Xenon inhalation increases norepinephrine release from the anterior and posterior hypothalamus in rats
H Yoshida1, T Kushikata, T Kubota
1Department of Anesthesiology University of Hirosaki School of Medicine Hirosaki, Japan.
Purpose:
To investigate the effect of xenon (Xe) and nitrous oxide (N(2)O) 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% N(2)O (n=6) or 60% N(2)O (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% N(2)O significantly increased norepinephrine release. The AUC in the 30% Xe, 60% Xe or 60% N(2)O group was 160 +/- 9 (P <0.05), 288 +/- 42 (P <0.01) or 237 +/- 46 pg x min/sample (P <0.01), respectively, compared to that in the control group: 77 +/- 14 pg x min/sample. In the PH, only 60% Xe significantly increased norepinephrine release compared to control (AUC: 191 +/- 38 vs. 71 +/- 1 pg x min/sample, P <0.01).
Conclusion:
The present data suggest that Xe stimulates norepinephrinergic neurons more potently than N(2)O; 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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