Uhelski Megan L, Bruce Daniel J, Séguéla Philippe, Wilcox George L, Simone Donald A
Department of Diagnostic & Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, Minnesota.
Department of Pharmacology, University of Minnesota, Minneapolis, Minnesota.
J Neurophysiol. 2017 Jun 1;117(6):2218-2223. doi: 10.1152/jn.00083.2017. Epub 2017 Mar 15.
Optogenetic methods that utilize expression of the light-sensitive protein channelrhodopsin-2 (ChR2) in neurons have enabled selective activation of specific subtypes or groups of neurons to determine their functions. Using a transgenic mouse model in which neurons natively expressing Na1.8 (a tetrodotoxin-resistant voltage-gated sodium channel) also express the light-gated channel ChR2, we have been able to determine the functional properties of Na1.8-expressing cutaneous nociceptors of the glabrous skin in vivo. Most (44 of 53) of the C-fiber nociceptors isolated from mice were found to be responsive to blue (470 nm) light. Response characteristics, including conduction velocity and responses to mechanical stimuli, were comparable between nociceptors isolated from and control mice. Interestingly, while none of the non-light-responsive C-fibers were sensitive to heat or cold, nearly all (77%) light-sensitive fibers were excited by mechanical and thermal stimuli, suggesting that Na1.8 is predominantly expressed by C-fiber nociceptors that are responsive to multiple stimulus modalities. The ability to activate peripheral nociceptors with light provides a method of stimulation that is noninvasive, does not require mechanical interruption of the skin, and accesses receptive fields that might be difficult or impossible to stimulate with standard stimuli while allowing repeated stimulation without injuring the skin. Transgenic mice that express the blue light-sensitive protein channelrhodopsin2 (ChR2) in nociceptive nerve fibers that contain voltage-gated sodium channel Na1.8 were used to determine functional properties of these afferent fibers. Electrophysiological recordings in vivo revealed that most nociceptive fibers that possess Na1.8 are C-fiber nociceptors that respond to multiple stimulus modalities. Furthermore, responses evoked by blue light stimulation were comparable to those elicited by noxious mechanical, heat, and cold stimuli.
利用光敏感蛋白通道视紫红质-2（ChR2）在神经元中表达的光遗传学方法，能够选择性激活特定亚型或神经元群体，以确定其功能。使用一种转基因小鼠模型，其中天然表达Na1.8（一种抗河豚毒素的电压门控钠通道）的神经元也表达光门控通道ChR2，我们已经能够在体内确定无毛皮肤中表达Na1.8的皮肤伤害感受器的功能特性。从转基因小鼠分离出的大多数（53个中的44个）C纤维伤害感受器对蓝光（470nm）有反应。从转基因小鼠和对照小鼠分离出的伤害感受器之间，包括传导速度和对机械刺激的反应在内的反应特性是可比的。有趣的是，虽然所有对光无反应的C纤维对热或冷都不敏感，但几乎所有（77%）对光敏感的纤维都能被机械和热刺激激活，这表明Na1.8主要由对多种刺激模式有反应的C纤维伤害感受器表达。用光激活外周伤害感受器的能力提供了一种非侵入性的刺激方法，不需要对皮肤进行机械干扰，并且能够刺激用标准刺激可能难以或无法刺激的感受野，同时允许重复刺激而不损伤皮肤。在含有电压门控钠通道Na1.8的伤害性神经纤维中表达蓝光敏感蛋白通道视紫红质2（ChR2）的转基因小鼠，被用于确定这些传入纤维的功能特性。体内电生理记录显示，大多数拥有Na1.8的伤害性纤维是对多种刺激模式有反应的C纤维伤害感受器。此外，蓝光刺激引起的反应与有害机械、热和冷刺激引起的反应相当。
