Ih电流——帕金森病异常HVSs节律的离子机制

Pathological oscillations in the cortex-BG loop are potentially causal to motor deficits in Parkinson's disease (PD). High-voltage spindles (HVSs) are 5- to 13-Hz oscillations with a characteristic spike-and-wave shape. They occur spontaneously in awake rats when the animal is quietly resting. It was shown in literature and our previous study that dopaminergic lesion resulted in a significant enhancement of HVSs in the cortex-BG loop in 6-OHDA PD rats. The exact mechanism underlying abnormal HVSs in PD still remain unclear. Intrinsic resonance properties of individual neurons provide a basis for network oscillations. We demonstrated for the first time that theta-frequency resonance properties were mediated by hyperpolarization-activated cation current (I(h)) in neurons of substantia nigra pars compacta (SNc), subthalamic nucleus (STN), and globus pallidus (GP). And downregulations of hyperpolarization and cyclic nucleotide-gated (HCN) channel expression were found in GP and STN neurons in PD models. Therefore we put forward a hypothesis: In PD rats, Ih current in BG neurons might decrease, membrane resonance might weaken, and in turn HVSs rhythm might be abnormal in cortex-BG loop. That is, Ih current is the ionic mechanism underlying abnormal HVSs rhythm in PD. This project intends to use the patch clamp and local field potential recording techniques, and focus on STN: (1)To make clear that Ih current and membrane resonance are altered in STN neurons of PD model rats. (2)By pharmacological methods or virus transfection to manipulate STN neurons, downregulating Ih current or HCN2 channel expression in control rats / upregulating Ih current or HCN2 channel expression in PD rats, to observe the effects on the membrane resonance, HVSs rhythm and related behavior. This is a new exploration to the mechanism underlying abnormal HVSs from a new point of view, and may bring a breakthrough in the pathophysiology of PD, being of vital significance.

皮层-基底节(BG)环路的异常振荡与帕金森病(PD)有直接关系,6-OHDA PD模型大鼠存在皮层-BG环路的HVSs节律异常,机制不明。细胞水平的神经元膜共振是网络水平神经振荡的基础。我们首次证实,正常大鼠BG区神经元存在超极化激活的阳离子流(Ih)介导的膜共振。而PD模型的BG区神经元HCN2通道下调。故提出假设:PD大鼠BG区神经元Ih电流减小,导致膜共振减弱,引发皮层-BG环路HVSs节律异常。即,Ih电流是PD异常HVSs节律的离子机制。本项目拟采用膜片钳及场电位记录技术,聚焦丘脑底核(STN):明确PD大鼠STN神经元Ih电流及膜共振发生变异；用药理学和重组病毒对STN局部操控，下调正常大鼠/上调PD大鼠的Ih电流或HCN2通道，考察对膜共振的影响、对HVSs节律的作用、及其行为相关性。这是从新的角度对HVSs节律异常机制的新探索，可能会在PD病理机制上有所突破，具有重要意义。

.节律性的大脑振荡活动在信息处理中起重要作用，如知觉、运动、意识的信息处理；皮层-基底节（BG）环路的异常振荡与帕金森病（PD）密切相关；我们前期的在体研究结果显示，6-OHDA PD模型大鼠的皮层、BG区的高电压纺锤波(HVSs)异常；PD病理状态下，皮层-BG环路HVSs异常的机制仍不清楚；现有理论认为，细胞水平的神经元共振是网络水平神经振荡活动的基础；我们前期的离体脑片研究结果显示，正常大鼠BG区神经元，均存在由Ih电流介导的膜共振；由此提出本项目的科学假设：Ih电流是PD异常HVSs节律的离子机制。.本项目运用膜片钳及场电位记录技术，以及用药理学和重组病毒对脑区局部进行操控，研究细胞水平的膜共振、整体动物的HVSs 节律、及其行为相关性。取得一系列发现和重要进展：1）首先证明了本项目提出的科学假设，即，Ih电流是PD异常HVSs节律的离子机制；2）其次在扩展研究中发现，两类多巴胺受体对膜共振、HVSs节律具有不同调节作用。可能成为PD病理情况下，直接通路、间接通路不平衡中的机制所在？.重要进展一：正常大鼠STN神经元存在膜共振，由Ih电流介导；PD模型大鼠STN神经元较对照组大鼠的Ih 电流显著减小、膜共振特性消失；随年龄增长，STN神经元的Ih电流也有减小、膜共振特性也有减弱。重要进展二：正常大鼠STN局部抑制Ih电流，可造成正常大鼠HVSs节律增强。重要进展三：PD大鼠STN HCN通道表达降低、HVSs节律增强；PD大鼠STN局部注射药物增大Ih电流，可减弱PD模型大鼠的HVSs异常增强。重要进展四：多巴胺D2受体可调节Ih电流，对STN神经元的膜共振以及皮层-基底节环路的HVSs活动均有调节作用。而多巴胺D1受体对STN 神经元的膜共振特性以及皮层-基底节环路的HVSs均没有调节作用。.这些发现和结果，是从新的角度对 HVSs 节律异常机制的新探索，对PD 病理机制和治疗有新的提示，具有重要意义。