We thank Atsushi Miyawaki and Hiroshi Hama for their advice on the AbScale experiments, Charles Yokoyama for editing of the manuscript, Eriko Ohshima and Miyuki Kishino for their technical assistance. This work was supported by research funds from RIKEN to T.H. and Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan to T.H. (Innovative Areas &#34;Mesoscopic Neurocircuitry&#34;; 22115004) and S.S. (25890023).

All experimental procedures were approved by the RIKEN Wako Animal Experiments Committee and RIKEN Genetic Recombinant Experiment Safety Committee and performed according to the institutional guidelines of the animal facilities of the RIKEN Brain Science Institute.
1. Preparation of Imaging Chambers
<ol>
	<li>Imaging chamber19
	<ol>
		<li>Using silicone rubber sheets, prepare a chamber with a thickness of approximately 5 mm and floor plates of various thicknesses. Also, prepare Petri dishes with and without a glass bottom (Figure 1A).</li>
	</ol>
	</li>
	<li>Slice spacer
	<ol>
		<li>Prepare spacers to hold samples, using silicone rubber sheets with a thickness of 0.5 mm (Figure 1C).</li>
	</ol>
	</li>
</ol>
2. Tracer Injection
NOTE: Make injections into either the pons (2.1) or superior colliculus (2.2). Injection into the pons label sub-cerebral projection neurons in a wide brain region including the visual and motor areas, while injection into the superior colliculus labels sub-cerebral projection neurons in the visual area. For control experiments, inject saline instead of fluorescently-labeled cholera toxin subunit B. For the maintenance of sterile condition use sterilized equipment and plastic gloves cleaned with ethanol.
<ol>
	<li>Make injections into the pons of adult mice.
	<ol>
		<li>Draw 1 &#181;L of fluorescently-labeled cholera toxin subunit B (25 &#181;g/&#181;L in PBS) into a 26G Hamilton syringe.</li>
		<li>Place an injector pump on the syringe.</li>
		<li>Place the syringe and pump on the tool holder of a manipulator placed on a stereotaxic instrument. Tilt the manipulator 12&#176; posteriorly from the vertical axis.</li>
		<li>Anesthetize a male or female adult mouse (C57BL/6J or Tlx3-cre/Ai9) by injecting sodium pentobarbital intraperitoneally (60 mg/kg body weight) or by administering isoflurane (2&#8211;3%). Wait until the mouse makes no response when its tail is pinched with forceps, indicating that the mouse is fully anesthetized.</li>
		<li>Place the mouse on the stereotaxic instrument.</li>
		<li>Carefully remove hair using a razor blade to prevent infection and cut 10 mm of the scalp so that the bregma and lambda are visible. Administer 0.1 mL of 1% lidocaine using a pipette. Set the angle of the head by adjusting the vertical position of the mouthpiece on the stereotaxic instrument so that the bregma and lambda have the same z-level.</li>
		<li>Adjust the position of the manipulator by sliding it on the stereotaxic instrument so that the tip of the syringe is close to the bregma and record the position of the manipulator. Retract the syringe by moving the tool holder on the manipulator.</li>
		<li>Move the manipulator 5.4 mm posteriorly and 0.4 mm laterally. Advance the syringe so that the tip is close to the entry point on the skull. Retract the syringe and mark the entry point.</li>
		<li>At the marked position, drill a hole with a diameter of approximately 1 mm.</li>
		<li>Insert the syringe tip through the hole so that the tip depth is 6.9 mm more than that measured at the bregma.</li>
		<li>Inject 1 &#181;L of tracers using the pump at 0.2 &#181;L/min.</li>
		<li>Remove the syringe from the brain.</li>
		<li>If necessary, cover the exposed brain with small fragments of microfibrillar hemostat and instant adhesive.</li>
		<li>Rinse the exposed brain using saline delivered with a pipette to prevent infection and suture the scalp.</li>
		<li>Remove the mouse from the stereotaxic instrument. Allow the mouse to recover from anesthesia in an incubator at 30 &#730;C, typically for 1 h. Do not leave the mouse unattended until it has regained sufficient consciousness to maintain sternal recumbency. Return the mouse to the company of other animals after it has fully recovered.</li>
		<li>Maintain the mouse for 3&#8211;7 days.</li>
	</ol>
	</li>
	<li>Make injections into the superior colliculus of adult mice.
