Optogenetic probing and manipulation of the calyx-type presynaptic terminal in the embryonic chick ciliary ganglion

PLoS One. 2013;8(3):e59179. doi: 10.1371/journal.pone.0059179. Epub 2013 Mar 21.

Abstract

The calyx-type synapse of chick ciliary ganglion (CG) has been intensively studied for decades as a model system for the synaptic development, morphology and physiology. Despite recent advances in optogenetics probing and/or manipulation of the elementary steps of the transmitter release such as membrane depolarization and Ca(2+) elevation, the current gene-manipulating methods are not suitable for targeting specifically the calyx-type presynaptic terminals. Here, we evaluated a method for manipulating the molecular and functional organization of the presynaptic terminals of this model synapse. We transfected progenitors of the Edinger-Westphal (EW) nucleus neurons with an EGFP expression vector by in ovo electroporation at embryonic day 2 (E2) and examined the CG at E8-14. We found that dozens of the calyx-type presynaptic terminals and axons were selectively labeled with EGFP fluorescence. When a Brainbow construct containing the membrane-tethered fluorescent proteins m-CFP, m-YFP and m-RFP, was introduced together with a Cre expression construct, the color coding of each presynaptic axon facilitated discrimination among inter-tangled projections, particularly during the developmental re-organization period of synaptic connections. With the simultaneous expression of one of the chimeric variants of channelrhodopsins, channelrhodopsin-fast receiver (ChRFR), and R-GECO1, a red-shifted fluorescent Ca(2+)-sensor, the Ca(2+) elevation was optically measured under direct photostimulation of the presynaptic terminal. Although this optically evoked Ca(2+) elevation was mostly dependent on the action potential, a significant component remained even in the absence of extracellular Ca(2+). It is suggested that the photo-activation of ChRFR facilitated the release of Ca(2+) from intracellular Ca(2+) stores directly or indirectly. The above system, by facilitating the molecular study of the calyx-type presynaptic terminal, would provide an experimental platform for unveiling the molecular mechanisms underlying the morphology, physiology and development of synapses.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials / physiology
  • Action Potentials / radiation effects
  • Animals
  • Axons / physiology
  • Axons / radiation effects
  • Calcium / metabolism
  • Cell Nucleus / physiology
  • Cell Nucleus / radiation effects
  • Chick Embryo
  • Electroporation
  • Ganglia, Parasympathetic / physiology*
  • Ganglia, Parasympathetic / radiation effects
  • Gene Expression / radiation effects
  • Genes, Reporter
  • Green Fluorescent Proteins
  • Ion Transport / radiation effects
  • Light
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism
  • Optogenetics / methods*
  • Presynaptic Terminals / physiology*
  • Presynaptic Terminals / radiation effects
  • Synapses / physiology*
  • Synapses / radiation effects
  • Synaptic Transmission / radiation effects*
  • Transfection

Substances

  • Nerve Tissue Proteins
  • enhanced green fluorescent protein
  • Green Fluorescent Proteins
  • Calcium

Grants and funding

Grant-in-Aid for Scientific Research on Innovative Areas “Mesoscopic Neurocircuitry” (No. 23115501), URL: http://www.meso-neurocircuitry.jp/index_eng.html; Grant-in-Aid for challenging Exploratory Research (No. 23659105) of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, URL: http://www.jsps.go.jp/english/e-grants/grants01.html; Global COE Program (Basic & Translational Research Center for Global Brain Science), MEXT, URL: http://www.med.tohoku.ac.jp/nsgcoe/en/index.html; Program for Promotion of Fundamental Studies in Health Sciences of the National Institute of Biomedical Innovation (NIBIO), URL: http://www.nibio.go.jp/english/index.html. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.