演題番号 : S3-1-1-6
柿木 隆介 / Ryusuke Kakigi:1
1:自然科学研究機構 生理学研究所 統合生理研究系 / Department of Integrative Physiology, National Institute for Physiological Sciences
The effects of human tobacco smoking and nicotine on pain-related brain activities were investigated. Electroencephalography (EEG) responses evoked by a painful laser beam (laser evoked potentials; LEPs), and the plasma nicotine concentration (PNC) were measured. Following A-delta fiber stimulation (first pain), there were two sessions, one after smoking (Smoking session), and the other in no smoking (Control session). Subjective ratings of pain perception were also measured using the visual analog scale (VAS). Two major components, N2 and P2 of LEPs, were recorded. The amplitude of P2 was significantly smaller in the Smoking session than in the Control session. A significant negative correlation was found between PNC and the amplitude of N2 as well as P2. The results were consistent with the hypothesis that smoking and/or nicotine have an antinociceptive effect, which supports most non-human studies and some human studies. Smoking of a single tobacco cigarette did not show a subjectively perceivable extent of reduction in the intensity of evoked pain. Folowing C fiber stimulation (second pain), ultralate LEPs were repeatedly measured in two sessions, one after smoking, and the other in abstinence from smoking. The dominant frequency of the background EEG alpha activity, heart rate and venous plasma nicotine concentration were also measured. The peak-to-peak amplitude of the two major components (N2 and P2) of ultralate LEPs was significantly correlated both with the plasma nicotine concentration and with the background alpha frequency. The results suggest an arousal effect of nicotine on C-fiber mediated pain. The effect of nicotine on C-fiber LEPs was in the opposite direction of that on A-delta fiber LEPs. The difference between C and A-delta fibers might indicate a difference in effects of nicotine on first and second pain responses.