Doubleday B, Robinson P P
Department of Oral and Maxillofacial Surgery, University of Sheffield, UK.
J Anat. 1995 Jun;186 ( Pt 3)(Pt 3):593-605.
Following nerve section, regenerating axons from the proximal stump grow preferentially towards the distal stump. It has been postulated that this may result from the release of a neurotropic factor. To investigate whether the protein nerve growth factor (NGF) plays such a role, we immunised adult rats against NGF and examined the effect on regeneration of sectioned nerves through Y-shaped silastic tubes towards either the distal stump or an empty arm. Regeneration through the tubes was assessed electrophysiologically and the number of myelinated and nonmyelinated fibres at different sites was quantified using electron microscopy. There was electrophysiological evidence of regeneration towards the distal nerve stump in all the animals and there was no significant difference between the immunised and control animals in the size of compound action potential (CAP) ratios. Histologically, the majority of axons were found to have regenerated towards the distal nerve stump in 9/10 of the control animals and 7/9 of the immunised animals and there was no significant difference between the two groups in the numbers of regenerating myelinated or unmyelinated axons. However, in the immunised animals both myelinated and unmyelinated axons were slightly but significantly smaller and the myelin sheaths were thinner than in the control animals. In 2 immunised animals and none of the controls a small CAP was recorded while stimulating distal to the 'empty arm' and the presence of a small number of myelinated and unmyelinated axons was confirmed histologically. We conclude that as depletion of NGF does not block the preferential growth of regenerating axons towards the distal nerve stump it does not play the major neurotropic role in nerve regeneration. The reduction in size and myelin thickness of the regenerated axons after immunisation confirms the neurotrophic effects of NGF.
神经切断后，近端残端再生的轴突优先向远端残端生长。据推测，这可能是由于神经营养因子的释放所致。为了研究蛋白质神经生长因子（NGF）是否发挥这样的作用，我们用NGF对成年大鼠进行免疫，并通过Y形硅橡胶管检查对切断神经向远端残端或空臂再生的影响。通过电生理学评估通过管子的再生情况，并使用电子显微镜对不同部位有髓和无髓纤维的数量进行定量。所有动物均有向远端神经残端再生的电生理证据，免疫动物和对照动物的复合动作电位（CAP）比值大小无显著差异。组织学上，在10只对照动物中有9只、9只免疫动物中有7只发现大多数轴突向远端神经残端再生，两组再生的有髓或无髓轴突数量无显著差异。然而，免疫动物中的有髓和无髓轴突均略小但显著小于对照动物，且髓鞘比对照动物薄。在2只免疫动物中，在刺激“空臂”远端时记录到一个小的CAP，而对照动物中没有，并且组织学证实存在少量有髓和无髓轴突。我们得出结论，由于NGF的耗竭并不阻止再生轴突向远端神经残端的优先生长，因此它在神经再生中不发挥主要的神经营养作用。免疫后再生轴突大小和髓鞘厚度的减小证实了NGF的神经营养作用。
