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) rats are used for neuronal cultures.
<ol>
	<li>Preparations of reagents 
	Note: Volumes of the following reagents are for one rat brain.
	<ol>
		<li>Prepare 10x modified N2 Supplement13: Insulin (50 &#956;g/mL), progesterone (200 nM), hydrocortisone (200 nM), sodium selenite (300 nM), transferrin (1 mg/mL), putrescine (1 mM), glucose (60 mg/mL)</li>
		<li>Prepare serum-containing culture medium (10 mL): 85% DMEM/F12, 10% 10x modified N2 supplement, 5% fetal bovine serum (FBS)</li>
		<li>Prepare serum-free culture medium (20 mL): 90% DMEM/F12, 10% 10x modified N2 supplement</li>
		<li>Prepare rat tail collagen solution (0.5 mL). In brief, take tender fibers from a rat tail under sterile conditions and incubate in acetic acid solution overnight. After centrifugation, collect the supernatant (a few mg/mL) and store in a refrigerator13.</li>
	</ol>
	</li>
	<li>Preparation of culture dishes
	<ol>
		<li>Place a membrane insert into a 35 mm Petri dish.</li>
		<li>Add 40 - 50 &#956;L of rat tail collagen solution to the membrane, and spread the collagen solution around the center.</li>
		<li>Air dry the membrane completely in a clean bench.</li>
		<li>Put 1.5 - 2 mL of the serum-containing culture medium into the dish, so that the membrane is soaked with the medium.</li>
		<li>Place the culture dish in an incubator (37 &#176;C, humidified 95% air, and 5% CO2) before plating.</li>
	</ol>
	</li>
	<li>Preparation of cortical slices
	<ol>
		<li>Sterilize all surgical instruments with 70% ethanol for 10 min or longer.</li>
		<li>Dissect the whole brain quickly from a postnatal day (P) 2 rat under ice-cold anesthesia (immersed in ice-chips for a few minutes).</li>
		<li>Place the brain into a 100 mm Petri dish containing 100 mL of cold Hanks&#8217; balanced salt solution.</li>
		<li>Remove the pia matter from the brain with fine forceps, and cut cortical slices (300 - 400 &#956;m thickness) from the visual and somatosensory cortex with microsurgical scissors (for detail, see Figure 1). 
		Note: The thickness of cortical slices is roughly estimated by the scale of grids under a binocular microscope. 
		Note: Alternatively, cortical slices can be made with a vibratome under sterile conditions.</li>
		<li>Transfer a few cortical slices onto the membrane insert with a disposable plastic pipette.</li>
		<li>Adjust the positions of the slices near the center of the culture insert with a fire-polished Pasteur pipette (for details, see8,13) and remove excess medium from the insert. 
		Note: Adjust the level of the medium slightly below the surface of the slices so that the slices can receive a sufficient supply of both the gas and medium. This is crucial for cell viability.</li>
		<li>Maintain the slices in the serum-containing culture medium at 37 &#176;C in an environment of humidified 95% air and 5% CO2, and culture alone for one day before a thalamic block is taken and placed next to it.</li>
	</ol>
	</li>
	<li>Preparation of thalamic blocks
	<ol>
		<li>Sterilize all surgical instruments with 70% ethanol for 10 min or longer.</li>
		<li>Anesthetize a pregnant rat (embryonic day 15) by intraperitoneal injection of pentobarbital (50 mg/kg) containing anesthetic.</li>
		<li>Dissect each embryo from the uterine horns, and place the embryos into a 100 mm Petri dish containing 100 mL of cold Hanks&#8217; balanced salt solution.</li>
		<li>Under a binocular microscope, remove the brain from each embryo and cut thalamic blocks which mainly contain the ventrobasal complex and lateral geniculate nucleus (approximately 0.5 mm x 3)7 using microsurgical scissors (see Figure 1).</li>
	</ol>
	</li>
	<li>Culture and maintain organotypic cocultures
	<ol>
		<li>Using a Pasteur pipette, place the thalamic block next to the ventricular surface of the cortical slice which has been placed on the membrane filter.</li>
		<li>Maintain the cocultures in the serum-containing culture medium at 37 &#176;C in an environment of humidified 95% air and 5% CO2.</li>
		<li>Exchange half of the medium with the serum-free culture medium after two days in culture. Thereafter, exchange the medium every 2 - 3 days. 
		Note: The level of the medium should be checked after the medium exchange, as it is important for cell survival.</li>
	</ol>
	</li>
</ol>
2. Electroporation
All procedures should be performed under sterile conditions.
Note: Perform electroporation one day after the preparation of the thalamic blocks to prevent detachment of the blocks.
<ol>
	<li>Plasmids
	<ol>
		<li>Make a mixture of plasmids as follows: pCAGGS-DsRed 2 &#956;g/&#956;L; pCAG-SYP-EGFP 3.5 &#956;g/&#956;L. 
