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From the *Department of Dental Anesthesiology, Division of Clinical Medical Science, Programs for Applied Biomedicine, and Department of Dental Pharmacology, Division of Integrated Medical Science, Programs for Biomedical Research, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan; Department of Applied Pharmacology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
Address correspondence and reprint requests to Masahiro Irifune, DDS, PhD, Department of Dental Anesthesiology, Division of Clinical Medical Science, Programs for Applied Biomedicine, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan. Address e-mail to mirifun{at}hiroshima-u.ac.jp.
BACKGROUND: The general anesthetic state comprises behavioral and perceptual components, including amnesia, unconsciousness, analgesia, and immobility. In vitro, glutamatergic excitatory neurons are important targets for anesthetic action at the cellular and microcircuits levels. Riluzole (2-amino-6-[trifluoromethoxy]benzothiazole) is a neuroprotective drug that inhibits glutamate release from nerve terminals in the central nervous system. Here, we examined in vivo the ability of riluzole to produce components of the general anesthetic state through a selective blockade of glutamatergic neurotransmission.
METHODS: Riluzole was administered intraperitoneally in adult male ddY mice. To assess the general anesthetic components, three end-points were used: 1) loss of righting reflex (LORR; as a measure of unconsciousness), 2) loss of movement in response to noxious stimulation (as a measure of immobility), and 3) loss of nociceptive response (as a measure of analgesia).
RESULTS: The intraperitoneal administration of riluzole induced LORR in a dose-dependent fashion with a 50% effective dose value of 27.4 (23.3–32.2; 95% confidence limits) mg/kg. The behavioral and microdialysis studies revealed that time-course changes in impairment and LORR induced by riluzole corresponded with decreased glutamate levels in the mouse brain. This suggests that riluzole-induced LORR (unconsciousness) could result, at least in part, from its ability to decrease brain glutamate concentrations. Riluzole dose-dependently produced not only LORR, but also loss of movement in response to painful stimulation (immobility), and loss of nociceptive response (analgesia) with 50% effective dose values of 43.0 (37.1–49.9), and 10.0 (7.4–13.5) mg/kg, respectively. These three dose–response curves were parallel, suggesting that the behavioral effects of riluzole may be mediated through a common site of action.
CONCLUSIONS: These findings suggest that riluzole-induced LORR, immobility, and antinociception appear to be associated with its ability to inhibit glutamatergic neurotransmission in the central nervous system.
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