Neuroscience Program, University of Illinois Urbana-Champaign, Urbana, Illinois, USA.
Department of Molecular and Integrative Physiology, University of Illinois Urbana-Champaign, Urbana, Illinois, USA.
Hippocampus. 2023 Dec;33(12):1277-1291. doi: 10.1002/hipo.23580. Epub 2023 Sep 28.
Astrocytes play active roles at synapses and can monitor, respond, and adapt to local synaptic activity. While there is abundant evidence that astrocytes modulate excitatory transmission in the hippocampus, evidence for astrocytic modulation of hippocampal synaptic inhibition remains more limited. Furthermore, to better investigate roles for astrocytes in modulating synaptic transmission, more tools that can selectively activate native G protein signaling pathways in astrocytes with both spatial and temporal precision are needed. Here, we utilized AAV8-GFAP-Optoα1AR-eYFP (Optoα1AR), a viral vector that enables activation of G signaling in astrocytes via light-sensitive α1-adrenergic receptors. To determine if stimulating astrocytic Optoα1AR modulates hippocampal synaptic transmission, recordings were made in CA1 pyramidal cells with surrounding astrocytes expressing Optoα1AR, channelrhodopsin (ChR2), or GFP. Both high-frequency (20 Hz, 45-ms light pulses, 5 mW, 5 min) and low-frequency (0.5 Hz, 1-s pulses at increasing 1, 5, and 10 mW intensities, 90 s per intensity) blue light stimulation were tested. 20 Hz Optoα1AR stimulation increased both inhibitory and excitatory postsynaptic current (IPSC and EPSC) frequency, and the effect on miniature IPSCs (mIPSCs) was largely reversible within 20 min. However, low-frequency stimulation of Optoα1AR did not modulate either IPSCs or EPSCs, suggesting that astrocytic G -dependent modulation of basal synaptic transmission in the hippocampus is stimulation-dependent. By contrast, low-frequency stimulation of astrocytic ChR2 was effective in increasing both synaptic excitation and inhibition. Together, these data demonstrate that Optoα1AR activation in astrocytes changes basal GABAergic and glutamatergic transmission, but only following high-frequency stimulation, highlighting the importance of temporal dynamics when using optical tools to manipulate astrocyte function.
星形胶质细胞在突触中发挥着积极的作用，能够监测、响应和适应局部突触活动。虽然有大量证据表明星形胶质细胞调节海马体中的兴奋性传递，但星形胶质细胞调节海马体抑制性突触传递的证据仍然更为有限。此外，为了更好地研究星形胶质细胞在调节突触传递中的作用，需要更多能够以时空精度选择性激活星形胶质细胞固有 G 蛋白信号通路的工具。在这里，我们利用 AAV8-GFAP-Optoα1AR-eYFP（Optoα1AR），一种通过光敏感α1-肾上腺素能受体激活星形胶质细胞 G 信号的病毒载体。为了确定刺激星形胶质细胞的 Optoα1AR 是否调节海马体突触传递，我们在表达 Optoα1AR、通道视紫红质（ChR2）或 GFP 的 CA1 锥体神经元中进行了记录。我们测试了高频（20 Hz，45 ms 光脉冲，5 mW，5 分钟）和低频（0.5 Hz，1 s 脉冲，强度逐渐增加至 1、5 和 10 mW，每个强度持续 90 s）蓝光刺激。20 Hz Optoα1AR 刺激增加了抑制性和兴奋性突触后电流（IPSC 和 EPSC）的频率，而对微小 IPSC（mIPSCs）的影响在 20 分钟内基本可逆。然而，Optoα1AR 的低频刺激不能调节 IPSC 或 EPSC，这表明星形胶质细胞 G 依赖性调节海马体基础突触传递是刺激依赖性的。相比之下，低频刺激星形胶质细胞的 ChR2 有效地增加了突触兴奋和抑制。这些数据共同表明，星形胶质细胞中 Optoα1AR 的激活改变了基础 GABA 能和谷氨酸能传递，但仅在高频刺激后发生，这突出了在使用光学工具来操纵星形胶质细胞功能时，时间动态的重要性。
