Elucidation of the mediodorsal thalamic regulation of prefrontal function

项目摘要/摘要 丘脑内侧背侧核(MD)通过其广泛的分布，在认知过程中发挥重要作用。 内侧前额叶皮质(MPFC)的谷氨酸能神经支配。这些MD终端提供AMPA介导的 兴奋兴奋性锥体神经元和γ-氨基丁酸(GABA)能抑制中间神经元。 GABA能中间神经元，特别是表达小白蛋白(PV)的快峰亚型，是 调节相邻锥体神经元的输出，维持兴奋/抑制(E/I)平衡， 以及协调神经元群体中的同步活动。有趣的是，这种神经元亚型会收到 MD输入，他们的活动与工作记忆、注意力和执行功能相关 和一等兵在一起。然而，MD丘脑皮质传入对抑制性中间神经元的调节作用仍然存在。 未知。我们假设MD传入驱动mPFC抑制活性，帮助调节局部 电路活动，从而优化mPFC依赖任务的性能。这是基于前馈的 不仅在初级丘脑中继器中观察到抑制，而且最近在丘脑中观察到这种现象的证据。 前扣带回皮质。鉴于此，我们认为MD活动的下调将损害GABA能 初步的mPFC的活动，导致局部回路活动的失调，以及认知障碍。去探索 这种可能性，我们利用专门由设计师药物(DREADD)激活的设计师受体，从而允许 US选择性靶向成年大鼠MD谷氨酸能神经元，并瞬时抑制其活动 抑制性hM4D受体的表达。利用药物遗传学，我们可以评估 通过两种主要方法抑制MD。在设计配体氯氮平-N-氧化物(CNO)的帮助下，我们将治疗 系统地研究了MD抑制对mPFC依赖行为的影响。 记忆和认知灵活性任务。我们还将采取含有mPFC和MD传入的切片，BASH 应用CNO，并使用整个细胞记录来确定电路中的结果变化。到目前为止，我们已经 成功地证明MD抑制导致GABAAR介导的IPSCs显著减少 前额叶锥体神经元。IPSC的这种损失在α1-GABAAR似乎更大。此外，这些下降 PFC中GABA活性的变化与我们的MD抑制动物的认知功能障碍有关。使用T- 迷宫延迟交替任务，我们发现MD抑制损害了工作记忆的表现，这是 可通过GABA能α1阳性变构调节剂Indiplon治疗而挽救。这些发现 提出耐人寻味的问题，MD抑制如何机械地影响mPFC局部电路，以及 MD通过PV中间神经元调节mPFC，从而影响认知。我们将进一步解决这些问题 使用外科、电生理学、行为学和药物遗传学技术的组合。

PROJECT SUMMARY/ABSTRACT The mediodorsal thalamus (MD) is suggested to play a critical role in cognition through its extensive glutamatergic innervation of the medial prefrontal cortex (mPFC). These MD terminals provide AMPA-mediated excitation to both excitatory pyramidal neurons and gamma-aminobutyric (GABA)-ergic inhibitory interneurons. GABAergic interneurons, particularly the parvalbumin (PV)-expressing fast-spiking subtype, are fundamental in regulating the output of their neighboring pyramidal neurons, maintaining the excitation/inhibition (E/I) balance, and coordinating synchronous activity in populations of neurons. Interestingly, this neuronal subtype receives MD inputs, and their activity has been linked to working memory, attention, and executive functions associated with the PFC. However, how inhibitory interneurons are modulated by MD thalamocortical input remains unknown. We hypothesize that MD afferents drive mPFC inhibitory activity, aiding in the regulation of local circuit activity and thus optimizing performance on mPFC dependent tasks. This is based on feedforward inhibition observed not only in primary thalamic relays, but also recent evidence of this phenomenon in the anterior cingulate cortex. Given this, we propose that downregulation of MD activity will impair GABAergic activity in the prelimbic mPFC, causing dysregulation of local circuit activity, and cognitive deficits. To explore this possibility, we utilize Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) that allow us to selectively target glutamatergic MD neurons, and transiently inhibit their activity in adult rats by expression of the inhibitory hM4D receptor. Using pharmacogenetics, we can evaluate the consequences of MD inhibition by two primary methodologies. With the designer ligand, Clozapine-N-Oxide (CNO), we will treat animals systemically and explore the effects of MD inhibition on mPFC-dependent behaviors using a working memory and cognitive flexibility task. We will also take slices containing the mPFC and MD afferents, bath apply CNO, and determine resultant changes in the circuitry using whole cell-recordings. Thus far, we have successfully demonstrated that MD inhibition resulted in a significant decrease of GABAAR-mediated IPSCs in PFC pyramidal neurons. This loss in IPSCs appears to be greater at α1- GABAARs. Further, these decreases of GABA activity in the PFC are associated with cognitive dysfunction in our MD-inhibited animals. Using a T- maze delayed-alternation task, we have shown that MD inhibition impairs working memory performance, which can be rescued by treatment with the GABAergic α1-positive allosteric modulator, indiplon. These findings raise intriguing questions of how MD inhibition mechanistically influences mPFC local circuitry, and whether the MD regulates the mPFC through PV interneurons to impact cognition. We will further address these questions using a combination of surgical, electrophysiological, behavioral, and pharmacogenetic techniques.