Muscarinic Receptor Induced LTD in Rat Hippocampus

描述（申请者提供）：海马体的胆碱能神经支配是某些形式的学习和记忆所必需的。胆碱能海马中隔事件的变性是阿尔茨海默病（AD）的一个标志，认知能力下降的严重程度与胆碱能损伤有关。乙酰胆碱（ACh）、海马突触可塑性、学习记忆和AD之间的重叠刺激了对ACh调节海马功能机制的研究，因为这些机制的改变可能是AD中一些认知缺陷的基础。我们对胆碱能调节突触功能和可塑性的理解尚不清楚，因此，除非这些机制被解开，否则我们治疗或预防胆碱能依赖性认知衰退的能力仍将处于次优状态。我们在体外研究了大鼠海马CA1区通过M1毒蕈碱受体（M1 AChRs）激活诱导的一种形式的长期抑郁（mLTD）。mLTD是活性和NMDA受体依赖的，并被低频刺激诱导的LTD阻断。心肌梗死achr的突触前和突触后位置尚不清楚，下游事件尚未确定。我们发现，海马体的胆碱能失神经支配（CD）是阿尔茨海默病发生的胆碱能功能减退的一种模型，它可以阻止mLTD的诱导。有趣的是，CD刺激交感轴突向海马内生长，并通过一种未知的机制将mLTD恢复到控制水平。在本文中，我们将验证以下假设：mLTD需要激活与M1 achr相关的信号级联，海马的胆碱能去神经控制通过改变M1 achr与其信号转导通路的耦合来改变mLTD的诱导。我们将使用脑切片电生理学与药理学工具、生物化学和免疫组织化学相结合的方法来实现所提出的目标：1)检查mLTD的细胞机制；2)将研究CD和交感神经向内生长如何改变mLTD的诱导/表达；3)检查去甲肾上腺素诱导的突触传递变化与mLTD的相互作用。期望本研究的结果将为设计新的治疗胆碱能损伤症状的策略提供见解。

DESCRIPTION (provided by applicant): Cholinergic innervation of hippocampus is required for some forms of learning and memory. The degeneration of cholinergic septohippocampal afferents is one hallmark of Alzheimer's Disease (AD) and the severity of cognitive decline is correlated with cholinergic impairment. The overlap between acetylcholine (ACh), hippocampal synaptic plasticity, learning and memory, and AD stimulates investigations into mechanisms by which ACh modulates hippocampal function, since alterations in these mechanisms may underlie some cognitive deficiencies in AD. Our understanding of cholinergic modulation of synaptic function and plasticity is not clear, hence our ability to treat or prevent cholinergic dependent cognitive decline will remain sub-optimal unless these mechanisms are unraveled. We have characterized a form of long-term depression (mLTD) in the CA1 region of rat hippocampus in vitro that is induced via activation of M1 muscarinic receptors (M1 AChRs). mLTD is activity and NMDA receptor dependent and is occluded by LTD induced by low frequency stimulation. The pre vs. postsynaptic location of the MI AChRs is unknown and the downstream events have not been identified. We have found that cholinergic denervation (CD) of hippocampus, a model of cholinergic hypofunction that occurs in AD, prevents the induction of mLTD. Interestingly, CD stimulates ingrowth of sympathetic axons into hippocampus and restores mLTD to control levels through an unknown mechanism. Herein we will test the hypothesis that mLTD requires activation of the signaling cascade linked to M1 AChRs and that cholinergic denervation of hippocampus alters the induction of mLTD by altering the coupling of M1 AChRs to their signal transduction pathway. We will use a combination of electrophysiology in brain slices together with pharmacological tools, biochemistry and immunohistochemistry to carry out the proposed aims: 1) examine the cellular mechanisms underlying mLTD; 2) will examine how CD and sympathetic ingrowth alters mLTD induction/expression; 3) examine norepinephrine-induced changes in synaptic transmission interact with mLTD. It is expected that results from this study will provide insight into designing novel therapeutic strategies for symptoms of cholinergic impairment.