Differential modes of cholinergic transmission onto cellular hippocampal targets

描述(申请人提供)：乙酰胆碱(ACh)从Broca的内侧隔-斜角带(MS-DBB)释放到海马区，深刻改变细胞的兴奋性、网络同步性和行为状态。胆碱能功能缺陷会导致记忆障碍，如阿尔茨海默病，而神经毒剂或有机磷农药中毒引起的过度胆碱能活动可导致癫痫发作和神经元死亡。ACh对海马区的谷氨酸能和GABA能细胞群有不同的突触前和突触后靶点。最近出现的证据表明，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，但由于系统研究确定的中间神经元群体的技术困难，缺乏关于海马靶细胞接收的胆碱能传入的密度和空间定位的信息，以及无法以选择性而又协调的方式激活广泛分布的MS-DBB神经元群体，对胆碱能突触向特定靶细胞的传递仍知之甚少。通过大纤维刺激，胆碱能反应只能通过突触受体拮抗剂的鸡尾酒才能观察到，但同时，这种药物隔离也阻碍了对MS-DBB传递如何影响兴奋性GABA能和谷氨酸能海马网的全面了解。此外，最近发现在MS-DBB胆碱能神经元中共存的GABA和谷氨酸传递机制增加了共传递的可能性，除非MS-DBB胆碱能纤维在谷氨酸和GABAA受体完整的情况下被选择性地激活，否则不可能观察到这种情况。在这个方案中，我们将结合MS-DBB传入的光激活、光激活纤维的后免疫细胞化学显示、电生理学和计算模型，检验MS-DBB胆碱能和GABA能传递的有效性取决于突触后中间神经元亚型的中心假设。我们将首次能够确定MS-DBB传入的空间定位与细胞类型特异性调制的生理后果之间的关系。在目标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有效性。在目标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有效性。最后，在目标3中，我们将确定存在于PV细胞上的M1 mAChRs在胆碱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.