		Note: Purify the both plasmids using an endotoxin-free Maxiprep kit and dissolve in Hanks&#8217; balanced salt solution.</li>
	</ol>
	</li>
	<li>Electroporation equipment setup 
	The electrical instruments such as a stimulator and an isolator should be connected as shown in Figure 2.
	<ol>
		<li>Connect the stimulator to the biphasic isolator.</li>
		<li>Connect an electrode (a silver wire 0.2 mm diameter) to the negative terminal of the isolator.</li>
		<li>Connect an electrode (a silver wire 1 mm diameter) in series to a 100 &#937; resistor and the positive terminal of the isolator.</li>
		<li>Connect the amplifier to the oscilloscope to monitor whether electrical currents are passed across the resistor by measuring the voltage with the amplifier.</li>
	</ol>
	</li>
	<li>Preparation of glass pipettes 
	Note: Two types of glass pipettes are used for ejection of the plasmid solution and application of electrical pulses.
	<ol>
		<li>Make the pipettes from glass capillaries with an electrode puller.</li>
		<li>Break the tip for the ejection pipette (the tip diameter should be 20 - 50 &#956;m).</li>
		<li>Grind and polish the tip of the electrode pipette with sandpaper followed by fire-polishing (the inner diameter should be 50 - 200 &#956;m). 
		Note: The electrode tip should be flat and smooth, as it directly touches the tissue.</li>
	</ol>
	</li>
	<li>Procedure of electroporation
	<ol>
		<li>Connect the ejection and electrode pipettes to the manipulators.</li>
		<li>Insert a silver wire (0.2 mm diameter) into the electrode pipette.</li>
		<li>Attach the ejection pipette to a 1 mL syringe with a plastic tube.</li>
		<li>Take up &#62;5 &#956;L of plasmid solution into the ejection pipette by syringe suction.</li>
		<li>Put the coculture on the electroporation stage, and insert the 1 mm diameter electrode into the culture medium.</li>
		<li>Place the ejection pipette on the thalamic explant.</li>
		<li>Push the syringe manually after the tip touches the surface of the thalamic block. 
		Note: About 0.5 &#956;L of the plasmid solution is usually used per one thalamic block.</li>
		<li>Place the electrode pipette on the thalamic block immediately after retraction of the ejection pipette.</li>
		<li>Deliver electrical pulses (50 - 400 &#956;A, 3 to 5 trains of 200 square pulses of 1 ms duration at 200 Hz). Monitor the amplitude and the number of trains on the oscilloscope. 
		Note: The amplitude of electrical currents depends on the inner diameter of an electrode pipette13.</li>
		<li>Retract the electrode pipette and return the dish to the incubator.</li>
	</ol>
	</li>
	<li>Microscopic observation
	<ol>
		<li>Put the culture dish on a microscopic stage of an upright confocal microscope equipped with two filter sets for EGFP (excitation, 488 nm; emission, 515 nm) and DsRed (excitation, 514 nm; emission, 565 nm).</li>
		<li>Take images of 10 - 25 optical sections at 1 - 7 &#181;m-step sizes with a 20X&#160;long-working distance objective lens. Select individually distinguishable labeled axons which express both DsRed and SYP-EGFP. 
		Note: The observed area is approximately 0.7 x 0.7 mm (corresponding to 1024 x 1024 pixels, that is, 0.68 &#956;m/pixel).</li>
		<li>Capture images every 24 h for daily imaging. Complete within 10 min at room temperature, and return the cultures to the incubator. For short-interval time lapse imaging, keep the culture in a culture chamber, which maintains the environment of humidified 95% air and 5% CO2 at 37 &#176;C.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Kageyama, G. H., Robertson, R. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+geniculocortical+projections+to+visual+cortex+in+rat:+evidence+early+ingrowth+and+synaptogenesis.">Development of geniculocortical projections to visual cortex in rat: evidence early ingrowth and synaptogenesis.</a> J. Comp. Neurol. 335 (1), 123-148 (1993).</li><li>Lopez-Bendito, G., Molnar, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thalamocortical+development:+how+are+we+going+to+get+there.">Thalamocortical development: how are we going to get there.</a> Nat. Rev. Neurosci. 4 (4), 276-289 (2003).</li><li>Espinosa, J. S., Stryker, M. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+and+plasticity+of+the+primary+visual+cortex.">Development and plasticity of the primary visual cortex.</a> Neuron. 75 (2), 230-249 (2012).</li><li>Portera-Cailliau, C., Weimer, R. M., De Paola, V., Caroni, P., Svoboda, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diverse+modes+of+axon+elaboration+in+the+developing+neocortex.">Diverse modes of axon elaboration in the developing neocortex.</a> PLoS Biol. 3 (8), 272 (2005).