This work was supported by MEXT KAKENHI on Innovative Areas Mesoscopic Neurocircuitry 23115102 and Dynamic Regulation of Brain Function by Scrap and Build System 16H06460 to N.Y.&#160;We also thank Gabriel Hand for critical reading.

All experiments were performed according to the guidelines established by the animal welfare committees of Osaka University and the Japan Neuroscience Society.
1. Organotypic cocultures of the thalamus and cerebral cortex
Note: For the detailed procedure, refer to the original publications7,8,13. All procedures should be performed under sterile conditions. Sprague-Dawley (SD)...

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The current protocol is also a powerful tool to study developmental aspects of growing axons other than of the TC projection11. For instance, a combination of cortical slice culture and the electroporation technique allows visualizing individual axonal morphology of cortical neurons and long term observation9,18.
By using the current protocol, the roles of interesting genes in axon branching and synapse formatio...

The thalamocortical (TC) projection in the mammalian brain is a suitable system to investigate axon guidance and targeting mechanisms. During development, sensory TC axons grow in the cortical plate, and form branches and synapses preferentially in layer IV of the primary sensory areas in the cerebral cortex1,2. Even after establishment of fundamental connections, axonal arbors and synaptic terminals are remodeled depending on environmental changes3,4. However, how TC axon morphology is dynamically altered is poorly understood. One of the main reasons is the lack of an adequate technique to observe structural changes at a single cell level. Although recent developments in microscopy, such as two-photon microscopy, have allowed direct observation of living cortical neurons in vivo, there are still technical limitations for capturing the overall TC trajectories5,6. Therefore, in vitro methods for live imaging of TC axons would provide powerful tools for structural analyses of axon branching and synapse formation.
Our group for the first time established a static slice culture method with permeable membrane7. Using this method, a rat cortical slice was cocultured with a sensory thalamic block, and lamina-specific TC connections were recapitulated in this organotypic cocultures7,8. Sparse labeling with a fluorescent protein further allowed us to observe TC axon growth and branch formation9,10,11. Recently, we have developed a novel method for simultaneous imaging of branching and synapse formation of individual TC axons in the organotypic cocultures12. To visualize TC axons and presynaptic sites simultaneously, DsRed and EGFP-tagged synaptophysin (SYP-EGFP) were co-transfected into a small number of thalamic neurons by electroporation of the organotypic coculture. The current method facilitates morphological analysis of TC axons and allows for long-term observation, which can be used to show the causal relationship between axon branching and synapse formation.

