Callaway E M, Soha J M, Van Essen D C
Nature. 1987;328(6129):422-6. doi: 10.1038/328422a0.
During normal postnatal maturation, mammalian muscles undergo an orderly process of synapse elimination, whereby each muscle fibre loses all but one of the multiple inputs with which it is endowed at birth. Experimental perturbations that increase or decrease the overall activity of nerve and/or muscle cause a corresponding increase or decrease in the overall rate of neuromuscular synapse elimination. On other grounds it has been suggested that competition among motor neurons is important in determining which synapses survive and which are eliminated. Would a difference in activity among the terminals at the same endplate affect the outcome of the competition and not just its rate? We investigated this issue by blocking activity for four days in a small fraction of the motor neurons innervating the neonatal rabbit soleus muscle. Twitch tensions of motor units were subsequently measured for both the active and inactive populations of neurons to assess whether the inactive neurons had lost fewer or more synapses than is normal. We found that inactive motor neurons have a significant advantage compared to active counterparts in control experiments, a finding opposite to that expected if the neuromuscular junction operated by classical 'Hebbian' rules of competition.
在出生后的正常发育过程中，哺乳动物的肌肉会经历一个有序的突触消除过程，在此过程中，每条肌纤维会失去其在出生时所具有的多个输入中的所有输入，仅保留一个。增加或减少神经和/或肌肉整体活动的实验性干扰会导致神经肌肉突触消除的整体速率相应增加或减少。基于其他理由，有人提出运动神经元之间的竞争对于决定哪些突触存活以及哪些突触被消除很重要。同一终板上的神经末梢之间的活动差异会影响竞争的结果，而不仅仅是其速率吗？我们通过在支配新生兔比目鱼肌的一小部分运动神经元中阻断活动四天来研究这个问题。随后测量了活动和不活动神经元群体的运动单位的抽搐张力，以评估不活动的神经元是否比正常情况失去了更少或更多的突触。我们发现，与对照实验中的活动神经元相比，不活动的运动神经元具有显著优势，这一发现与如果神经肌肉接头按照经典的“赫布”竞争规则运作所预期的结果相反。
