Selective 5-HT7 receptor agonists LP 44 and LP 211 elicit an analgesic effect on formalin-induced orofacial pain in mice

OBJECTIVE To investigate the antinociceptive effects of pharmacological activation of 5-HT7 receptors on orofacial pain in mice. MATERIAL AND METHODS Nociception was evaluated by using an orofacial formalin test in male Balb-C mice. Selective 5-HT7 receptor agonists, LP 44 and LP 211 (1, 5, and 10 mg/kg), were given intraperitoneally 30 min prior to a formalin injection. A bolus of 10 µl of 4% subcutaneous formalin was injected into the upper lip of mice and facial grooming behaviors were monitored. The behavioral responses consisted of two distinct periods, the early phase corresponding to acute pain (Phase I: 0-12 min) and the late phase (Phase II: 12-30 min). RESULTS LP 44 and LP 211 (1, 5, and 10 mg/kg) produced an analgesic effect with reductions in face rubbing time in both Phase I and Phase II of the formalin test. CONCLUSION Our results suggest that 5-HT7 receptor agonists may be promising analgesic drugs in the treatment of orofacial pain.