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			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">DMEM/F12</td>
			<td class="xl20" style="width:89pt" width="119">GIBCO</td>
			<td class="xl20" style="width:84pt" width="112">11320-033</td>
			<td class="xl20" style="width:58pt" width="77"></td>
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		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Hanks&#8217; balanced salt solution (HBSS)</td>
			<td class="xl20" style="width:89pt" width="119">Nissui</td>
			<td class="xl21" style="width:84pt" width="112">5905</td>
			<td class="xl20" style="width:58pt" width="77"></td>
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		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Fetal bovine serum (FBS)</td>
			<td class="xl20" style="width:89pt" width="119">Thermo Scientific</td>
			<td class="xl20" style="width:84pt" width="112">SH30396-03</td>
			<td class="xl20" style="width:58pt" width="77">Hyclone</td>
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			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Insulin</td>
			<td class="xl20" style="width:89pt" width="119">Sigma</td>
			<td class="xl20" style="width:84pt" width="112">I6634</td>
			<td class="xl20" style="width:58pt" width="77"></td>
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			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Progesterone</td>
			<td class="xl20" style="width:89pt" width="119">Sigma</td>
			<td class="xl20" style="width:84pt" width="112">P8783</td>
			<td class="xl20" style="width:58pt" width="77"></td>
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		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Hydrocortisone</td>
			<td class="xl20" style="width:89pt" width="119">Sigma&#160;</td>
			<td class="xl20" style="width:84pt" width="112">H0888</td>
			<td class="xl20" style="width:58pt" width="77"></td>
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			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Sodium selenite</td>
			<td class="xl20" style="width:89pt" width="119">Wako Pure 
			Chemical Industries</td>
			<td class="xl20" style="width:84pt" width="112">192-10843</td>
			<td class="xl20" style="width:58pt" width="77"></td>
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			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Transferrin&#160;</td>
			<td class="xl20" style="width:89pt" width="119">Sigma</td>
			<td class="xl20" style="width:84pt" width="112">T1147</td>
			<td class="xl20" style="width:58pt" width="77"></td>
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		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Putrescine&#160;</td>
			<td class="xl20" style="width:89pt" width="119">Sigma</td>
			<td class="xl20" style="width:84pt" width="112">P5780</td>
			<td class="xl20" style="width:58pt" width="77"></td>
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		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Glucose</td>
			<td class="xl20" style="width:89pt" width="119">Wako 
			Pure Chemical Industries</td>
			<td class="xl20" style="width:84pt" width="112">16806-25</td>
			<td class="xl20" style="width:58pt" width="77"></td>
		</tr>
		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">35 mm petri dishes</td>
			<td class="xl20" style="width:89pt" width="119">Falcon</td>
			<td class="xl21" style="width:84pt" width="112">351008</td>
			<td class="xl20" style="width:58pt" width="77"></td>
		</tr>
		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Millicell-CM insert</td>
			<td class="xl20" style="width:89pt" width="119">Millipore</td>
			<td class="xl20" style="width:84pt" width="112">PICMORG50</td>
			<td class="xl20" style="width:58pt" width="77"></td>
		</tr>
		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">100 mm petri dishes</td>
			<td class="xl20" style="width:89pt" width="119">BIO-BIK</td>
			<td class="xl20" style="width:84pt" width="112">I-90-20</td>
			<td class="xl20" style="width:58pt" width="77">petri dish sterrile</td>
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		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">HiPure Plasmid Maxiprep Kit</td>
			<td class="xl20" style="width:89pt" width="119">Invitrogen</td>
			<td class="xl20" style="width:84pt" width="112">K210006</td>
			<td class="xl23" style="width:58pt" width="77"></td>
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		<tr height="59" style="height:44.25pt">
			<td class="xl20" height="59" style="width:113pt;height:44.25pt" width="151">Disposable sterile plastic pipettes</td>
			<td class="xl20" style="width:89pt" width="119"></td>
			<td class="xl20" style="width:84pt" width="112">202-IS</td>
			<td class="xl20" style="width:58pt" width="77">transfer pipets sterile</td>
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		<tr height="54" style="height:40.5pt">
			<td class="xl20" height="54" style="width:113pt;height:40.5pt" width="151">Glass capillary: OD 1.2 mm</td>
			<td class="xl20" style="width:89pt" width="119">Narishige</td>
			<td class="xl20" style="width:84pt" width="112">&#160;G-1.2</td>
			<td class="xl20" style="width:58pt" width="77">inner diameter, 1.2 mm</td>
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		<tr height="53" style="height:39.75pt">
			<td class="xl20" height="53" style="width:113pt;height:39.75pt" width="151">Silver wire: 0.2 and 1 mm&#160;</td>
			<td class="xl20" style="width:89pt" width="119">Nilaco</td>
			<td class="xl20" style="width:84pt" width="112">AG-401265 (diameter, 0.2 mm), AG-401485 (diameter, 1.0 mm)</td>
			<td class="xl20" style="width:58pt" width="77"></td>
		</tr>
		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">1 mL syringe</td>
			<td class="xl20" style="width:89pt" width="119">Terumo</td>
			<td class="xl20" style="width:84pt" width="112">SS-01T</td>
			<td class="xl20" style="width:58pt" width="77"></td>
		</tr>
		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Stimulator&#160;</td>
			<td class="xl20" style="width:89pt" width="119">A.M.P.I</td>
			<td class="xl20" style="width:84pt" width="112">Master 8</td>
			<td class="xl20" style="width:58pt" width="77"></td>
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		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Biphasic isolator&#160;</td>
			<td class="xl20" style="width:89pt" width="119">BAK ELECTRONICS</td>
			<td class="xl20" style="width:84pt" width="112">BSI-2</td>
			<td class="xl20" style="width:58pt" width="77"></td>
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		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Amplifier&#160;</td>
			<td class="xl20" style="width:89pt" width="119">A-M Systems</td>
			<td class="xl20" style="width:84pt" width="112">Model 1800</td>
			<td class="xl20" style="width:58pt" width="77"></td>
		</tr>
		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Oscilloscope</td>
			<td class="xl20" style="width:89pt" width="119">Hitachi</td>
			<td class="xl20" style="width:84pt" width="112">VC-6723</td>
			<td class="xl20" style="width:58pt" width="77"></td>
		</tr>
		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Manipulator</td>
			<td class="xl20" style="width:89pt" width="119">Narishige</td>
			<td class="xl20" style="width:84pt" width="112">SM-15</td>
			<td class="xl20" style="width:58pt" width="77"></td>
		</tr>
		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Micromanipulator</td>
			<td class="xl20" style="width:89pt" width="119">Narishige</td>
			<td class="xl20" style="width:84pt" width="112">MO-10</td>
			<td class="xl20" style="width:58pt" width="77"></td>
		</tr>
		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Stereomicroscope&#160;</td>
			<td class="xl20" style="width:89pt" width="119">Olympus</td>
			<td class="xl20" style="width:84pt" width="112">SZ40</td>
			<td class="xl20" style="width:58pt" width="77"></td>
		</tr>
		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Universal stand&#160;</td>
			<td class="xl20" style="width:89pt" width="119">Olympus</td>
			<td class="xl20" style="width:84pt" width="112">SZ-STU2</td>
			<td class="xl20" style="width:58pt" width="77"></td>
		</tr>
		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Light illumination system&#160;</td>
			<td class="xl20" style="width:89pt" width="119">Olympus</td>
			<td class="xl20" style="width:84pt" width="112">LG-PS2, LG-DI, HLL301</td>
			<td class="xl20" style="width:58pt" width="77"></td>
		</tr>
		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Electrode puller&#160;</td>
			<td class="xl20" style="width:89pt" width="119">Narishige</td>
			<td class="xl20" style="width:84pt" width="112">PC-10</td>
			<td class="xl20" style="width:58pt" width="77"></td>
		</tr>
		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Confocal microscope</td>
			<td class="xl20" style="width:89pt" width="119">Nikon</td>
			<td class="xl20" style="width:84pt" width="112">Digital eclipse C1 laser</td>
			<td class="xl20" style="width:58pt" width="77"></td>
		</tr>
		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">x20 objective</td>
			<td class="xl20" style="width:89pt" width="119">Nikon</td>
			<td class="xl20" style="width:84pt" width="112">ELWD 20x/0.45</td>
			<td class="xl20" style="width:58pt" width="77"></td>
		</tr>
		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Culture chamber</td>
			<td class="xl20" style="width:89pt" width="119">Tokai Hit</td>
			<td class="xl20" style="width:84pt" width="112">UK A16-U</td>
			<td class="xl20" style="width:58pt" width="77"></td>
		</tr>
		<tr height="40" style="height:30.0pt">
			<td class="xl20" height="40" style="width:113pt;height:30.0pt" width="151">Sprague-Dawley (SD) rat</td>
			<td class="xl20" style="width:89pt" width="119">Japan SLC and Nihon-Dobutsu</td>
			<td class="xl20" style="width:84pt" width="112"></td>
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			<td class="xl20" style="width:84pt" width="112">MB-54-1</td>
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visualization of thalamocortical axon branching and synapse formation in organotypic cocultures

