Forti Lia, Cesana Elisabetta, Mapelli Jonathan, D'Angelo Egidio
Dipartimento di Scienze Fisiologiche e Farmacologiche, Università di Pavia, Via Forlanini 6, 27100 Pavia, Italy.
J Physiol. 2006 Aug 1;574(Pt 3):711-29. doi: 10.1113/jphysiol.2006.110858. Epub 2006 May 11.
Although Golgi cells (GoCs), the main type of inhibitory interneuron in the cerebellar granular layer (GL), are thought to play a central role in cerebellar network function, their excitable properties have remained unexplored. GoCs fire rhythmically in vivo and in slices, but it was unclear whether this activity originated from pacemaker ionic mechanisms. We explored this issue in acute cerebellar slices from 3-week-old rats by combining loose cell-attached (LCA) and whole-cell (WC) recordings. GoCs displayed spontaneous firing at 1-10 Hz (room temperature) and 2-20 Hz (35-37 degrees C), which persisted in the presence of blockers of fast synaptic receptors and mGluR and GABAB receptors, thus behaving, in our conditions, as pacemaker neurons. ZD 7288 (20 microM), a potent hyperpolarization-activated current (Ih) blocker, slowed down pacemaker frequency. The role of subthreshold Na+ currents (INa,sub) could not be tested directly, but we observed a robust TTX-sensitive, non-inactivating Na+ current in the subthreshold voltage range. When studying repolarizing currents, we found that retigabine (5 microM), an activator of KCNQ K+ channels generating neuronal M-type K+ (IM) currents, reduced GoC excitability in the threshold region. The KCNQ channel antagonist XE991 (5 microM) did not modify firing, suggesting that GoC IM has low XE991 sensitivity. Spike repolarization was followed by an after-hyperpolarization (AHP) supported by apamin-sensitive Ca2+-dependent K+ currents (I(apa)). Block of I(apa) decreased pacemaker precision without altering average frequency. We propose that feed-forward depolarization is sustained by Ih and INa,sub, and that delayed repolarizing feedback involves an IM-like current whose properties remain to be characterized. The multiple ionic mechanisms shown here to contribute to GoC pacemaking should provide the substrate for fine regulation of firing frequency and precision, thus influencing the cyclic inhibition exerted by GoCs onto the cerebellar GL.
尽管高尔基细胞（GoC）是小脑颗粒层（GL）中主要的抑制性中间神经元类型，被认为在小脑网络功能中起核心作用，但其兴奋性特性尚未得到探索。GoC在体内和切片中会有节律地放电，但尚不清楚这种活动是否源于起搏器离子机制。我们通过结合松散细胞贴附（LCA）和全细胞（WC）记录，对3周龄大鼠的急性小脑切片中的这一问题进行了探索。GoC在室温下以1 - 10 Hz、在35 - 37摄氏度时以2 - 20 Hz的频率自发放电，在存在快速突触受体阻滞剂以及代谢型谷氨酸受体（mGluR）和GABAB受体阻滞剂的情况下仍持续放电，因此在我们的实验条件下表现为起搏器神经元。强效超极化激活电流（Ih）阻滞剂ZD 7288（20微摩尔）减慢了起搏器频率。阈下钠电流（INa,sub）的作用无法直接测试，但我们在阈下电压范围内观察到了一种强大的、对河豚毒素（TTX）敏感的非失活钠电流。在研究复极化电流时，我们发现瑞替加滨（5微摩尔），一种可激活KCNQ钾通道从而产生神经元M型钾电流（IM）的物质，降低了GoC在阈值区域的兴奋性。KCNQ通道拮抗剂XE991（5微摩尔）并未改变放电情况，这表明GoC的IM对XE991敏感性较低。动作电位复极化之后是由蜂毒明敏感的钙依赖性钾电流（I(apa)）支持的超极化后电位（AHP）。阻断I(apa)会降低起搏器的精确性，但不改变平均频率。我们提出，前馈去极化由Ih和INa,sub维持，而延迟复极化反馈涉及一种类似IM的电流，其特性仍有待确定。此处显示的多种离子机制有助于GoC的起搏活动，应为精细调节放电频率和精确性提供基础，从而影响GoC对小脑颗粒层施加的周期性抑制。
