Name: laser-guided neuronal tracing in brain explants
Uploaded: 2015-11-25T14:00:00
Description: Watch this Scientific Journal Video about Laser-guided Neuronal Tracing In Brain Explants at JoVE.com

Supported by NIH/NIDCD R01 DC 011582. Imaging experiments were performed in the University of Colorado Anschutz Medical Campus Advanced Light Microscopy Core supported in part by NIH/NCRR Colorado CTSI Grant Number UL1 RR025780 and the Rocky Mountain Neurlogical Disorders Core Center Grant NIH P30NS048154. Dr. Sascha du Lac from the Salk Institute provided us with the GlyT2-GFP mice.

1. Optical Genotyping
1. Optical Genotyping of Mouse Pups
<ol>
	<li>Check for expression of the respective fluorescent marker using a laser pointer of the appropriate excitation wavelength (405 nm in the experiments described here) and corresponding filter goggles blocking the excitation wavelength but passing the emission wavelength (450 - 700 nm in the experiments described here). Point the laser pointer at the back of the head or the spinal cord of the mouse pup (see Figure&#160;1</s...

<ol>
	<li>Waller, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experiments+on+the+sections+of+glossopharyngeal+and+hypoglossal+nerves+of+the+frog+and+observations+of+the+alterations+produced+thereby+in+the+structure+of+their+primitive+fibers.">Experiments on the sections of glossopharyngeal and hypoglossal nerves of the frog and observations of the alterations produced thereby in the structure of their primitive fibers.</a> Philos. Trans. R. Soc. Lond. 140, 423-429 (1850).</li><li>Fink, R. 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Electron microscopical localization in the neuronal perikaryon.</a> Acta Neuropathol. 19, 1-9 (1971).</li><li>Kristensson, K., Olsson, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Retrograde+axonal+transport+of+protein.">Retrograde axonal transport of protein.</a> Brain Res. 29, 363-365 (1971).</li><li>Burger, R. M., Cramer, K. S., Pfeiffer, J. D., Rubel, E. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Avian+superior+olivary+nucleus+provides+divergent+inhibitory+input+to+parallel+auditory+pathways.">Avian superior olivary nucleus provides divergent inhibitory input to parallel auditory pathways.</a> J. Comp. Neurol. 481, 6-18 (2005).</li><li>Ford, M. 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Neurol. 482, 123-141 (2005).</li><li>Poyatos, I., Ponce, J., Arag&#246;n, C., Gim&#233;nez, C., Zafra, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+glycine+transporter+GLYT2+is+a+reliable+marker+for+glycine-immunoreactive+neurons.">The glycine transporter GLYT2 is a reliable marker for glycine-immunoreactive neurons.</a> Brain. Res. Mol. 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J., Paxinos, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Mouse Brain in Stereotaxic Coordinates. , (2008).</li><li>Kuwajima, T., Sitko, A. A., Bhansali, P., Jurgens, C., Guido, W., Mason, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ClearT:+a+detergent-+and+solvent-free+clearing+method+for+neuronal+and+non-neuronal+tissue.">ClearT: a detergent- and solvent-free clearing method for neuronal and non-neuronal tissue.</a> Development. 140, 1364-1368 (2013).</li><li>Wouterlood, F. G., Jorritsma-Byham, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+anterograde+neuroanatomical+tracer+biotinylated+dextran+amine:+comparison+with+the+tracer+PHA-L+in+preparations+for+electron+microscopy.">The anterograde neuroanatomical tracer biotinylated dextran amine: comparison with the tracer PHA-L in preparations for electron microscopy.</a> J. Neurosci. Methods. 48, 75-87 (1993).</li><li>Lanciego, J. L., Wouterlood, F. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+half+century+of+experimental+neuroanatomical+tracing.">A half century of experimental neuroanatomical tracing.</a> J. Chem. Neuroanat. 42, 157-183 (2011).</li><li>Rodriguez-Contreras, A., Silvio, J., van Hoeve, S., Habets, L. P., Locher, H., Borst, J. G. 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C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single+unit+of+binaural+interaction+in+the+auditory+cortex+of+the+chinchilla.">Single unit of binaural interaction in the auditory cortex of the chinchilla.</a> Brain Res. 103, 313-338 (1976).</li><li>Koka, K., Jones, H. G., Thornton, J. L., Lupo, J. E., Tollin, D. 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Am. 59 (5), 1222-1226 (1976).</li><li>Zwicker, E., Fastl, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Psychoacoustics Facts and Models. , (1990).</li><li>Chu, G., Hayakawa, H., Berg, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electroporation+for+the+efficient+transfection+of+mammalian+cells+with+DNA.">Electroporation for the efficient transfection of mammalian cells with DNA.</a> Nucleic Acids Res. 15 (3), 1311-1326 (1987).</li><li>Klenchin, V. A., Sukharev, S. I., Serov, S. M., Chernomordik, L. V., Chizmadzhev, Y. 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A general strength of in vitro tracer electroporation, as opposed to in&#160;vivo tracing studies, is that it gives researchers better access to the brain area of interest and hence, does not involve expensive stereotactic (and often electrophysiological) equipment. In addition, the survival period required for the brain explants spans only a few hours (1 - 4) instead of days or even weeks in the case of in vivo tracer injections (see a detailed review on the use of dextran amines and other tra...