</li><li>Holtmaat, A., Svoboda, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experience-dependent+structural+synaptic+plasticity+in+the+mammalian+brain.">Experience-dependent structural synaptic plasticity in the mammalian brain.</a> Nat. Rev. Neurosci. 10 (9), 647-658 (2009).</li><li>Bhatt, D. H., Zhang, S., Gan, W. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dendritic+spine+dynamics.">Dendritic spine dynamics.</a> Annu Rev Physiol. 71, 261-282 (2009).</li><li>Yamamoto, N., Kurotani, T., Toyama, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neural+connections+between+the+lateral+geniculate+nucleus+and+visual+cortex+in+vitro.">Neural connections between the lateral geniculate nucleus and visual cortex in vitro.</a> Science. 245 (4914), 192-194 (1989).</li><li>Yamamoto, N., Yamada, K., Kurotani, T., Toyama, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laminar+specificity+of+extrinsic+cortical+connections+studied+in+coculture+preparations.">Laminar specificity of extrinsic cortical connections studied in coculture preparations.</a> Neuron. 9 (2), 217-228 (1992).</li><li>Uesaka, N., Hirai, S., Maruyama, T., Ruthazer, E. S., Yamamoto, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activity+dependence+of+cortical+axon+branch+formation:+a+morphological+and+electrophysiological+study+using+organotypic+slice+cultures.">Activity dependence of cortical axon branch formation: a morphological and electrophysiological study using organotypic slice cultures.</a> J. Neurosci. 25 (1), 1-9 (2005).</li><li>Uesaka, N., Hayano, Y., Yamada, A., Yamamoto, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interplay+between+laminar+specificity+and+activity-dependent+mechanisms+of+thalamocortical+axon+branching.">Interplay between laminar specificity and activity-dependent mechanisms of thalamocortical axon branching.</a> J. Neurosci. 27 (19), 5215-5223 (2007).</li><li>Uesaka, N., Nishiwaki, M., Yamamoto, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single+cell+electroporation+method+for+axon+tracing+in+cultured+slices.">Single cell electroporation method for axon tracing in cultured slices.</a> Dev. Growth Differ. 50 (6), 475-477 (2008).</li><li>Matsumoto, N., Hoshiko, M., Sugo, N., Fukazawa, Y., Yamamoto, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synapse-dependent+and+independent+mechanisms+of+thalamocortical+axon+branching+are+regulated+by+neuronal+activity.">Synapse-dependent and independent mechanisms of thalamocortical axon branching are regulated by neuronal activity.</a> Dev Neurobiol. 76 (3), 323-336 (2016).</li><li>Matsumoto, N., Sasaki, K., Yamamoto, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electroporation+Method+for+Mammalian+CNS+Neurons+in+Organotypic+Slice+Cultures.">Electroporation Method for Mammalian CNS Neurons in Organotypic Slice Cultures.</a> Electroporation Methods in Neuroscience. , 159-168 (2015).</li><li>Molnar, Z., Blakemore, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lack+of+regional+specificity+for+connections+formed+between+thalamus+and+cortex+in+coculture.">Lack of regional specificity for connections formed between thalamus and cortex in coculture.</a> Nature. 351 (6326), 475-477 (1991).</li><li>Bolz, J., Novak, N., Staiger, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Formation+of+specific+afferent+connections+in+organotypic+slice+cultures+from+rat+visual+cortex+cocultured+with+lateral+geniculate+nucleus.">Formation of specific afferent connections in organotypic slice cultures from rat visual cortex cocultured with lateral geniculate nucleus.</a> J. Neurosci. 12 (8), 3054-3070 (1992).</li><li>Yamamoto, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inhibitory+mechanism+by+polysialic+acid+for+lamina-specific+branch+formation+of+thalamocortical+axons.">Inhibitory mechanism by polysialic acid for lamina-specific branch formation of thalamocortical axons.</a> J. Neurosci. 20 (24), 9145-9151 (2000).</li><li>Yamamoto, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+factors+regulating+lamina-specific+growth+of+thalamocortical+axons.">Characterization of factors regulating lamina-specific growth of thalamocortical axons.</a> J Neurobiol. 42 (1), 56-68 (2000).</li><li>Ohnami, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+RhoA+in+activity-dependent+cortical+axon+branching.">Role of RhoA in activity-dependent cortical axon branching.</a> J. Neurosci. 28 (37), 9117-9121 (2008).</li><li>Yamada, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+pre-+and+postsynaptic+activity+in+thalamocortical+axon+branching.">Role of pre- and postsynaptic activity in thalamocortical axon branching.</a> Proc Natl Acad Sci U S A. 107 (16), 7562-7567 (2010).</li></ol>

