Intrinsic properties of neurons are one major determinant for how neurons respond to their synaptic inputs and shape their outputs in neural circuits. Here, we studied the intrinsic properties of neurons in the chicken posterior portion of the dorsal nucleus of the lateral lemniscus (LLDp), the first interaural level difference (ILD) encoder of the avian auditory pathway. Using whole-cell recordings in brain slices, we revealed that the LLDp is composed of a heterogeneous neuron population based on their firing patterns. LLDp neurons were broadly classified as either phasic or tonic firing neurons, with further classification applied to tonic firing neurons, such as regular (most dominant, n=82 out of 125 cells, 65.6%), pauser, or adaptive firing. Neurons with different firing patterns were distributed about evenly across the dorsoventral as well as mediolateral axis of LLDp. Phasic firing neurons were of faster membrane time constant, and lower excitability than tonic firing neurons. The action potentials (APs) elicited at the current thresholds displayed significant differences in first spike latency, AP peak amplitude, half-width, and maximal rising and falling rates. Interestingly, for APs elicited at suprathreshold currents (400 pA above thresholds), some of the differences diminished while a few others emerged. Remarkably, most parameters of the APs at thresholds were significantly different from those of APs at suprathresholds. Combined with our previous study (Curry and Lu, 2016), the results lend support to the two-cell type model for ILD coding in the avian system.

神经元的内在特性是神经元如何响应其突触输入并在神经回路中塑造其输出的主要决定因素之一。在这里，我们研究了鸡外侧丘系背核 (LLDp) 后部神经元的内在特性，这是鸟类听觉通路的第一个耳间水平差 (ILD) 编码器。使用脑切片中的全细胞记录，我们发现 LLDp 由基于其放电模式的异质神经元群体组成。LLDp 神经元被广泛分为阶段性或强直性放电神经元，进一步分类适用于强直性放电神经元，例如常规（125 个细胞中 n = 82，65.6%）、暂停或自适应放电。具有不同放电模式的神经元均匀分布在 LLDp 的背腹轴和中间轴上。阶段性放电神经元具有更快的膜时间常数，并且比强直性放电神经元具有更低的兴奋性。在当前阈值处引发的动作电位 (AP) 在第一次尖峰潜伏期、AP 峰值幅度、半宽度和最大上升和下降率方面显示出显着差异。有趣的是，对于以超阈值电流（高于阈值 400 pA）引发的 AP，一些差异减少了，而其他一些差异出现了。值得注意的是，大多数阈值 AP 的参数与超阈值 AP 的参数显着不同。结合我们之前的研究（Curry 和 Lu，2016），结果为鸟类系统中 ILD 编码的双细胞类型模型提供了支持。