Elucidation of the mediodorsal thalamic regulation of prefrontal function

项目总结/摘要 中背丘脑（MD）通过其广泛的功能在认知中起着关键作用。 内侧前额叶皮层（mPFC）的神经支配。这些MD末端提供AMPA介导的 兴奋性锥体神经元和γ-氨基丁酸（GABA）能抑制性中间神经元的兴奋。 GABA能中间神经元，特别是表达小白蛋白（PV）的快速尖峰亚型，是神经元内分泌的基础。 调节其相邻锥体神经元的输出，维持兴奋/抑制（E/I）平衡， 和协调神经元群体的同步活动。有趣的是，这种神经元亚型 MD的输入，它们的活动已经与工作记忆、注意力和执行功能相关联 然而，抑制性中间神经元是如何被MD丘脑皮质输入调制的仍然存在。 未知我们推测，MD传入驱动mPFC抑制活性，有助于调节局部的 电路活动，从而优化mPFC相关任务的性能。这是基于前馈 不仅在初级丘脑中继中观察到抑制，而且最近在 前扣带皮层鉴于此，我们认为MD活性的下调将损害GABA能 前边缘mPFC的活动，导致局部电路活动失调和认知缺陷。探讨 这种可能性，我们利用设计师受体独家激活的设计师药物（DREADD），允许 我们选择性地靶向多巴胺能MD神经元，并通过以下方法短暂抑制成年大鼠的活动： 抑制性hM 4D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。与设计师配体，氯氮平-N-氧化物（CNO），我们将治疗 动物全身，并探讨MD抑制对mPFC依赖性行为的影响，使用工作 记忆和认知灵活性任务。我们还将采取切片含有mPFC和MD传入，浴 应用CNO，并使用全细胞记录确定电路中的结果变化。到目前为止， 成功地证明了MD抑制导致GABAAR介导的IPSC的显著减少， PFC锥体神经元。IPSC中的这种损失似乎在α1-GABAAR中更大。此外，这些下降 PFC中的GABA活性与我们的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，我们已经表明，MD抑制损害工作记忆的表现， 可通过GABA能α1阳性变构调节剂indiplon治疗来挽救。这些发现 提出了一个有趣的问题，即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以影响认知。我们将进一步解决这些问题 使用手术、电生理、行为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.