Rasmusson D D, Louw D F, Northgrave S A
Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada.
Somatosens Mot Res. 1993;10(1):69-80. doi: 10.3109/08990229309028825.
Multiunit recordings were made in the ventroposterior lateral nucleus of the thalamus in anesthetized raccoons. During recording from cells responding to cutaneous stimulation of a forepaw digit, the corresponding digit was denervated permanently (by cutting its four digital nerves) or temporarily (by injecting lidocaine into the base of the digit). Both procedures resulted in immediate increases in the inhibition that could be induced by stimulation of the adjacent digits when the original cutaneous receptive field was on the glabrous skin. In each case with temporary denervation, this enhanced off-focus inhibition decreased when the excitatory responses returned to normal. In contrast, temporary denervation of the digit during recording at sites in the hairy skin representation did not reveal this increased inhibition from adjacent digits. When capsaicin was applied to the digital nerves in two animals, the excitatory receptive fields of thalamic neurons increased in area, but were still restricted to the same part of the digit. These data indicate that the immediate unmasking of inhibitory responses, previously reported in primary somatosensory cortex of the raccoon, is also present in the thalamus. The capsaicin-induced expansion of excitatory receptive fields confirms previous experiments in other species, and suggests that C fibers play a role in modulating the size of cutaneous receptive fields. However, the enlargement of excitatory receptive fields by capsaicin is much less than the unmasking of inhibitory fields induced by digit denervation, and indicates that different mechanisms are involved in controlling these various inputs to thalamic neurons.
在麻醉的浣熊丘脑腹后外侧核进行多单位记录。在记录对前爪趾皮肤刺激有反应的细胞时，相应的趾被永久性去神经支配（通过切断其四条指神经）或临时性去神经支配（通过向趾基部注射利多卡因）。当原始皮肤感受野位于无毛皮肤时，这两种操作都会导致刺激相邻趾所诱发的抑制立即增加。在每次临时性去神经支配的情况下，当兴奋性反应恢复正常时，这种增强的离焦抑制就会减弱。相比之下，在有毛皮肤代表区的记录部位对趾进行临时性去神经支配时，并未发现来自相邻趾的这种抑制增加。当向两只动物的指神经施加辣椒素时，丘脑神经元的兴奋性感受野面积增大，但仍局限于趾的同一部分。这些数据表明，先前在浣熊初级体感皮层中报道的抑制性反应的立即暴露在丘脑中也存在。辣椒素诱导的兴奋性感受野扩大证实了在其他物种中的先前实验，并表明C纤维在调节皮肤感受野大小中起作用。然而，辣椒素引起的兴奋性感受野扩大远小于趾去神经支配所诱发的抑制性感受野的暴露，这表明控制丘脑神经元的这些不同输入涉及不同机制。
