We investigated the influence of hypnotics, including the orexin receptor antagonist suvorexant and the melatonin receptor agonist ramelteon, on the loss of righting reflex induced by anesthesia with isoflurane or a mixture of medetomidine, midazolam and butorphanol (MMB) in mice. In the case of MMB anesthesia, male ICR mice were given a single intraperitoneal injection of MMB (0.75 / 4 / 5 mg/kg), followed by intraperitoneal injection of atipamezole (3 mg/kg), for reversal of anesthetic effects, after 1 hour. Each hypnotic agent was orally administered 1 hour before anesthesia induction. Mice lost righting reflex within 5 min after administration of MMB, and administration of atipamezole made mice recover quickly from anesthesia.  While chlorpromazine prolonged significantly the loss of righting reflex induced by both isoflurane and MMB, suvorexant enhanced the loss of righting reflex induced by MMB, but not isoflurane. On the other hand, ramelteon had no effect on the loss of righting reflex. These results suggested that the simple method with these anesthetic agents may be usable to investigate the characteristics of hypnotics.

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