Relationship between gamma-hydroxybutyric acid receptors and the hypnotic and analgesic effects of emulsified inhalation anesthetics.

OBJECTIVES This study was designed to investigate the role of gamma-hydroxybutyric acid receptors (GHBR) in hypnosis and analgesia induced by emulsified inhalation anesthetics. MATERIALS AND METHODS After having established the mice model of hypnosis and analgesia by intraperitoneal injections of appropriate doses of enflurane, isoflurane, or sevoflurane, we intracerebroventricularly (i.c.v.) or intrathecally injected different doses of NCS-382 (antagonist of GHBR) and, then, observed the effects on the sleeping time using awaken test and the pain threshold in hot-plate test (HPPT) using HPPT. RESULTS In the awaken test, 1, 5, and 25 μg of NCS-382 (i.c.v.) significantly decreased the sleeping time of the mice treated with the three emulsified inhalation anesthetics mentioned above (p < 0.05 or 0.01). In the HPPT, 1, 5, and 25 μg of NCS-382 (intrathecally) did not affect the HPPT in conscious mice (p > 0.05); in contrast, 1, 5, and 25 μg of NCS-382 (intrathecally) significantly decreased the HPPT of the mice treated with emulsified inhalation anesthetics (p < 0.05 or 0.01). CONCLUSIONS The data presented in this study suggest that GHBR may be important targets for the hypnotic and analgesic effects induced by emulsified enflurane, isoflurane, and sevoflurane.