Sensitivity of the negative mucosal potential to the trigeminal target stimulus CO(2)

CO(2) is frequently used in an experimental pain model and in imaging studies investigating the central processing of trigeminal nociceptive information because of its specific trigeminal stimulation properties. The aim of the current study was (1) to investigate the sensitivity of the NMP to small increments of CO(2) stimulus concentrations (3% CO(2), v/v) and (2) to characterize the sensory input of CO(2) by determining NMP, detection and pain thresholds and by registering subjective verbal descriptions. Ten subjects participated in the first experimental sessions investigating NMP responses to stimuli of 62, 65, 68% CO(2) (v/v) (stimulus duration: 1000 ms). Our statistical analysis revealed a dose-dependent increase of the NMP amplitudes and areas under the curves (AUCs) demonstrating the high dynamic resolution of the NMP. Ten subjects participated in the second experimental sessions determining thresholds for NMP, detection and pain (stimulus duration: 1000 ms). MANOVA analysis revealed significantly different thresholds for detection, NMP and subjective pain judgements (mean and S.D. as percentage CO(2) (v/v): detection: 20.6+/-9.6, NMP: 42.6+/-12.5, pain: 50.4+/-12.0). We could demonstrate the existence of a prepain range below subjective pain thresholds with activation of trigeminal nociceptive sensors resulting in the generation of NMPs. The detection threshold of 20.6% CO(2) (v/v) was surprisingly low, i.e. 22% CO(2) (v/v) below the NMP threshold. The involvement of newly discovered alpha-gustducin positive trigeminal chemosensory cells in CO(2) detection is hypothesized.