Spherical bushy cells (SBCs) in the 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 3D-representation of the bushy dendrite we thus explored this proposal. 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 rate, entrainment and temporal precision of output action potentials. However, these effects showed differential dependency on the stimulus 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.

中文翻译：

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小树突触增强了耳蜗核浓密细胞模型中的时间编码

前腹耳蜗核中的球形丛状细胞 (SBC) 接受来自听觉神经的单个或极少数强大的轴突输入。然而，SBC 也与位于其树突树中的听觉神经的小规则 bouton 突触接触。这些小输入的功能是未知的。据推测，轴突输入与小树突输入的相互作用提高了时间精度，但缺少直接证据。在球形浓密细胞的隔室模型中，我们因此探索了这个提议。锁相树突输入导致强直去极化和刺激频率下模型 SBC 膜电位的调制。对于似是而非的模型参数，树突输入是亚阈值。反而，强直去极化增加了 SBC 模型的兴奋性，并且膜电位的调制导致主要轴突输入的功效的相位依赖性增加。这提高了输出动作电位的速率、夹带和时间精度。然而，这些影响显示出对刺激频率的不同依赖性。对浓密树突的形态学和生物物理参数的仔细探索提出了对浓密树突奇特形状的功能解释。我们的模型首次直接暗示了小的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的时间精度和保真度的合理机制。