Department of Anatomy, College of Medicine and Health Sciences, United Arab Emirates University, Al-Ain, United Arab Emirates.
J Comp Neurol. 2018 Dec 15;526(18):2984-2999. doi: 10.1002/cne.24509. Epub 2018 Nov 19.
GAD67-EGFP mice were used in a series of experiments to provide anatomical evidence for the role of the reduction in myelinated primary afferent input to GABA spinal neurons in the production of neuropathic pain following peripheral L5 nerve injury. First, we confirmed that L5 injury in these mice produced mechanical and thermal hyperalgesia in the ipsilateral foot. Second, we injected a mixture of cholera toxin subunit-B (CTb) and isolectin B4 (IB4) in the sciatic nerve to selectively label its myelinated and unmyelinated primary afferents. Results showed that primary afferents of sciatic nerve extend from L2-L6 spinal segments. Third, we determined the central terminations of myelinated primary afferents of L4 and L5 spinal nerves following CTb injection in either nerve. The myelinated primary afferents of both nerves terminated in the corresponding and two to three rostral spinal segments with some fibers descending to terminate in the segment caudal to the level at which they entered indicating an intermingling of their terminals at the dorsal horn of the spinal cord. Fourthly, we injected CTb in L5 nerve and CTb HRP-conjugate in L4 nerve. Confocal microscopy and subsequent image analyses showed that individual EGFP-labeled neurons in L4 segment receive myelinated primary afferent contacts from both L4 and L5 nerves. Eliminating inputs from L5 nerve following its injury would result in less involvement of spinal GABA neurons which would very likely initiate neuronal sensitization in L4 segment. This could lead to the development of hyperalgesia in response to the stimulation of the adjacent uninjured L4 nerve.
GAD67-EGFP 小鼠被用于一系列实验中，为周围 L5 神经损伤后 GABA 脊髓神经元中髓鞘初级传入减少导致神经病理性疼痛的作用提供解剖学证据。首先，我们证实这些小鼠的 L5 损伤导致同侧足部产生机械性和热痛觉过敏。其次，我们将霍乱毒素亚单位-B（CTb）和异硫氰酸荧光素-B4（IB4）混合物注入坐骨神经中，以选择性标记其有髓和无髓初级传入。结果表明，坐骨神经的初级传入纤维来自 L2-L6 脊髓节段。第三，我们在 L4 和 L5 脊神经中的 CTb 注射后确定了 L4 和 L5 脊神经的有髓初级传入纤维的中枢末端。这两根神经的有髓初级传入纤维都终止在相应的和 2-3 个头侧脊髓节段，有些纤维下降到它们进入的节段以下，表明它们的末梢在脊髓背角混合。第四，我们在 L5 神经中注射 CTb，在 L4 神经中注射 CTb HRP 缀合物。共聚焦显微镜和随后的图像分析表明，L4 节段中单个 EGFP 标记神经元接收来自 L4 和 L5 神经的有髓初级传入接触。L5 神经损伤后消除其传入，将导致更少的脊髓 GABA 神经元参与，这很可能导致 L4 节段神经元致敏。这可能导致对相邻未受伤的 L4 神经的刺激产生痛觉过敏。
