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Ca 2+ transients in astrocyte fine processes occur via Ca 2+ influx in the adult mouse hippocampus
Author(s) -
Rungta Ravi L.,
Bernier LouisPhilippe,
DissingOlesen Lasse,
Groten Christopher J.,
LeDue Jeffrey M.,
Ko Rebecca,
Drissler Sibyl,
MacVicar Brian A.
Publication year - 2016
Publication title -
glia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.954
H-Index - 164
eISSN - 1098-1136
pISSN - 0894-1491
DOI - 10.1002/glia.23042
Subject(s) - astrocyte , extracellular , hippocampal formation , soma , biology , metabotropic glutamate receptor , neuroscience , hippocampus , biophysics , glutamate receptor , neuroglia , calcium imaging , calcium , microbiology and biotechnology , chemistry , biochemistry , receptor , central nervous system , organic chemistry
Astrocytes display complex morphologies with an array of fine extensions extending from the soma and the primary thick processes. Until the use of genetically encoded calcium indicators (GECIs) selectively expressed in astrocytes, Ca 2+ signaling was only examined in soma and thick primary processes of astrocytes where Ca 2+ ‐sensitive fluorescent dyes could be imaged. GECI imaging in astrocytes revealed a previously unsuspected pattern of spontaneous Ca 2+ transients in fine processes that has not been observed without chronic expression of GECIs, raising potential concerns about the effects of GECI expression. Here, we perform two‐photon imaging of Ca 2+ transients in adult CA1 hippocampal astrocytes using a new single‐cell patch‐loading strategy to image Ca 2+ ‐sensitive fluorescent dyes in the cytoplasm of fine processes. We observed that astrocyte fine processes exhibited a high frequency of spontaneous Ca 2+ transients whereas astrocyte soma rarely showed spontaneous Ca 2+ oscillations similar to previous reports using GECIs. We exploited this new approach to show these signals were independent of neuronal spiking, metabotropic glutamate receptor (mGluR) activity, TRPA1 channels, and L‐ or T‐type voltage‐gated calcium channels. Removal of extracellular Ca 2+ almost completely and reversibly abolished the spontaneous signals while IP 3 R2 KO mice also exhibited spontaneous and compartmentalized signals, suggesting they rely on influx of extracellular Ca 2+ . The Ca 2+ influx dependency of the spontaneous signals in patch‐loaded astrocytes was also observed in astrocytes expressing GCaMP3, further highlighting the presence of Ca 2+ influx pathways in astrocytes. The mechanisms underlying these localized Ca 2+ signals are critical for understanding how astrocytes regulate important functions in the adult brain. GLIA 2016;64:2093–2103