The authors have nothing to disclose.

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 formation can also be analyzed by co-expression of fluorescent proteins and the interest genes. Typically, over 90% of fluorescent protein expressing cells are co-transfected with a second plasmid when the molar ratio of the plasmid solutions is adjusted to 1:218,19. However, the optimal ratio may be different as co-transfection efficacy and expression level are varied among vectors.
Although the current protocol is efficient for time-lapse experiments, there are some technical problems. For daily imaging, a coculture was placed on a microscopic stage every day. Although axonal development did not seem to be affected seriously by daily imaging10, each observation should be completed within 10 min to minimize evaporation of culture solution and changes in pH of the culture medium. Alternatively, it would be better to maintain the temperature, humidity and pH of the cultures on the microscopic stage12.

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.

<table style="border-collapse:collapse;width:344pt" width="459">
	<colgroup>
		<col style="width:113pt" width="151" />
		<col style="width:89pt" width="119" />
		<col style="width:84pt" width="112" />
		<col style="width:58pt" width="77" />
	</colgroup>
	<tbody>
		<tr height="40" style="height:30.0pt">
			<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>
		</tr>
		<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>
		</tr>
		<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>
		</tr>
		<tr height="40" style="height:30.0pt">
			<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>
		</tr>
		<tr height="40" style="height:30.0pt">
			<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>
		</tr>
		<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>
		</tr>
		<tr height="40" style="height:30.0pt">
			<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>
		</tr>
		<tr height="40" style="height:30.0pt">
			<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>
		</tr>
		<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>
		</tr>
		<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>
		</tr>
		<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>
		</tr>
		<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>
		</tr>
		<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>
		</tr>
		<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>
		</tr>
		<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>
		</tr>
		<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>
			<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">Microsurgery scissors</td>
			<td class="xl20" style="width:89pt" width="119">Natsume&#160;</td>
			<td class="xl20" style="width:84pt" width="112">MB-54-1</td>
			<td class="xl20" style="width:58pt" width="77"></td>
		</tr>
	</tbody>
</table>

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 axons that exhibited DsRed and SYP-EGFP were selected for observation. Labeled TC axons invaded the cortical slice and formed branches primarily in the upper layers, indicating that thalamic axons in the organotypic cocultures form branches with laminar specificity resembling that found in vivo7,8,10,14,15,16,17. At the same time, punctate aggregations of SYP-EGFP (SYP-EGFP puncta) could be observed along DsRed-labeled TC axons (Figure 3D-3F). Since these SYP-EGFP puncta were mostly colocalized with immunopositive signals for VGLUT2, which is a presynaptic marker of thalamic cells, and for PSD95, which is a general postsynaptic marker, it is likely that SYP-EGFP puncta mostly represent presynaptic sites on TC axons12.
Time-lapse imaging of TC axons further showed that axon branching and synapse formation of thalamic neurons were continuous and dynamic with addition and elimination (Figure 4)12. Moreover, most branches were found to emerge from SYP-EGFP puncta, indicating that presynaptic sites trigger branch formation (for details, see12).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56553/56553fig1.jpg" /> 
Figure 1. The procedure for preparation of an organotypic cocultures of the thalamus and cerebral cortex.&#160;(A) The top view of a neonatal rat brain. The first cut is made parallel to the midline (1). Then, 300 - 500-&#956;m-thick coronal sections are cut from the primary visual and somatosensory cortex (2). Finally, make a parasagittal cut to obtain the cortical slices (3). (B) A schematic representation of an organotypic coculture of the thalamus and cerebral cortex. Cortical slices from postnatal day 2 rat and thalamic blocks from embryonic day 15 are cocultured on the membrane filter. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56553/56553fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56553/56553fig2.jpg" /> 
Figure 2. A schematic diagram of electrical instruments for electroporation. The stimulator, the isolator, and the electrode pipette are connected in series. To deliver negatively charged DNA, the electrode pipette is connected to the negative terminal of the isolator. The electrical currents for electroporation can be monitored with the oscilloscope. TH: thalamus. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56553/56553fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56553/56553fig3.jpg" /> 
Figure 3. Thalamocortical axons in a coculture after 2 weeks in culture. (A-F) Coexpression of SYP-EGFP with DsRed in a thalamocortical (TC) axon. DsRed plus SYP-EGFP plasmids were introduced into cultured thalamic cells at 1 day in vitro (DIV) using electroporation. (A) An organotypic coculture of thalamic and cortical slices after 12 DIV. (B) A DsRed-labeled thalamic cell extends an axon into the cortical slice and forms branches in upper layers. (C) A magnified image of the boxed region in (A). (D-F) show the DsRed-labeled TC axon (D) and SYP-EGFP puncta (E) in the boxed region of (C). Discrete accumulation of SYP-EGFP was observed along a single TC axon. Th: thalamus. Scale bars: (B) 1 mm, (C) 100 &#181;m, and (F) 20 &#181;m. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56553/56553fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56553/56553fig4v2.jpg" /> 
Figure 4. Time-lapse imaging of a thalamocortical axon expressing SYP-EGFP and DsRed in an organotypic coculture. DsRed plus SYP-EGFP plasmids were introduced into cultured thalamic cells at 1 DIV using electroporation. This axon was imaged daily over 4 days (11 DIV to 14 DIV). Scale bar: 50 &#181;m.&#160;<a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56553/56553fig4v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Visualization of Thalamocortical Axon Branching and Synapse Formation in Organotypic Cocultures at JoVE.com

