5-HT3 receptor antagonists inhibit the response of kappa opioid receptors in the morphine-induced Straub tail [corrected].

We used the morphine-induced Straub tail to examine the actions of a 5-HT3 receptor antagonist and kappa opioid receptor agonist. The kappa opioid receptor agonist, U-50,488H (4-16 mg/kg i.p.), produced a dose-related inhibition of the tail elevation induced by morphine (10 mg/kg s.c.) in ICR male mice. ICS-205-930 (3 and 10 mg/kg i.p.) and zacopride (0.3 and 1 mg/kg i.p.), 5-HT3 receptor antagonists, attenuated the inhibitory effect of U-50,488H in a dose-dependent manner. ICS-205-930 and zacopride did not inhibit the morphine-induced Straub tail. These observations suggest that the actions of kappa opioid receptors may be modulated by 5-HT3 receptors in the morphine-induced Straub tail.