Axon branching and synapse formation are crucial processes for establishing precise neuronal circuits. During development, sensory thalamocortical (TC) axons form branches and synapses in specific layers of the cerebral cortex. Despite the obvious spatial correlation between axon branching and synapse formation, the causal relationship between them is poorly understood. To address this issue, we recently developed a method for simultaneous imaging of branching and synapse formation of individual TC axons in organotypic cocultures.
This protocol describes a method which consists of a combination of an organotypic coculture and electroporation. Organotypic cocultures of the thalamus and cerebral cortex facilitate gene manipulation and observation of axonal processes, preserving characteristic structures such as laminar configuration. Two distinct plasmids encoding DsRed and EGFP-tagged synaptophysin (SYP-EGFP) were co-transfected into a small number of thalamic neurons by an electroporation technique. This method allowed us to visualize individual axonal morphologies of TC neurons and their presynaptic sites simultaneously. The method also enabled long-term observation which revealed the causal relationship between axon branching and synapse formation.

The experiment described here aims to reveal the relationship between TC axon branching and synapse formation. To simultaneously visualize axonal trajectories and locations of presynaptic sites, single or a few thalamic cells in organotypic cocultures were transfected with two plasmids encoding SYP-EGFP and DsRed using electroporation. During the second week in culture, individually distinguishable TC axons were clearly labeled by DsRed (Figure 3). Only the a...

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Visualization of Thalamocortical Axon Branching and Synapse Formation in Organotypic Cocultures

This protocol describes a method for simultaneous imaging of thalamocortical axon branching and synapse formation in organotypic cocultures of the thalamus and cerebral cortex. Individual thalamocortical axons and their presynaptic terminals are visualized by a single cell electroporation technique with DsRed and GFP-tagged synaptophysin.