	<ol>
		<li>Prepare a glass pipette with a tip diameter of 30&#8211;50 &#181;m.</li>
		<li>Connect the glass pipette to a Hamilton syringe through a plastic tube (Figure 2A).</li>
		<li>Fill the glass pipette, plastic tube, and Hamilton syringe with the paraffin liquid.</li>
		<li>Place an injector pump on the syringe.</li>
		<li>Place the glass pipette on the manipulator and tilt the manipulator 60&#176; posteriorly from the vertical axis (Figure 2B).</li>
		<li>Perform 2.1.4&#8211;2.1.9. The position of the manipulator is 1.4 mm posterior, 0.5 mm lateral to the lambda.</li>
		<li>Place a small plastic paraffin film on the skull, then put approximately 1 &#181;L of the tracer solution on it. Quickly advance the glass pipette and fill it with at least 0.5 &#181;L of the tracer solution.</li>
		<li>Insert the glass pipette so that the tip depth is 3.0 mm from the brain surface.</li>
		<li>Inject 0.5 &#181;L of tracers using the pump at 0.2 &#181;L/min.</li>
		<li>Remove the glass pipette from the brain.</li>
		<li>Perform 2.1.13&#8211;2.1.16.</li>
	</ol>
	</li>
</ol>
3. Fixation and Trimming
<ol>
	<li>Inject sodium pentobarbital (60 mg/kg body weight) intraperitoneally into a mouse (C57BL/6J or Tlx3-cre/Ai9, with or without the tracer injection as described in step 2. Wait until the mouse makes no response when its tail is pinched with forceps, indicating that the mouse is fully anesthetized.</li>
	<li>Euthanize the mouse humanely by perfusing&#160;the mouse transcardially20 with 0.9% saline.</li>
	<li>Fix the mouse20 by perfusing 4% paraformaldehyde (PFA) in 0.1 M phosphate buffer (pH 7.5).</li>
	<li>Cut the scalp using a pair of scissors to expose the skull as described20.
	<ol>
		<li>Cut the midline of the exposed skull using a pair of scissors. Remove the skull using forceps.</li>
		<li>If marking the position of the bregma and lambda is necessary, first remove one hemisphere of the skull. Insert thin tungsten needles into the brain at the positions of the bregma and lambda on the skull remaining on the brain, then remove the remaining skull. 
		NOTE: The brain can be stored in PBS at 4 &#730;C.</li>
	</ol>
	</li>
	<li>To perform antibody staining of inhibitory neurons, cut the brain samples into slices.
	<ol>
		<li>Place the brain sample on a vibratome.</li>
		<li>Cut slices up to 500 &#181;m thick in PBS at room temperature and proceed to step 5 (the AbScale method).</li>
	</ol>
	</li>
	<li>If antibody staining is unnecessary, trim the brain sample to blocks (up to 3 mm thick) using a razor blade (Figure 3) and proceed to step 4 (the SeeDB method). 
	NOTE: The brain can be stored in PBS at 4 &#176;C after cutting or trimming. The SeeDB method is preferable when antibody staining is not necessary because it requires less time than the AbScale method.</li>
</ol>
4. Clearing without Antibody Staining (the SeeDB Method)
<ol>
	<li>Transfer the sample using a spatula to a 50 mL plastic tube containing 20 mL of 0.5% &#945;-thioglycerol and 20% (w/v) fructose and incubate it for 4 h with gentle shaking at room temperature.</li>
	<li>Transfer the sample using a spatula to a 50 mL plastic tube containing 20 mL of 0.5% &#945;-thioglycerol and 40% (w/v) fructose and incubate it for 4 h with gentle shaking at room temperature.</li>
	<li>Transfer the sample using a spatula to a 50 mL plastic tube containing 20 mL of 0.5% &#945;-thioglycerol and 60% (w/v) fructose and incubate it for 4 h with gentle shaking at room temperature.</li>
	<li>Transfer the sample using a spatula to a 50 mL plastic tube containing 20 mL of 0.5% &#945;-thioglycerol and 80% (w/v) fructose and incubate it for 12 h with gentle shaking at room temperature.</li>
	<li>Transfer the sample using a spatula to a 50 mL plastic tube containing 20 mL of 0.5% &#945;-thioglycerol and 100% (w/v) fructose and incubate it for 12 h with gentle shaking at room temperature.</li>
	<li>Transfer the sample using a spatula to a 50 mL plastic tube containing 20 mL of 0.5% &#945;-thioglycerol and 80.2% (w/w) fructose and incubate it for 24 h with gentle shaking at room temperature. 
