Xenon does not affect gamma-aminobutyric acid type A receptor binding in humans.
BACKGROUND
The noble gas xenon acts as an anesthetic with favorable hemodynamic and neuroprotective properties. Based on animal and in vitro data, it is thought to exert its anesthetic effects by inhibiting glutamatergic signaling, but effects on gamma-aminobutyric acid type A (GABA(A)) receptors also have been reported. The mechanism of anesthetic action of xenon in the living human brain still remains to be determined.


METHODS
We used the specific GABA(A) receptor benzodiazepine-site ligand 11C-flumazenil and positron emission tomography to study the GABAergic effects of xenon in eight healthy male volunteers. Each subject underwent two dynamic 60-min positron emission tomography studies awake and during approximately one minimum alveolar concentration of xenon (65%). Bispectral index was recorded. Cortical and subcortical gray matter regions were analyzed using both automated regions-of-interest analysis and voxel-based analysis.


RESULTS
During anesthesia, the mean +/- sd bispectral index was 23 +/- 7, and there were no significant changes in heart rate or mean arterial blood pressure. Xenon did not significantly affect 11C-flumazenil binding in any brain region.


CONCLUSIONS
Xenon did not affect 11C-flumazenil binding in the living human brain, indicating that the anesthetic effect of xenon is not mediated via the GABA(A) receptor system.
Salmi
Elina
E
Turku PET Centre, Turku, Finland. anelsa@utu.fi
Laitio
Ruut M
RM
Aalto
Sargo
S
Maksimow
Anu T
AT
Långsjö
Jaakko W
JW
Kaisti
Kaike K
KK
Aantaa
Riku
R
Oikonen
Vesa
V
Metsähonkala
Liisa
L
Någren
Kjell
K
Korpi
Esa R
ER
Scheinin
Harry
H
D000328:Adult; D000777:Anesthetics / Q000008:administration & dosage / Q000494:pharmacology*; D001921:Brain / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000378:metabolism; D002250:Carbon Radioisotopes; D004569:Electroencephalography; D005442:Flumazenil / Q000378:metabolism; D018757:GABA Modulators / Q000378:metabolism; D006439:Hemodynamics / Q000187:drug effects; D006801:Humans; D008024:Ligands; D008297:Male; D049268:Positron-Emission Tomography; D011485:Protein Binding; D019275:Radiopharmaceuticals / Q000378:metabolism; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000378:metabolism; D014978:Xenon / Q000008:administration & dosage / Q000494:pharmacology*
D000777:Anesthetics; D002250:Carbon Radioisotopes; D018757:GABA Modulators; D008024:Ligands; D019275:Radiopharmaceuticals; D011963:Receptors, GABA-A; D014978:Xenon; D005442:Flumazenil