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) ...

visualization-thalamocortical-axon-branching-synapse-formation

Nanyang Technological University

Research

JoVE Journal

Neuroscience

6.4K Views.  Kanazawa University. 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.

Video: Visualization of Thalamocortical Axon Branching and Synapse Formation in Organotypic Cocultures

Automated Interactive Video Playback for Studies of Animal Communication

Video playback is a widely-used technique for the controlled manipulation and presentation of visual signals in animal communication. In particular, parameter-based computer animation offers the opportunity to independently manipulate any number of behavioral, morphological, or spectral characteristics in the context of realistic, moving images of animals on screen. A major limitation of conventional playback, however, is that the visual stimulus lacks the ability to interact with the live animal. Borrowing from video-game technology, we have created an automated, interactive system for video playback that controls animations in response to real-time signals from a video tracking system. We demonstrated this method by conducting mate-choice trials on female swordtail fish, Xiphophorus birchmanni. Females were given a simultaneous choice between a courting male conspecific and a courting male heterospecific (X. malinche) on opposite sides of an aquarium. The virtual male stimulus was programmed to track the horizontal position of the female, as courting males do in the wild. Mate-choice trials on wild-caught X. birchmanni females were used to validate the prototype's ability to effectively generate a realistic visual stimulus.

Video playback is a widely used technique in animal behavior. We created and evaluated a program that applies rules-based, interactive playback of 3-D computer animations in response to real-time, automated data on subject behavior.

Video playback is a widely-used technique for the controlled manipulation and presentation of visual signals in animal communication. In particular, ...

Visualization of Proprioceptors in Drosophila Larvae and Pupae

Proprioception is the ability to sense the motion, or position, of body parts by responding to stimuli arising within the body. In fruitflies and other insects proprioception is provided by specialized sensory organs termed chordotonal organs (ChOs) 2. Like many other organs in Drosophila, ChOs develop twice during the life cycle of the fly. First, the larval ChOs develop during embryogenesis. Then, the adult ChOs start to develop in the larval imaginal discs and continue to differentiate during metamorphosis.
The development of larval ChOs during embryogenesis has been studied extensively 10,11,13,15,16. The centerpiece of each ChO is a sensory unit composed of a neuron and a scolopale cell. The sensory unit is stretched between two types of accessory cells that attach to the cuticle via specialized epidermal attachment cells 1,9,14. When a fly larva moves, the relative displacement of the epidermal attachment cells leads to stretching of the sensory unit and consequent opening of specific transient receptor potential vanilloid (TRPV) channels at the outer segment of the dendrite 8,12. The elicited signal is then transferred to the locomotor central pattern generator circuit in the central nervous system.
Multiple ChOs have been described in the adult fly 7. These are located near the joints of the adult fly appendages (legs, wings and halters) and in the thorax and abdomen. In addition, several hundreds of ChOs collectively form the Johnston's organ in the adult antenna that transduce acoustic to mechanical energy 3,5,17,4.
In contrast to the extensive knowledge about the development of ChOs in embryonic stages, very little is known about the morphology of these organs during larval stages. Moreover, with the exception of femoral ChOs 18 and Johnston's organ, our knowledge about the development and structure of ChOs in the adult fly is very fragmentary.
Here we describe a method for staining and visualizing ChOs in third instar larvae and pupae. This method can be applied together with genetic tools to better characterize the morphology and understand the development of the various ChOs in the fly.

Visualization of Proprioceptors in Drosophila Larvae and Pupae

A method to immunostain and visualize chordotonal organs in larvae and pupae of Drosophila melanogaster is described.

