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Xenon inhalation increases norepinephrine release from the anterior and posterior hypothalamus in rats

[L'inhalation de xénon augmente la libération de noradrénaline de l'hypothalamus antérieur et postérieur chez les rats]

From the Department of Anesthesiology University of Hirosaki School of Medicine Hirosaki, Japan.

Address correspondence to: Dr. T. Kushikata, Department of Anesthesiology, University of Hirosaki School of Medicine, 5 Zaifu-cho, Hirosaki 036-8562, Japan. Phone: +81-172-39-5111; Fax: +81-172-39-5112; E-mail: masuika{at}cc.hirosaki-u.ac.jp

Purpose: To investigate the effect of xenon (Xe) and nitrous oxide (N₂O) on norepinephrinergic neuronal activity in the rat medial preoptic area (mPOA) and posterior hypothalamus (PH) using microdialysis.

Methods: Sixty male Wistar rats were equally allocated to two groups: mPOA and PH. A microdialysis probe was implanted into the mPOA or the PH. In both groups, each animal was exposed to one of the following inhalations: 25% oxygen (control, n=6), 30% Xe (n=6), 60% Xe (n=6), 30% N₂O (n=6) or 60% N₂O (n=6). Norepinephrine concentration in the perfused artificial cerebrospinal fluid was measured by high pressure liquid chromatography at ten-minute intervals. After plotting the time-norepinephrine concentration curve, the area under the curve (AUC) in each group was calculated.

Results: In the mPOA, 30 and 60% Xe, but only 60% N₂O significantly increased norepinephrine release. The AUC in the 30% Xe, 60% Xe or 60% N₂O group was 160 ± 9 (P <0.05), 288 ± 42 (P <0.01) or 237 ± 46 pg•min/sample (P <0.01), respectively, compared to that in the control group: 77 ± 14 pg•min/sample. In the PH, only 60% Xe significantly increased norepinephrine release compared to control (AUC: 191 ± 38 vs 71 ± 1 pg•min/sample, P <0.01).

Conclusion: The present data suggest that Xe stimulates norepinephrinergic neurons more potently than N₂O; 1.2 times more in the mPOA and 2.5 times more in the PH. This stimulant effect may contribute to the hypnotic and sympathotonic effects of Xe in rats.

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