Acute hyperbilirubinaemia induces presynaptic neurodegeneration at a central glutamatergic synapse
Acute hyperbilirubinaemia induces presynaptic neurodegeneration at a central glutamatergic synapse
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DOI：
10.1113/jphysiol.2010.199778
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发表时间：
2010-12-01
影响因子：
5.5
通讯作者：
Forsythe, Ian D.
中科院分区：
文献类型：
--
作者：
Haustein, Martin D.;Read, David J.;Forsythe, Ian D.
高胆红素血症和儿科听力损失之间存在明确的联系，但细胞机制尚未阐明。在这里，我们使用高胆红素血症的古恩大鼠模型来研究胆红素引起的听力损失。在体内的听觉脑干反应显示，古恩大鼠有严重的听觉缺陷在18小时内暴露于高胆红素水平。使用这些大鼠的听觉脑干的体外制备，从斜方体内侧核（MNTB）的细胞外多电极阵列记录显示胆红素暴露后诱发场电位的潜伏期较长，振幅降低，提示在此突触中继传输失败。全细胞膜片钳记录证实，突触后MNTB神经元的电生理特性不受胆红素的影响，动作电位波形或电流-电压关系没有变化。然而，刺激的梯形体是无法引起大calycal EPSCs在高胆红素血症大鼠的MNTB神经元，表明在突触前部位的损害。顺行标记的肾盏投射的多光子成像显示MNTB主要神经元胞体周围的轴突染色和突触前分布。诱导高胆红素血症后，巨大的突触大部分被破坏。电子显微镜检查证实突触前盏终端的损失，并支持健康的突触后神经元的电生理证据。MNTB神经元表达高水平的神经元型一氧化氮合酶（nNOS）。一氧化氮与大脑其他部位的胆红素毒性机制有关，7-硝基吲唑对nNOS的拮抗作用可在胆红素暴露期间保护听力。我们的结论是，胆红素引起的耳聋是由于在听觉脑干兴奋性突触末梢的变性。
There is a well-established link between hyperbilirubinaemia and hearing loss in paediatrics, but the cellular mechanisms have not been elucidated. Here we used the Gunn rat model of hyperbilirubinaemia to investigate bilirubin-induced hearing loss. In vivo auditory brainstem responses revealed that Gunn rats have severe auditory deficits within 18 h of exposure to high bilirubin levels. Using an in vitro preparation of the auditory brainstem from these rats, extracellular multi-electrode array recording from the medial nucleus of the trapezoid body (MNTB) showed longer latency and decreased amplitude of evoked field potentials following bilirubin exposure, suggestive of transmission failure at this synaptic relay. Whole-cell patch-clamp recordings confirmed that the electrophysiological properties of the postsynaptic MNTB neurons were unaffected by bilirubin, with no change in action potential waveforms or current-voltage relationships. However, stimulation of the trapezoid body was unable to elicit large calyceal EPSCs in MNTB neurons of hyperbilirubinaemic rats, indicative of damage at a presynaptic site. Multi-photon imaging of anterograde-labelled calyceal projections revealed axonal staining and presynaptic profiles around MNTB principal neuron somata. Following induction of hyperbilirubinaemia the giant synapses were largely destroyed. Electron microscopy confirmed loss of presynaptic calyceal terminals and supported the electrophysiological evidence for healthy postsynaptic neurons. MNTB neurons express high levels of neuronal nitric oxide synthase (nNOS). Nitric oxide has been implicated in mechanisms of bilirubin toxicity elsewhere in the brain, and antagonism of nNOS by 7-nitroindazole protected hearing during bilirubin exposure. We conclude that bilirubin-induced deafness is caused by degeneration of excitatory synaptic terminals in the auditory brainstem.