A Possible Vagal Adrenergic Release of Serotonin from Enterochromaffin Cells in the Cat

Abstract

The intracellular concentrations of serotonin (5-HT) in enterochromaffin cells (EC) in the cat small intestine have been studied by a cytofluorimetric method before and after long-lasting efferent vagal nerve stimulation in the neck. Such stimulation induces a decrease of 5-HT in EC of the gut as observed previously. Pretreatment with atropine could not block this decrease, suggesting a noncholinergic mechanism. Pretreatment with a beta-blocking agent, propranolol, or bilateral removal of the superior cervical ganglia could, however, block this 5-HT decrease. Pretreatment with an alpha-blocking agent, phenoxybenzamine, caused an increase in the 5-HT content of EC both with and without nerve stimulation; the reason for this is obscure. The results indicate, that vagal nerve stimulation induces a neurogenic 5-HT release from EC in the gut, and that adrenergic fibres, originating in the superior cervical ganglia, mediate this release probably via a beta-receptor mechanism. Whether or not an alpha-receptor mechanism is also involved cannot be judged at present.

Maintenance of Serotonin in the Intestinal Mucosa and Ganglia of Mice that Lack the High-Affinity Serotonin Transporter: Abnormal Intestinal Motility and the Expression of Cation Transporters

“…Desensitization of 5-HT receptors occurs when SERT is inhibited in the guinea pig distal colon in vitro, and when this does occur, the peristaltic reflex is blocked (Wade et al, 1996). Catecholamines strongly stimulate 5-HT release from EC cells (Ahlman et al, 1976;Racké et al, 1988;Racké and Schwörer, 1991), and sympathetic nerves innervate enteric serotonergic neurons (Gershon and Sherman, 1987). Infections or fright, which causes the release of catecholamines from sympathetic nerves or the adrenal medulla, might release enough 5-HT to overcome compensatory mechanisms in the SERT Ϫ/Ϫ bowel and desensitize enteric 5-HT receptors.…”

Heart rate variability is related to pain severity and predominant bowel pattern in women with irritable bowel syndrome

“…vagal or sympathetic modulation of descending inhibitory pathways 11,32 . There is, however, evidence that efferent neural stimuli to the intestine have a direct effect on enterocyte secretion and motility 33–35 . Enterochromaffin (EC) cells are innervated by sympathetic and parasympathetic fibres.…”

“…Enterochromaffin (EC) cells are innervated by sympathetic and parasympathetic fibres. Isolated ileum EC cells and intact mucosa have been shown to release serotonin in response to norepinephrine, suggesting that sympathetic nervous system dominance may result in serotonin release and subsequent changes in motility and secretion 33–35 …”

The effects of splanchnic nerve stimulation on the plasma levels of serotonin and substance P in the portal vein of the cat

“…Cytofluorimetric studies of duodenal EC have demonstrated decreased intracellular levels of 5-HT aflcer efferent electrical stimulation of the cervical vagi. This response was probably not cholinergic since it was unaffected by atropine pretreatment or by a selective adrenergic denervation of the cervical vagi by ectomy of superior cervical ganglia prior to the nerve stimulation in favour of an adrenergic mechanism (Ahlrnan et al, 1976 b). Also, in vitro incubations of gut biopsies with adrenergic agonists and antagonists followed by cytofluorimetric observations have indicated that EC are under adrenergic control, probably via /32 adrenoceptors .…”