A new competitive α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor antagonist,(2, 3-dioxo-7-[1H-imidazol-1-yl]-6-nitro-1, 2, 3, 4-tetrahydro-1-quinoxalinyl) acetic acid (YM872) has analgesic effects on acute thermal-and formalin-induced nociception by intrathecal administration. The purpose of this study was to determine the analgesic effects of systemically administered YM872 in both acute thermal-and irritant-induced pain. Sprague-Dawley rats were tested for tail withdrawal response by the tail flick test and for paw flinches by formalin injection after intraperitoneal administration of YM872. The tail flick latency increased dose-dependently with a 50% effective dose value of 156.3 μg. The number of flinches in both first and second phases of the formalin test decreased with increasing the dose of YM872. The 50% effective dose values were 1.0 μg in the first phase and 38.7 μg in the second phase. Transiently, intraperitoneal administration of 1 and 10 mg of YM872 induced motor disturbance and 10 mg induced loss of pinna reflex. We conclude that intraperitoneal administration of YM872 had analgesic effects on both acute thermal-and formalin-induced nociceptions in rats. Transient motor disturbance and loss of pinna reflex occurred only with large doses.

Implications

Intraperitoneally administered YM872, a new α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor antagonist, had analgesic effects on thermal-and formalin-induced pain in rats. Larger doses induced transient motor disturbance and loss of pinna reflex mediated in the brain.