	NOTE: Handle the sample carefully to keep deformations as small as possible. Do not incubate samples longer than indicated, as samples can quickly become opaque.</li>
	<li>Embed the sample in an imaging chamber filled with the 80.2% fructose solution (Figure 1B). If necessary, fix the sample by putting small pieces of rubber adhesive around. If the chamber is too deep, put a floor plate in the chamber before placing the samples.</li>
	<li>Place the Petri dish with a glass cover on the imaging chamber and put water in the dish, and image using confocal or two-photon microscopy with a water-immersion long working distance objective. Excitation wavelengths and emission filters are described in Table 1. If necessary, use a motorized stage.</li>
</ol>
5. Clearing with Antibody Staining (the AbScale Method)
<ol>
	<li>Prepare reagents as described in Table 2.</li>
	<li>Transfer the slices using a spatula to a 5 mL plastic tube containing 4 mL of Sca/eS0 solution and incubate them for 12 h with gentle shaking at 37 &#176;C (Figure 4B).</li>
	<li>Remove the solution from the tube using a pipette and add 4 mL of Sca/eA2 solution, and incubate the slices for 36 h with gentle shaking at 37 &#176;C.</li>
	<li>Remove the solution from the tube using a pipette and add 4 mL of Sca/eB4 solution, and incubate the slices for 24 h with gentle shaking at 37 &#176;C.</li>
	<li>Remove the solution from the tube using a pipette and add 4 mL of Sca/eA2 solution, and incubate the slices for 12 h with gentle shaking at 37 &#176;C.</li>
	<li>Remove the solution from the tube using a pipette and add 4 mL of PBS and incubate the slices for 6 h with gentle shaking at room temperature.</li>
	<li>Carefully remove the slices to a 2 mL plastic tube using a spatula.</li>
	<li>Incubate with primary antibodies (Table 3) in 1 mL of AbScale solution for 48-72 h at 37 &#176;C (Figure 4C) with gentle shaking.</li>
	<li>Carefully remove the slices to a 5 mL plastic tube using a spatula.</li>
	<li>Incubate in 4 mL of AbScale solution for 2 h 2 times at room temperature with gentle shaking.</li>
	<li>Carefully remove the slices to a 2 mL plastic tube using a spatula.</li>
	<li>Incubate with fluorescently-labeled secondary antibodies (Table of Materials, 1:100) in 1 mL of AbScale solution for 48 h at 37 &#176;C with gentle shaking.</li>
	<li>Carefully remove the slices using a spatula to a 5 mL plastic tube containing 4 mL of the AbScale solution and incubate the slices for 6 h with gentle shaking at room temperature.</li>
	<li>Remove the solution from the tube using a pipette and add 4 mL of the AbScale solution and incubate the slices for 2 h 2 times with gentle shaking at room temperature.</li>
	<li>Remove the solution from the tube using a pipette and add 4 mL of 4% PFA and incubate the slices for 1 h with gentle shaking at room temperature.</li>
	<li>Remove the solution from the tube using a pipette and add 4 mL of PBS and incubate the slices for 1 h with gentle shaking at room temperature.</li>
	<li>Remove the solution from the tube using a pipette and add 4 mL of the Sca/eS4 solution, and incubate the slices for 12 h with gentle shaking at 37 &#176;C.</li>
	<li>Place the spacer on a glass slide and place the slices in the spacer and immerse the slices with Sca/eS4 solution. Seal the spacer with a cover glass (Figure 1D).</li>
	<li>Put water on the cover glass and image using confocal or two-photon microscopy with a water-immersion long working distance objective. If necessary, use a motorized stage. 
