Erowid References Database
Costa M, Furness JB.
“On the Possibility that an Indoleamine is a Neurotransmitter in the Gastrointestinal Tract”.
Evidence for an indoleamine neurotransmitter in the gastrointestinal tract is reviewed, with reference to studies in the guinea pig, mouse, rat, and cat, Histochemical studies using methyl tyrosine, 6 -hydroxydopamine, reserpine, guanethidine, fenclonine and R o-4 -4602 treated animals revealed the ability synthesize 5-hydroxytryptamine (5-HT) and the presence of somatic-1-amino acid decarboxylase, tryptophan hydroxylase and MAO, but not tyrosine hydroxylase or dopamine-betahydroxylase in intrinsic intestinal nerves. No 5-HT stores have been found, but specific 5-HT uptake systems blocked by chlorimipramine and desmethylimipramine are present, 5-HT Has similar effects on inhibitory nerves to the guinea-pig stomach to ACh or vagal stimulation but is not antagonized by pentolinium or hexamethonium. Transmural stimulation of mouse stomach causes tetrodotoxin-sensitive release of a 5-HT-like substance. Contractions of the canine esophagus elicited by transmural stimulation were blocked by bromolysergic acid and 5-HT desensitization but were not modified by atropine or eserine. Vagal stimulation re faxes the lower esophageal sphincter in the presence of hexamethonium and atropine and this relaxation is blocked by 5-methoxydimethyltryptamine. 5-HT Acts on smooth muscle receptors which are blocked by LSD, bromolysergic acid or methysergide and on enteric nerve receptors which are blocked by biguanides-and quaternary derivatives of 5-HT but not by morphine. Nicotine causes relaxation of the guinea-pig colon blocked by metoclopramide or desensitization of receptors to 5-HT. Inhibitory nerves to the colon were stimulated by 5-HT but it had no direct effect on the muscle. In the presence of hyoscine and tetrodotoxin, 5-HT causes a slow contraction of proximal colon blocked by methysergide and phentolamine. Vasodialator responses to mucosal stimulation were mimicked by 5-HT -a tetrodotoxin-sensitive manner and blocked by bromolysergic acid and dihydroergotamine. Atropine and blockers of nicotinic or alpha- or beta-adrenergic receptors had no effect.
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