Differential modes of cholinergic transmission onto cellular hippocampal targets

描述（由申请人提供）：乙酰胆碱（ACh）从Broca内侧隔-对角带（MS-DBB）释放到海马，深刻改变细胞兴奋性、网络同步性和行为状态。胆碱能功能的缺陷会导致记忆障碍，如阿尔茨海默氏病，而神经毒剂或有机磷农药中毒导致的胆碱能活动过度会诱发癫痫发作并导致神经元死亡。乙酰胆碱在海马体中具有不同的突触前和突触后靶点，作用于谷氨酸能和γ-氨基丁酸能细胞群。最近的证据表明，ACh的作用可以是高度特异性的，以细胞类型特异性的方式改变不同GABA能回路的兴奋性。尽管中间神经元和主细胞的激活是这些振荡的基础，但由于系统地研究定义的中间神经元群体的技术困难，缺乏海马靶细胞接收的胆碱能传入的密度和空间定位的信息，以及不能以选择性但协调的方式激活扩散分布的MS-DBB神经元群。通过大量的纤维刺激，胆碱能反应只能通过突触受体拮抗剂的鸡尾酒，但在同一时间，这种药理学隔离禁止MS-DBB传输如何影响兴奋性GABA能和海马神经元网络的完整理解。此外，最近发现的GABA和谷氨酸传输机制共存于MS-DBB胆碱能神经元提出了共传输的可能性，这将不会被观察到，除非MS-DBB胆碱能纤维可以选择性激活与谷氨酸和GABAA受体完整。在这个建议中，使用MS-DBB传入的光活化，事后免疫细胞化学可视化的光活化纤维，电生理学和计算建模的组合，我们将测试的中心假设，即MS-DBB胆碱能和GABA能传输的疗效取决于突触后中间神经元亚型。这是第一次，我们将能够定义MS-DBB传入的空间定位和细胞类型特异性调制的生理后果之间的关系。在目的1中，我们将确定MS-DBB胆碱能神经元和突触后海马中间神经元亚型之间的突触传递的功效。在目的2中，我们将确定MS-DBB GABA能神经元和突触后海马中间神经元亚型之间的突触传递的功效。最后，在目标3中，我们将确定PV细胞上存在的M1 mAChR在胆碱能诱导的网络振荡中的作用。

DESCRIPTION (provided by applicant): Acetylcholine (ACh) release from the medial septum-diagonal band of Broca (MS-DBB) to the hippocampus profoundly alters cellular excitability, network synchronization, and behavioral state. Deficits in cholinergic function induce memory impairments, such as in Alzheimer's disease, while excessive cholinergic activity resulting from nerve agent or organophosphate pesticide poisoning can induce seizures and lead to neuronal death. ACh has diverse pre- and postsynaptic targets onto both glutamatergic and GABAergic cell populations in the hippocampus. Recent evidence has emerged indicating that the actions of ACh can be highly specific, altering the excitability of distinct GABAergic circuits a cell type-specific manner. Although activation of interneurons and principal cells underlie these oscillations, cholinergic synaptic transmission onto specific target cells remains poorly understood due to technical difficulties in systematically studying defined interneuron populations, the lack of information on the density and spatial localization of cholinergic afferents received by hippocampal target cells, and the inability to activate diffusely distributed populations of MS-DBB neurons in a selective yet coordinated manner. Through bulk fiber stimulation, cholinergic responses can be observed only through a cocktail of synaptic receptor antagonists, yet at the same time, this pharmacological isolation prohibits a complete understanding of how MS-DBB transmission impacts the excitability GABAergic and glutamatergic hippocampal networks. Moreover, the recent discovery of GABA and glutamate transmission machinery co-existing in MS-DBB cholinergic neurons raises the possibility of co-transmission, which would not be observed unless MS-DBB cholinergic fibers can be selectively activated with glutamate and GABAA receptors intact. In this proposal, using a combination of photoactivation of MS-DBB afferents, post-hoc immunocytochemical visualization of photoactivated fibers, electrophysiology, and computational modeling, we will test the central hypothesis that the efficacy of MS-DBB cholinergic and GABAergic transmission depends on the postsynaptic interneuron subtype. For the first time, we will be able to define the relationship between the spatial localization of MS-DBB afferents and the physiological consequence of cell type specific modulation. In Aim 1, we will determine the efficacy of synaptic transmission between MS-DBB cholinergic neurons and postsynaptic hippocampal interneuron subtypes. In Aim 2, we will determine the efficacy of synaptic transmission between MS-DBB GABAergic neurons and postsynaptic hippocampal interneuron subtypes. Finally, in Aim 3, we will determine the role of M1 mAChRs present on PV cells in cholinergically-induced network oscillations.