Name: zebrafish in situ spinal cord preparation for electrophysiological recordings from spinal sensory and motor neurons
Uploaded: 2017-04-18T14:00:00
Description: Watch this Scientific Journal Video about Zebrafish In Situ Spinal Cord Preparation for Electrophysiological Recordings from Spinal Sensory and Motor Neurons at JoVE.com

This work was supported by grants from the NIH (F32 NS059120 to RLM and R01NS25217 and P30NS048154 to ABR).

All animal procedures were approved by the Institutional Animal Care and Use Committee (IACUC; Office of Laboratory Animal Resources, University of Colorado Anschutz Medical Campus).
1. Zebrafish Husbandry
<ol>
	<li>Raise and maintain adult zebrafish (Danio rerio) at 28.5 &#176;C on a 10 h dark/14 h light cycle and with appropriate water treatment and exchange52.</li>
	<li>Raise zebrafish embryos/larvae at 28.5 &#176;C in embryo medium until they reach the de...

The methods described here allow for the electrical and morphological characterization of sensory and motor neurons of zebrafish embryos after minimal dissection of the spinal cord. Neurons remain healthy for at least 1 h, the time limit imposed on these recordings. Neurons have been recorded using the standard whole-cell configuration, as well as from nucleated patches; the latter method minimizes space-clamp issues that can preclude a detailed biophysical study of ion currents9.
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George Streisinger pioneered the use of Danio rerio, commonly known as zebrafish, as a model system for the genetic analysis of vertebrate development10. The model offers several advantages including: (1) relatively simple and inexpensive animal husbandry; (2) external fertilization, allowing easy access to embryos from the earliest developmental stages; and (3) a transparent embryo, permitting direct and repeated observations of cells, tissues, and organs as they form.
Over the ensuing decades, several advances further increased the power of the zebrafish model. In particular, forward genetic screens and whole-genome sequencing efforts played key roles in the identification of mutations and genes critical to many developmental processes11,12,13,14,15,16. Gateway cloning methods have allowed the routine application of transgenic approaches17,18. Recent advances in genome editing, exemplified by transcription activator-like (TALENs) and clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 nucleases, allow for the targeted introduction of mutations, as well as knock-out and knock-in approaches19,20,21,22. Combined, these methods make zebrafish a powerful model for the study of the genetic mechanisms underlying specific behaviors and several human diseases23,24,25,26,27.
This work focuses on developmental regulation and the role of electrical activity in neuronal development. The focus is on the spinal cord, for which the zebrafish model provides several advantages. First, it is relatively easy to access zebrafish at embryonic and larval stages; therefore, one can study spinal cord function during developmental stages that have fewer neurons and simpler circuitry28,29. Moreover, the zebrafish spinal cord has a diverse set of neurons, similar to other vertebrates, as demonstrated by characteristic and distinguishing patterns of transcription factors30,31,32,33,34,35.
The majority of studies in zebrafish that aim to uncover the mechanisms that underlie the function of spinal cord circuits, especially ones that support locomotion, are understandably focused on larval stages36,37,38,39,40,41,42,43. However, many of the neurons that form the spinal locomotive networks initiate their differentiation at early embryonic stages, ~9-10 h post-fertilization (hpf)44,45,46,47,48,49,50,51. In view of this, understanding how the morphological and electrical properties of spinal neurons arise and change between the embryonic and larval stages is important for an overall understanding of locomotor circuit formation and function.
