Unitat d'Histologia i Neurobiologia (UHN), Facultat de Medicina i Ciències de la Salut, Universitat Rovira i Virgili, Carrer Sant Llorenç, Spain.
J Neurosci Res. 2010 May 15;88(7):1406-19. doi: 10.1002/jnr.22320.
We use immunohistochemistry to describe the localization of brain-derived neurotrophic factor (BDNF) and its receptors trkB and p75(NTR) in the neuromuscular synapses of postnatal rats (P6-P7) during the synapse elimination period. The receptor protein p75(NTR) is present in the nerve terminal, muscle cell and glial Schwann cell whereas BDNF and trkB proteins can be detected mainly in the pre- and postsynaptic elements. Exogenously applied BDNF (10 nM for 3 hr or 50 nM for 1 hr) increases ACh release from singly and dually innervated synapses. This effect may be specific for BDNF because the neurotrophin NT-4 (2-8 nM) does not modulate release at P6-P7. Blocking the receptors trkB and p75(NTR) (with K-252a and anti-p75-192-IgG, respectively) completely abolishes the potentiating effect of exogenous BDNF. In addition, exogenous BDNF transiently recruits functionally depressed silent terminals, and this effect seems to be mediated by trkB. Calcium ions, the L-type voltage-dependent calcium channels and protein kinase C are involved in BDNF-mediated nerve ending recruitment. Blocking experiments suggest that endogenous BDNF could operate through p75(NTR) receptors coupled to potentiate ACh release in all nerve terminals because the anti-p75-192-IgG reduces release. However, blocking the trkB receptor (K-252a) or neutralizing endogenous BDNF with the trkB-IgG fusion protein reveals a trkB-mediated release inhibition on almost mature strong endings in dual junctions. Taken together these results suggest that a BDNF-induced p75(NTR)-mediated ACh release potentiating mechanism and a BDNF-induced trkB-mediated release inhibitory mechanism may contribute to developmental synapse disconnection.
我们利用免疫组织化学方法描述了脑源性神经营养因子（BDNF）及其受体 trkB 和 p75（NTR）在突触消除期出生后大鼠（P6-P7）的神经肌肉突触中的定位。受体蛋白 p75（NTR）存在于神经末梢、肌肉细胞和神经胶质雪旺细胞中，而 BDNF 和 trkB 蛋白主要存在于突触前和突触后成分中。外源性 BDNF（10 nM 作用 3 小时或 50 nM 作用 1 小时）可增加单和双支配突触的 ACh 释放。这种效应可能是 BDNF 特异性的，因为神经营养因子 NT-4（2-8 nM）在 P6-P7 时不会调节释放。阻断受体 trkB 和 p75（NTR）（分别用 K-252a 和抗 p75-192-IgG）完全消除外源性 BDNF 的增强作用。此外，外源性 BDNF 短暂募集功能抑制的沉默终末，这种效应似乎是由 trkB 介导的。钙离子、L 型电压依赖性钙通道和蛋白激酶 C 参与 BDNF 介导的神经末梢募集。阻断实验表明，内源性 BDNF 可能通过与增强所有神经末梢 ACh 释放相关的 p75（NTR）受体起作用，因为抗 p75-192-IgG 降低了释放。然而，阻断 trkB 受体（K-252a）或用 trkB-IgG 融合蛋白中和内源性 BDNF 会揭示在双结中几乎成熟的强终末上 trkB 介导的释放抑制。综上所述，这些结果表明，BDNF 诱导的 p75（NTR）介导的 ACh 释放增强机制和 BDNF 诱导的 trkB 介导的释放抑制机制可能有助于发育性突触分离。
