Excitatory–Inhibitory Synaptic Coupling in Avian Nucleus Magnocellularis
Excitatory–Inhibitory Synaptic Coupling in Avian Nucleus Magnocellularis
复制标题
禽类大细胞核的兴奋性-抑制性突触耦合
作者：
M. Al;Rei Yamada;H. Kuba
神经元的活动由其兴奋性和抑制性突触输入之间的平衡决定。鸟类大细胞核（NM）中的神经元整合来自听觉神经的单突触兴奋性和多突触抑制性输入，并将锁相输出传输到更高的听觉中枢。兴奋性输入按音调分级，使得调谐到更高频率的神经元接收更少但更大的轴突末端。然而，NM 中兴奋性输入和抑制性输入之间的平衡是如何确定的仍然未知。我们在这里检查了刺激两性鸡厚脑片的听觉神经期间 NM 神经元的突触和尖峰反应，发现兴奋-抑制平衡根据音调区域而变化，确保了跨频率的可靠尖峰输出。无论音调区域如何，听觉神经刺激都会在 NM 神经元中引发 IPSC，但 IPSC 对强度的依赖性存在系统性变化。在调谐到低频的神经元中，IPSC 出现并与 EPSC 平行增加，强度升高，这通过防止尖峰生成的饱和来扩大动态范围。另一方面，在调谐到更高频率的神经元中，IPSC 比 EPSC 更小，并且具有更高的激活阈值，从而有利于高保真传输。计算机模拟证实，抑制性输入的这些差异与兴奋性输入的模式最佳匹配，并为听觉系统中广泛的声音强度和频率范围提供适当的神经元输出水平。意义声明 大细胞核中的神经元通过整合来自听觉神经的兴奋性和抑制性突触输入来编码宽强度范围内的声音计时信息，但这种整合的潜在突触机制尚未完全了解。我们在这里表明，兴奋-抑制关系在每个音调区域有不同的表达。在调谐到低频的神经元中，这种关系是线性的，通过防止尖峰生成的饱和来扩大动态范围；相比之下，在调谐到更高频率的神经元中，抑制输入仍然比兴奋输入小得多，从而确保了高保真传输。兴奋性和抑制性输入的音调调节优化了频率和强度的输出，在听觉系统的时序编码通路中发挥着基础作用。
The activity of neurons is determined by the balance between their excitatory and inhibitory synaptic inputs. Neurons in the avian nucleus magnocellularis (NM) integrate monosynaptic excitatory and polysynaptic inhibitory inputs from the auditory nerve, and transmit phase-locked output to higher auditory centers. The excitatory input is graded tonotopically, such that neurons tuned to higher frequency receive fewer, but larger, axon terminals. However, it remains unknown how the balance between excitatory and inhibitory inputs is determined in NM. We here examined synaptic and spike responses of NM neurons during stimulation of the auditory nerve in thick brain slices of chicken of both sexes, and found that the excitatory–inhibitory balance varied according to tonotopic region, ensuring reliable spike output across frequencies. Auditory nerve stimulation elicited IPSCs in NM neurons regardless of tonotopic region, but the dependence of IPSCs on intensity varied in a systematic way. In neurons tuned to low frequency, IPSCs appeared and increased in parallel with EPSCs with elevation of intensity, which expanded dynamic range by preventing saturation of spike generation. On the other hand, in neurons tuned to higher frequency, IPSCs were smaller than EPSCs and had higher thresholds for activation, thus facilitating high-fidelity transmission. Computer simulation confirmed that these differences in inhibitory input were optimally matched to the patterns of excitatory input, and enabled appropriate level of neuronal output for wide intensity and frequency ranges of sound in the auditory system. SIGNIFICANCE STATEMENT Neurons in nucleus magnocellularis encode timing information of sound across wide intensity ranges by integrating excitatory and inhibitory synaptic inputs from the auditory nerve, but underlying synaptic mechanisms of this integration are not fully understood. We here show that the excitatory–inhibitory relationship was expressed differentially at each tonotopic region; the relationship was linear in neurons tuned to low-frequency, expanding dynamic range by preventing saturation of spike generation; by contrast inhibitory input remained much smaller than excitatory input in neurons tuned to higher frequency, thus ensuring high-fidelity transmission. The tonotopic regulation of excitatory and inhibitory input optimized the output across frequencies and intensities, playing a fundamental role in the timing coding pathway in the auditory system.
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