excitatory and an inhibitory component, resembled the response to 5-hydroxytryptamine (5-HT), which has no direct action on the muscle but acts on intrinsic excitatory and inhibitory ganglia.3. In the presence of hyoscine, the effect of vagal stimulation, of nicotinic compounds and of 5-HT were all purely relaxant. Competitive block of ganglionic receptors for acetylcholine reduced the vagal relaxation without antagonizing 5-HT. Specific desensitization of ganglionic receptors for 5-HT reduced the vagal relaxation without antagonizing nicotinic compounds.4. During the early phase of the blocking action of nicotine, responses to vagal stimulation and to 5-HT were both abolished. As the non-specific antagonism changed to the later phase of specific antagonism to acetylcholine, the inhibitory (but not the excitatory) component of the vagal response recovered partially, in parallel with the recovery of the relaxant effect of 5-HT.5. The vagal inhibitory effect was completely abolished only when competitive block of acetylcholine receptors was combined with desensitization of 5-HT receptors.6. Stimulation of the mouse stomach (after asphyxiation of the mucosa and exclusion of the luminal content) in the presence of hyoscine caused the release of 5-HT; this release was blocked by tetrodotoxin.7. The results, together with previous observations that 5-HT is contained within preganglionic nerve fibres in the myenteric plexus, are consistent with the hypothesis that 5-HT, with acetylcholine, may be a neurotransmitter in the vagal inhibitory innervation of the stomach.

Effects of 5‐hydroxytryptamine on isolated strips of the guinea‐pig stomach

“…In the isolated intact stomach of the guinea-pig, 5-HT caused either a reduction in intraluminal pressure or a diphasic response, namely, an increase followed by a decrease (Gershon, 1967;Bulbring & Gershon, 1967). Since all responses to 5-HT in concentrations of up to 1 ug/ml were abolished by tetrodotoxin, it was concluded 108 T. Yamaguchi that, in the guinea-pig stomach, 5-HT acts indirectly through the nervous components.…”

“…On the other hand, the guinea-pig stomach may contain mainly M receptors, because the effects of 5-hydroxytryptamine (5-HT) (01-1 yg/ml) on intraluminal pressure are blocked by tetrodotoxin (Gershon, 1967;Bulbring & Gershon, 1967). In the presence of tetrodotoxin, only a high concentration of 5-HT (10-100 yg/ml) produces a slight contraction, followed by a slight relaxation (Paton & Vane, 1963;Gershon, 1967).…”

Morphology and serotonergic innervation of physiologically identified cells of the guinea pig's myenteric plexus

“…In addition, enteric serotonergic neurons specifically and avidly take up 5-HT, providing an adequate inactivating mechanism for the amine as a transmitter (Gershon and Altman, 1971;Robinson and Gershon, 1971;Gershon et al, 1976;Gershon and Jonakait, 1979). On a gross level, 5-HT also mimics many of the authentic neurally mediated responses of the gut (Brownlee and Johnson, 1963;Bulbring and Gershon, 1967;Furness and Costa, 1973;Costa and Furness, 1979a;Jule, 1980); however, considerable controversy has arisen over whether these gross effects can be traced to physiological actions of 5-HT (see Costa and Furness, 1979b;Gershon, 1982) and over whether nerve-activated, slow excitatory postsynaptic potentials (EPSPs) in enteric neurons are mediated by 5-HT Johnson et al, 1981). Neurons of the myenteric plexus have been categorized as type I or S, type II or AH (Holman et al, 1972;Nishi and North, 1973;Hirst et al, 1974) and, more recently, types III (non-spiking) and IV (delayed spiking; Wood, 1983).…”

MECHANISM OF ACTION OF DOPAMINE ON THE GUINEA‐PIG GASTRO‐OESOPHAGEAL JUNCTION in vitro

“…It has been suggested that 5-hydroxytryptamine may be involved in the modulation of gastric activity (Bulbring & Gershon, 1967). Therefore an examination of the effects of this compound was included in this study.…”