PDF(Pubmed)
Abstract：
The neuromuscular junction (NMJ) mediates neural control of skeletal muscle fibers. Neurotrophic signaling, specifically brain derived neurotrophic factor (BDNF) acting through its high-affinity tropomyosin related kinase B (TrkB) receptor is known to improve neuromuscular transmission. BDNF/TrkB signaling also maintains the integrity of antero- and retrograde communication between the motor neuron soma, its distal axons and pre-synaptic terminals and influences neuromuscular transmission. In this study, we employed a novel rat chemogenetic mutation (TrkB F616), in which a 1-naphthylmethyl phosphoprotein phosphatase 1 (1NMPP1) sensitive knock-in allele allowed specific, rapid and sustained inhibition of TrkB kinase activity. In adult female and male TrkB F616 rats, treatment with either 1NMPP1 (TrkB kinase inhibition) or DMSO (vehicle) was administered in drinking water for 14 days. To assess the extent of neuromuscular transmission failure (NMTF), diaphragm muscle isometric force evoked by nerve stimulation at 40 Hz (330 ms duration trains repeated each s) was compared to isometric forces evoked by superimposed direct muscle stimulation (every 15 s). Chronic TrkB kinase inhibition (1NMPP1 group) markedly worsened NMTF compared to vehicle controls. Acute BDNF treatment did not rescue NMTF in the 1NMPP1 group. Chronic TrkB kinase inhibition did not affect the apposition of pre-synaptic terminals (labeled with synaptophysin) and post-synaptic endplates (labeled with α-Bungarotoxin) at diaphragm NMJs. We conclude that inhibition of BDNF/TrkB signaling in TrkB F616 rats disrupts diaphragm neuromuscular transmission in a similar manner to TrkB F616A mice, likely via a pre-synaptic mechanism independent of axonal branch point failure.
摘要：
神经肌肉接头(NMJ)介导骨骼肌纤维的神经控制。神经营养信号,特别是脑源性神经营养因子（BDNF）通过其高亲和力原肌球蛋白相关激酶B（TrkB）受体发挥作用，已知可改善神经肌肉传递。BDNF/TrkB信号还维持运动神经元体细胞之间的前和逆行通信的完整性，其远端轴突和突触前末端并影响神经肌肉传递。在这项研究中,我们采用了一种新的大鼠化学遗传突变(TrkBF616)，其中1-萘甲基磷蛋白磷酸酶1（1NMPP1）敏感的敲入等位基因允许特异性，TrkB激酶活性的快速和持续抑制。在成年雌性和雄性TrkBF616大鼠中，在饮用水中施用1NMPP1(TrkB激酶抑制)或DMSO(媒介物)治疗14天。为了评估神经肌肉传递衰竭（NMTF）的程度，将神经刺激在40Hz（每个s重复330ms的持续时间序列）下引起的diaphragm肌等距力与叠加的直接肌肉刺激（每15s）引起的等距力进行比较。与载体对照相比,慢性TrkB激酶抑制(1NMPP1组)显著恶化NMTF。急性BDNF治疗不能挽救1NMPP1组的NMTF。慢性TrkB激酶抑制不影响突触前终末（用突触素标记）和突触后终板（用α-银环蛇毒素标记）在隔膜NMJ上的并置。我们得出的结论是，在TrkBF616大鼠中抑制BDNF/TrkB信号传导以与TrkBF616A小鼠相似的方式破坏隔膜神经肌肉传递，可能通过独立于轴突分支点衰竭的突触前机制。
