Cassam A K, Rogers K A, Weaver L C
The John P. Robarts Research Institute and The Department of Physiology, University of Western Ontario, London, Canada.
Neuroscience. 1999;88(4):1275-88. doi: 10.1016/s0306-4522(98)00262-0.
After spinal cord injury, abnormal responses of spinal cord neurons to sensory input lead to conditions such as autonomic dysreflexia, urinary bladder dyssynergia, muscle spasticity and chronic pain syndromes. These responses suggest that the spinal cord undergoes marked reorganization after an injury. In previous studies, we demonstrated changes in individual patterns of immunoreactivity for growth-associated protein-43, dopamine beta-hydroxylase and substance P that suggest growth and/or changes in expression of neurotransmitter enzymes and peptides in the cord caudal to a transection injury. In the present study we determined whether (i) growth-associated protein-43 and dopamine beta-hydroxylase or substance P were co-expressed in the same neurons prior to cord injury, and (ii) these patterns of expression changed after injury. A change in co-localization patterns caudal to an injury would suggest diversity in responses of different populations of spinal neurons. We used double-labelling immunocytochemistry to determine whether either dopamine beta-hydroxylase or substance P was co-localized with growth-associated protein-43 in control rats and in rats one, two or six weeks after spinal cord transection. We focused on the intermediate gray matter, especially the sympathetic intermediolateral cell column. In control rats, fibres travelling in a stereotyped ladder-like pattern in the thoracic gray matter contained growth-associated protein-43 co-localized with dopamine beta-hydroxylase or substance P. In spinal rats, such co-localization was also observed in spinal cord segments rostral to the cord transection. In contrast, caudal to the transection, substance P and growth-associated protein-43 were found in separate reticular networks. Immunoreactivity for dopamine beta-hydroxylase disappeared in fibres during this time, but was clearly present in somata. Immunoreactivity for growth-associated protein-43 was also found in somata, but never co-localized with that for dopamine beta-hydroxylase. These observations demonstrated co-localization of growth-associated protein-43 with dopamine beta-hydroxylase and substance P in descending spinal cord pathways. Caudal to a cord transection, this co-localization was no longer found, although each substance was present either in an abundant neural network or in somata. One population of spinal neurons responded to cord injury by expressing the growth-associated protein, whereas two others changed in the intensity of their expression of neurotransmitter peptides or enzymes or in the abundance of fibres expressing them. Thus, three populations of spinal neurons had distinct responses to cord injury, two of them increasing their potential input to spinal sensory, sympathetic or motor neurons. Such responses would enhance transmission through spinal pathways after cord injury.
脊髓损伤后，脊髓神经元对感觉输入的异常反应会导致诸如自主神经反射异常、膀胱协同失调、肌肉痉挛和慢性疼痛综合征等情况。这些反应表明脊髓在损伤后会发生显著的重组。在先前的研究中，我们证明了生长相关蛋白-43、多巴胺β-羟化酶和P物质的个体免疫反应模式发生了变化，这表明在横断损伤尾侧的脊髓中，神经递质酶和肽的表达出现了生长和/或变化。在本研究中，我们确定了：（i）在脊髓损伤前，生长相关蛋白-43与多巴胺β-羟化酶或P物质是否在同一神经元中共表达；（ii）损伤后这些表达模式是否发生了变化。损伤尾侧共定位模式的改变将表明不同脊髓神经元群体反应的多样性。我们使用双标记免疫细胞化学来确定在对照大鼠以及脊髓横断后1周、2周或6周的大鼠中，多巴胺β-羟化酶或P物质是否与生长相关蛋白-43共定位。我们聚焦于中间灰质，尤其是交感神经中间外侧细胞柱。在对照大鼠中，在胸段灰质中呈刻板的梯状模式走行的纤维含有与多巴胺β-羟化酶或P物质共定位的生长相关蛋白-43。在脊髓损伤的大鼠中，在脊髓横断上方的脊髓节段也观察到了这种共定位。相反，在横断下方，P物质和生长相关蛋白-43存在于不同的网状网络中。在此期间，多巴胺β-羟化酶的免疫反应性在纤维中消失，但在胞体中明显存在。生长相关蛋白-43的免疫反应性也在胞体中发现，但从未与多巴胺β-羟化酶的免疫反应性共定位。这些观察结果证明了生长相关蛋白-43与多巴胺β-羟化酶和P物质在脊髓下行通路中共定位。在脊髓横断下方，尽管每种物质都存在于丰富的神经网络或胞体中，但不再发现这种共定位。一群脊髓神经元通过表达生长相关蛋白对脊髓损伤做出反应，而另外两群神经元在神经递质肽或酶的表达强度或表达它们的纤维丰度方面发生了变化。因此，三群脊髓神经元对脊髓损伤有不同的反应，其中两群增加了它们对脊髓感觉、交感或运动神经元的潜在输入。这种反应将增强脊髓损伤后通过脊髓通路的传导。
