Personius K E, Arbas E A
Physiological Sciences Graduate Program and ARL Division of Neurobiology, University of Arizona, Tucson 85721, USA.
J Neurobiol. 1998 Sep 15;36(4):497-508.
Muscle depends upon innervation and contraction to maintain a differentiated state. Denervation can therefore induce muscle atrophy. In grasshoppers, muscle degeneration can also be triggered by the severing of a leg during autotomy. In this case, the muscles that degenerate are neither damaged nor denervated. This phenomenon suggests the existence of transneuronal mechanisms that influence muscle survival. To characterize this autotomy-induced process, we studied the degeneration of a thoracic tergotrochanteral depressor muscle (M#133b,c) subsequent to the shedding of a hindlimb in the grasshoppers Barytettix psolus and Barytettix humphreysii. Both histochemical and electrophysiological methods were used to follow muscle degeneration 1, 3, 5, 10, and 15 days postautotomy. Muscle fibers began to show denervation-like electrophysiological changes (i.e., depolarized resting membrane potentials and postinhibitory rebound) as soon as 3 days postautotomy. By 10 days, significant muscle degeneration was evident and electrophysiological changes were found in all animals tested. Muscle anatomical degeneration was not induced by synaptic transmission failure, because neuromuscular transmission was maintained in most fibers. The rate of muscle degeneration was not constant. Between 1 and 10 days, mean fiber cross-sectional area did not change on the autotomized side, although this is normally a time of muscle growth. However after 10 days, cross-sectional area became drastically reduced and the number of muscle fibers within M#133b,c was decreased. The variability in rate of fiber degeneration was not dependent upon fiber type, since M#133b,c only contains fast-type fibers.
肌肉依赖神经支配和收缩来维持分化状态。因此，去神经支配可导致肌肉萎缩。在蚱蜢中，自切过程中腿部的切断也可引发肌肉退化。在这种情况下，退化的肌肉既未受损也未去神经支配。这种现象表明存在影响肌肉存活的跨神经元机制。为了描述这种自切诱导的过程，我们研究了蚱蜢Barytettix psolus和Barytettix humphreysii后肢脱落后背胸转子降肌（M#133b、c）的退化情况。在自切后1、3、5、10和15天，使用组织化学和电生理方法追踪肌肉退化情况。自切后3天，肌肉纤维就开始出现类似去神经支配的电生理变化（即静息膜电位去极化和抑制后反弹）。到10天时，明显的肌肉退化很明显，并且在所有测试动物中都发现了电生理变化。肌肉解剖学退化不是由突触传递失败引起的，因为大多数纤维中的神经肌肉传递得以维持。肌肉退化的速度并不恒定。在1至10天之间，自切侧的平均纤维横截面积没有变化，尽管这通常是肌肉生长的时期。然而，10天后，横截面积急剧减小，M#133b、c内的肌肉纤维数量减少。纤维退化速度的变异性不取决于纤维类型，因为M#133b、c仅包含快肌纤维。