Proprioception is the ability to sense the motion, or position, of body parts by responding to stimuli arising within the body. In fruitflies and other ...

Paired Whole Cell Recordings in Organotypic Hippocampal Slices

Pair recordings involve simultaneous whole cell patch clamp recordings from two synaptically connected neurons, enabling not only direct electrophysiological characterization of the synaptic connections between individual neurons, but also pharmacological manipulation of either the presynaptic or the postsynaptic neuron. When carried out in organotypic hippocampal slice cultures, the probability that two neurons are synaptically connected is significantly increased. This preparation readily enables identification of cell types, and the neurons maintain their morphology and properties of synaptic function similar to that in native brain tissue. A major advantage of paired whole cell recordings is the highly precise information it can provide on the properties of synaptic transmission and plasticity that are not possible with other more crude techniques utilizing extracellular axonal stimulation. Paired whole cell recordings are often perceived as too challenging to perform. While there are challenging aspects to this technique, paired recordings can be performed by anyone trained in whole cell patch clamping provided specific hardware and methodological criteria are followed. The probability of attaining synaptically connected paired recordings significantly increases with healthy organotypic slices and stable micromanipulation allowing independent attainment of pre- and postsynaptic whole cell recordings. While CA3-CA3 pyramidal cell pairs are most widely used in the organotypic slice hippocampal preparation, this technique has also been successful in CA3-CA1 pairs and can be adapted to any neurons that are synaptically connected in the same slice preparation. In this manuscript we provide the detailed methodology and requirements for establishing this technique in any laboratory equipped for electrophysiology.

Pair recordings are simultaneous whole cell patch clamp recordings from two synaptically connected neurons, enabling precise electrophysiological and pharmacological characterization of the synapses between individual neurons. Here we describe the detailed methodology and requirements for establishing this technique in organotypic hippocampal slice cultures in any laboratory equipped for electrophysiology.

Pair recordings involve simultaneous whole cell patch clamp recordings from two synaptically connected neurons, enabling not only direct ...

Inhibitory Synapse Formation in a Co-culture Model Incorporating GABAergic Medium Spiny Neurons and HEK293 Cells Stably Expressing GABAA Receptors

Inhibitory neurons act in the central nervous system to regulate the dynamics and spatio-temporal co-ordination of neuronal networks. GABA (&#947;-aminobutyric acid) is the predominant inhibitory neurotransmitter in the brain. It is released from the presynaptic terminals of inhibitory neurons within highly specialized intercellular junctions known as synapses, where it binds to GABAA receptors (GABAARs) present at the plasma membrane of the synapse-receiving, postsynaptic neurons. Activation of these GABA-gated ion channels leads to influx of chloride resulting in postsynaptic potential changes that decrease the probability that these neurons will generate action potentials. 
During development, diverse types of inhibitory neurons with distinct morphological, electrophysiological and neurochemical characteristics have the ability to recognize their target neurons and form synapses which incorporate specific GABAARs subtypes. This principle of selective innervation of neuronal targets raises the question as to how the appropriate synaptic partners identify each other. 
To elucidate the underlying molecular mechanisms, a novel in vitro co-culture model system was established, in which medium spiny GABAergic neurons, a highly homogenous population of neurons isolated from the embryonic striatum, were cultured with stably transfected HEK293 cell lines that express different GABAAR subtypes. Synapses form rapidly, efficiently and selectively in this system, and are easily accessible for quantification. Our results indicate that various GABAAR subtypes differ in their ability to promote synapse formation, suggesting that this reduced in vitro model system can be used to reproduce, at least in part, the in vivo conditions required for the recognition of the appropriate synaptic partners and formation of specific synapses. Here the protocols for culturing the medium spiny neurons and generating HEK293 cells lines expressing GABAARs are first described, followed by detailed instructions on how to combine these two cell types in co-culture and analyze the formation of synaptic contacts.

Inhibitory Synapse Formation in a Co-culture Model Incorporating GABAergic Medium Spiny Neurons and HEK293 Cells Stably Expressing GABAA Receptors

The molecular mechanisms that co-ordinate the formation of inhibitory GABAergic synapses during ontogeny are largely unknown. To study these processes,we have developed a co-culture model system which incorporates embryonic medium spiny GABAergic neurons cultured together with stably transfected human embryonic kidney 293 (HEK293) cells expressing functional GABAA receptors.

Inhibitory neurons act in the central nervous system to regulate the dynamics and spatio-temporal co-ordination of neuronal networks. GABA ...

