Long-term expression of optogenetic proteins including channelrhodopsin-2 (ChR2) is widely used to study neural circuit function, but whether ChR2 expression itself perturbs circuits is not known. We expressed a common construct, CAG::ChR2 (H134R)-EYFP-WPRE, in L2/3 pyramidal cells in rat somatosensory cortex via in utero DNA electroporation (IUE). L2/3 pyramidal cells expressed ChR2-EYFP, but histology revealed abnormal morphology and targeting of ChR2-EYFP expressing axons, beginning at postnatal day (P) 33 and increasing with age. Axonal abnormalities included cylinders that enveloped pyramidal cell proximal apical dendrites, and spherical, calyx-like structures that surrounded neuronal cell bodies, including in L4. These are abnormal subcellular and laminar targets for L2/3 pyramidal cell synapses. Abnormalities did not occur in cells expressing GFP instead of ChR2, or in intermixed ChR2-negative axons. Long-term viral-mediated expression (80 d) did not cause axonal abnormalities when the CAG promoter was used, but produced some abnormalities with the stronger αCaMKII promoter (albeit much less than with in utero electroporation). Thus, under some circumstances high-level, long-term expression of ChR2-EYFP can perturb the structural organization of cortical circuits.
Keywords: optogenetics, in utero electroporation, axon development, circuit
Citation: Miyashita T, Shao YR, Chung J, Pourzia O and Feldman DE (2013) Long-term channelrhodopsin-2 (ChR2) expression can induce abnormal axonal morphology and targeting in cerebral cortex. Front. Neural Circuits 7:8. doi: 10.3389/fncir.2013.00008
Received: 30 November 2012; Accepted: 15 January 2013;
Published online: 31 January 2013.
Edited by:Timothy A. Ryan, Weill Medical College of Cornell University, USA
Copyright © 2013 Miyashita, Shao, Chung, Pourzia and Feldman. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.
*Correspondence: Daniel E. Feldman, Department of Molecular and Cell Biology, University of California Berkeley, 142 Life Sciences Addition, Mail Code 3200, Berkeley, CA 94720-3200, USA. e-mail: firstname.lastname@example.org
†Present address: Toshio Miyashita, Division of Developmental Neurophysiology, National Institute for Physiological Sciences, National Institutes of Natural Sciences, Okazaki, Aichi, Japan.