Peripheral Nerve Regeneration and Dorsal Horn Plasticity

描述（由申请人提供）：周围神经损伤相对常见。正常情况下，受损的神经再生，使周围组织重新受到神经支配。这一过程导致躯体感觉系统具有显著的可塑性。在神经再支配后立即出现正常触觉敏锐度的丧失，这种丧失通常随着时间的推移而改善。这些病变还可能导致其他症状，如超敏反应，其范围可以从轻度无害的痛觉过敏到疼痛状况，包括可能持续的异常性疼痛或头痛，极大地影响个体的生活质量。据信，这些疼痛综合征的主要贡献涉及通常发出轻触信号的感觉纤维的异位发芽，进入脊髓的疼痛区域。在最后一个资助期间，发现这种发芽不会发生，与以前的研究结果相反，有髓鞘的伤害性纤维项目广泛遍及浅表背角。这些发现表明，有髓鞘的伤害感受器提供了观察到的新的快速传导输入到浅表背角细胞以前认为来自低阈值纤维。这项提议的长期目标是确定有髓鞘伤害感受器及其脊髓连接对这些慢性疼痛状态的贡献。拟议的研究将解决三个具体假设： 假设1：周围神经再生后，有髓伤害感受器对机械和热刺激的敏感性增加。 假设二：在周围神经再生后，浅层背角中的细胞表现出对低阈值机械感受性和热输入的敏感性增加， 假设三：在周围神经再生后，浅层背角中的细胞接受来自有髓伤害感受器的增加的功能输入，但不接受来自有髓低阈值机械感受器的功能输入。 将使用离体小鼠脊髓/皮肤/神经制备物来测试这些假设，所述离体小鼠脊髓/皮肤/神经制备物允许在神经再生之前、期间和之后细胞内记录和表征位于脊髓背角浅层中的单个皮肤感觉神经元和细胞的皮肤反应特性。在其表征之后，对单个细胞进行染色并进行组织学回收，以允许在光镜和电镜水平上进行进一步分析。这种制备还允许单个识别的感觉神经元和表面背角细胞的双重细胞内记录。然后可以单独刺激个体伤害感受性或非伤害感受性有髓鞘纤维以确定再生之前和之后的突触连接。 这些实验的结果将大大增加我们对躯体感觉系统中神经损伤后可塑性的理解，并可能揭示可能导致伴随这些损伤的持续疼痛状态的机制。

DESCRIPTION (provided by applicant): Peripheral nerve injury is a relatively common occurrence. Normally the damaged nerve regenerates to reinnervate peripheral tissues. This process results in significant plasticity in the somatosensory system. Immediately following reinnervation there is a loss of normal tactile acuity that often improves with time. These lesions can also result in other symptoms such as hypersensitivity, which can range from mild innocuous hyperalgesia to painful conditions including allodynia or causalgia that can persist, greatly affecting the individual's quality of life. It is believed that a major contribution to these pain syndromes involves the ectopic sprouting of sensory fibers normally signaling light touch, into the pain regions of the spinal cord. During the last funding period it was found that this sprouting does not occur, and in contrast to previous findings, that myelinated nociceptive fibers project extensively throughout the superficial dorsal horn. These findings suggest that myelinated nociceptors provide the observed novel fast conducting inputs to superficial dorsal horn cells previously thought to come from low-threshold fibers. The long-term goal of this proposal is to determine the contribution of myelinated nociceptors and their spinal connection to these chronic pain states. The proposed research will address three specific hypotheses: Hypothesis 1: Following peripheral nerve regeneration myelinated nociceptors exhibit increased sensitivity to mechanical and thermal stimulation. Hypothesis 2: Following peripheral nerve regeneration cells in the superficial dorsal horn exhibit an increased sensitivity to low threshold mechanoreceptive and thermal inputs, Hypothesis 3: Following peripheral nerve regeneration cells in the superficial dorsal horn receive increased functional inputs from myelinated nociceptors, but not from myelinated low threshold mechanoreceptors. These hypotheses will be tested using an ex vivo mouse spinal cord/skin/nerve preparation that allows the intracellular recording and characterization of cutaneous response properties of individual cutaneous sensory neurons and cells located in the superficial laminae of the spinal dorsal horn before, during and after nerve regeneration. Following their characterization individual cells are stained and histologically recovered to allow for further analysis at both the light and electron microscopic levels. This preparation also allows for the dual intracellular recording of individual identified sensory neurons and superficial dorsal horn cells. The individual nociceptive or non-nociceptive myelinated fibers can then be individually stimulated to determine synaptic linkage before and after regeneration. The results of these experiments will greatly increase our understanding of post nerve injury plasticity in the somatosensory system and possible reveal mechanisms that could contribute to persistent pain states that can accompany these injuries.