Whole-mount Imaging of Mouse Embryo Sensory Axon Projections

The visualization of full-length neuronal projections in embryos is essential to gain an understanding of how mammalian neuronal networks develop. Here we describe a method to label in situ a subset of dorsal root ganglion (DRG) axon projections to assess their phenotypic characteristics using several genetically manipulated mouse lines. The TrkA-positive neurons are nociceptor neurons, dedicated to the transmission of pain signals. We utilize a TrkAtaulacZ mouse line to label the trajectories of all TrkA-positive peripheral axons in the intact mouse embryo. We further breed the TrkAtaulacZ line onto a Bax null background, which essentially abolishes neuronal apoptosis, in order to assess growth-related questions independently of possible effects of genetic manipulations on neuronal survival. Subsequently, genetically modified mice of interest are bred with the TrkAtaulacZ/Bax null line and are then ready for study using the techniques described herein. This presentation includes detailed information on mouse breeding plans, genotyping at the time of dissection, tissue preparation, staining and clearing to allow for visualization of full-length axonal trajectories in whole-mount preparation.

We present here an optimized protocol to genotype, stain and prepare fetal mice for the imaging of peripheral nociceptor axon projections in the whole animal, as an effective method to assess sensory axon growth phenotypes in developing genetically engineered mice.

The visualization of full-length neuronal projections in embryos is essential to gain an understanding of how mammalian neuronal networks develop. Here we ...

Utilizing Combined Methodologies to Define the Role of Plasma Membrane Delivery During Axon Branching and Neuronal Morphogenesis

During neural development, growing axons extend to multiple synaptic partners by elaborating axonal branches. Axon branching is promoted by extracellular guidance cues like netrin-1 and results in dramatic increases to the surface area of the axonal plasma membrane. Netrin-1-dependent axon branching likely involves temporal and spatial control of plasma membrane expansion, the components of which are supplied through exocytic vesicle fusion. These fusion events are preceded by formation of SNARE complexes, comprising a v-SNARE, such as VAMP2 (vesicle-associated membrane protein 2), and plasma membrane t-SNAREs, syntaxin-1 and SNAP25 (synaptosomal-associated protein 25). Detailed herein isa multi-pronged approach used to examine the role of SNARE mediated exocytosis in axon branching. The strength of the combined approach is data acquisition at a range of spatial and temporal resolutions, spanning from the dynamics of single vesicle fusion events in individual neurons to SNARE complex formation and axon branching in populations of cultured neurons. This protocol takes advantage of established biochemical approaches to assay levels of endogenous SNARE complexes and Total Internal Reflection Fluorescence (TIRF) microscopy of cortical neurons expressing VAMP2 tagged with a pH-sensitive GFP (VAMP2-pHlourin) to identify netrin-1 dependent changes in exocytic activity in individual neurons. To elucidate the timing of netrin-1-dependent branching, time-lapse differential interference contrast (DIC) microscopy of single neurons over the order of hours is utilized. Fixed cell immunofluorescence paired with botulinum neurotoxins that cleave SNARE machinery and block exocytosis demonstrates that netrin-1 dependent axon branching requires SNARE-mediated exocytic activity.

Light microscopy techniques coupled with biochemical assays elucidate the involvement of SNARE-mediated exocytosis in netrin-dependent axon branching. This combination of techniques permits identification of molecular mechanisms controlling axon branching and cell shape change.

During neural development, growing axons extend to multiple synaptic partners by elaborating axonal branches. Axon branching is promoted by extracellular ...

Quadruple Immunostaining of the Olfactory Bulb for Visualization of Olfactory Sensory Axon Molecular Identity Codes

The mouse olfactory system is often used to study mechanisms of neural circuit formation&#12288;because of its simple anatomical structure. An Olfactory Sensory Neuron (OSN) is a bipolar cell with a single dendrite and a single unbranched axon. An OSN expresses only one Olfactory Receptor (OR) gene, OSNs expressing a given type of OR converge their axons to a few sets of invariant glomeruli in the Olfactory Bulb (OB). A remarkable feature of OSN projection is that the expressed ORs play instructive roles in axonal projection. ORs regulate the expression of multiple axon-sorting molecules and generate the combinatorial molecular code of axon-sorting molecules at the OSN axon termini. Thus, to understand the molecular mechanisms of OR-specific axon guidance mechanisms, it is vital to characterize their expression profiles at the OSN axon termini within the same glomerulus. The aim of this article was to introduce methods for collecting as many glomeruli as possible on a single OB section and for performing immunostaining using multiple antibodies. This would allow the comparison and analysis of the expression patterns of axon-sorting molecules without staining variation between OB sections.

