Abstract

This study was performed in rats to determine if serotonin and its receptors are involved in the increase of gastric emptying (GE) induced by benzodiazepine (BZ) withdrawal. GE was measured with a test meal (2 ml) containing 1 microCi/ml of 51Cr sodium chromate administered in rats, either previously receiving injections with diazepam (15 mg/kg/day i.p.) or with DMSO (0.9 ml/day i.p.) during 7 days. On the 8th day, animals received the different serotonin (5-HT) agonists or antagonists, and flumazenil (BZ antagonist; 15 mg/kg i.p.) 30 and 15 min, respectively, before the test meal. Methiotepin (5-HT1 antagonist) either i.p. (0.1-1 mg/kg) or intracerebroventricularly (10 micrograms/kg) had no effect on the increase of GE induced by precipitated-withdrawal. 8-OH-DPAT (5-HT1A agonist) administered i.c.v. (1-10 micrograms/kg) dose dependently reduced GE increase. Administered i.p. (0.1 mg/kg), it blocked GE increase in control and diazepam-withdrawn rats. Ritanserin (5-HT2 antagonist) antagonized GE increase only when administered i.p. (0.1 mg/kg). Granisetron (5-HT3 antagonist) was active both i.p. (0.01-0.1 mg/kg) and intracerebroventricularly (1-10 micrograms/kg). Administered intracerebroventricularly (1 microgram/kg) in diazepam-treated rats, 5-HTP mimicked the effect of flumazenil. It is concluded that diazepam-withdrawal increases GE by stimulating central release of 5-HT and/or central activation of 5-HT neurons. At least central 5-HT3 receptors, and in less extend, peripheral 5-HT2 receptors are involved in this mechanism.