Jacob J M, Robbins N
Center for Neurosciences, Case Western Reserve University, Cleveland, Ohio 44106.
J Neurosci. 1990 May;10(5):1522-9. doi: 10.1523/JNEUROSCI.10-05-01522.1990.
The response of the neuromuscular junction to expansion of the motor unit after partial denervation (section of L5 root) was compared in soleus muscles from young (5-8 month) and old (25-30 month) mice. The object was to determine the relative capacity of young and old motor neurons to adapt to an enlarged functional field of innervation, and to delineate physiological parameters that are compromised under these conditions. Neuromuscular function was studied at 30, 60, and 120 d after partial denervation. The initial (18-23) and postoperative number (5-8) of motor units was the same in both age groups. Twitch strength declined in proportion to loss of motor units at 30 d but returned completely (young) or nearly completely (old) by 60 d. In old but not young muscle, the safety factor (assayed by twitch depression in low calcium) was decreased even before functional sprouting had occurred, indicating a reduced safety factor in nondenervated junctions. The proportion of fibers with "long" latencies (delay between stimulation and endplate potential) increased transiently (at 30 d) in young muscle but persisted without recovery at 120 d in regenerated junctions in old muscle. After partial denervation, decline in miniature endplate potential (mepp) amplitude, in mepp frequency, and in estimated quantal content of evoked release was relatively more pronounced in old than in young mice, and in the case of mepp amplitude and frequency, more persistent. Mepp amplitude was also decreased in presumed nondenervated junctions of old muscles.(ABSTRACT TRUNCATED AT 250 WORDS)
在年轻（5 - 8个月）和老年（25 - 30个月）小鼠的比目鱼肌中，比较了部分去神经支配（L5神经根切断）后神经肌肉接头对运动单位扩张的反应。目的是确定年轻和老年运动神经元适应扩大的神经支配功能区域的相对能力，并描绘在这些条件下受损的生理参数。在部分去神经支配后的30、60和120天研究神经肌肉功能。两个年龄组的初始（18 - 23个）和术后运动单位数量（5 - 8个）相同。30天时，抽搐强度与运动单位的丧失成比例下降，但到60天时完全恢复（年轻小鼠）或几乎完全恢复（老年小鼠）。在老年而非年轻肌肉中，甚至在功能性发芽发生之前，安全系数（通过低钙时的抽搐抑制测定）就降低了，这表明未去神经支配的接头处安全系数降低。年轻肌肉中具有“长”潜伏期（刺激与终板电位之间的延迟）的纤维比例在30天时短暂增加，但在老年肌肉再生接头中，120天时持续存在且未恢复。部分去神经支配后，老年小鼠的微小终板电位（mepp）幅度、mepp频率以及诱发释放的估计量子含量的下降比年轻小鼠相对更明显，就mepp幅度和频率而言，下降更持久。老年肌肉假定未去神经支配的接头处mepp幅度也降低。（摘要截断于250字）
