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Abstract

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Representative Results

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Acknowledgements

Materials

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Neuroscience

Optogenetic Activation of Zebrafish Somatosensory Neurons using ChEF-tdTomato

Published: January 31st, 2013

DOI:

10.3791/50184

1Department of Molecular, Cell, and Developmental Biology, University of California, Los Angeles

Optogenetic techniques have made it possible to study the contribution of specific neurons to behavior. We describe a method in larval zebrafish for activating single somatosensory neurons expressing a channelrhodopsin variant (ChEF) with a diode-pumped solid state (DPSS) laser and recording the elicited behaviors with a high-speed video camera.

Larval zebrafish are emerging as a model for describing the development and function of simple neural circuits. Due to their external fertilization, rapid development, and translucency, zebrafish are particularly well suited for optogenetic approaches to investigate neural circuit function. In this approach, light-sensitive ion channels are expressed in specific neurons, enabling the experimenter to activate or inhibit them at will and thus assess their contribution to specific behaviors. Applying these methods in larval zebrafish is conceptually simple but requires the optimization of technical details. Here we demonstrate a procedure for expressing a channelrhodopsin variant in larval zebrafish somatosensory neurons, photo-activating single cells, and recording the resulting behaviors. By introducing a few modifications to previously established methods, this approach could be used to elicit behavioral responses from single neurons activated up to at least 4 days post-fertilization (dpf). Specifically, we created a transgene using a somatosensory neuron enhancer, CREST3, to drive the expression of the tagged channelrhodopsin variant, ChEF-tdTomato. Injecting this transgene into 1-cell stage embryos results in mosaic expression in somatosensory neurons, which can be imaged with confocal microscopy. Illuminating identified cells in these animals with light from a 473 nm DPSS laser, guided through a fiber optic cable, elicits behaviors that can be recorded with a high-speed video camera and analyzed quantitatively. This technique could be adapted to study behaviors elicited by activating any zebrafish neuron. Combining this approach with genetic or pharmacological perturbations will be a powerful way to investigate circuit formation and function.

The development of optogenetic methods for promoting or inhibiting neuronal excitability with defined wavelengths of light has made it possible to study the function of distinct populations of neurons in neural circuits controlling behavior 1, 19, 21. This technique is often used to activate groups of neurons, but it can also be used to activate individual neurons. Zebrafish larvae are particularly amenable to these methods since they are translucent, their nervous system develops quickly, and creating transgenic animals is fast and routine. However, significant technical hurdles must be overcome to reliably achieve single neuron activation.

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Prepare the following ahead of time.

1. Prepare Optic Cable

  1. Create a storage unit for the optic cable by melting the tapered neck of a glass Pasteur pipette over a Bunsen burner to create a ~150 ° angle.
  2. Using a wire cutter or a razor blade, carefully cut the optic cable into two pieces. Each piece should have one end with a FC/PC adaptor and one exposed end. Store one piece as a reserve cable.
  3. Strip the optic cable down to the cladding by removing the fiber.......

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Figure 1
Figure 1. Optic cable set up. (A) Layers of a fiber optic cable. (B) Stripped fiber optic cable in a Pasteur pipette. (C) Fiber optic cable in Pasteur pipette positioned using a micromanipulator.

Figure 2
Figure 2. Injection mold template.

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We have described an approach for optogenetic activation of single RB neurons in live zebrafish. Our method employs transient transgenesis to express a fluorescently tagged channelrhodopsin variant, ChEF-tdTomato13, in specific somatosensory neurons. This approach could easily be adapted for use in other larval zebrafish cell populations.

Using this approach we consistently elicited behavioral responses from 34-48 hpf larvae expressing ChEF-tdTomato. Using a 5 msec pulse of bl.......

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We thank Fumi Kubo, Tod Thiele and HerwigBaier (UCSF/Max Planck Institute) for advice on behavior experiments and DPSS laser set up; Heesoo Kim and Chiara Cerri from the MBL Neurobiology Course for assisting in ChEF-tdTomato experiments; PetronellaKettunen (University of Gothenburg)for initial collaboration on optogenetic experiments; BaljitKhakh, Eric Hudson, Mike Baca and John Milligan (UCLA) for technical advice; and Roger Tsien (UCSD) for the ChEF-tdTomato construct. This work was supported by an NRSA (5F31NS064817) award to AMSP and a grant from the NSF (RIG:0819010) to AS.

....

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Name Company Catalog Number Comments
Name of Reagent/Material Company Catalog Number Comments
Materials
Glass Pasteur pipette Fisher 1367820B or equivalent (10-15 mm diameter)
200 μm optic fiber ThorLabs AFS200/220Y-CUSTOM Patch Cord, Length: 3 m, End A: FC/PC, End B: FC/PC, Jacket: FT030
50 μm optic fiber ThorLabs AFS50/125Y-CUSTOM Patch Cord, Length: 3 m, End A: FC/PC, End B: FC/PC, Jacket: FT030
Adjustable Stripping Tool ThorLabs AFS900 or Three-Hole Stripping Tool (FTS4)
Diamond Wedge scribe ThorLabs S90W
Flaming/Brown Micropipette Puller Sutter Instruments P-97 or equivalent
Borosilicate glass tubing with filament Sutter Instruments BF-100-78-10
Injection mold n/a n/a Figure 5
1.5 ml centrifuge tubes Any Any
Petri dish (100x15 mm) Any Any
Petri dish (60x15 mm) Any Any
Pressure injector ASI MPPI-3 or equivalent
Micromanipulator and metal stand Narashige M152 or equivalent
Disposable plastic pipettes Fisherbrand 13-711-7 or equivalent
Poker (Pin holder and Insect pin) Fine Science Tools, Inc. 26018-17 and 26000-70 or equivalent
Forceps Fine Science Tools, Inc. 11255-20 or equivalent
Microloader pipette tips Eppendorf 9300001007
28.5 °C incubator any any
42 °C heat block Any Any
Non-Sterile scalpel blades #11 Fine Scientific Tools, Inc. 10011-00 or equivalent
Dissecting scope Zeiss Stemi or equivalent
Fluorescent dissecting scope with standard filter Any any or equivalent
Confocal microscope Zeiss LSM 510 or 710 or equivalent with lasers for GFP and RFP, and 10x, 20x and 40x objectives
High speed camera AOS Technologies, Inc. X-PRI (130025-10) or equivalent
473 nm portable laser Crystal lasers CL-473-050 or higher power, with TTL option
S48 Stimulator Astro-Med, Inc. Grass Instrument division S48K or equivalent
FC/PC to FC/PC mating sleeve ThorLabs ADAFC1 May need for optic cable connection
Laser Safety Glasses ThorLabs LG10 or equivalent
24 culture plates Genesee 25-102 or equivalent
Single depression slides Fisher S175201 Or equivalent
Reagent
Instant ocean Aquatic Ecosystems IS50
Methylene blue Fisher S71325
Phenol red Sigma P4758
Agarose EMD 2125 or equivalent
Low Melt agarose Sigma A9045 or equivalent
PTU Sigma P7629
Tricaine Sigma A5040
blue/embryo water 10 L ddH2O
0.6 g Instant Ocean
6 drops methylene blue
phenol red (5 mg/ml in 0.2 M KCl)
100x PTU 0.150 g PTU
50 ml ddH2O
dissolve at 70 °C, shake often
aliquot and store at -20 °C
1x PTU 1 ml 100x PTU
99 ml blue/fish water
Tricaine stock solution 400 mg tricaine
97.9 ddH2O
~2.1 ml 1M Tris, pH9.0 adjust pH to ~7.0
store in 4 °C or -20 °C for long term storage

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