Memory trace formation at and beyond individual synapses in the intact brain

完整大脑中单个突触内外的记忆痕迹形成

• 批准号: BB/Y003926/1
• 负责人: Dmitri Rusakov
• 金额: $ 90.67万
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2024
• 资助国家: 英国
• 起止时间: 2024 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=BB%2FY003926%2F1
• 关键词: Memory; trace; formation; beyond; individual

The principle of memory trace formation formulated by Donal Hebb refers to the strengthening of functional neuronal connections upon coincidence of informative inputs. This principle has found its empirical validation in the long-term potentiation (LTP) of synaptic transmission, an elemental model of synaptic memory. However, our understanding of its cellular mechanisms remains limited, mainly because attempts to relate LTP to a memory trace in the intact brain have never achieved resolution of individual synapses. Published evidence suggests that the increase in neuronal responses representing LTP could arise form either increased postsynaptic current or from increased probability of presynaptic neurotransmitter release (synaptic fidelity), or both. The present project will take advantage of the recent emergence of genetically encoded indicators (GEIs), which we have shown could provide robust monitoring of neurotransmitter release from individual synaptic connections. Our pilot data and other studies also indicate that the excitatory neurotransmitter glutamate could escape the active synaptic connection reaching its receptors at micron distances from its synaptic release site. Because synapses in the brain are less than a micron apart, this suggests a significant volume-transmitted component of excitatory transmission, challenging the principle of wired, one-to-one connectivity in neuronal networks. Whether memory formation involves changes in synaptic fidelity, whether the volume-transmitted excitatory signal is significant in the intact brain, and what could be its neurocomputational implications - these questions are fundamental for our understanding of the memory machinery. Addressing them has been a key motive for the present proposal. Our overall aim is therefore to understand the dynamics of synaptic fidelity and the extent and role of extrasynaptic excitatory signalling during memory trace formation in the brain. Built on our in-house established innovative methods and our preliminary results, this aim breaks down into several specific objectives. - To determine population dynamics of synaptic release probability during LTP induction in organised brain tissue and the key underlying mechanisms. - To establish the dynamics of synaptic fidelity at thalamocortical synapses during a sensory stimulation induced LTP in vivo. - To evaluate the extent and plasticity-associated changes in the extrasynaptic actions of glutamate at excitatory cortical synapses in vivo. - To understand physiological significance and network implications of the documented extrasynaptic glutamate escape. We will achieve these objectives by combining single-cell electrophysiology with high-resolution, high-speed multiplexed two-photon excitation imaging of cell-targeted GEIs. Control tests in ex vivo preparations will help us to optimise experiments in vivo in which we will monitor function of individual identified thalamocortical synapses in our tested paradigm of whisker stimulation. We will use our established high-end computer models to evaluate the significance of our observations for brain network activity. The established experimental protocols and pilot data that we have accumulated to date should ensure technical feasibility of the proposed research strategy.

唐纳尔·赫布（Donal Hebb）提出的记忆痕迹形成原理是指在信息输入一致时加强功能性神经元连接。这一原理在突触传递的长时程增强（LTP）（突触记忆的基本模型）中得到了实证验证。然而，我们对其细胞机制的理解仍然有限，主要是因为将 LTP 与完整大脑中的记忆痕迹联系起来的尝试从未实现单个突触的解析。已发表的证据表明，代表 LTP 的神经元反应的增加可能源于突触后电流的增加或突触前神经递质释放（突触保真度）概率的增加，或两者兼而有之。本项目将利用最近出现的基因编码指示器（GEIs），我们已经证明它可以对单个突触连接的神经递质释放进行强有力的监测。我们的试验数据和其他研究还表明，兴奋性神经递质谷氨酸可以逃避活跃的突触连接，到达距其突触释放位点微米距离的受体。由于大脑中的突触间距小于一微米，这表明兴奋性传输中存在重要的体积传输成分，挑战了神经元网络中有线、一对一连接的原理。记忆形成是否涉及突触保真度的变化，体积传输的兴奋信号在完整的大脑中是否重要，以及它对神经计算的影响是什么——这些问题对于我们理解记忆机制至关重要。解决这些问题是本提案的一个关键动机。因此，我们的总体目标是了解突触保真度的动态以及大脑记忆痕迹形成过程中突触外兴奋信号的程度和作用。基于我们内部既定的创新方法和初步结果，这一目标分为几个具体目标。 - 确定有组织的脑组织中 LTP 诱导过程中突触释放概率的群体动态以及关键的潜在机制。 - 建立体内感觉刺激诱导 LTP 期间丘脑皮质突触突触保真度的动态。 - 评估体内兴奋性皮质突触中谷氨酸突触外作用的程度和可塑性相关变化。 - 了解已记录的突触外谷氨酸逃逸的生理意义和网络影响。我们将通过将单细胞电生理学与细胞靶向 GEIs 的高分辨率、高速复用双光子激发成像相结合来实现这些目标。离体制剂的对照测试将帮助我们优化体内实验，其中我们将在我们测试的胡须刺激范例中监测个体识别的丘脑皮质突触的功能。我们将使用我们已建立的高端计算机模型来评估我们观察到的大脑网络活动的重要性。我们迄今为止积累的已建立的实验方案和试点数据应确保所提出的研究策略的技术可行性。