Department of Developmental Biology and Neuroscience, Tohoku University Graduate School of Life Sciences and JST, CREST, Sendai, Japan.
PLoS One. 2012;7(3):e32699. doi: 10.1371/journal.pone.0032699. Epub 2012 Mar 6.
In vertebrate somatosensory systems, each mode of touch-pressure, temperature or pain is sensed by sensory endings of different dorsal root ganglion (DRG) neurons, which conducted to the specific cortical loci as nerve impulses. Therefore, direct electrical stimulation of the peripheral nerve endings causes an erroneous sensation to be conducted by the nerve. We have recently generated several transgenic lines of rat in which channelrhodopsin-2 (ChR2) transgene is driven by the Thy-1.2 promoter. In one of them, W-TChR2V4, some neurons were endowed with photosensitivity by the introduction of the ChR2 gene, coding an algal photoreceptor molecule. The DRG neurons expressing ChR2 were immunohistochemically identified using specific antibodies to the markers of mechanoreceptive or nociceptive neurons. Their peripheral nerve endings in the plantar skin as well as the central endings in the spinal cord were also examined. We identified that ChR2 is expressed in a certain population of large neurons in the DRG of W-TChR2V4. On the basis of their morphology and molecular markers, these neurons were classified as mechanoreceptive but not nociceptive. ChR2 was also distributed in their peripheral sensory nerve endings, some of which were closely associated with CK20-positive cells to form Merkel cell-neurite complexes or with S-100-positive cells to form structures like Meissner's corpuscles. These nerve endings are thus suggested to be involved in the sensing of touch. Each W-TChR2V4 rat showed a sensory-evoked behavior in response to blue LED flashes on the plantar skin. It is thus suggested that each rat acquired an unusual sensory modality of sensing blue light through the skin as touch-pressure. This light-evoked somatosensory perception should facilitate study of how the complex tactile sense emerges in the brain.
在脊椎动物的躯体感觉系统中，每种触摸压力、温度或疼痛模式都是由不同背根神经节 (DRG) 神经元的感觉末梢感知的，这些神经元作为神经冲动传导到特定的皮质部位。因此，直接电刺激外周神经末梢会导致错误的感觉通过神经传导。我们最近生成了几种转基因大鼠品系，其中通道视紫红质-2 (ChR2) 转基因由 Thy-1.2 启动子驱动。在其中一种，W-TChR2V4 中，一些神经元通过引入 ChR2 基因而具有光敏性，该基因编码一种藻类光感受器分子。使用针对机械感受器或伤害感受器神经元标记物的特异性抗体，对表达 ChR2 的 DRG 神经元进行免疫组织化学鉴定。还检查了它们在足底皮肤中的外周神经末梢和脊髓中的中枢末梢。我们确定 ChR2 在 W-TChR2V4 的 DRG 中的某些大神经元中表达。根据它们的形态和分子标记，这些神经元被归类为机械感受器神经元，但不是伤害感受器神经元。ChR2 也分布在它们的外周感觉神经末梢中，其中一些与 CK20 阳性细胞密切相关，形成 Merkel 细胞-神经突复合物，或与 S-100 阳性细胞形成类似于 Meissner 小体的结构。这些神经末梢因此被认为参与触摸感的感知。每只 W-TChR2V4 大鼠在足底皮肤上的蓝色 LED 闪烁时都会表现出感觉诱发行为。因此，每只大鼠都通过皮肤获得了一种不寻常的感知蓝光的感觉方式，即触摸压力。这种光诱发的躯体感觉感知应该有助于研究复杂触觉感是如何在大脑中产生的。
