A putative relay circuit providing low-threshold mechanoreceptive input to lamina I projection neurons via vertical cells in lamina II of the rat dorsal horn.
A putative relay circuit providing low-threshold mechanoreceptive input to lamina I projection neurons via vertical cells in lamina II of the rat dorsal horn.
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DOI：
10.1186/1744-8069-10-3
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发表时间：
2014-01-17
期刊：
影响因子：
3.3
通讯作者：
Todd AJ
中科院分区：
文献类型：
--
作者：
Yasaka T;Tiong SY;Polgár E;Watanabe M;Kumamoto E;Riddell JS;Todd AJ
板层I投射神经元对疼痛刺激作出反应，有些也被触摸或毛发运动激活。由周围神经损伤引起的神经性疼痛通常与触觉异常性疼痛（触摸诱发的疼痛）相关，并且这可能是由于I层投射神经元对非伤害性机械刺激的反应性增加。据认为，涉及兴奋性中间神经元的多突触通路可以将触觉输入传递到板层I投射神经元，但这些通常被抑制性中间神经元抑制。垂直细胞在第二层提供了一个潜在的途径，通过触觉刺激可以激活第一层投射神经元，因为它们的树突延伸到触觉传入终止的区域，而它们的轴突可以支配投射细胞。本研究的目的是确定是否垂直细胞树突接触的低阈值机械感受性初级传入的中央末梢。我们最初展示了在脊髓切片和轴突终扣中记录的垂直细胞的树突棘之间的接触，轴突终扣含有囊泡谷氨酸转运蛋白1（VGLUT 1），其由有髓低阈值机械感受性传入神经表达。为了证实VGLUT 1终扣包括初级传入，我们随后检查了在接受霍乱毒素B亚单位（CT B）注射到坐骨神经的大鼠中记录的垂直细胞。我们发现，超过一半的VGLUT1扣接接触垂直细胞CTb免疫反应，表明他们是初级传入起源。这些结果表明，垂直细胞树突棘经常接触的有髓低阈值机械感受性传入的中央终端。由于树突棘与兴奋性突触有关，因此这些接触很可能大多数是突触性的。因此，第二层的垂直细胞是触觉传入激活第一层投射神经元的潜在途径，这条途径可能在触觉异常性疼痛中发挥作用。
Lamina I projection neurons respond to painful stimuli, and some are also activated by touch or hair movement. Neuropathic pain resulting from peripheral nerve damage is often associated with tactile allodynia (touch-evoked pain), and this may result from increased responsiveness of lamina I projection neurons to non-noxious mechanical stimuli. It is thought that polysynaptic pathways involving excitatory interneurons can transmit tactile inputs to lamina I projection neurons, but that these are normally suppressed by inhibitory interneurons. Vertical cells in lamina II provide a potential route through which tactile stimuli can activate lamina I projection neurons, since their dendrites extend into the region where tactile afferents terminate, while their axons can innervate the projection cells. The aim of this study was to determine whether vertical cell dendrites were contacted by the central terminals of low-threshold mechanoreceptive primary afferents. We initially demonstrated contacts between dendritic spines of vertical cells that had been recorded in spinal cord slices and axonal boutons containing the vesicular glutamate transporter 1 (VGLUT1), which is expressed by myelinated low-threshold mechanoreceptive afferents. To confirm that the VGLUT1 boutons included primary afferents, we then examined vertical cells recorded in rats that had received injections of cholera toxin B subunit (CTb) into the sciatic nerve. We found that over half of the VGLUT1 boutons contacting the vertical cells were CTb-immunoreactive, indicating that they were of primary afferent origin. These results show that vertical cell dendritic spines are frequently contacted by the central terminals of myelinated low-threshold mechanoreceptive afferents. Since dendritic spines are associated with excitatory synapses, it is likely that most of these contacts were synaptic. Vertical cells in lamina II are therefore a potential route through which tactile afferents can activate lamina I projection neurons, and this pathway could play a role in tactile allodynia.
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