Valeriani Massimiliano, Tinazzi Michele, Le Pera Domenica, Restuccia Domenico, De Armas Liala, Maiese Toni, Tonali Pietro, Arendt-Nielsen Lars
Divisione di Neurologia, Ospedale Pediatrico Bambino Gesů, IRCCS, Piazza Sant'Onofrio 4, 00165 Rome, Italy.
Exp Brain Res. 2005 Jan;160(1):29-37. doi: 10.1007/s00221-004-1983-1.
The aim of the study was to evaluate the effect of tonic pain evoked by topical application of capsaicin on the somatosensory sensation of warmth. The warmth pathways were studied in ten healthy subjects by recording the scalp potentials evoked by non-painful warm laser stimuli delivered on both the right and left perioral region (warmth C-fiber related laser-evoked potentials (C-LEPs)). Tonic pain was induced by topical capsaicin application above the lateral part of the right upper lip. The area of primary and secondary hyperalgesia were mapped. C-LEPs were obtained from 31 scalp electrodes before, during, and after capsaicin application. C-LEPs from the right perioral region were evoked by laser stimuli delivered to the area of secondary hyperalgesia during capsaicin application and on both the areas of primary and secondary hyperalgesia after capsaicin removal. While the lateralized N1/P1 component (around 185 ms of latency) was not affected by the capsaicin, the amplitudes of the later vertex C-LEPs (around 260 and 410 ms of latency for the N2a and P2 potentials, respectively) evoked from the secondary hyperalgesic area on the right side and from a symmetrical non-hyperalgesic area on the left perioral region were significantly decreased during capsaicin application and after capsaicin removal, as compared with the baseline recordings. At the same times, the rating of the laser-evoked warmth sensation was reduced significantly. This inhibitory effect can occur at brainstem level and is possibly due to: 1) trigemino-cortico-trigeminal circuits, similar to those mediating the classical diffuse noxious inhibitory control, or 2) an increased background activity of the capsaicin-insensitive A-fibers, which mediate the secondary hyperalgesia. Probably due to a peripheral inhibitory mechanism, neither reliable C-LEP components nor warmth sensation were evoked by laser pulses delivered to the primary hyperalgesic area. This is the first neurophysiological evidence in humans of an inhibitory effect of pain on warmth sensation.
本研究的目的是评估局部应用辣椒素诱发的持续性疼痛对热觉躯体感觉的影响。通过记录在左右口周区域施加非疼痛性温热激光刺激所诱发的头皮电位（与热觉C纤维相关的激光诱发电位（C-LEPs）），对10名健康受试者的热觉通路进行了研究。在右上唇外侧局部应用辣椒素诱发持续性疼痛。绘制了原发性和继发性痛觉过敏区域。在应用辣椒素之前、期间和之后，从31个头皮电极获取C-LEPs。在应用辣椒素期间，激光刺激施加于继发性痛觉过敏区域时诱发右侧口周区域的C-LEPs，在去除辣椒素后，激光刺激施加于原发性和继发性痛觉过敏区域时均诱发右侧口周区域的C-LEPs。虽然偏侧化的N1/P1成分（潜伏期约185毫秒）不受辣椒素影响，但在应用辣椒素期间和去除辣椒素后，与基线记录相比，从右侧继发性痛觉过敏区域以及左侧口周对称的非痛觉过敏区域诱发的后期顶点C-LEPs（N2a和P2电位的潜伏期分别约为260毫秒和410毫秒）的波幅显著降低。同时，激光诱发的热觉评分显著降低。这种抑制作用可能发生在脑干水平，其原因可能是：1）三叉神经-皮质-三叉神经回路，类似于介导经典的弥漫性伤害性抑制控制的回路；或2）介导继发性痛觉过敏的辣椒素不敏感A纤维的背景活动增加。可能由于外周抑制机制，施加于原发性痛觉过敏区域的激光脉冲既未诱发可靠的C-LEP成分，也未诱发热觉。这是人类中疼痛对热觉具有抑制作用的首个神经生理学证据。
