Astrocytes are considered active partners to neurons in information processing. Heterogeneous, bidirectional interaction between neurons and astrocytes alludes to circuit specific communication. However, the role of astrocytes in information processing, primarily established through ex vivo experiments, has been challenged by a series of controversies that highlighted the importance of studying astrocytes under fully physiological conditions in behaving mice. Astrocytes extend highly ramified processes that cradle synapses. They form functionally independent microdomains where they exhibit a rich repertoire of localized calcium signals. How astrocyte Ca²+ microdomain signals relate to neuronal activity and behaviour in vivo is still unclear. My objective was to investigate circuit specific, single-astrocyte Ca²+ microdomain activity in mice during behavioural states and sensory stimuli. I found that adeno-associated viruses (AAVs) can transfer anterogradely along thalamocortical projections to transduce cortical astrocytes and neurons. This axo-astrocytic AAV transfer enables the study of astrocytes and neurons embedded in specific neuronal circuits. Intersectional approaches, using anterograde axo-astrocytic AAV transfer in combination with membrane tagged genetically encoded calcium indicators (GECIs), enabled sparse, high contrast labelling of cortical astrocytes embedded in the somatosensory system of mice. Continuous imaging with two-photon microscopy of single astrocytes for about ≈1 hour combined with automatic, unbiased extraction of Ca²+ activity revealed a rich repertoire of subsecond, µm scale, localized Ca²+ signals. The number, size and duration of astrocytic Ca²+ signals were modulated with locomotion but not with intermittent whisker-touch stimulation. Locomotion and whisker stimuli evoked rapid [Ca²+]i elevation in thalamocortical axon boutons, whose activity was not correlated with nearby astrocyte Ca²+ microdomain signalling. Astrocyte fine processes exhibit heterogeneous, non-random, Ca²+ signalling patterns giving rise to hotspots of higher activity that are stable over time. Hotspot patterns allude to subcellular specialization. Our study: a) provides a new toolkit for studying neuron-astrocyte interactions within brain circuits, b) extends our understanding of astrocyte Ca²+ microdomain signalling and relationship to neuronal activity in behaving animals and c) suggests that there are astrocyte Ca²+ activity maps in the brain.
Exam Date
2020-02-26
Degree Conferral Date
2020-03-31
Degree
Doctor of Philosophy
Degree Referral Number
38005甲第48号
Degree Conferrral Institution
Okinawa Institute of Science and Technology Graduate University
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Astrocyte calcium activity mapping in behaving mice using anterograde axo-astrocytic AAV transfer
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