Kuang R Z, Kalil K
Department of Anatomy, University of Wisconsin, Madison 53706.
J Comp Neurol. 1990 Dec 15;302(3):461-72. doi: 10.1002/cne.903020304.
Previous studies have reported considerable plasticity in the rodent corticospinal pathway in response to injury. This includes sprouting of intact axons from the normal pathway into the contralateral spinal cord denervated by an early corticospinal lesion. We carried out the present study to obtain detailed information about the time course, origin, and degree of specificity of corticospinal axons sprouting in response to denervation. Hamsters (Mesocricetus auratus) ranging in age from 5 to 23 days received unilateral lesions of the left medullary pyramidal tract. Two weeks after the lesion, small regions of the right sensorimotor cortex opposite the lesion were injected with the plant lectin Phaseolus vulgaris leucoagglutinin (PHA-L). After a further 2 week survival period, immunohistochemistry was carried out on frozen sections of the fixed brains and spinal cords. Detailed morphological analysis of PHA-L labeled corticospinal axons revealed that sprouting from the intact corticospinal pathway into the contralateral denervated spinal cord occurred only at local spinal levels and not at the pyramidal decussation. Arbors sprouting into the denervated cord frequently arose from corticospinal axons that branched into the normal side of the cord as well. Sprouting was maximal after early lesions (5 days) and declined with lesions at later ages up to 19 days. Sprouting corticospinal axons arborized with the same degree of functional and topographic specificity as previously reported for normal corticospinal arbors (Kuang and Kalil: J. Comp. Neurol. 292:585-598, '90), such that axons arising from somatosensory cortex projected only to the dorsal horn, those from motor cortex innervated only the ventral horn, and normal forelimb and hindlimb topography was preserved. Sprouting fibers also had normal branching patterns. Parallel studies of developing corticospinal arbors showed that sprouting could not be attributed to maintenance or expansion of early bilateral connections. These results suggest that local signals, most likely similar to those governing normal corticospinal development, elicit corticospinal sprouting and determine specificity of axon arbors.
先前的研究报道，啮齿动物的皮质脊髓通路在受到损伤时具有相当大的可塑性。这包括正常通路中完整的轴突发芽，长入因早期皮质脊髓损伤而失神经支配的对侧脊髓。我们开展了本研究，以获取有关皮质脊髓轴突发芽的时间进程、起源和特异性程度的详细信息，这些芽是对失神经支配的反应。年龄在5至23天的仓鼠接受了左侧延髓锥体束的单侧损伤。损伤两周后，在损伤对侧的右侧感觉运动皮层的小区域注射植物凝集素菜豆白细胞凝集素（PHA-L）。在又经过2周的存活期后，对固定的脑和脊髓的冰冻切片进行免疫组织化学分析。对PHA-L标记的皮质脊髓轴突的详细形态学分析表明，从完整的皮质脊髓通路长入对侧失神经支配脊髓的芽生仅发生在局部脊髓水平，而不是在锥体交叉处。长入失神经支配脊髓的分支通常也来自分支到脊髓正常侧的皮质脊髓轴突。早期损伤（5天）后芽生最大，随着损伤年龄增加至19天，芽生逐渐减少。芽生的皮质脊髓轴突形成的分支在功能和地形特异性方面与先前报道的正常皮质脊髓分支相同（匡和卡利尔：《比较神经学杂志》292:585-598，1990年），即来自体感皮层的轴突仅投射到背角，来自运动皮层的轴突仅支配腹角，并且正常的前肢和后肢地形得以保留。芽生纤维也具有正常的分支模式。对发育中的皮质脊髓分支的平行研究表明，芽生不能归因于早期双侧连接的维持或扩展。这些结果表明，局部信号，很可能类似于那些控制正常皮质脊髓发育的信号，引发皮质脊髓芽生并决定轴突分支的特异性。