	NOTE: Check whether the deep parts of the sample are labeled similarly to the superficial parts to confirm the absence of a significant labeling bias. 
	NOTE: Penetration of the tested antibodies is described in Table 3.</li>
</ol>
6. Cell Position Determination
<ol>
	<li>For each position in the scanned images, calculate correlation values using a three-dimensional image filter14 (Figure 5A-5D).</li>
	<li>Determine the positions of the peaks of the correlation value (Figure 5D).</li>
	<li>Investigate images around the peaks to locate cells (Figure 5E).</li>
</ol>

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The authors have nothing to disclose.

We have presented procedures to obtain large-scale three-dimensional images of the cell type-specific organization of the major cell types in mouse neocortical layer 5. Compared to the conventional slice staining, the method is more useful in determining the three-dimensional organization of the neocortex. The method enables image acquisition from the wider and the deeper brain regions compared to the typical in vivo 2-photon microscopy or conventional confocal microscopy and, thus, can allow the comprehensive a...

The mammalian neocortex is composed of a large number of cell types, each with the specific gene expression patterns, electrophysiological and biochemical properties, synaptic connections, and in vivo functions1,2,3,4,5,6,7. Whether these cell types are organized into repeated structures has been unclear. Cortical columns, including visual orientation columns and somatosensory barrels, have repeated structures, but their cellular organization remains unclear8,9. These are present in the specific cortical areas and are not a brain-wide system.
In neocortical layer 5, the large majority of neurons are classified into four major types. A major type of excitatory neurons, sub-cerebral projection neurons, projects axons to subcortical targets including the pons, spinal cord, and superior colliculus, and, therefore, represents the major cortical output pathway10. Cortical projection neurons, another major type of excitatory neurons, innervate the cortex10. Inhibitory neurons also contain two major classes: parvalbumin-expressing and somatostatin-expressing cells11.
Recent analyses indicate that the four cell types are organized into repeated structures12,13,14. Both sub-cerebral projection neurons12,13,14 and cortical projection neurons14 organize into cell-type specific microcolumns with a diameter of 1&#8211;2 cells. Parvalbumin-expressing and somatostatin-expressing cells align specifically with microcolumns of sub-cerebral projection neurons but not with microcolumns of cortical projection neurons14. Microcolumns themselves periodically align to form a hexagonal lattice array14 and are present in multiple cortical areas including visual, somatosensory, and motor areas in mouse brain12,14 and in language areas of human brain13. Neurons in the individual microcolumn exhibit synchronized activity and have similar sensory responses14. These observations indicate that layer 5 cell types organize into a microcolumn lattice structure representing the first known brain-wide organization of repeating functional modules.
Microcolumns have a radius of approximately 10 &#181;m and have a spatial periodicity of approximately 40 &#181;m. In addition, the orientation of microcolumns is parallel to their apical dendrites and changes depending on their position in the cortex14. Therefore, the microcolumn system is difficult to analyze using conventional cortical slices with a typical thickness of a few tens of micrometers. In addition, the analysis of periodicity requires three-dimensional data from a wide-range of brain areas, and, therefore, the typical imaging area of confocal microscopy or in vivo 2-photon imaging is too narrow.
Recently, techniques have been developed to clear thick tissues15,16. Here we describe the application of these methods to obtain large-scale, three-dimensional images of the major cell types in mouse neocortical layer 5 that comprise the microcolumn system. Subcerebral projection neurons are labeled by the retrograde labeling or by the expression of the enhanced green fluorescent protein in Crym-egfp transgenic mice12, and cortical projection neurons are labeled by either the retrograde labeling or by the tdTomato expression in Tlx3-cre/Ai9 mice17. Parvalbumin-expressing and somatostatin-expressing cells are labeled by immunohistochemistry. The (Antibody Scale S) AbScale method18 is used for the antibody staining experiments, while the (See Deep Brain) SeeDB method19 is used for other experiments. These methods overcome the above-mentioned difficulties of the conventional imaging methods and reveal the accurate cellular organization of layer 514.

