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ANESTHETIC PHARMACOLOGY

The Analgesic Effect of Xenon on the Formalin Test in Rats: A Comparison with Nitrous Oxide

Taeko Fukuda, MD^*, Chikako Nishimoto, MD^*, Setsuji Hisano, PhD, Masayuki Miyabe, MD^*, and Hidenori Toyooka, MD^*

*Department of Anesthesiology, Institute of Clinical Medicine; and Laboratory of Neuroendocrinology, Institute of Basic Medical Sciences, Tsukuba University, Tsukuba-city, Japan

Address correspondence and reprint requests to Taeko Fukuda, MD, Department of Anesthesiology, Institute of Clinical Medicine, Tsukuba University, Tsukuba-city, 305-8575 Japan. Address e-mail to taekof{at}md.tsukuba.ac.jp

To investigate the analgesic effects of xenon, we performed formalin tests in rats under 0.5 minimum alveolar anesthetic concentration xenon or nitrous oxide and stained the lumbar spinal cord for c-fos (n = 18) and the phosphorylated N-methyl-D-aspartate (NMDA) receptor (n = 24) by using the avidin-biotin-peroxidase method. After 20 min of 79% xenon, 68% nitrous oxide, or 100% inhaled oxygen, 10% formalin (100 µL) was injected into the left rear paw of the animals except for a control group. Nociceptive behavior was observed for 1 h. The rats were killed 2 h after the formalin injection, and the lumbar spinal cord was stained for c-fos or the phosphorylated NMDA receptor immunohistochemically. Animals in the xenon and nitrous oxide groups showed less nociceptive behavior than did the oxygen group. Although the number of c-fos-positive cells in the lumbar spinal cord in the nitrous oxide group was not decreased, that in the xenon group decreased. The number of phosphorylated NMDA receptor-positive cells in the xenon group was significantly less than in the nitrous oxide and oxygen groups. Inhaled xenon suppressed nociceptive behaviors, c-fos expression, and activation of the NMDA receptor during the formalin test in rats. These results confirm that xenon’s analgesic effects result from inhibition of the NMDA receptor.

IMPLICATIONS: Inhaled xenon suppressed nociceptive behaviors, c-fos expression, and activation of the N-methyl-D-aspartate receptor during the formalin test in rats. Xenon’s analgesic effect was speculated to result from the inhibition of the N-methyl-D-aspartate receptor in vivo.

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999