In order to define a certain neuronal (micro)circuit, one must start by finding the various participants of said circuit, and their connection pattern. Ever since Waller&#39;s publication about neurofiber tracing through lesioning1 a large variety of neuroanatomical tracing techniques has been established. Some of these techniques can be applied in fixed tissue post mortem2-4, others rely on the active transport of the dye in live neurons, as discovered in 19715-6. The latter can be further subdivided in two groups discriminating between methods taking advantage of active retrograde (from the injected area to the source of a given projection, i.e. the somata of neurons that are projecting to said area) and active anterograde (from the injected area to the target of a given projection, i.e. the axonal projections and the axonal terminals of the labeled neurons) transport. Also, in some cases tracer material is injected into live animals which then survive the injection by several days or weeks (in&#160;vivo tracer injections), while in other cases explanted brains are injected and incubate for several hours after the injection in artificial cerebrospinal fluid (in vitro tracer injections).
In this protocol we modified an existing in vitro electroporation technique7-8 to label neuronal somata and processes in anterograde and retrograde tracing experiments using choleratoxin subunit-b and tetramethylrhodamine dextran as the tracing substances. The overall goal of this protocol is to provide neuroscientists with an efficient tool to trace neuronal connectivity patterns between different brain nuclei, while taking advantage of available transgenic mouse lines and basic optical equipment in order to increase targeting accuracy during tracer injections. Although the method of anterograde and retrograde tracing using choleratoxin and dextran amine and their respective fluorescently labeled conjugates is not new9-13 (as is the method of electroporation, e.g. Haas et al.14), the combination of tracer injections with electroporation in an in vitro preparation involving blocks of brain tissue is a more recent development7. Its main advantage over neuronal tracing techniques using the same type of tracer dyes in live animals is the increased labeling intensity, because of the higher efficiency with which the electroporated dye is being taken up by neurons. An additional advantage is the shortened incubation period (required for the dye transport) and its increased target accuracy during the tracer injection, because the experimenter has visual control over the target area of the injection. The latter also means that no expensive stereotactic equipment is required to find the nucleus or brain area of interest.
To additionally increase targeting accuracy, we took advantage of a transgenic mouse line, which expresses GFP in its glycinergic subpopulation of neurons15 and basic optical equipment consisting of a hand-held laser pointer of 405 nm wavelength and matching band-pass filtering goggles (450 - 700 nm). Thus, we achieved a significant further increase in targeting accuracy by identifying the injection area through its fluorescent signal and by providing a finer way to control for the dye spread within the injection area through the observation of the interaction between the indigenous GFP signal and the tracer fluorescence. Our technique also allows to uncover the functionality of a circuit along with its connectivity by identifying GFP-positive inhibitory neurons (or excitatory in other mouse lines) that were filled with the tracer.
In summary, we further enhanced a powerful neuroscientific tool to study the connectome of the vertebrate brain and assess the different neuroanatomical features of a given neurocircuit. By using transgenic mice along with inexpensive and widely available optical equipment we were able to significantly increase the targeting accuracy of our injections. Furthermore, the transgenic mice allowed us to identify the type of the traced connections, which helped uncovering the functionality of an inhibitory microcircuit in the auditory brainstem.

