Favero Morgana, Cangiano Alberto, Busetto Giuseppe
Department of Neurological and Movement Sciences, Section of Physiology and Psychology, University of Verona, 37134, Verona, Italy; National Institute of Neuroscience, 37134, Verona, Italy.
PLoS One. 2015 Apr 13;10(4):e0123576. doi: 10.1371/journal.pone.0123576. eCollection 2015.
Gap junctions (GJs) between neurons are present in both the newborn and the adult nervous system, and although important roles have been suggested or demonstrated in a number of instances, in many other cases a full understanding of their physiological role is still missing. GJs are expressed in the rodent lumbar cord at birth and mediate both dye and electrical coupling between motor neurons. This expression has been proposed to mediate: (i) fast synchronization of motoneuronal spike activity, in turn linked to the process of refinement of neuromuscular connections, and (ii) slow synchronization of locomotor-like oscillatory activity. Soon after birth this coupling disappears. Since in the adult rat regeneration of motor fibers after peripheral nerve injury leads to a recapitulation of synaptic refinement at the target muscles, we tested whether GJs between motor neurons are transiently re-expressed. We found that in conditions of maximal responsiveness of lumbar motor neurons (such as no depression by anesthetics, decerebrate release of activity of subsets of motor neurons, use of temporal and spatial summation by antidromic and orthodromic stimulations, testing of large ensembles of motor neurons) no firing is observed in ventral root axons in response to antidromic spike invasion of nearby counterparts. We conclude that junctional coupling between motor neurons is not required for the refinement of neuromuscular innervation in the adult.
神经元之间的缝隙连接（GJs）在新生和成年神经系统中均有存在，尽管在许多情况下已表明或证实了其重要作用，但在许多其他情况下，对其生理作用仍缺乏全面了解。缝隙连接在出生时即在啮齿动物的腰髓中表达，并介导运动神经元之间的染料耦合和电耦合。这种表达被认为介导了：（i）运动神经元动作电位活动的快速同步，这又与神经肌肉连接的精细化过程相关；（ii）类似运动的振荡活动的缓慢同步。出生后不久这种耦合就消失了。由于成年大鼠外周神经损伤后运动纤维的再生会导致靶肌肉突触精细化的重现，我们测试了运动神经元之间的缝隙连接是否会短暂重新表达。我们发现，在腰段运动神经元最大反应性的条件下（如未被麻醉剂抑制、运动神经元亚群的去大脑释放活动、通过逆向和正向刺激进行时间和空间总和、测试大量运动神经元），对附近对应神经元的逆向动作电位入侵，腹根轴突未观察到放电。我们得出结论，成年期神经肌肉支配的精细化不需要运动神经元之间的连接耦合。
