Koch Ursula, Grothe Benedikt
Max-Planck Institute of Neurobiology, 82152 Martinsried, Germany.
J Neurophysiol. 2003 Dec;90(6):3679-87. doi: 10.1152/jn.00375.2003. Epub 2003 Sep 10.
Neurons in the inferior colliculus (IC) process acoustic information converging from inputs from almost all nuclei of the auditory brain stem. Despite its importance in auditory processing, little is known about the distribution of ion currents in IC neurons, namely the hyperpolarization-activated current Ih. This current, as shown in neurons of the auditory brain stem, contributes to the precise analysis of temporal information. Distribution and properties of the Ih current and its contribution to membrane properties and synaptic integration were examined by current- and voltage-clamp recordings obtained from IC neurons in acute slices of rats (P17-P19). Based on firing patterns to positive current injection, three basic response types were distinguished: onset, adapting, and sustained firing neurons. Onset and adapting cells showed an Ih-dependent depolarizing sag and had a more depolarized resting membrane potential and lower input resistance than sustained neurons. Ih amplitudes were largest in onset, medium in adapting, and small in sustained neurons. Ih activation kinetics was voltage dependent in all neurons and faster in onset and adapting compared with sustained neurons. Injecting trains of simulated synaptic currents into the neurons or evoking inhibitory postsynaptic potentials (IPSPs) by stimulating the lemniscal tract showed that Ih reduced temporal summation of excitatory and inhibitory potentials in onset but not in sustained neurons. Blocking Ih also abolished afterhyperpolarization and rebound spiking. These results suggest that, in a large proportion of IC cells, namely the onset and adapting neurons, Ih improves precise temporal processing and contributes to the temporal analysis of input patterns.
下丘（IC）中的神经元处理着几乎所有听觉脑干核输入汇聚而来的听觉信息。尽管其在听觉处理中很重要，但对于IC神经元中离子电流的分布，即超极化激活电流Ih，却知之甚少。正如在听觉脑干神经元中所显示的那样，这种电流有助于对时间信息进行精确分析。通过从大鼠（P17 - P19）急性脑片中的IC神经元进行电流钳和电压钳记录，研究了Ih电流的分布、特性及其对膜特性和突触整合的贡献。根据对正向电流注入的放电模式，区分出三种基本反应类型：起始型、适应型和持续放电型神经元。起始型和适应型细胞表现出Ih依赖性去极化下陷，并且与持续放电型神经元相比，具有更去极化的静息膜电位和更低的输入电阻。Ih幅度在起始型神经元中最大，在适应型神经元中中等，在持续放电型神经元中最小。Ih激活动力学在所有神经元中均依赖于电压，并且与持续放电型神经元相比，在起始型和适应型神经元中更快。向神经元中注入模拟突触电流序列或通过刺激lemniscal束诱发抑制性突触后电位（IPSPs）表明，Ih减少了起始型神经元而非持续放电型神经元中兴奋性和抑制性电位的时间总和。阻断Ih也消除了超极化后电位和反弹放电。这些结果表明，在很大一部分IC细胞中，即起始型和适应型神经元中，Ih改善了精确的时间处理，并有助于对输入模式进行时间分析。
