Astrow S H, Pitaevski V, Herrera A A
Department of Biological Sciences, University of Southern California, Los Angeles 90089-2520, USA.
J Neurosci. 1996 Aug 15;16(16):5130-40. doi: 10.1523/JNEUROSCI.16-16-05130.1996.
Repeated in vivo observations were used to study regenerated nerve terminals in neuromuscular junctions of the adult frog Rana pipiens. Sartorius junctions in living animals were stained with the fluorescent vital dye RH414 and viewed with video fluorescence microscopy. Each junction was observed in the intact muscle and then again 7, 10, and 13 weeks after nerve crush. At 13 weeks, junctions were determined to be mono- or polyneuronally innervated using intracellular recording. Between 7 and 13 weeks, most identified junctions were reinnervated less precisely and completely than described previously. Although some of the original synaptic gutters were reoccupied by regenerated terminal branches, other gutters were only partially occupied, and many appeared abandoned. Junctions showing precise recapitulation of original terminal arborizations comprised a small number of the total examined, as did those where reinnervation was very imprecise. Striking differences in the precision of reinnervation were found within the muscle such that distal terminals regenerated more precisely and completely than did proximal terminals. Terminals in reinnervated muscles were more dynamic than terminals in unoperated muscles over equivalent times. In singly innervated junctions, terminal growth was favored over regression. In doubly innervated junctions, regressive events were more common. Imprecise reinnervation is explained in terms of multisite innervation of muscle fibers and the activity dependence of synaptic stability. We hypothesize that when axons reinnervate the second or third junctions on a fiber, they do so less precisely, because the activity restored by reinnervation of the first junction renders later sites less attractive or less stable.
通过重复的体内观察来研究成年北美豹蛙神经肌肉接头处再生的神经末梢。用荧光活性染料RH414对活体动物的缝匠肌接头进行染色，并通过视频荧光显微镜观察。在完整肌肉中观察每个接头，然后在神经挤压后7周、10周和13周再次观察。在13周时，使用细胞内记录确定接头是单神经元还是多神经元支配。在7至13周之间，大多数已识别的接头重新支配的精确性和完整性低于先前描述的情况。虽然一些原来的突触沟被再生的终末分支重新占据，但其他沟只是部分被占据，许多似乎被遗弃了。显示精确重现原始终末分支的接头占总检查接头的少数，重新支配非常不精确的接头也是如此。在肌肉内发现重新支配的精确性存在显著差异，即远端终末比近端终末再生得更精确和完整。在相同时间内，重新支配肌肉中的终末比未手术肌肉中的终末更具动态性。在单神经元支配的接头中，终末生长比消退更受青睐。在双神经元支配的接头中，消退事件更常见。不精确的重新支配可以用肌纤维的多位点支配和突触稳定性的活动依赖性来解释。我们假设，当轴突重新支配纤维上的第二个或第三个接头时，它们的精确性较低，因为第一个接头重新支配恢复的活动使后续位点吸引力降低或稳定性降低。
