Rose P K, MacDermid V, Joshi M, Neuber-Hess M
CIHR Group in Sensory-Motor Systems, Department of Physiology, Queen's University, Kingston, Ont., Canada.
Eur J Neurosci. 2001 Mar;13(6):1166-76. doi: 10.1046/j.0953-816x.2001.1490.x.
The distinctive features of axons and dendrites divide most neurons into two compartments. This polarity is fundamental to the ability of most neurons to integrate synaptic signals and transmit action potentials. It is not known, however, if the polarity of neurons in the adult mammalian nervous system is fixed or plastic. Following axotomy, some distal dendrites of neck motoneurons in the adult cat give rise to unusual processes that, at a light microscopic level, resemble axons (Rose, P.K. & Odlozinski, M., J. Comp. Neurol., 1998, 390, 392). The goal of the present experiments was to characterize these unusual processes using well-established ultrastructural and molecular criteria that differentiate dendrites and axons. These processes were immunoreactive for growth-associated protein-43 (GAP-43), a protein that is normally confined to axons. In contrast, immunoreactivity for a protein that is widely used as a marker for dendrites, microtubule-associated protein (MAP)-2a/b, could not be detected in the unusual distal arborizations. At the electron microscopic level, unusual distal processes contained dense collections of neurofilaments and were frequently myelinated. These molecular and structural characteristics are typical of axons and suggest that the polarity of adult neurons in the mammalian nervous system can be disrupted by axotomy. If this transformation in neuronal polarity is common to other types of neurons, axon-like processes emerging from distal dendrites may represent a mechanism for replacing connections lost due to injury. Alternatively, the connections formed by these axons may be aberrant and therefore maladaptive.
轴突和树突的显著特征将大多数神经元分为两个部分。这种极性对于大多数神经元整合突触信号和传递动作电位的能力至关重要。然而，目前尚不清楚成年哺乳动物神经系统中神经元的极性是固定的还是可变的。切断轴突后，成年猫颈部运动神经元的一些远端树突会产生异常突起，在光学显微镜下，这些突起类似于轴突（罗斯，P.K. & 奥德洛津斯基，M.，《比较神经学杂志》，1998年，390卷，392页）。本实验的目的是使用成熟的超微结构和分子标准来表征这些异常突起，这些标准可区分树突和轴突。这些突起对生长相关蛋白-43（GAP-43）具有免疫反应性，该蛋白通常仅存在于轴突中。相比之下，在异常的远端分支中未检测到广泛用作树突标记物的微管相关蛋白（MAP）-2a/b的免疫反应性。在电子显微镜水平上，异常的远端突起含有密集的神经丝聚集，并且经常有髓鞘。这些分子和结构特征是轴突所特有的，表明哺乳动物神经系统中成年神经元的极性可因轴突切断而被破坏。如果这种神经元极性的转变在其他类型的神经元中也很常见，那么从远端树突产生的轴突样突起可能代表一种机制，用于替代因损伤而失去的连接。或者，这些轴突形成的连接可能是异常的，因此是适应不良的。
