DIFFERENT SENSITIVITY OF PAIN-RELATED CHEMOSENSORY POTENTIALS-EVOKED BY STIMULATION WITH CO2, TOOTH-PULP EVENT-RELATED POTENTIALS, AND ACOUSTIC EVENT-RELATED POTENTIALS TO THE TRANQUILIZER DIAZEPAM

1 The aim of this study was to investigate the sensitivity of pain-rel ated potentials used in experimental pain models to the non-specific e ffects of the tranquilizer diazepam. Pain-related potentials were reco rded after painful stimulation of the nasal mucosa with CO2 and after painful stimulation of the tooth pulp. Acoustically evoked potentials were measured in order to compare their sensitivity to the tranquilize r diazepam with the sensitivity of the pain-related potentials. 2 Twen ty volunteers participated in this randomised, double-blind, three-fol d crossover study. Measurements were obtained before and 20 min after the administration of the drug. Event-related potentials were recorded after painful stimulation of the nasal mucosa with CO2 (two stimulus intensities: 60% v/v and 70% v/v CO2), after painful stimulation of th e tooth pulp (two stimulus intensities: 2.2 x and 3.3 x detection thre shold), and after non-painful acoustical stimulation of the right ear. The subjects rated the perceived intensity of the painful stimuli by means of a visual analogue scale. In addition the spontaneous EEG was analysed in the frequency domain and the vigilance of the subjects was assessed in a tracking task. 3 Diazepam reduced significantly the amp litudes of the event-related potentials after painful stimulation of t he tooth pulp and after acoustical stimulation. In contrast only a sma ll, statistically non-significant reduction could be found after painf ul stimulation with CO2. The pain ratings of the painful stimuli were not affected by diazepam. Diazepam reduced the performance of the trac king task. A decrease of arousal could be found in the alpha(2)-range, whereas in the beta(2) and the theta-range the power density increase d under diazepam. 4 We demonstrated that event-related potentials afte r painful stimulation of the nasal mucosa with CO2 are less affected b y the nonspecific effects of the tranquilizer diazepam than event-rela ted potentials after painful stimulation of the tooth pulp. The effect s of diazepam on the tracking task, the spontaneous EEG and the event- related potentials clearly confirm its sedative properties. Diazepam h ad no analgesic effect measurable by pain intensity estimates.