Objective    To investigate the effect and mechanism of serotonin (5-HT) and secretin(SEC) on afferent discharge of vagus in rats.     Methods    Spontaneous afferent discharge of subdiaphragmatic vagus nerve was recorded in urethane anesthetized rats. The effects of 5-HT

5-HT

3

receptor antagonist and 5-HT+SEC on the discharge of subdiaphragmatic vagus nerve were investigated by intravenous injection of different dosage of 5-HT(3

10

30 μg/kg)

Granisetron (1 mg/kg) and 5-HT+SEC.     Results    Intravenous 5-HT caused obvious exciting effect on spontaneous afferent discharge of subdiaphragmatic vagus nerve. The 5-HT

3

  receptor antagonist signific

antly inhibited the effects of 5-HT. 5-HT+SEC could augment the effect of 5-HT on spontaneous discharge.     Conclusion    The exciting effect of 5-HT on afferent discharge of subdiaphragmatic vagus nerve is possibly mediated by 5-HT

3

receptor related to vagus nerve afference. Secretin can augment the exciting effect of 5-HT on spontaneous discharge of vagus afferent nerve.