<table>
	<tbody>
		<tr>
			<td>Crym-egfp transgenic mice</td>
			<td>MMRRC</td>
			<td>012003-UCD</td>
			<td></td>
		</tr>
		<tr>
			<td>Tlx3-cre transgenic mice</td>
			<td>MMRRC</td>
			<td>36547-UCD</td>
			<td></td>
		</tr>
		<tr>
			<td>ROSA-CAG-flox-tdTomato mice</td>
			<td>Jackson Laboratory</td>
			<td>JAX #7909</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicone rubber sheet</td>
			<td>AS ONE</td>
			<td>6-611-01</td>
			<td>0.5 mm thickness</td>
		</tr>
		<tr>
			<td>Silicone rubber sheet</td>
			<td>AS ONE</td>
			<td>6-611-02</td>
			<td>1.0 mm thickness</td>
		</tr>
		<tr>
			<td>Silicone rubber sheet</td>
			<td>AS ONE</td>
			<td>6-611-05</td>
			<td>3.0 mm thickness</td>
		</tr>
		<tr>
			<td>Petri dishes</td>
			<td>Falcon</td>
			<td>351008</td>
			<td></td>
		</tr>
		<tr>
			<td>Cover glass</td>
			<td>Matsunami</td>
			<td>C022241</td>
			<td></td>
		</tr>
		<tr>
			<td>Cholera toxin subunit B (recombinant), Alexa Fluor 488 conjugate</td>
			<td>Invitrogen</td>
			<td>C22841</td>
			<td></td>
		</tr>
		<tr>
			<td>Cholera toxin subunit B (recombinant), Alexa Fluor 555 conjugate</td>
			<td>Invitrogen</td>
			<td>C22843</td>
			<td></td>
		</tr>
		<tr>
			<td>Cholera toxin subunit B (recombinant), Alexa Fluor 594 conjugate</td>
			<td>Invitrogen</td>
			<td>C22842</td>
			<td></td>
		</tr>
		<tr>
			<td>Cholera toxin subunit B (recombinant), Alexa Fluor 647 conjugate</td>
			<td>Invitrogen</td>
			<td>C34778</td>
			<td></td>
		</tr>
		<tr>
			<td>26G Hamilton syringe</td>
			<td>Hamilton</td>
			<td>701N</td>
			<td></td>
		</tr>
		<tr>
			<td>Injector pump</td>
			<td>KD Scientific</td>
			<td>KDS 310</td>
			<td>Pons injection</td>
		</tr>
		<tr>
			<td>Injector pump</td>
			<td>KD Scientific</td>
			<td>KDS 100</td>
			<td>Superior colliculus injection</td>
		</tr>
		<tr>
			<td>Manipulator</td>
			<td>Narishige</td>
			<td>SM-15</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium pentobarbital</td>
			<td>Kyoritsu Seiyaku</td>
			<td>Somnopentyl</td>
			<td></td>
		</tr>
		<tr>
			<td>Isoflurane</td>
			<td>Pfizer</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Lidocaine</td>
			<td>AstraZeneca</td>
			<td>Xylocaine injection 1% with epinephrine</td>
			<td></td>
		</tr>
		<tr>
			<td>Drill</td>
			<td>Toyo Associates</td>
			<td>HP-200</td>
			<td></td>
		</tr>
		<tr>
			<td>Avitene microfibrillar hemostat</td>
			<td>Davol Inc</td>
			<td>1010090</td>
			<td></td>
		</tr>
		<tr>
			<td>Alonalfa</td>
			<td>Daiichi-Sankyo</td>
			<td>Alonalpha A</td>
			<td></td>
		</tr>
		<tr>
			<td>Surgical silk</td>
			<td>Ethicon</td>
			<td>K881H</td>
			<td></td>
		</tr>
		<tr>
			<td>Incubator</td>
			<td>UVP</td>
			<td>HB-1000 Hybridizer</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass pipette</td>
			<td>Drummond Scientific Company</td>
			<td>2-000-075</td>
			<td></td>
		</tr>
		<tr>
			<td>Electrode puller</td>
			<td>Sutter Instrument Company</td>
			<td>P-97</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraffin Liquid, light</td>
			<td>Nacalai tesque</td>
			<td>26132-35</td>
			<td></td>
		</tr>
		<tr>
			<td>Saline</td>
			<td>Otsuka</td>
			<td>1326</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Nacalai tesque</td>
			<td>26126-54</td>
			<td></td>
		</tr>
		<tr>
			<td>Tungsten needle</td>
			<td>Inter medical</td>
			<td>&#934;0.1 *L200 mm</td>
			<td></td>
		</tr>
		<tr>
			<td>Vibratome</td>
			<td>Leica</td>
			<td>VT1000S</td>
			<td></td>
		</tr>
