Synaptic integration and intrinsic firing properties of basal ganglia neurons

细胞神经生理科研究位于中脑多巴胺系统中的神经元的生理学，以及它们在基底节的电路整合。我们的实验室一直致力于了解纹状体中的多巴胺信号是如何由多巴胺能轴突终末上的配体门控受体塑造的。具体地说，多巴胺能细胞的轴突接受纹状体内乙酰胆碱释放神经元的输入，这可能会影响多巴胺的释放。此外，我们已经证明，多巴胺能轴突表达GABA-A受体，该受体可以局部抑制纹状体多巴胺的释放。最近，我们一直在研究轴突GABA-A受体如何影响来自局部胆碱能中间神经元的输入整合，以塑造轴突兴奋性和多巴胺释放。在我们使用GCaMP对体外组织切片中的轴突钙内流进行分析时，我们分离了轴突钙信号的两个主要成分，一个成分来自于直接轴突刺激，另一个成分来自于传递到轴突尼古丁受体的成分。我们发现轴突GABA-A受体抑制直接诱发的轴突信号，但对烟碱成分的幅度和速度有更强的影响。通过直接记录轴突，我们发现GABA-A受体阳性变构调节剂地西潘降低了阈值下尼古丁传入多巴胺轴突的幅度。在我们研究GABA-A受体与尼古丁受体相互作用的研究中，我们发现印防己毒素在通常用于生理实验的浓度下有效地阻断纹状体尼古丁受体，这表明在选择GABA-A受体拮抗剂时必须谨慎。总之，我们的结果强调了纹状体多巴胺轴突以一种受轴突GABAA受体调节的方式整合来自胆碱能中间神经元的信息。 在另一个单独的项目中，我们研究了钠泄漏电导NALCN对不同多巴胺神经元亚群起搏的贡献。我们发现，NALCN参与了位于腹侧被盖区(VTA DAN)的多巴胺能神经元的放电，特别是投射到伏隔内侧核和外侧核的神经元。具体地说，我们发现NALCN的急性药物阻断大大减缓了内侧VTA DAN的起搏速度。因此，NALCN是VTA DAN起搏的主要驱动力。然而，我们发现在黑质(SNC)DAN中，NALCN在功能上存在，但SNC DAN的起搏不受NALCN抑制的影响。相反，我们表明，NALCN降低了以比自发放电慢的速度测量的放电频率的频率-电流曲线的增益。在单独的实验中，我们探索了超极化激活电流(Ih)的作用，发现同时抑制NALCN和Ih可显著降低SNC神经元的起搏率。因此，我们发现，在VTA DAN亚群中，NALCN对驱动起搏做出了重要贡献，而在SNC DAN中，NALCN对起搏并不是关键的，但抑制这一电流使细胞对超极化刺激更加敏感。这项研究已经提交发表，并被《神经科学杂志》(Cobb-Lewis等人)接受。2023年)。这些发现将指导未来的努力，以获得多巴胺能神经元亚群的特定治疗神经精神和运动障碍，如帕金森氏病。 在另一项研究中，我们一直在研究钠泄漏电导NALCN在减缓不同多巴胺神经元亚群中被称为起搏的自发放电中的作用。我们发现，虽然NALCN对黑质神经元的放电有贡献，但NALCN对内侧多巴胺能神经元的贡献要强得多，特别是那些投射到伏隔内侧核的神经元。这项研究已经提交发表，目前正在修订中。

The Cellular Neurophysiology Section studies the physiology of neurons located in the midbrain dopamine system and as well as their circuit integration in the basal ganglia. Our laboratory has focused on understanding how dopamine signaling in the striatum is shaped by ligand-gated receptors on dopaminergic axon terminals. In particular, the axons of dopaminergic cells receive input from acetylcholine-releasing neurons within the striatum that may influence dopamine release. In addition, we have demonstrated that the dopaminergic axons express GABA-A receptors that many locally inhibit striatal dopamine release. Recently, we have been examining how axonal GABA-A receptors influence the integration of input arriving from local cholinergic interneurons to shape axonal excitability and dopamine release. In our analysis of axonal calcium influx using GCaMP in ex vivo tissue slices, we isolated the two main components of the axonal calcium signals one component resulting from direct axonal stimulation and a later component due to transmission onto axonal nicotinic receptors. We find that axonal GABA-A receptors inhibits directly-evoked axonal signal but has a stronger effect on the amplitude and speed of the nicotinic component. Using direct axonal recordings, we show that the GABA-A receptor positive allosteric modulator, diazepam, decreases the magnitude of subthreshold nicotinic input onto dopamine axons. In our studies examining the GABA-A receptor interaction with nicotinic receptors, we found show that picrotoxin potently blocks striatal nicotinic receptors at concentrations that have typically been used for physiology experiments suggesting that caution must be used when selecting GABA-A receptor antagonists. Together, our results highlight that striatal dopamine axons integrate information from cholinergic interneurons in a manner that is regulated by axonal GABAA receptors. In a separate project, we investigated the contribution of the sodium leak conductance, NALCN, to pacemaking in different dopamine neuron subpopulations. We found that NALCN contributes to firing in dopaminergic neurons located in the ventral tegmental area (VTA DANs), particularly those that project to medial and lateral nucleus accumbens. Specifically, we found acute pharmacological blockade of NALCN substantially slowed pacemaking in medial VTA DANs. Thus, NALCN is a primary driver of pacemaking in VTA DANs. In substantia nigra (SNc) DANs, however, we found that NALCN is functionally present but pacemaking in SNc DANs was unaffected by inhibition of NALCN. Instead, we show that NALCN reduces the gain of frequency-current plots of firing frequencies measured at rates slower than spontaneous firing. In separate experiments, we explored to role of the hyperpolarization-activated current (Ih) and found that simultaneous inhibition of NALCN and Ih resulted in significant reduction in pacemaker rate in SNc neurons. Thus, we found NALCN makes substantial contributions to driving pacemaking in VTA DAN subpopulations while in SNc DANs, NALCN is not critical for pacemaking but inhibition of this current makes cells more sensitive to hyperpolarizing stimuli. This study has been submitted for publication and was accepted at the Journal of Neuroscience (Cobb-Lewis et al. 2023). These findings will inform future efforts to obtain dopaminergic neuron subpopulation specific treatments in neuropsychiatric and motor disorders such as Parkinsons Disease. In a separate study, we have been investigating the role of the sodium leak conductance, NALCN, to slow spontaneous firing called pacemaking in different dopamine neuron subpopulations. We have found that while NALCN contributes to firing in substantia nigra neurons, the contribution of NALCN is much stronger in medial dopaminergic neurons, particularly those that project to medial nucleus accumbens. This study has been submitted for publication and is currently in revisions.