Consequences of HCN/h pacemarker channel deficency for cortico-basal ganglia circuit function

帕金森病（PD）是一种常见的、使人衰弱的神经退行性疾病，其特征在于基底神经节核中的严重回路功能障碍。运动障碍与基底神经节神经元的过度β（11-30 Hz）振荡和同步、节律性尖峰的出现特别相关。异常的β振荡在慢性多巴胺耗竭后发展，在皮质和基底神经节核中很大程度上是连贯的，并且可以通过多巴胺替代疗法正常化。异常基底神经节β振荡可能反映了由局部微回路产生的同步节律神经元活动，其在基底神经节-皮质回路内病理性放大。然而，这种同步的具体分子和电路机制还没有很好地理解。所有基底神经节微回路的关键元件是起搏神经元，其被认为是维持运动功能的正常节律性局部和网络活动的产生所必需的。这些神经元可以产生内在的膜电位振荡，强烈地偏置其动作电位输出的时间。基底神经节中的起搏器非常多样化。它们的范围从黑质网状部（SNc）和腹侧被盖区（VTA）中的缓慢尖峰多巴胺神经元到快速尖峰（超过20 Hz）的GABA能黑质网状部（SNr）神经元和胆碱能纹状体中间神经元（张力活性神经元或TAN）。这些细胞中的每一个表达HCN通道，其产生超极化激活的Ih电流。IH可引起膜共振，这是一种支持起搏器尖峰的固有生物物理特性。改变的Ih幅度或HCN亚基表达可见于许多神经疾病状态和疾病模型中。为了更好地了解基底神经节起搏神经元在细胞水平上，以及它们在网络和行为水平上的整合，我们将通过遗传抑制HCN/h通道活性来改变它们的内在膜特性。我们假设HCN/h通道功能的丧失将特异性地改变这些神经元的起搏特性，并且在改变其放电模式时，改变突触和网络活动，从而影响认知和运动功能。我们将使用条件表达的显性阴性HCN亚基，在体外和体内电生理学，和行为分析的组合，以表征衰减HCN/h电流的后果。我们将记录单位和网络活动的关键基底神经节核，如背侧纹状体，苍白球（GPe）的外部部分，丘脑底核（ESTA），和VTA/SN在急性和清醒的行为准备。此外，我们将研究是否以及如何改变发射模式，因此SNc神经元的代谢负荷影响这些神经元在慢性PD模型的脆弱性。

Parkinson¿s disease (PD) is a common, debilitating neurodegenerative disorder characterized by profound circuit dysfunction in basal ganglia nuclei. The motor disability is specifically associated with the emergence of exaggerated beta (11-30 Hz) oscillations and synchronous, rhythmic spiking of neurons in basal ganglia. Abnormal beta oscillations develop after chronic dopamine depletion, are largely coherent in cortex and basal ganglia nuclei, and may be normalized by dopamine replacement therapies. Aberrant basal ganglia beta oscillations likely reflect synchronized rhythmic neuronal activities generated by local microcircuits, which become pathologically amplified within basal ganglia-cortical loops. However, the specific molecular and circuit mechanisms of this synchronization are not well understood. A crucial element of all basal ganglia microcircuits are pacemaker neurons, which are thought to be necessary for the generation of the normal rhythmic local and network activity sustaining motor function. These neurons can generate intrinsic membrane potential oscillations that strongly bias the timing of their action potential output. Pacemakers in the basal ganglia are very diverse. They range from the slow-spiking dopamine neurons in the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) to the fast-spiking (over 20 Hz) GABAergic substantia nigra pars reticulata (SNr) neurons and the cholinergic striatal interneurons (tonically active neurons or TANs.) Each of these cells expresses HCN channels, which produce the hyperpolarization-activated Ih-current. Ih can cause membrane resonance, an intrinsic biophysical property supporting pacemaker spiking. Altered Ih amplitude or HCN subunit expression is seen in many neurological disease states and disease models. To better understand basal ganglia pacemaker neurons at the cellular level, and their integration at the network and behavioral levels, we will alter their intrinsic membrane properties by genetic suppression of HCN/h channel activity. We hypothesize that a loss of function of HCN/h channels will specifically alter the pacemaker properties of these neurons and, in changing their firing patterns, alter synaptic and network activities, thus affecting both cognitive and motor function. We will use a combination of conditional expression of a dominant-negative HCN subunit, in vitro and in vivo electrophysiology, and behavioral analyses to characterize the consequences of attenuated HCN/h currents. We will record unit and network activity in key basal ganglia nuclei such as the dorsal striatum, the external segment of the globus pallidus (GPe), the subthalamic nucleus (STN), and the VTA/SN in both acute and awake-behaving preparations. In addition, we will investigate whether and how altered firing patterns and consequently the metabolic load of SNc neurons influence the vulnerability of these neurons in chronic PD models.