		<tr>
			<td>50 mL plastic tube</td>
			<td>Falcon</td>
			<td>352070</td>
			<td></td>
		</tr>
		<tr>
			<td>&#945;-thioglycerol</td>
			<td>Nacalai tesque</td>
			<td>33709-62</td>
			<td></td>
		</tr>
		<tr>
			<td>D(-) Fructose</td>
			<td>Nacalai tesque</td>
			<td>16315-55</td>
			<td></td>
		</tr>
		<tr>
			<td>BluTack</td>
			<td>Bostik</td>
			<td>CKBT-450000</td>
			<td></td>
		</tr>
		<tr>
			<td>Two-photon microscope</td>
			<td>Nikon</td>
			<td>A1RMP</td>
			<td></td>
		</tr>
		<tr>
			<td>Water-immersion long working distance objectives</td>
			<td>Nikon</td>
			<td colspan="2">CFI Apo LWD 25XW, NA 1.1, WD 2 mm</td>
		</tr>
		<tr>
			<td>Water-immersion long working distance objectives</td>
			<td>Nikon</td>
			<td>CFI LWD 16XW, NA 0.8, WD 3 mm</td>
			<td></td>
		</tr>
		<tr>
			<td>Motorized stage</td>
			<td>COMS</td>
			<td>PT100C-50XY</td>
			<td></td>
		</tr>
		<tr>
			<td>Filter</td>
			<td>Semrock</td>
			<td>FF01-492/SP-25</td>
			<td></td>
		</tr>
		<tr>
			<td>Filter</td>
			<td>Semrock</td>
			<td>FF03-525/50-25</td>
			<td></td>
		</tr>
		<tr>
			<td>Filter</td>
			<td>Semrock</td>
			<td>FF03-575/25-25</td>
			<td></td>
		</tr>
		<tr>
			<td>Filter</td>
			<td>Semrock</td>
			<td>FF01-629/56</td>
			<td></td>
		</tr>
		<tr>
			<td>Filter</td>
			<td>Chroma</td>
			<td>D605/55m</td>
			<td></td>
		</tr>
		<tr>
			<td>5 mL plastic tube</td>
			<td>AS ONE</td>
			<td>VIO-5B</td>
			<td></td>
		</tr>
		<tr>
			<td>2 mL plastic tube</td>
			<td>Eppendorf&#160;</td>
			<td>0030120094</td>
			<td></td>
		</tr>
		<tr>
			<td>Urea</td>
			<td>Nacalai tesque</td>
			<td>35905-35</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Nacalai tesque</td>
			<td>35501-15</td>
			<td></td>
		</tr>
		<tr>
			<td>Glyserol</td>
			<td>Sigma-aldrich</td>
			<td>191612</td>
			<td></td>
		</tr>
		<tr>
			<td>D(-)-sorbitol</td>
			<td>Wako</td>
			<td>191-14735</td>
			<td></td>
		</tr>
		<tr>
			<td>Methyl-&#946;-cyclodextrin</td>
			<td>Tokyo chemical industry</td>
			<td>M1356</td>
			<td></td>
		</tr>
		<tr>
			<td>&#947;-Cyclodextrin</td>
			<td>Wako</td>
			<td>037-10643</td>
			<td></td>
		</tr>
		<tr>
			<td>N-acetyl-L-hydroxyproline</td>
			<td>Skin Essential Actives</td>
			<td>33996-33-7</td>
			<td></td>
		</tr>
		<tr>
			<td>DMSO</td>
			<td>Nacalai tesque</td>
			<td>13445-45</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine Serum Albumin</td>
			<td>Sigma-aldrich</td>
			<td>A7906</td>
			<td></td>
		</tr>
		<tr>
			<td>Tween-20 (1.1 g/mL)</td>
			<td>Nacalai tesque</td>
			<td>35624-15</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat anti-Mouse IgG (H+L) Cross-Adsorbed Secondary Antibody, Alexa Fluor 555</td>
			<td>Invitrogen</td>
			<td>A21422</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat anti-Rabbit IgG (H+L) Cross-Adsorbed Secondary Antibody, Alexa Fluor 555</td>
			<td>Invitrogen</td>
			<td>A21428</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat anti-Mouse IgG (H+L) Cross-Adsorbed Secondary Antibody, Alexa Fluor 647</td>
			<td>Invitrogen</td>
			<td>A21235</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat anti-Mouse IgG (H+L) Highly CrossAdsorbed Secondary Antibody, Alexa Fluor 488</td>
			<td>Invitrogen</td>
			<td>A11029</td>
			<td></td>
		</tr>
		<tr>
			<td>Donkey anti-Rabbit IgG (H+L) Highly CrossAdsorbed Secondary Antibody, Alexa Fluor 488</td>
			<td>Invitrogen</td>
			<td>A21206</td>
			<td></td>
		</tr>
		<tr>
			<td>Confocal microscope</td>
