The close relationship between decreases in extracellular GABA concentrations and increases in the incidence of hyperbaric oxygen-induced electrical discharge.
To elucidate the mechanism by which hyperbaric oxygen (HBO2) induces electrical discharge, changes in the extracellular concentrations of GABA and glutamate were measured every 5 min using a microdialysis technique in rats during a period of exposure to HBO2 (5 atm abs). Electrical discharge was observed at 28 +/- 4 min after the onset of exposure. Though the extracellular concentrations of glutamate remained unchanged, the extracellular GABA concentrations (pre-exposure level, 0.026 +/- 0.005 microM in dialysate) began to decrease 15 min after the onset of exposure and reached their lowest level (74 +/- 14%, 0.019 +/- 0.004 microM) at the time of appearance of the discharge. There was a close logistic relationship between extracellular GABA concentrations and the discharge incidence, and the extracellular concentrations of GABA causing electrical discharge in 50% of the animals were estimated to be 80% of the pre-exposure level. These results suggest a possible mechanism that HBO2 exposure-induced discharge is caused by the decrease in extracellular concentration of GABA.
Zhang
Shan
S
Department of Anesthesiology and Resuscitology, Okayama University Medical School, Okayama 700 8558, Japan.
Takeda
Yoshimasa
Y
Hagioka
Shingo
S
Goto
Keiji
K
Morita
Kiyoshi
K
D000818:Animals; D004553:Electric Conductivity; D005110:Extracellular Space / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism; D006931:Hyperbaric Oxygenation; D008297:Male; D017551:Microdialysis; D010100:Oxygen / Q000494:pharmacology*; D010296:Parietal Lobe / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D010100:Oxygen