Vierck C J, Cannon R L, Fry G, Maixner W, Whitsel B L
Department of Neuroscience, University of Florida College of Medicine, Gainesville 32610-0244, USA.
J Neurophysiol. 1997 Aug;78(2):992-1002. doi: 10.1152/jn.1997.78.2.992.
Temporal summation of sensory intensity was investigated in normal subjects using novel methods of thermal stimulation. A Peltier thermode was heated and then applied in a series of brief (700 ms) contacts to different sites on the glabrous skin of either hand. Repetitive contacts on the thenar or hypothenar eminence, at interstimulus intervals (ISIs) of 3 s, progressively increased the perceived intensity of a thermal sensation that followed each contact at an onset latency > 2 s. Temporal summation of these delayed (late) sensations was proportional to thermode temperature over a range of 45-53 degrees C, progressing from a nonpainful level (warmth) to painful sensations that could be rated as very strong after 10 contacts. Short-latency pain sensations rarely were evoked by such stimuli and never attained levels substantially above pain threshold for the sequences and temperatures presented. Temporal summation produced by brief contacts was greater in rate and amount than increases in sensory intensity resulting from repetitive ramping to the same temperature by a thermode in constant contact with the skin. Variation of the interval between contacts revealed a dependence of sensory intensity on interstimulus interval that is similar to physiological demonstrations of windup, where increasing frequencies of spike train activity are evoked from spinal neurons by repetitive activation of unmyelinated nociceptors. However, substantial summation at repetition rates of > or = 0.33 Hz was observed for temperatures that produced only late sensations of warmth when presented at frequencies < 0.16 Hz. Measurements of subepidermal skin temperature from anesthetized monkeys revealed different time courses for storage and dissipation of heat by the skin than for temporal summation and decay of sensory intensity for the human subjects. For example, negligible heat loss occurred during a 6-s interval between two trials of 10 contacts at 0.33 Hz, but ratings of sensory magnitude decreased from very strong levels of pain to sensations of warmth during the same interval. Evidence that temporal summation of sensory intensity during series of brief contacts relies on central integration, rather than a sensitization of peripheral receptors, was obtained using two approaches. In the first, a moderate degree of temporal summation was observed during alternating stimulation of adjacent but nonoverlapping skin sites at 0.33 Hz. Second, temporal summation was significantly attenuated by prior administration of dextromethorphan, a N-methyl-D-aspartate receptor antagonist.
使用新型热刺激方法，在正常受试者中研究了感觉强度的时间总和。珀耳帖热电极被加热，然后以一系列短暂（700毫秒）的接触应用于任何一只手无毛皮肤的不同部位。在鱼际或小鱼际隆起处，以3秒的刺激间隔（ISI）进行重复接触，逐渐增加了每次接触后在起始潜伏期>2秒时所感觉到的热感觉强度。这些延迟（晚期）感觉的时间总和在45 - 53摄氏度范围内与热电极温度成正比，从无痛水平（温暖）逐渐发展为疼痛感觉，在10次接触后可被评为非常强烈。这种刺激很少诱发短潜伏期疼痛感觉，对于所呈现的序列和温度，其强度从未显著超过疼痛阈值。短暂接触产生的时间总和在速率和量上比热电极与皮肤持续接触并重复升温到相同温度所导致的感觉强度增加更大。接触间隔的变化揭示了感觉强度对刺激间隔的依赖性，这类似于windup的生理学表现，即通过重复激活无髓伤害感受器从脊髓神经元诱发的动作电位发放频率增加。然而，对于在频率<0.16赫兹时仅产生晚期温暖感觉的温度，在重复率≥0.33赫兹时观察到了显著的总和。对麻醉猴子的表皮下皮肤温度测量显示，皮肤储存和散发热量的时间过程与人类受试者感觉强度的时间总和及衰减不同。例如，在以0.33赫兹进行10次接触的两次试验之间的6秒间隔内，热量损失可忽略不计，但在相同间隔内，感觉强度评分从非常强烈的疼痛水平降至温暖感觉。使用两种方法获得了证据，表明在一系列短暂接触过程中感觉强度的时间总和依赖于中枢整合，而不是外周感受器的敏化。第一种方法是，在以0.33赫兹交替刺激相邻但不重叠的皮肤部位时，观察到了中等程度的时间总和。第二种方法是，预先给予N - 甲基 - D - 天冬氨酸受体拮抗剂右美沙芬后，时间总和显著减弱。
