A possible 5-HT3 component of thyrotropin-releasing hormone-induced increases in gastric motility in developing rats.

Intracisternal injection of thyrotropin-releasing hormone (TRH) increases gastric motility primarily via a vagal cholinergic mechanism. However, a serotonergic (5-HT) component may also exist. Rats (7, 10, 14, and > or = 50 days of age) were anesthetized and gastric motility monitored via an extraluminal strain gauge. Following baseline, ICS 205-930 which blocks 5-HT3 and 5-HT4 receptors (0.01, 0.10, or 1.0 mg/kg) was administered intraperitoneally, then 30 min later intracisternal TRH (5 or 10 micrograms). ICS 205-930 0.1 and 1.0 mg/kg blocked TRH-induced motility in 7-day-old rats. Results support a 5-HT3 or 5-HT4 receptor contribution to TRH-induced gastric motility stimulation, and suggest that receptor expression is dynamic during development.