Olfactory sensory neurons express a wide variety of axon-sorting molecules to establish proper neural circuitry. This protocol describes an immunohistochemical staining method to visualize combinatorial expressions of axon-sorting molecules at the axon termini of olfactory sensory neurons.

The mouse olfactory system is often used to study mechanisms of neural circuit formation&#12288;because of its simple anatomical structure. An Olfactory ...

Improving the Application of High Molecular Weight Biotinylated Dextran Amine for Thalamocortical Projection Tracing in the Rat

High molecular weight biotinylated dextran amine (BDA) has been used as a highly sensitive neuroanatomical tracer for many decades. Since the quality of its labeling was affected by various factors, here, we provide a refined protocol for the application of high molecular weight BDA for studying optimal neural labeling in the central nervous system. After stereotactic injection of BDA into the ventral posteromedial nucleus (VPM) of the thalamus in the rat through a delicate glass pipette, BDA was stained with fluorescent streptavidin-Alexa (AF) 594 and counterstained with fluorescent Nissl stain AF500/525. On the background of green Nissl staining, the red BDA labeling, including neuronal cell bodies and axonal terminals, was more distinctly demonstrated in the somatosensory cortex. Furthermore, double fluorescent staining for BDA and the calcium-binding protein parvalbumin (PV) was carried out to observe the correlation of BDA labeling and PV-positive interneurons in the cortical target, providing the opportunity to study the local neural circuits and their chemical characteristics. Thus, this refined method is not only suitable for visualizing high quality neural labeling with the high molecular weight BDA through reciprocal neural pathways between the thalamus and cerebral cortex, but also will permit the simultaneous demonstration of other neural markers with fluorescent histochemistry or immunochemistry.

Here, we present a refined protocol to effectively reveal biotinylated dextran amine (BDA) labeling with a fluorescent staining method through a reciprocal neural pathway. It is suitable for analyzing the fine structure of BDA labeling and distinguishing it from other neural elements under a confocal laser scanning microscope.

High molecular weight biotinylated dextran amine (BDA) has been used as a highly sensitive neuroanatomical tracer for many decades. Since the quality of ...

Evaluation of Synapse Density in Hippocampal Rodent Brain Slices

In the brain, synapses are specialized junctions between neurons, determining the strength and spread of neuronal signaling. The number of synapses is tightly regulated during development and neuronal maturation. Importantly, deficits in synapse number can lead to cognitive dysfunction. Therefore, the evaluation of synapse number is an integral part of neurobiology. However, as synapses are small and highly compact in the intact brain, the assessment of absolute number is challenging. This protocol describes a method to easily identify and evaluate synapses in hippocampal rodent slices using immunofluorescence microscopy. It includes a three-step procedure to evaluate synapses in high-quality confocal microscopy images by analyzing the co-localization of pre- and postsynaptic proteins in hippocampal slices. It also explains how the analysis is performed and gives representative examples from both excitatory and inhibitory synapses. This protocol provides a solid foundation for the analysis of synapses and can be applied to any research investigating the structure and function of the brain.

A protocol for accurately identifying and analyzing synapses in hippocampal slices using immunofluorescence is outlined in this article.

In the brain, synapses are specialized junctions between neurons, determining the strength and spread of neuronal signaling. The number of synapses is ...

Visualization and Live Imaging of Oligodendrocyte Organelles in Organotypic Brain Slices Using Adeno-associated Virus and Confocal Microscopy

Neurons rely on the electric insulation and trophic support of myelinating oligodendrocytes. Despite the importance of oligodendrocytes, the advanced tools currently used to study neurons, have only partly been taken on by oligodendrocyte researchers. Cell type-specific staining by viral transduction is a useful approach to study live organelle dynamics. This paper describes a protocol for visualizing oligodendrocyte mitochondria in organotypic brain slices by transduction with adeno-associated virus (AAV) carrying genes for mitochondrial targeted fluorescent proteins under the transcriptional control of the myelin basic protein promoter. It includes the protocol for making organotypic coronal mouse brain slices. A procedure for time-lapse imaging of mitochondria then follows. These methods can be transferred to other organelles and may be particularly useful for studying organelles in the myelin sheath. Finally, we describe a readily available technique for visualization of unstained myelin in living slices by Confocal Reflectance microscopy (CoRe). CoRe requires no extra equipment and can be useful to identify the myelin sheath during live imaging.

Myelinating oligodendrocytes promote rapid action potential propagation and neuronal survival. Described here is a protocol for oligodendrocyte-specific expression of fluorescent proteins in organotypic brain slices with subsequent time-lapse imaging. Further, a simple procedure for visualizing unstained myelin is presented.

Neurons rely on the electric insulation and trophic support of myelinating oligodendrocytes. Despite the importance of oligodendrocytes, the advanced ...