Abstract
Monitoring astrocytic Ca2+ activity is essential to understand the physiological and pathological roles of astrocytes in the brain. However, previous commonly used methods for studying astrocytic Ca2+ activities can be applied in only anesthetized or head-fixed animals, which significantly affects in vivo astrocytic Ca2+ dynamics. In the current study, we combined optic fiber recordings with genetically encoded Ca2+ indicators (GECIs) to monitor astrocytic activity in freely behaving mice. This approach enabled selective and reliable measurement of astrocytic Ca2+ activity, which was verified by the astrocyte-specific labeling of GECIs and few movement artifacts. Additionally, astrocytic Ca2+ activities induced by locomotion or footshock were stably recorded in the cortices and hippocampi of freely behaving mice. Furthermore, this method allowed for the longitudinal study of astrocytic activities over several weeks. This work provides a powerful approach to record astrocytic activity selectively, stably, and chronically in freely behaving mice.
Highlights
Brain astrocytes are abundant glial cells that tile the central nervous system (Khakh and Sofroniew, 2015)
The results indicate that optic fiber-based Ca2+ recording combined with genetically encoded Ca2+ indicators (GECIs) is an ideal approach to dissect the functions of astrocytes in physiological and pathological brain processes
We used serotype 5 of Associated Virus (AAV) (Ortinski et al, 2010) and the minimal astrocyte-specific GfaABC1D promoter (Xie et al, 2010; Shigetomi et al, 2016; Nagai et al, 2019; Yu et al, 2020) to selectively express cytosolic GCaMP6f within astrocytes located in the cortex and hippocampus of the adult mouse (Figure 1A)
Summary
Brain astrocytes are abundant glial cells that tile the central nervous system (Khakh and Sofroniew, 2015) These ubiquitous cells respond to neuronal activity with increased intracellular Ca2+ concentrations via the activation of various receptors and release gliotransmitters, which in turn act on neurons (Haydon and Nedergaard, 2014; Bazargani and Attwell, 2016; Zhang and Chen, 2017). By such direct bidirectional interactions, astrocytic Ca2+ transients serve as significant markers of astrocyte integration into neuronal networks (Halassa and Haydon, 2010; Santello et al, 2019). Recording these transients in freely behaving mice is essential to elucidate the role of astrocytes in physiological and pathological processes and diseases, such as learning and memory (Adamsky et al, 2018), hyperactivity (Nagai et al, 2019), depression (Wang et al, 2017) and Alzheimer’s disease (Verkhratsky et al, 2017)
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