Rebound electroencephalographic responses to nitrous oxide exposure in men

Abstract

Nitrous oxide (N2O) may elicit antidepressant effects after its elimination from the brain. We sought to investigate whether short-term administration of N2O triggers power within the delta (0.5–4 Hz) and/or theta (4–7 Hz) frequency ranges in the electroencephalogram (EEG) after it’s administration, as we have recently seen such rebound effects to N2O in studies conducted on mice. Twenty healthy male participants were randomly allocated to receive 50% N2O either continuously for 20 min (continuous group) or in two 10-min inhalations (repeated group) with 19-channel EEG. Median-averaged power spectral densities (PSDs) were calculated subject-, electrode-, and state-wise. Group-level data are topographically plotted and significant changes within specific frequency ranges for each condition are highlighted. The subjective effects in response to N2O were studied with questionnaires. Fourteen participants completed the study (n ¼ 7 participants/group). Spectrograms showed that the EEG transitions between N2O and its withdrawal were extremely rapid in both groups and the effects remained stationary during specific states. Power in high-frequency bands (gamma) generally enhanced during N2O administration along with power reductions in beta (and alpha) frequencies. Power in specific theta, but not delta, frequencies increase after the cessation of N2O in several electrodes. However, direct comparison of the rebound EEG between the two treatment groups revealed negligible differences. Short-term administration of N2O evokes increase of power in theta frequency, but not delta, band power upon gas withdrawal.