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

帕金森病（PD）是一种常见的衰弱性神经退行性疾病，其特征是基底神经节核的深度电路功能障碍。运动障碍与基底神经节神经元的β (11-30 Hz)振荡和同步、节律性尖峰的出现特别相关。在慢性多巴胺耗竭后出现异常的β振荡，在皮层和基底神经节核中大部分是一致的，并且可能通过多巴胺替代疗法正常化。异常的基底神经节β振荡可能反映了局部微回路产生的同步节律性神经元活动，这些活动在基底神经节-皮层回路中被病理放大。然而，这种同步的具体分子和电路机制尚不清楚。所有基底神经节微回路的一个关键元素是起搏器神经元，它被认为是产生维持运动功能的正常节律局部和网络活动所必需的。这些神经元可以产生固有的膜电位振荡，这强烈地影响了它们动作电位输出的时间。基底神经节的起搏器种类繁多。它们的范围从黑质致密部（SNc）和腹侧被盖区（VTA）的慢脉冲多巴胺神经元到快速脉冲（超过20赫兹）的gaba能黑质网状部（SNr）神经元和胆碱能纹状体中间神经元（张力活跃神经元或TANs）。这些细胞中的每一个都表达HCN通道，产生超极化激活的ih电流。它可以引起膜共振，这是一种支持起搏器尖峰的内在生物物理特性。在许多神经疾病状态和疾病模型中都可以看到Ih振幅或HCN亚基表达的改变。为了更好地了解基底神经节起搏器神经元的细胞水平及其在网络和行为水平上的整合，我们将通过基因抑制HCN/h通道活性来改变其固有的膜特性。我们假设HCN/h通道功能的丧失会特异性地改变这些神经元的起搏器特性，并在改变它们的放电模式时，改变突触和网络活动，从而影响认知和运动功能。我们将结合HCN显性阴性亚基的条件表达、体外和体内电生理以及行为分析来表征HCN/h电流减弱的后果。我们将记录关键的基底神经节核的单位和网络活动，如背纹状体、苍白球外段（GPe）、丘脑下核（STN）和VTA/SN在急性和清醒状态下的活动。此外，我们将研究慢性PD模型中SNc神经元的放电模式改变以及代谢负荷是否以及如何影响这些神经元的易损性。

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.