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1 Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg 199034, Russia; and 2 The F. G. Hall Laboratory, Duke University Medical Center, Durham, North Carolina 27710
We
have tested the hypothesis that cerebral nitric oxide (NO) production
is involved in hyperbaric O2 (HBO2)
neurotoxicity. Regional cerebral blood flow (rCBF) and
electroencephalogram (EEG) were measured in anesthetized rats during
O2 exposure to 1, 3, 4, and 5 ATA with or without
administration of the NO synthase inhibitor
(N
-nitro-L-arginine methyl
ester), L-arginine, NO donors, or the N-methyl-D-aspartate receptor inhibitor MK-801.
After 30 min of O2 exposure at 3 and 4 ATA, rCBF decreased
by 26-39% and by 37-43%, respectively, and was sustained
for 75 min. At 5 ATA, rCBF decreased over 30 min in the substantia
nigra by one-third but, thereafter, gradually returned to preexposure
levels, preceding the onset of EEG spiking activity. Rats pretreated
with N
-nitro-L-arginine methyl
ester and exposed to HBO2 at 5 ATA maintained a low rCBF.
MK-801 did not alter the cerebrovascular responses to HBO2
at 5 ATA but prevented the EEG spikes. NO donors increased rCBF in
control rats but were ineffective during HBO2 exposures. The data provide evidence that relative lack of NO activity contributes to decreased rCBF under HBO2, but, as exposure time is
prolonged, NO production increases and augments rCBF in anticipation of
neuronal excitation.
oxygen toxicity; glutamate neurotransmission; central nervous system
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