AIMTo explore the effect of central serotonin (5-hydroxytryptamine, 5-HT) on gastric motility in rabbit and to analysis its mechanism.

METHODSIntracerebroventricular (icv) microinjection of drugs were used. The frequency and the amplitude of contractions of gastric motility were recorded.

RESULTS(1) Injection (icv) of 25 microg 5-HT increased the amplitude of contractions and decreased the frequency of gastric motility. (2) The effects of 5-HT were inhibited by injection (icv) of atropine, but intravenous(iv) injection of atropine could only block the increase effect of 5-HT on intragastric pressure. After injection (icv or iv) of phentolamine or propranolol, the effects of 5-HT on gastric motility were not changed markedly. (3) Microinjection (icv) of naloxone or diphenhydramine inhibited the inhibitory effect of 5-HT on the frequency of gastric contractions, and the diphenhydramine reversed the increase effect of 5-HT on intragastric pressure. (4) Vagotomy abolished the effects of 5-HT completely.

CONCLUSIONThere may be different nerve mechanisms in regulation of central 5-HT on the frequency and amplitude of contractions of gastric motility. The increase effect of 5-HT on intragastric pressure is medicated by the cholinergic system in brain, and histamine may be one of the important element on the effect of 5-HT. The cholinergic fibers in vagus nerve transmit the effect. The inhibitory effect of 5-HT on the frequency of contractions is also medicated by activating the cholinergic system in brain, enkephalin and histamine are also involved, and it is transmitted via noncholinergic and nonadrenergic fibers in vagus nerve.