[abstract] THE NARCOTIC EFFECT OF NITROGEN ON EVOKED RESPONSES OF THE VISUAL PATHWAY.

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[abstract] THE NARCOTIC EFFECT OF NITROGEN ON EVOKED RESPONSES OF THE VISUAL PATHWAY.

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Title: [abstract] THE NARCOTIC EFFECT OF NITROGEN ON EVOKED RESPONSES OF THE VISUAL PATHWAY.
Author: Hempel, FG; Kaufmann, PG; Bennett, PB
Abstract: Typically, the narcotic state in animals is assessed by such indirect measures as the EEG and by brain responses to sensory stimulation. The complex origins of these gross signals makes interpretation of the mechanisms of narcosis difficult. To further dissect these signals into simpler components which have a direct primary response to N2 at pressure we used electrically evoked signals in the guinea pig visual pathway as an indicator of narcosis. Guinea pigs were implanted with stimulating electrodes in the optic chiasm, and with recording electrodes in the lateral geniculate nucleus and visual cortex. The EEG was recorded with bilateral screw electrodes. After 2-3 days of post-operative recovery, they were given N2 in 2 ata increments up to 16 ata. From 16 ata until convulsions occurred (near 95 ata), they were further pressurized with He in 10 ata increments. Signals were averaged and compared with surface controls. The optic tract volley (latency less than 3 msec) in the LGN potential was unaffected by N2 or He, but longer latency components (greater than 15 msec) were reduced in N2 as much as 55 percent. Long latency components were not restored in amplitude by He, although restructuring of the waveform sometimes occurred. Cortical responses were depressed about 30 percent by N2 without reversal by He. The EEG showed augmentation of the 2-4 Hz band from 10 to 80 percent in N2, and 5-28 percent in the 4-8 Hz band, with reversal to surface values as the convulsion threshold was approached. The alpha frequency (8-12 Hz) was unaffected by N2 or He, while the 12-20 Hz and 20-30 Hz bands were depressed in N2 and remained so in He. We conclude that complex neural activity provides first evidence of narcosis, and that evidence for reversal of the effect depends entirely on which component of the signal is selected for examination.
URI: http://archive.rubicon-foundation.org/4414
Date: 1978

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  • UHMS Meeting Abstracts
    This is a collection of the published abstracts from the Undersea and Hyperbaric Medical Society (UHMS) annual meetings.

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