The dissection methods described here allow patch clamp recordings from spinal neurons and have been successfully applied at embryonic stages (~17-48 hpf) and larval stages (~3-7 days post fertilization [dpf]). This approach limits the amount of dissection required to provide access to the neurons of interest. The protocol differs from the majority of the other published methods for recording from zebrafish spinal neurons in that veterinarian suture glue is used, rather than a fine tungsten pin, to attach the embryo or larva to the recording chamber. The availability of two different approaches (i.e., suture glue versus the tungsten pin) for mounting the zebrafish embryos or larvae for electrophysiological analysis provides researchers with alternative options to achieve their specific experimental goals.
First, procedures for accessing and recording from a population of primary sensory neurons, Rohon-Beard cells, are described. The cell bodies of these neurons lie within the dorsal spinal cord. Rohon-Beard cells exist in numerous vertebrate species, differentiate early in development, and underlie the embryonic touch response6,44,47,48.
Second, procedures for accessing and recording from spinal motor neurons are detailed. Zebrafish spinal motor neurons arise during two waves of neurogenesis. The earlier-born primary motor neurons arise at the end of gastrulation (~9-16 hpf), with only 3-4 primary motor neurons present per hemisegment45,46,49. In contrast, the later-born population of secondary motor neurons is more numerous and arises during a prolonged period, starting at ~14 hpf45,50. Secondary motor neuron genesis in mid-trunk segments is mostly completed by 51 hpf50. Secondary motor neurons are considered to be the counterpart of motor neurons in amniotes46. Interestingly, supraspinal neurons, via dopamine, regulate locomotion in the larva and secondary motor neuron genesis in the embryo and young larva50,51. Primary and secondary motor neurons each comprise several different subtypes. Each primary motor neuron subtype projects a peripheral axon that innervates a characteristic muscle group, resulting in a stereotypical, identifying axonal trajectory. Generally, secondary motor neurons follow the axonal pathways previously established by primary motor neurons. Thus, with respect to axonal trajectories, primary and secondary motor neurons are similar, with the exception that axonal thickness and somata size are greater for primary motor neurons45.
Third, methods for recording from a few types of interneurons are discussed. However, in these cases, a limited amount of removal of other spinal cord cells is required, and thus the spinal cord is less intact than for recordings from Rohon-Beard cells or motor neurons.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Vacuum filter/Storage bottle, 0.22 mm pore</td>
			<td>Corning</td>
			<td>431096</td>
			<td></td>
		</tr>
		<tr>
			<td>Syringe filter 0.2 mm</td>
			<td>Whatman</td>
			<td>6780-2502</td>
			<td></td>
		</tr>
		<tr>
			<td>Tricaine</td>
			<td>Sigma</td>
			<td>A-5040</td>
			<td>Ethyl 3-aminobenzoate methanesulfonate salt&#160;</td>
		</tr>
		<tr>
			<td>a-bugarotoxin</td>
			<td>Tocris</td>
			<td>11032-79-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Tetrodotoxin</td>
			<td>Tocris</td>
			<td>4368-28-9</td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa-549 hydrazine salt</td>
			<td>Molecular Probes</td>
			<td>A-10438</td>
			<td>fluorescent dye</td>
		</tr>
		<tr>
			<td>Spin-X centrifuge tube filter</td>
			<td>Corning</td>
			<td>8161</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass microscope slide</td>
			<td>Fisher</td>
			<td>12-550C</td>
			<td></td>
		</tr>
		<tr>
			<td>Sylgard silicone elastomer kit</td>
			<td>Dow Corning</td>
			<td>184</td>
			<td>silicone elastomer</td>
		</tr>
		<tr>
			<td>Petri dishes</td>
			<td>Falcon</td>
			<td>351029</td>
			<td></td>
		</tr>
		<tr>
			<td>Borosilicate glass capillaries</td>
			<td>Harvard Apparatus</td>
			<td>30-0038</td>
			<td>inner and outer diameters of 0.78 and 1.0 mm (thin walled glass capillaries)</td>
		</tr>
		<tr>
			<td>Borosilicate glass capillaries</td>
			<td>Drummond Scientific</td>
			<td>1-000-1000-100</td>
			<td>inner and outer diameters of 1.13 and 1.55 mm (thick walled glass capillaries)</td>
		</tr>
		<tr>
			<td>Miniature barbed polypropylene fitting&#160;</td>
			<td>Cole-Palmer</td>
			<td>6365-90</td>
			<td></td>
		</tr>
		<tr>
			<td>Vetbond tissue adhesive&#160;</td>
			<td>3M</td>
			<td>1469SB</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagenase XI</td>
