The subject of the article is to investigate the mechanism of increased reactions by electrical stimulation of the sympathetic nerve.Materials and methods: Experiments on Dugouts dogs have shown that stimulant reactions during blockade of a-adrenergic by phentolamine and (3-adrenergic receptors with propranolol were completely eliminated by lizer-gol —the blocker of 5-HT12-receptors.Results: Infusion of lizergol did not influence on duodenal motor activity and the function of the vagus nerve.Conclusion: Effector neuron is found out to be serotonergic and its action is Mystery Shirt provided by 5-HT1 2 receptors.