Heterogeneous glial regulation of inhibitory hippocampal synapses

海马网由负责整合和远距离通讯的主兴奋神经元和调节主细胞活动的局部抑制性中间神经元(IN)组成，特别是生长抑素(SOM)和小白蛋白(PV)中间神经元。此外，星形胶质细胞是中枢神经系统中的主要胶质细胞，它与兴奋性和抑制性神经元相互作用，调节它们的活动，并调节神经元网络中的通讯。有趣的是，与IN相似，最近的研究表明星形胶质细胞也表现出异质性。虽然星形胶质细胞调节兴奋性突触的活性和可塑性的证据很多，但星形胶质细胞在抑制突触调节中的作用仍然不清楚。我们最近的工作表明，星形胶质细胞对IN突触的这两个亚群进行了不同的调节。因此，我们假设：由于星形胶质细胞的异质性，它们对锥体细胞上不同类型的GABA能突触有不同的调节作用，并控制局部网络的兴奋性。我们建议探索抑制性神经元亚群与神经胶质细胞之间的相互作用，以研究星形胶质细胞的差异调节及其潜在的基本分子、细胞和网络机制。将有四个目标。1.检测大鼠海马区CA1区星形胶质细胞的功能异质性。我们将描述选择性地与锥体神经元上的两种抑制性突触相关的星形胶质细胞的特性。图2.我们将测试星形胶质细胞的激活机制是否针对抑制性突触的类型。我们将使用星形胶质细胞内的钙离子成像测量和锥体细胞中光遗传诱发的突触抑制的全细胞记录来确定星形胶质细胞激活的SOM和PV中间神经元选择性机制。3.我们将使用两种策略来研究SOM和PV神经元间神经元特异性突触抑制的选择性神经胶质调节的影响：1.选择性钙离子螯合或GDPbS阻断G蛋白活性将阻断星形胶质细胞亚群的活性。2.DREADD受体将在GFAP启动子的调控下在星形胶质细胞中表达。星形胶质细胞的激活对SOM和PV中间神经元在锥体体内光遗传诱发的突触抑制的影响将被测试。4.我们将研究星形胶质细胞调节对IN亚群海马网活动的影响。我们预测，阻断与SOM突触相关的星形胶质细胞将影响突触的可塑性事件，而阻断与PV突触相关的星形胶质细胞将主要改变海马回路的放电输出。展望：这项工作将使我们能够揭示海马区星形胶质细胞的功能异质性及其在海马区网络中的作用。这将为神经元网络的适应性、选择性和整合的神经胶质调节提供直接证据。

The hippocampal network is composed of principal excitatory neurons responsible for integration and long distance communication, and local inhibitory interneurons (IN) that regulate the activity of principal cells, in particular the somatostatin (SOM) and parvalbumin (PV) interneurons. In addition, astrocytes, the main glial cells in the CNS, interact with excitatory and inhibitory neurons to regulate their activity and tune communication in the neuronal network. Interestingly, similar to IN, recent work revealed that astrocytes also show heterogeneity. While evidence of astrocyte modulation of excitatory synapses activity and plasticity is extensive, the roles of astrocytes in the regulation of inhibitory synapses remains ill defined. Our recent work suggests that astrocytes differentially regulate these two subsets of IN synapses. Hence, we hypothesize that: Owing to their heterogeneity, astrocytes differentially regulate distinct types of GABAergic synapses on pyramidal cells and control local networks excitability    We propose to probe interactions between subsets of inhibitory neurons and glial cells, to study the differential regulation of astrocytes and the underlying fundamental molecular, cellular and network mechanisms. Four objectives will be targeted.     1. We will examine the functional heterogeneity of astrocytes in CA1 area of hippocampus. We will characterise the properties of astrocytes that are selectively associated with the two types of inhibitory synapses on pyramidal neurons.    2. We will test if the mechanisms of activation of astrocytes are specific to the types of inhibitory synapses. We will use Ca2+ imaging measurements in astrocytes and whole cell recordings of optogenetically-evoked synaptic inhibition in pyramidal cells to determine the SOM and PV interneuron selective mechanisms of astrocyte activation.    3. We will study the impact of the selective glial regulation of SOM and PV interneuron specific synaptic inhibition using two strategies: 1. Activity of the subpopulation of astrocytes will be blocked by selective Ca2+ chelating or G-protein activity blockade with GDPbS. 2. DREADD receptors will be expressed in astrocytes under the control of a GFAP promoter. Effects of astrocyte activation on the optogenetically-evoked synaptic inhibition in pyramidal by SOM and PV interneurons will be tested.    4. We will examine the impact of astrocyte regulation on hippocampal network activity on subset of IN. We predict that blockade of astrocytes associated with SOM synapses will influence synaptic plasticity events while blocking those associated with PV synapses will mainly alter the firing output of the hippocampal circuit.    Perspectives: This work would allow us to unravel a functional heterogeneity of hippocampal astrocytes and its role in the hippocampal network. This would provide direct evidence of adaptive, selective and integrated glial regulation of a neuronal network.