The lateral lemniscus encompasses processing stages for binaural hearing, suppressing spurious frequencies and frequency integration. Within the lemniscal fibres three nuclei can be identified, termed after their location as dorsal, intermediate and ventral nucleus of the lateral lemniscus (DNLL, INLL and VNLL). While the DNLL and VNLL have been functionally and anatomically characterized, less is known about INLL neurons. Here, we quantitatively describe the morphology, the cellular orientation and distribution of synaptic contact sites along dendrites in mature Mongolian gerbils. INLL neurons are largely non-inhibitory and morphologically heterogeneous with an overall perpendicular orientation regarding the lemniscal fibers. Dendritic ranges are heterogeneous and can extend beyond the nucleus border. INLL neurons receive VGluT1/2 containing glutamatergic and a mix of GABA- and glycinergic inputs distributed over the entire dendrite. Input counts suggest that numbers of excitatory exceed the inhibitory contact sites. Axonal projections indicate connectivity to ascending and descending auditory structures. Our data show that INLL neurons form a morphologically heterogeneous continuum and incoming auditory information is processed on thin dendrites of various length and biased to perpendicular orientation. Together with the different axonal projection patterns, this indicates that the INLL is a highly complex structure that might hold many unexplored auditory functions.

外侧丘系包括双耳听力、抑制杂散频率和频率积分的处理阶段。在丘系纤维内，可以识别三个核，根据其位置称为外侧丘系的背核、中间核和腹核（DNLL、INLL 和 VNLL）。虽然 DNLL 和 VNLL 已在功能和解剖学上得到表征，但人们对 INLL 神经元知之甚少。在这里，我们定量描述了成熟蒙古沙鼠树突突触接触位点的形态、细胞方向和分布。INLL 神经元在很大程度上是非抑制性的且形态异质，总体上垂直于丘系纤维。树突范围是异质的并且可以延伸到核边界之外。INLL 神经元接收 VGluT1/2，其中包含分布在整个树突上的谷氨酸能以及 GABA 和甘氨酸能输入的混合物。输入计数表明兴奋性接触位点的数量超过了抑制性接触位点的数量。轴突投影表明与上升和下降听觉结构的连接。我们的数据表明，INLL 神经元形成形态上异质的连续体，传入的听觉信息在不同长度且偏向垂直方向的薄树突上进行处理。与不同的轴突投影模式一起，这表明 INLL 是一个高度复杂的结构，可能拥有许多未开发的听觉功能。