Nociceptin receptor antagonist JTC-801 inhibits nitrous oxide-induced analgesia in mice

The mechanism of the analgesic effect of nitrous oxide (N(2)O) has not been completely clarified. Although we have reported that the analgesic effect of N(2)O was significantly decreased in nociceptin-orphanin FQ (N/OFQ) receptor (NOP)-deficient mice, the effect of nociceptin receptor antagonists on N(2)O-induced analgesia has not been reported. In this investigation, we examined the effect of the NOP antagonist JTC-801 on N(2)O-induced analgesia in 129Sv mice by the writhing test and tail flick test, and demonstrated that the analgesic effect of N(2)O was suppressed by the intraperitoneal administration of JTC-801.