Intranasal midazolam administration enhances amnesic effect in rats

Intranasal (i.n.) administration of midazolam has been shown to be effective and safe for its sedative, anxiolytic, and anticonvulsant effects. However, there has been no investigation on the influence of i.n. administration on midazolam-induced anterograde amnesia. In addition, although the potential of direct drug delivery from the nose to the central nervous system (CNS) has recently become a topic of great interest, it remains unclear whether this pathway is also involved after i.n. midazolam. In this study, we examined the efficacy and the underlying mechanism of i.n. administration compared with intramuscular (i.m.) administration on midazolam-induced amnesia in rats. Equivalent doses of 0.6 mg/kg midazolam were administered via either the i.m or the i.n. route. Anterograde amnesia was assessed by a contextual/cued fear conditioning test. Each animal was conditioned 20 min after drug administration and then tested for a freezing response 24 h later. Midazolam administration by either route produced a similar level of light sedation (minimum spontaneous activity). However, i.n. administration of midazolam induced significantly less freezing behavior compared with i.m. midazolam. Furthermore, in rats with disrupted electrical input from the olfactory epithelium after an olfactotoxicant 3-methylindole administration, the i.n.-mediated enhanced amnesic effect of midazolam was not observed. Our findings indicate that i.n midazolam could probably generate olfactory signals to the brain via benzodiazepine receptors and, compared with i.m. administration, can produce a more significant amnesic effect without alteration in sedative levels. Further clinical studies are warranted.