Auditory Neurophysiology Group, Department of Chemosensation, RWTH Aachen University, Aachen, Germany.
J Neurophysiol. 2021 Mar 1;125(3):915-937. doi: 10.1152/jn.00331.2020. Epub 2021 Jan 20.
Spherical bushy cells (SBCs) in the anteroventral cochlear nucleus receive a single or very few powerful axosomatic inputs from the auditory nerve. However, SBCs are also contacted by small regular bouton synapses of the auditory nerve, located in their dendritic tree. The function of these small inputs is unknown. It was speculated that the interaction of axosomatic inputs with small dendritic inputs improved temporal precision, but direct evidence for this is missing. In a compartment model of spherical bushy cells with a stylized or realistic three-dimensional (3-D) representation of the bushy dendrite, we explored this hypothesis. Phase-locked dendritic inputs caused both tonic depolarization and a modulation of the model SBC membrane potential at the frequency of the stimulus. For plausible model parameters, dendritic inputs were subthreshold. Instead, the tonic depolarization increased the excitability of the SBC model and the modulation of the membrane potential caused a phase-dependent increase in the efficacy of the main axosomatic input. This improved response rate and entrainment for low-input frequencies and temporal precision of output at and above the characteristic frequency. A careful exploration of morphological and biophysical parameters of the bushy dendrite suggested a functional explanation for the peculiar shape of the bushy dendrite. Our model for the first time directly implied a role for the small excitatory dendritic inputs in auditory processing: they modulate the efficacy of the main input and are thus a plausible mechanism for the improvement of temporal precision and fidelity in these central auditory neurons. We modeled dendritic inputs from the auditory nerve that spherical bushy cells of the cochlear nucleus receive. Dendritic inputs caused both tonic depolarization and modulation of the membrane potential at the input frequency. This improved the rate, entrainment, and temporal precision of output action potentials. Our simulations suggest a role for small dendritic inputs in auditory processing: they modulate the efficacy of the main input supporting temporal precision and fidelity in these central auditory neurons.
球周细胞（SBC）在前庭耳蜗核接受来自听神经的单个或少数几个强大的轴体细胞输入。然而，SBC 也被听神经的小规则bouton 突触接触，位于其树突中。这些小输入的功能尚不清楚。有人推测，轴体细胞输入与小树突输入的相互作用提高了时间精度，但缺乏直接证据。在具有球周树突的理想化或现实的三维（3-D）表示的球周细胞模型中，我们探索了这一假说。锁定相位的树突输入导致模型 SBC 膜电位在刺激频率处产生紧张性去极化和调制。对于合理的模型参数，树突输入处于亚阈值。相反，紧张性去极化增加了 SBC 模型的兴奋性，而膜电位的调制导致主要轴体细胞输入的功效随相位的增加而增加。这提高了低输入频率的响应率和同步性，以及特征频率以上的输出的时间精度。对树突形态和生物物理参数的仔细探索为球周树突的奇特形状提供了功能解释。我们的模型首次直接暗示了小兴奋性树突输入在听觉处理中的作用：它们调节主要输入的功效，因此是提高这些中枢听觉神经元时间精度和保真度的合理机制。我们模拟了听神经对耳蜗核球周细胞的输入。树突输入导致紧张性去极化和输入频率的膜电位调制。这提高了输出动作电位的速率、同步性和时间精度。我们的模拟表明，小树突输入在听觉处理中发挥作用：它们调节主要输入的功效，支持这些中枢听觉神经元的时间精度和保真度。