<table>
	<tbody>
		<tr>
			<td>Sodium chloride</td>
			<td>Sigma-Aldrich</td>
			<td>S7653</td>
			<td>All chemicals are from Sigma-Aldrich, unless noted otherwise.</td>
		</tr>
		<tr>
			<td>Potassium chloride&#160;</td>
			<td></td>
			<td>P9333</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium phosphate monobasic</td>
			<td></td>
			<td>P5655</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium phosphate di-basic</td>
			<td></td>
			<td>S907</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium chloride</td>
			<td></td>
			<td>M2670</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium chloride</td>
			<td></td>
			<td>C5080</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td></td>
			<td>G7528</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium bicarbonate</td>
			<td></td>
			<td>S6297</td>
			<td></td>
		</tr>
		<tr>
			<td>Ascorbic acid</td>
			<td></td>
			<td>A4544</td>
			<td></td>
		</tr>
		<tr>
			<td>Myo-inositol</td>
			<td></td>
			<td>I5125</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium pyruvate</td>
			<td></td>
			<td>P2256</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine serum albumine</td>
			<td></td>
			<td>A2153</td>
			<td>optional, for additional (immuno)histochemistry</td>
		</tr>
		<tr>
			<td>Triton-X-100</td>
			<td></td>
			<td>X100</td>
			<td>optional, for additional (immuno)histochemistry</td>
		</tr>
		<tr>
			<td>Poly(ethylene glycol), 8000 MW</td>
			<td></td>
			<td>P2139</td>
			<td>optional, for brain clearing</td>
		</tr>
		<tr>
			<td>Formamide</td>
			<td>Fisher Scientific</td>
			<td>F84</td>
			<td>optional, for brain clearing</td>
		</tr>
		<tr>
			<td>Choleratoxin subunit-b</td>
			<td>Molecular Probes</td>
			<td>C-34776 (Alexa 555)&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Dextrane tetramethyl-rhodamine</td>
			<td>Molecular Probes</td>
			<td>D-7162 (Alexa 555)</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescent Nissl</td>
			<td>Invitrogen</td>
			<td>N-21479 (blue)</td>
			<td>optional</td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Fisher Scientific</td>
			<td>SF93</td>
			<td></td>
		</tr>
		<tr>
			<td>Agarose</td>
			<td>Invitrogen</td>
			<td>16520</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluoromount-G</td>
			<td>Southern Biotech</td>
			<td>0100-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Pentobarbi-tal</td>
			<td>Vortech Pharmaceuticals</td>
			<td>Fatal-Plus&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Borosilicate glass filaments</td>
			<td>Harvard Apparatus</td>
			<td>G150F-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Pipette puller</td>
			<td>Zeitz Instruments, Germany</td>
			<td>DMZ Universal Puller</td>
			<td></td>
		</tr>
		<tr>
			<td>Perfusion setup</td>
			<td>Custom-made</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Laser pointer&#160;</td>
			<td>laserpointerpro.com, Hong Kong</td>
			<td>HK-88007294 (405 nm)</td>
			<td></td>
		</tr>
		<tr>
			<td>Filter/safety goggles</td>
			<td>Dragon Lasers, China</td>
			<td>LSG09 (band-pass 450-700 nm)</td>
			<td></td>
		</tr>
		<tr>
			<td>Bionocular microscope&#160;</td>
			<td>Wild Heerbrugg, Switzerland</td>
			<td>Wild M3</td>
			<td>Equipped with high-intensity illuminator (MI-150; Dolan-Jenner Inc.)&#160;</td>
		</tr>
		<tr>
			<td>Picospritzer</td>
			<td>Parker Instruments</td>
			<td>Picospritzer III</td>
			<td></td>
		</tr>
		<tr>
			<td>PC with installed MC Stimulus software</td>
			<td>Multi Channel Sys-tems, Germany (software)</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>2-channel stimulator</td>
			<td>Multi Channel Sys-tems, Germany</td>
			<td>STG-1002</td>
			<td></td>
		</tr>
		<tr>
			<td>Stimulation isolation unit</td>
			<td>A.M.P.I., Israel</td>
			<td>Iso-Flex</td>
			<td></td>
		</tr>
		<tr>
			<td>Micromanipulator</td>
			<td>Narishige, Japan</td>
			<td>YOU-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Vibratome</td>
			<td>Leica, Germany</td>
			<td>VT1000S</td>
			<td></td>
		</tr>
	</tbody>
</table>

laser-guided neuronal tracing in brain explants

We present a technique which combines an in vitro tracer injection protocol, which uses a series of electrical and pressure pulses to increase dye uptake through electroporation in brain explants with targeted laser illumination and matching filter goggles during the procedure. The described technique of in vitro electroporation by itself yields relatively good visual control for targetting certain areas of the brain. By combining it with laser excitation of fluorescent genetic markers and their read-out through band-passing filter goggles, which can pick up the emissions of the genetically labeled cells/nuclei and the fluorescent tracing dye, a researcher can substantially increase the accuracy of injections by finding the area of interest and controlling for the dye-spread/uptake in the injection area much more efficiently. In addition, the laser illumination technique allows to study the functionality of a given neurocircuit by providing information about the type of neurons projecting to a certain area in cases where the GFP expression is linked to the type of transmitter expressed by a subpopulation of neurons.

