Centre for the Neural Basis of Hearing, The Physiological Laboratory, Downing Street, Cambridge, United Kingdom.
PLoS One. 2018 Oct 4;13(10):e0203712. doi: 10.1371/journal.pone.0203712. eCollection 2018.
The presence of 'giant' synapses in the auditory brainstem is thought to be a specialization designed to encode temporal information to support perception of pitch, frequency, and sound-source localisation. These 'giant' synapses have been found in the ventral cochlear nucleus, the medial nucleus of the trapezoid body and the ventral nucleus of the lateral lemniscus. An interpretation of these synapses as simple relays has, however, been challenged by the observation in the gerbil that the action potential frequently fails in the ventral cochlear nucleus. Given the prominence of these synapses it is important to establish whether this phenomenon is unique to the gerbil or can be observed in other species. Here we examine the responses of units, thought to be the output of neurons in receipt of 'giant' synaptic endings, in the ventral cochlear nucleus and the medial nucleus of the trapezoid body in the guinea pig. We found that failure of the action-potential component, recorded from cells in the ventral cochlear nucleus, occurred in ~60% of spike waveforms when recording spontaneous activity. In the medial nucleus of the trapezoid body, we did not find evidence for action-potential failure. In the ventral cochlear nucleus action-potential failures transform the receptive field between input and output of bushy cells. Additionally, the action-potential failures result in "non-primary-like" temporal-adaptation patterns. This is important for computational models of the auditory system, which commonly assume the responses of ventral cochlear nucleus bushy cells are very similar to their "primary like" auditory-nerve-fibre inputs.
听觉脑干中“巨大”突触的存在被认为是一种专门化的结构，旨在编码时间信息，以支持对音高、频率和声源定位的感知。这些“巨大”突触存在于耳蜗腹核、斜方体束内侧核和外侧丘系腹核中。然而，这些突触作为简单中继的解释受到了挑战，因为在沙鼠中的观察表明，动作电位在耳蜗腹核中经常失败。鉴于这些突触的重要性，重要的是要确定这种现象是否仅存在于沙鼠中，还是可以在其他物种中观察到。在这里，我们检查了被认为是接收“巨大”突触末梢神经元输出的单位在豚鼠耳蜗腹核和斜方体束内侧核中的反应。我们发现，当记录自发活动时，来自耳蜗腹核细胞的动作电位成分的失败发生在约 60%的尖峰波形中。在斜方体束内侧核中，我们没有发现动作电位失败的证据。在耳蜗腹核中，动作电位失败会改变丛状细胞输入和输出之间的感受野。此外，动作电位失败会导致“非原发性”的时间适应模式。这对于听觉系统的计算模型很重要，因为这些模型通常假设耳蜗腹核丛状细胞的反应与其“原发性”听觉神经纤维输入非常相似。
