Woodward S K, Treherne J M, Knott G W, Fernandez J, Varga Z M, Nicholls J G
Pharmacology Department, University of Basel, Switzerland.
J Exp Biol. 1993 Mar;176:77-88. doi: 10.1242/jeb.176.1.77.
The ability of neurites to grow through a lesion and form synaptic connections has been analyzed in a developing mammalian spinal cord in vitro. After isolation of the entire central nervous system (CNS) of the newly born South American opossum (Monodelphis domestica) the spinal cord was crushed. Outgrowth through and beyond the lesion was observed in living preparations for 2-5 days by staining axons with carbocyanine dyes. The structure of the acute crush and the growing neurites was examined by light and electron microscopy in tissue fixed immediately after the crush had been made. All axons had been severed and the site was filled with debris and amorphous vesicular structures. By 3 days after injury, numerous labelled neurites had grown into the lesion; by 4 days, many had extended several millimetres beyond it. At this time normal axonal profiles were apparent in electron micrographs of the crush site. Although fewer axons grew across the lesion than had been severed by the crush, the amplitudes of compound action potential volleys conducted across the crush in injured preparations were comparable with those recorded from uninjured spinal cords. Physiological experiments made with raised concentrations of extracellular magnesium in the culture fluid indicated that growing axons had formed synaptic connections. Thus, delayed major peaks of the response were abolished while the small component corresponding to through conduction remained unaffected by magnesium. These experiments demonstrate the development of synaptic interactions by the growing neurites and confirm the far greater powers of repair in neonatal mammals compared to adults. They set the stage for comparing molecular mechanisms involved in development and regeneration of the mammalian CNS.
在体外培养的发育中的哺乳动物脊髓中，已对神经突穿过损伤部位并形成突触连接的能力进行了分析。分离新生南美负鼠（Monodelphis domestica）的整个中枢神经系统（CNS）后，对脊髓进行挤压。通过用碳青霉烯染料对轴突进行染色，在活体标本中观察到损伤部位及损伤部位以外的神经突生长情况，持续2至5天。在挤压后立即固定的组织中，通过光学显微镜和电子显微镜检查急性挤压部位和生长中的神经突的结构。所有轴突均已被切断，损伤部位充满了碎片和无定形的囊泡结构。损伤后3天，大量标记的神经突生长到损伤部位；到4天时，许多神经突已延伸到损伤部位几毫米以外。此时，在挤压部位的电子显微镜照片中可见正常的轴突形态。尽管穿过损伤部位生长的轴突数量少于被挤压切断的轴突数量，但在损伤标本中穿过挤压部位传导的复合动作电位波幅与未损伤脊髓记录的波幅相当。在培养液中提高细胞外镁离子浓度进行的生理学实验表明，生长中的轴突已形成突触连接。因此，反应的延迟主峰被消除，而与直接传导相对应的小成分不受镁的影响。这些实验证明了生长中的神经突会发生突触相互作用，并证实了新生哺乳动物与成年哺乳动物相比具有更强的修复能力。它们为比较哺乳动物中枢神经系统发育和再生所涉及的分子机制奠定了基础。