			<td>Sigma</td>
			<td>C7657</td>
			<td></td>
		</tr>
		<tr>
			<td>Microelectrode puller</td>
			<td>Sutter Instruments</td>
			<td>&#160;Model P-97&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Amplifier</td>
			<td>Molecular Devices</td>
			<td>Axopatch 200B</td>
			<td></td>
		</tr>
		<tr>
			<td>Head stage</td>
			<td>Molecular Devices</td>
			<td>CV203BU</td>
			<td></td>
		</tr>
		<tr>
			<td>Motorized micromanipulator&#160;&#160;</td>
			<td>Sutter Instruments</td>
			<td>MP-285</td>
			<td></td>
		</tr>
		<tr>
			<td>Tygon tubing</td>
			<td>Fisher</td>
			<td>14-169-1B</td>
			<td>ID 1/16 IN, OD 1/8 IN and WALL 1/32 IN (flexible laboratory tubing)</td>
		</tr>
		<tr>
			<td>Electrode holder</td>
			<td>Molecular Devices</td>
			<td>1-HC-U</td>
			<td></td>
		</tr>
		<tr>
			<td>Pharmaseal Three-Way Stopcocks&#160;</td>
			<td>Baxter</td>
			<td>K75</td>
			<td></td>
		</tr>
		<tr>
			<td>Digitizer</td>
			<td>Axon Instruments</td>
			<td>Digidata 1440A</td>
			<td></td>
		</tr>
		<tr>
			<td>Inverted microscope&#160;</td>
			<td>Zeiss</td>
			<td>Axioskop2 FS plus</td>
			<td></td>
		</tr>
		<tr>
			<td>40x/0.80w Achroplan objective</td>
			<td>Zeiss</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Data acquisition and analysis software&#160;</td>
			<td>Axon Instruments</td>
			<td colspan="2">PClamp 10 - Clampex and Clampfit&#160;</td>
		</tr>
		<tr>
			<td>Micropipette puller</td>
			<td>Sutter Instruments</td>
			<td>Model P-97</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td colspan="2">Dissection and Recording Solutions(in mM)</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td colspan="4">All solutions, except the intracellular, are stable for ~ 2 - 3 months when filtered (0.22 mm filter cups) and stored at room temperature (RT).</td>
		</tr>
		<tr>
			<td colspan="4">The intracellular solution is filtered (0.2 mm syringe filters) and stored frozen (-20&#176;C) in small aliquots that are individually thawed on the day of use.&#160;</td>
		</tr>
		<tr>
			<td colspan="2" rowspan="1">Dissection/Ringer&#8217;s solution</td>
			<td></td>
			<td colspan="2">145 NaCl, 3 KCl, 1.8 CaCl2.2H2O, 10 HEPES; pH 7.4 (with NaOH)</td>
		</tr>
		<tr>
			<td colspan="2">Pipette (intracellular) recording solution</td>
			<td></td>
			<td colspan="2">135 KCl, 10 EGTA-acid, 10 HEPES; pH 7.4 (with KOH).</td>
		</tr>
		<tr>
			<td colspan="2">Bath (extracellular) recording solution/voltage and current-clamp</td>
			<td></td>
			<td colspan="2">125 NaCl, 2 KCl, 10 CaCl2.2H2O, 5 HEPES; pH 7.4 (with NaOH).</td>
		</tr>
		<tr>
			<td colspan="2">Alexa-594 hydrazine salt stock solution.&#160;</td>
			<td></td>
			<td colspan="2">Prepare a 13.2 mM stock in ddH2O, aliquot (~ 100 &#181;l) and store at -20&#176;C. For use, dilute the stock solutiond 132 fold with pipette solution to a final concentration of 100 mM. After dilution, filter the Alexa-594 containing pipette solution&#160; with a centrifuge tube filter.</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Immobilizing agents</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td colspan="2">0.4 % ethyl 3-aminobenzoate methanesulfonate salt (Tricaine)</td>
			<td></td>
			<td colspan="2">Prepare a 0.4% stock solution in 0.2M Tris, pH9 (0.4 g Tricaine/100 ml 0.2 M Tris</td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td colspan="2">Adjust pH to 7 with NaOH and store at -20&#176;C.</td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td colspan="2">For use, dilute the stock solution ~ 25 fold in embryo media</td>
		</tr>
		<tr>
			<td>250 &#956;M &#945;-bungarotoxin</td>
			<td></td>
			<td colspan="2">Prepare a 250 &#956;M stock in ddH2O (1 mg/500 &#956;l), prepare 100 &#181;l aliquots, and sotre at -20&#176;C.</td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td colspan="2">For use, dilute 2,500-fold with extracellular solution to a final concentration of 100 nM.</td>
		</tr>
		<tr>
			<td>1 mM Tetrodotoxin</td>
			<td></td>
			<td colspan="2">Prepare a 1 mM stock in ddH2O (1 mg/3 ml), prepare 100 &#181;l aliquots, and sotre at -20&#176;C.</td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td colspan="2">For use, dilute 2,000-fold with extracellular solution to a final concentration of 500 nM.</td>
		</tr>
	</tbody>
</table>

