Cochlear neurons innervate the brainstem cochlear nucleus in a tonotopic fashion according to their sensitivity to different sound frequencies (known as the neuron’s characteristic frequency). It is unclear whether these neurons with distinct characteristic frequencies use different strategies to innervate the cochlear nucleus. Here, we use genetic approaches to differentially label spiral ganglion neurons (SGNs) and their auditory nerve fibers (ANFs) that relay different characteristic frequencies in mice. We found that SGN populations that supply distinct regions of the cochlea employ different cellular strategies to target and innervate neurons in the cochlear nucleus during tonotopic map formation. ANFs that will exhibit high-characteristic frequencies initially overshoot and sample a large area of targets before refining their connections to correct targets, while fibers that will exhibit low-characteristic frequencies are more accurate in initial targeting and undergo minimal target sampling. Moreover, similar to their peripheral projections, the central projections of ANFs show a gradient of development along the tonotopic axis, with outgrowth and branching of prospective high-frequency ANFs initiated about two days earlier than those of prospective low-frequency ANFs. The processes of synaptogenesis are similar between high- and low-frequency ANFs, but a higher proportion of low-frequency ANFs form smaller endbulb synaptic endings. These observations reveal the diversity of cellular mechanisms that auditory neurons that will become functionally distinct use to innervate their targets during tonotopic map formation.

耳蜗神经元根据它们对不同声音频率（称为神经元的特征频率）的敏感性以音调方式支配脑干耳蜗核。目前尚不清楚这些具有不同特征频率的神经元是否使用不同的策略来支配耳蜗核。在这里，我们使用遗传方法来差异标记螺旋神经节神经元 (SGN) 及其在小鼠中传递不同特征频率的听觉神经纤维 (ANF)。我们发现提供耳蜗不同区域的 SGN 种群采用不同的细胞策略在音调图形成期间靶向和支配耳蜗核中的神经元。表现出高特征频率的 ANF 最初会超调并对大面积目标进行采样，然后再将它们的连接细化为正确的目标，而表现出低特征频率的光纤在初始瞄准时更准确，并且进行的目标采样最少。此外，与其外围投影类似，ANF 的中心投影显示出沿音调轴的发展梯度，预期高频 ANF 的生长和分支比预期低频 ANF 早两天开始。高频和低频 ANF 的突触发生过程相似，但较高比例的低频 ANF 形成较小的球泡突触末梢。