Hutchison W D, Tsoukatos J, Dostrovsky J O
Department of Physiology, Medical Sciences, University of Toronto, Ontario, Canada.
J Neurophysiol. 1997 Jun;77(6):3252-66. doi: 10.1152/jn.1997.77.6.3252.
Surprisingly little is known concerning the central processing of innocuous thermal somatosensory information. The aim of the present study was to obtain quantitative data on the characteristics of neurons in the rat superficial medullary dorsal horn (sMDH) that responded to innocuous thermal stimulation of the rat's face and tongue. Single-unit extracellular recordings were obtained in chloralose-urethane anesthetized rats. A total of 153 thermoreceptive neurons was studied. Of these, 146 were excited by cooling and inhibited by warming and were classified as COLD cells. The remaining seven cells were excited by innocuous warming of the skin or tongue. Of 123 COLD cells tested, 33% were excited by touch and 22% by pinch stimuli delivered to the thermoreceptive field. Of the 50 COLD cells tested, 46% were excited also by noxious heating (> or = 50 degrees C for 5 s). Most (82/121) of the receptive fields were located on the upper lip, 25 on the tongue, and most of the remaining on the lower lip. Receptive fields were generally small (1-5 mm2). In some experiments, electrical stimulation in the thalamus was performed, and nine COLD cells could be activated antidromically. The responses of 38 COLD cells to incremental 5 degrees C cooling steps were examined quantitatively. Thermal stimuli were applied to facial or lingual receptive fields of sMDH neurons with a computer-controlled Peltier thermode starting from 33 degrees C, decreasing to 8 or 3 degrees C, and returning to 33 degrees C. Most COLD cells (26/38) had both static and dynamic responses; 7 had mainly dynamic and 5 mainly static responses to step decreases in temperature. Rat sMDH COLD cells could be classified into three groups depending on their stimulus-response functions. The first group (Type 1, n = 19) had a bell-shaped static stimulus response function. The second group (Type 2) had a high maintained or increasing static firing rate as the temperature decreased < 18 degrees C (n = 10). Type 3 COLD cells had mainly dynamic properties (n = 7). Many of the cells in all groups were excited by noxious mechanical stimulation. Type 2 cells differed from the other two groups in that most did not respond to noxious thermal stimuli (hot) and many responded to innocuous tactile stimuli. Neurons from each of the three groups of COLD cells could be activated antidromically from contralateral thalamus. These data suggest that there is little central processing of thermal information at the first central synapse for Type 1 neurons, however, the responses of the other two types may be due to central processing and convergence. The demonstration of rat sMDH COLD cells with distinctive stimulus-response functions to thermal shifts suggests separate functional roles of these neurons in the ascending thermal sensory pathway.
令人惊讶的是，对于无害热躯体感觉信息的中枢处理，我们所知甚少。本研究的目的是获取关于大鼠浅表延髓背角（sMDH）中对大鼠面部和舌部进行无害热刺激有反应的神经元特征的定量数据。在水合氯醛 - 乌拉坦麻醉的大鼠中进行单单位细胞外记录。总共研究了153个温度感受神经元。其中，146个神经元在冷却时被兴奋，在加热时被抑制，被归类为冷敏细胞。其余7个细胞在皮肤或舌部进行无害加热时被兴奋。在测试的123个冷敏细胞中，33%在触觉刺激时被兴奋，22%在施加到温度感受野的捏压刺激时被兴奋。在测试的50个冷敏细胞中，46%在有害加热（≥50℃持续5秒）时也被兴奋。大多数（82/121）感受野位于上唇，25个位于舌部，其余大部分位于下唇。感受野通常较小（1 - 5平方毫米）。在一些实验中，在丘脑进行电刺激，9个冷敏细胞可被逆向激活。定量检查了38个冷敏细胞对5℃递增冷却步骤的反应。热刺激通过计算机控制的珀尔帖热电极施加到sMDH神经元的面部或舌部感受野，从33℃开始，降至8℃或3℃，然后回到33℃。大多数冷敏细胞（26/38）具有静态和动态反应；7个主要具有动态反应，5个对温度阶梯下降主要具有静态反应。大鼠sMDH冷敏细胞可根据其刺激 - 反应功能分为三组。第一组（1型，n = 19）具有钟形静态刺激反应功能。第二组（2型）在温度降至<18℃时具有高且持续或增加的静态放电率（n = 10）。3型冷敏细胞主要具有动态特性（n = 7）。所有组中的许多细胞在有害机械刺激时被兴奋。2型细胞与其他两组不同，因为大多数对有害热刺激（热）无反应，许多对无害触觉刺激有反应。来自三组冷敏细胞中的每一组的神经元都可从对侧丘脑逆向激活。这些数据表明，对于1型神经元，在第一个中枢突触处对热信息的中枢处理很少，然而，其他两种类型的反应可能归因于中枢处理和汇聚。对热变化具有独特刺激 - 反应功能的大鼠sMDH冷敏细胞的证明表明这些神经元在热感觉上行通路中具有不同的功能作用。