Figures 1 and 2 show how the laser pointer and laser goggles can be used to quickly and inexpensively genotype GFP positive animals from a litter. In cases of young mouse pups, the technique can be used to noninvasively identify GFP label in the animal&#39;s brains through the skull and overlying skin (Figure&#160;1A - D). Emitted fluorescence can be seen through the skin and the skull of mouse pups at least up to postnatal day 3 (Figure&#160;1C). The procedure is shown ...

Watch this Scientific Journal Video about Laser-guided Neuronal Tracing In Brain Explants at JoVE.com

Laser-guided Neuronal Tracing In Brain Explants

We describe a technique to label neurons and their processes via anterograde or retrograde tracer injections into brain nuclei using an in vitro preparation. We modified an existing method of in vitro tracer electroporation by taking advantage of fluorescently labeled mouse mutants and basic optical equipment in order to increase labeling accuracy.

We present a technique which combines an in vitro tracer injection protocol, which uses a series of electrical and pressure pulses to increase dye uptake ...

Research

JoVE Journal

Neuroscience

Multi-electrode Array Recordings of Neuronal Avalanches in Organotypic Cultures

The cortex is spontaneously active, even in the absence of any particular input or motor output.  During development, this activity is important for the ...

Methods for Study of Neuronal Morphogenesis: Ex vivo RNAi Electroporation in Embryonic Murine Cerebral Cortex

Methods for Study of Neuronal Morphogenesis: Ex vivo RNAi Electroporation in Embryonic Murine Cerebral Cortex

The cerebral cortex directs higher cognitive functions. This six layered structure is generated in an inside-first, outside-last manner, in which the ...

Fast Micro-iontophoresis of Glutamate and GABA: A Useful Tool to Investigate Synaptic Integration

One of the fundamental interests in neuroscience is to understand the integration of excitatory and inhibitory inputs along the very complex structure of ...

Genetic Manipulation of Cerebellar Granule Neurons In Vitro and In Vivo to Study Neuronal Morphology and Migration

Genetic Manipulation of Cerebellar Granule Neurons In Vitro and In Vivo to Study Neuronal Morphology and Migration

Developmental events in the brain including neuronal morphogenesis and migration are highly orchestrated processes. In vitro and in vivo analyses allow ...

Intracerebroventricular Viral Injection of the Neonatal Mouse Brain for Persistent and Widespread Neuronal Transduction

With the pace of scientific advancement accelerating rapidly, new methods are needed for experimental neuroscience to quickly and easily manipulate gene ...

Closed-loop Neuro-robotic Experiments to Test Computational Properties of Neuronal Networks

Information coding in the Central Nervous System (CNS) remains unexplored. There is mounting evidence that, even at a very low level, the representation ...

Conditional Genetic Transsynaptic Tracing in the Embryonic Mouse Brain

Anatomical path tracing is of pivotal importance to decipher the relationship between brain and behavior. Unraveling the formation of neural circuits ...

Two-photon Calcium Imaging in Neuronal Dendrites in Brain Slices

Calcium (Ca2+) imaging is a powerful tool to investigate the spatiotemporal dynamics of intracellular Ca2+ signals in neuronal dendrites. Ca2+ ...

In Vitro Wedge Slice Preparation for Mimicking In Vivo Neuronal Circuit Connectivity

In vitro slice electrophysiology techniques measure single-cell activity with precise electrical and temporal resolution. Brain slices must be relatively ...

Preparing Adult Drosophila melanogaster for Whole Brain Imaging during Behavior and Stimuli Responses

Preparing Adult Drosophila melanogaster for Whole Brain Imaging during Behavior and Stimuli Responses

We present a method developed specifically to image the whole Drosophila brain during ongoing behavior such as walking. Head fixation and dissection are ...