zebrafish in situ spinal cord preparation for electrophysiological recordings from spinal sensory and motor neurons

Zebrafish, first introduced as a developmental model, have gained popularity in many other fields. The ease of rearing large numbers of rapidly developing organisms, combined with the embryonic optical clarity, served as initial compelling attributes of this model. Over the past two decades, the success of this model has been further propelled by its amenability to large-scale mutagenesis screens and by the ease of transgenesis. More recently, gene-editing approaches have extended the power of the model.
For neurodevelopmental studies, the zebrafish embryo and larva provide a model to which multiple methods can be applied. Here, we focus on methods that allow the study of an essential property of neurons, electrical excitability. Our preparation for the electrophysiological study of zebrafish spinal neurons involves the use of veterinarian suture glue to secure the preparation to a recording chamber. Alternative methods for recording from zebrafish embryos and larvae involve the attachment of the preparation to the chamber using a fine tungsten pin1,2,3,4,5. A tungsten pin is most often used to mount the preparation in a lateral orientation, although it has been used to mount larvae dorsal-side up4. The suture glue has been used to mount embryos and larvae in both orientations. Using the glue, a minimal dissection can be performed, allowing access to spinal neurons without the use of an enzymatic treatment, thereby avoiding any resultant damage. However, for larvae, it is necessary to apply a brief enzyme treatment to remove the muscle tissue surrounding the spinal cord. The methods described here have been used to study the intrinsic electrical properties of motor neurons, interneurons, and sensory neurons at several developmental stages6,7,8,9.

We have successfully recorded from Rohon-Beard neurons in 17 hpf embryos through 7 dpf larvae (Figure 5A and 5B). When Rohon-Beard cells were recorded, the preparation was mounted dorsal-side up. Such mounting allows for the unambiguous identification of Rohon-Beard cells based on their superficial dorsal positions and large soma sizes. The identification is additionally confirmed by the stereotypical hyperpolarized resting membrane potential of these neu...

Watch this Scientific Journal Video about Zebrafish In Situ Spinal Cord Preparation for Electrophysiological Recordings from Spinal Sensory and Motor Neurons at JoVE.com

Zebrafish In Situ Spinal Cord Preparation for Electrophysiological Recordings from Spinal Sensory and Motor Neurons

This manuscript describes methods for electrophysiological recordings from spinal neurons of zebrafish embryos and larvae. The preparation maintains neurons in situ and often involves minimum dissection. These methods allow for the electrophysiological study of a variety of spinal neurons, from the initial electrical excitability acquisition through the early larval stages.

Zebrafish In Situ Spinal Cord Preparation for Electrophysiological Recordings from Spinal Sensory and Motor Neurons

Zebrafish, first introduced as a developmental model, have gained popularity in many other fields. The ease of rearing large numbers of rapidly developing ...

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