Friauf Eckhard, Fischer Alexander U, Fuhr Martin F
Animal Physiology Group, Department of Biology, University of Kaiserslautern, Postfach 3049, 67653, Kaiserslautern, Germany,
Cell Tissue Res. 2015 Jul;361(1):177-213. doi: 10.1007/s00441-015-2176-x. Epub 2015 Apr 21.
Synaptic transmission via chemical synapses is dynamic, i.e., the strength of postsynaptic responses may change considerably in response to repeated synaptic activation. Synaptic strength is increased during facilitation, augmentation and potentiation, whereas a decrease in synaptic strength is characteristic for depression and attenuation. This review attempts to discuss the literature on short-term and long-term synaptic plasticity in the auditory brainstem of mammals and birds. One hallmark of the auditory system, particularly the inner ear and lower brainstem stations, is information transfer through neurons that fire action potentials at very high frequency, thereby activating synapses >500 times per second. Some auditory synapses display morphological specializations of the presynaptic terminals, e.g., calyceal extensions, whereas other auditory synapses do not. The review focuses on short-term depression and short-term facilitation, i.e., plastic changes with durations in the millisecond range. Other types of short-term synaptic plasticity, e.g., posttetanic potentiation and depolarization-induced suppression of excitation, will be discussed much more briefly. The same holds true for subtypes of long-term plasticity, like prolonged depolarizations and spike-time-dependent plasticity. We also address forms of plasticity in the auditory brainstem that do not comprise synaptic plasticity in a strict sense, namely short-term suppression, paired tone facilitation, short-term adaptation, synaptic adaptation and neural adaptation. Finally, we perform a meta-analysis of 61 studies in which short-term depression (STD) in the auditory system is opposed to short-term depression at non-auditory synapses in order to compare high-frequency neurons with those that fire action potentials at a lower rate. This meta-analysis reveals considerably less STD in most auditory synapses than in non-auditory ones, enabling reliable, failure-free synaptic transmission even at frequencies >100 Hz. Surprisingly, the calyx of Held, arguably the best-investigated synapse in the central nervous system, depresses most robustly. It will be exciting to reveal the molecular mechanisms that set high-fidelity synapses apart from other synapses that function much less reliably.
通过化学突触的突触传递是动态的，即突触后反应的强度可能会因反复的突触激活而发生显著变化。在易化、增强和强化过程中突触强度增加，而突触强度降低则是抑制和衰减的特征。本综述试图讨论关于哺乳动物和鸟类听觉脑干中短期和长期突触可塑性的文献。听觉系统的一个标志，特别是内耳和低位脑干区域，是通过以非常高的频率发放动作电位的神经元进行信息传递，从而每秒激活突触超过500次。一些听觉突触在突触前终末表现出形态学特化，例如杯状延伸，而其他听觉突触则没有。本综述重点关注短期抑制和短期易化，即持续时间在毫秒范围内的可塑性变化。其他类型的短期突触可塑性，例如强直后增强和去极化诱导的兴奋抑制，将更简要地讨论。长期可塑性的亚型，如延长的去极化和放电时间依赖性可塑性也是如此。我们还讨论了听觉脑干中严格意义上不包括突触可塑性的可塑性形式，即短期抑制、配对音易化、短期适应、突触适应和神经适应。最后，我们对61项研究进行了荟萃分析，其中比较了听觉系统中的短期抑制与非听觉突触处的短期抑制，以便将高频神经元与以较低频率发放动作电位的神经元进行比较。该荟萃分析表明，大多数听觉突触中的短期抑制比非听觉突触中的要少得多，即使在频率>100Hz时也能实现可靠的、无故障的突触传递。令人惊讶的是，Held壶腹，可说是中枢神经系统中研究得最透彻的突触，其抑制作用最为强烈。揭示使高保真突触与其他功能可靠性低得多的突触区分开来的分子机制将是令人兴奋的。
