CTBS对活体YFP卒中小鼠E/I平衡的调控机制与神经可塑性研究

Damage to the posterior parietal cortices (PPC), usually caused by ischemic events or traumatic head injury, lead to spatial movement disorders. Several lines of evidence have indicated the involvement of neural excitation and inhibition (E/I) imbalance in stroke patients. Moreover, E/I imbalance are involved not only in brain disorders but also in neuroplasticity. However, how the effects of E/I balance on neuroplasticity for the stroke patients are poorly understood. Generally, brain function depends on the homeostatic regulation between excitation and inhibition. The relationship between synaptic excitation and inhibition (E/I ratio), two opposing forces in the mammalian cerebral cortex, affects many cortical functions. Individual L2/3 pyramidal cells show stable E/I ratios in time despite fluctuating cortical activity levels. This is because when excitation increases, inhibition increases proportionally through the increased recruitment of inhibitory neurons, a phenomenon referred to as excitation-inhibition balance. Whilst most studies report that GABAergic neurons were the prime source of modulating excitation-inhibition balance in the cortex. That is to say, E/I balance between layer-4-mediated excitation and layer-2/3-mediated inhibition is equalized across pyramidal cells through the bidirectional modulation of the strength of GABA cell synapses. An increase in excitability should selectively increase GABA-cell-mediated inhibition. GABA cells can provide stronger inhibition onto neurons that receive stronger layer-4-mediated excitation, thereby contributing to the equalization of E/I ratios. Under certain pathological conditions, GABAergic inhibition is largely reduced, resulting in the disinhibition of neural network, such as that in brain ischemia, TBI, Pain and epilepsy. Based on the E/I balance through GABA-cell-mediated inhibition theory, we hypothesize that cTBS stimulation, multiple bursts delivered at theta frequency (3-7Hz), should be an important strategy in the treatment of E/I imbalance in brain lesions. In this study, we should investigate the effect of cTBS on the synaptic transmission and neuronal excitation in the PPC of mice. To address the role for GABA-cell-mediated inhibition, induced by cTBS, for controlling neuronal E/I balance. In this project, we design and use several novel tools to causally investigate the cellular E/I imbalance hypothesis in vivo YFP stroke mice, and explore the associated circuit physiology. Indeed, Indeed, we can demonstrate that (1) the relationship between E/I imbalance, gamma synchrony, and cTBS-induced in vivo YFP stroke mice; (2) the neural plasticity across the maintenance of E/I balance through cTBS-induced; (3) the specific facet of cTBS-induced neural E/I balance after stroke. The findings will be put in context by investigation of structural determinants of this relation through data-driven analysis and theoretical models.

脑梗死后兴奋-抑制（E/I）失平衡是阻碍神经功能重塑的关键因素，然而有关E/I失平衡的调控机制及其对突触可塑性的作用尚未可知。我们前期研究发现，抑制性神经元是调控E/I平衡和维持正常脑功能的核心，据此我们设想：模拟GABA能神经元活动节律的持续θ爆发式刺激（cTBS）应该可以调控锥体神经元接收的兴奋和抑制信号，从而有助于脑梗死后E/I平衡的恢复，促进神经功能连接的重构与重塑。为此，本项目拟采用cTBS作用于大脑皮层兴奋-抑制-锥体细胞微环路，通过记录锥体神经元的兴奋性和抑制性突触后电流来分析E/I比率，从而阐明cTBS对E/I平衡的调控机制。然后，利用不同强度cTBS在不同时期干预后顶叶梗死小鼠，采用活体双光子神经成像技术评测E/I平衡和突触重塑，揭示cTBS通过调控E/I平衡对神经可塑性的作用机制。这不仅在探讨cTBS对中枢的调控机制上具有创新，还为脑卒中康复提供了新的治疗策略。

脑卒中后定向和运动障碍是最常见的功能损害，严重影响患者日常生活活动能力的恢复。人们日常的定向运动、空间导航和记忆活动与后顶叶（PPC）密切相关，虽然后顶叶作为空间定向功能的关键脑区已经明确，但是目前很多治疗手段疗效并不肯定，这与卒中后脑功能重塑的调控机制仍不清楚有关。竞争性抑制是一个越来越为临床和研究人员广泛接受的理论假说，单侧脑损害后会出现双侧半球同源脑区间竞争性抑制“失平衡”，这既是半球间竞争性抑制理论的结果反映，也是半球间竞争性抑制理论的反证。脑梗死后神经环路兴奋-抑制（E/I）失平衡是阻碍神经功能重塑的关键因素，然而有关神经环路E/I失平衡的调控机制及其对突触可塑性的作用尚未可知。因此，本课题以抑制性神经元是调控E/I平衡和维持正常脑功能的核心作为研究导向，利用膜片钳、双光子活体成像技术，研究发现模拟GABA能神经元活动节律的持续θ爆发式刺激（cTBS）可以双向调控锥体神经元接收的兴奋和抑制信号，从而有助于脑梗死后神经环路E/I平衡的恢复，促进神经功能连接的重构与重塑。此外，cTBS在脑梗死急性和慢性期通过不同的机制促进了脑梗死后功能的康复：在脑梗死急性期，cTBS刺激扩张毛细血管，促进了血流灌注，并因此减小了梗死灶并抑制了炎症；在脑梗死慢性期，梗死灶周围GABA介导的相位性抑制信号有升高，cTBS通过提高相位性抑制改善了其学习记忆能力。这不仅是cTBS对中枢的调控机制的创新，还为脑卒中康复提供了新的治疗策略。