Cholinergic interneurons (CINs) are believed to form synchronous cell assemblies that modulate the striatal microcircuitry and possibly orchestrate local dopamine release. We expressed GCaMP6s, a genetically encoded calcium indicator (GECIs), selectively in CINs, and used microendoscopes to visualize the putative CIN assemblies in the dorsal striatum of freely moving mice. The GECI fluorescence signal from the dorsal striatum was composed of signals from individual CIN somata that were engulfed by a widespread fluorescent neuropil. Bouts of synchronous activation of the cholinergic neuropil revealed patterns of activity that preceded the signal from individual somata. To investigate the nature of the neuropil signal and why it precedes the somatic signal, we target-patched GECI-expressing CINs in acute striatal slices in conjunction with multiphoton imaging or wide-field imaging that emulates the microendoscopes’ specifications. The ability to detect fluorescent transients associated with individual action potential was constrained by the long decay constant of GECIs (relative to common inorganic dyes) to slowly firing (<2 spikes/s) CINs. The microendoscopes’ resolving power and sampling rate further diminished this ability. Additionally, we found that only back-propagating action potentials but not synchronous optogenetic activation of thalamic inputs elicited observable calcium transients in CIN dendrites. Our data suggest that only bursts of CIN activity (but not their tonic firing) are visible using endoscopic imaging, and that the neuropil patterns are a physiological measure of the collective recurrent CIN network spiking activity.
Bibliographical noteFunding Information:
Received September 6, 2018; accepted December 27, 2018; First published January 4, 2019. The authors declare no competing financial interests. Author Contributions: R.R., Y.A., L.T., G.J.M., G.A.J., and J.A.G. designed research; R.R., Y.A., L.T., W.-H.C., and J.J.A.B. performed research; R.R., Y.A., L.T., and G.A.J. analyzed data; R.R., Y.A., L.T., G.A.J., and J.A.G. wrote the paper. This work was funded by a European Research Council Consolidator Grant (646886–SynChI) and two grants from the Israel Science Foundation (154/14 and 155/14) to J.A.G. We thank Dr. Yaniv Ziv for his expert guidance and advice, and Anatoly Shapochnikov for excellent technical support. *R.R., Y.A., and L.T. contributed equally to this work. J. J. Aceves Buendía’s present address: Departmento de Neurología y Psiquiatría, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubi-ran, 14080, Ciudad de México, Mexico. Correspondence should be addressed to Joshua A. Goldberg at firstname.lastname@example.org. https://doi.org/10.1523/ENEURO.0351-18.2018 Copyright © 2019 Rehani et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
© 2019 Rehani et al.
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