The electrophysiological studies in the action of xenon on the central nervous system

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We have compared the effects of xenon (Xe) and nitrous oxide (N2O) on central nervous system electrical activity. We recorded the electroencephalogram (EEG), multi-unit activity of midbrain reticular formation (R-MUA) and somatosensory evoked potentials (SEP) in cats. Basal anesthesia with 2% and 5% sevoflurane was used. With 2% sevoflurane, 70% Xe initially produced rhythmic slow waves that were followed by bursts of high-amplitude sharp waves interrupted by low amplitude slow waves on the EEG.Xe induced an initial increase, followed by a decrease in R-MUA.N20 70% decreased the amplitude of EEG activity that was associated with an increase in R-MUA.Xe suppressed the amplitude of both the initial positive and negative deflections of the SEP to a greater extent than N2O.With 5% sevoflurane anesthesia, both anesthetics increased the frequency of spikes on the EEG and facilitated R-MUA.We also assessed the potency of both anesthetics by the inhibition of the responses of wide dynamic range neuron in the spinal cord evoked by cutaneous noxious (pinch) stimulation to a hindpow in cats anesthetized with chrolarose and urethane. During 70% Xe inhalation, the responses of 7 of 11 neurons to pinch stimulation were suppressed. N2O,70%, suppressed it in 8 of 11 neurons. The potency of Xe and N2O was compared in six neurons that were suppressed by both anesthetics. After 20min of Xe inhalation, the response to pinch was suppressed to 49.5%, while N2O,70% in oxygen, suppressed it to 45.9%. The difference between N2O and Xe was not significant. These findings indicate that Xe has a stimulatory action on brain background activity and a suppressive action on brain reactive capability that is more potent than that of N2O ; Xe and N2O suppresses the spinal dorsal horn neurons to a similar degree.