Axon branching and synapse formation are crucial processes for establishing precise neuronal circuits. During development, sensory thalamocortical (TC) ...

The overall goal of this method is to study dynamic morphological changes of axon branching and synapse formation in the thalamocortical projection. This method can help answer key questions in the field of neurobiology, such as new neural circuit formation. The main advantage of this technique is simultaneous observation of axon growth and the synapse formation in individual living cells.This method can provide insight into the relationship between axon branching and synapse formation in the thalamocortical projections. It can also be applied to other neural circuits, such as intrinsic connection in the cerebral cortex. To begin this procedure, sterilize all the surgical instruments with 70%ethanol for 10 minutes or longer.Next, dissect the whole brain quickly from a postnatal day-two rat under ice-cold anesthesia. Then, place the brain into a 100-millimeter petri dish containing 40 milliliters of cold Hank's Balanced Salt Solution. Under a binocular microscope, remove the pia matter carefully with fine forceps, and cut the primary visual and somatosensory cortex into 300 to 400-micron thick slices using microsurgical scissors.After that, transfer the cortical slices onto the membrane filter of the culture insert using a disposable plastic pipette. Adjust the positions of the slices near the center of the culture insert with the disposable plastic pipette, and remove excess medium from the insert. Maintain the slices in the serum-containing culture medium at 37 degrees Celsius, and culture them alone for one day before placing a thalamic block from an E15 embryo next to it.Adjust the level of the medium slightly below the surface of the slice, so that the slices can receive sufficient supply of both the gas and the medium. This is crucial for the viability of the slices. In this step, make the glass capillaries with an electrode puller.Then break the tips of the glass capillaries for plasmid injection. For the electrode pipettes, grind and polish the tips of the glass capillaries with sandpaper. And then fire polish them to achieve an inner diameter of 50 to 200 microns.Next, attach the electrode pipette and the ejection pipette to the manipulators. Transfer five microliters of plasmid solution to a petri dish. Then draw the solution into the electrode pipette with capillary action.Insert the 0.2-millimeter diameter electrode into the electrode pipette. After connecting the ejection pipette to a one-milliliter syringe with a plastic tube, transfer five microliters of plasmid solution to a petri dish again. Then slowly draw the solution into the ejection pipette using the syringe.Following that, transfer the coculture on the electroporation stage and insert the one-millimeter diameter electrode into the culture medium. Subsequently, place the ejection pipette on the cultured thalamic block. Push the syringe manually after the tip touches the surface of the thalamic block.Place the electrode pipette on the thalamic block immediately after the retraction of the ejection pipette. Now, deliver the electrical pulses. Monitor the amplitude and the number of trains on the oscilloscope.Afterward, retract the electrode pipette and return the dish to the incubator. To observe the sample, place the culture dish on the stage of an upright confocal microscope equipped with two filter sets for EGFP and DsRed. Then take images of 10 to 25 optical sections, at one to seven-micron step sizes, with a 20x long working distance objective lens.Select individually-distinguishable labeled axons, which express both DsRed and Syp-EGFP. Shown here is an organotypic coculture of thalamic and cortical slices after 12 DIV. Here is a magnified image of the boxed region.And here is a DsRed-labeled thalamic cell extending an axon into the cortical slice, and forming branches in upper layers. These images show the DsRed-labeled thalamocortical axon and Syp-EGFP puncta. Discrete accumulation of Syp-EGFP was observed along a single thalamocortical axon.DsRed plus Syp-EGFP plasmids were introduced into cultured thalamic cells at one DIV using electroporation. This axon was imaged daily over four days. Axon branching and synapse formation were dynamic, with addition and elimination.Following these procedures, electroporation with interesting genes together with Syp-EGFP and DsRed can be performed in order to investigate the role of the gene in axon branching and synapse formations. This technique paves the way for researchers in the field of the neurobiology to explore the mechanisms of dynamic changes of neural circuits.

visualization-thalamocortical-axon-branching-synapse-formation

Research

JoVE Journal

Neuroscience

6.4K visualizações.  Kanazawa University. The overall goal of this method is to study dynamic morphological changes of axon branching and synapse formation in the thalamocortical projection. This method can help answer key questions in the field of neurobiology, such as new neural circuit formation. The main advantage of this technique is simultaneous observation of axon growth and the synapse formation in individual living cells.This method can provide insight into the relationship between axon branching and synapse formation...