			<td>Olympus</td>
			<td>FV1000</td>
			<td></td>
		</tr>
		<tr>
			<td>Water-immersion long working distance objectives</td>
			<td>Olympus</td>
			<td>XLUMPLFLN 20XW, NA 1.0, WD 2 mm</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-NeuN</td>
			<td>Millipore</td>
			<td>MAB377</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-NeuN</td>
			<td>Millipore</td>
			<td>ABN78</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-CTIP2</td>
			<td>Abcam</td>
			<td>ab18465</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-Statb2</td>
			<td>Abcam</td>
			<td>ab51502</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-GAD67</td>
			<td>Millipore</td>
			<td>MAB5406</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-GABA</td>
			<td>Sigma</td>
			<td>A2052</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-Parvalbumin</td>
			<td>Swant</td>
			<td>235</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-Parvalbumin</td>
			<td>Frontier Institute</td>
			<td>PV-Go-Af460</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-Parvalbumin</td>
			<td>Sigma</td>
			<td>P3088</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-Parvalbumin</td>
			<td>Abcam</td>
			<td>ab11427</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-Somatostatin</td>
			<td>Peninsula Laboratories</td>
			<td>T-4103</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-c-Fos</td>
			<td>CalbioChem</td>
			<td>PC38</td>
			<td></td>
		</tr>
	</tbody>
</table>

large-scale three-dimensional imaging of cellular organization in the mouse neocortex

The mammalian neocortex is composed of many types of excitatory and inhibitory neurons, each with specific electrophysiological and biochemical properties, synaptic connections, and in vivo functions, but their basic functional and anatomical organization from cellular to network scale is poorly understood. Here we describe a method for the three-dimensional imaging of fluorescently-labeled neurons across large areas of the brain for the investigation of the cortical cellular organization. Specific types of neurons are labeled by the injection of fluorescent retrograde neuronal tracers or expression of fluorescent proteins in transgenic mice. Block brain samples, e.g., a hemisphere, are prepared after fixation, made transparent with tissue clearing methods, and subjected to fluorescent immunolabeling of the specific cell types. Large areas are scanned using confocal or two-photon microscopes equipped with large working distance objectives and motorized stages. This method can resolve the periodic organization of the cell type-specific microcolumn functional modules in the mouse neocortex. The procedure can be useful for the study of three-dimensional cellular architecture in the diverse brain areas and other complex tissues.

We labeled cortical projection neurons by expression of tdTomato in Tlx3-cre/Ai9 transgenic mice and visualized sub-cerebral projection neurons by injecting the retrograde tracer CTB488 into the pons. The left hemisphere of the brain was subjected to the SeeDB method and scanned using a two-photon microscope equipped with a water-immersion long working distance objective (25X, N.A. 1.1, working distance 2 mm) and a motorized stage. A stack of 401 images (512 x 512 pixels...

Watch this Scientific Journal Video about Large-scale Three-dimensional Imaging of Cellular Organization in the Mouse Neocortex at JoVE.com

Large-scale Three-dimensional Imaging of Cellular Organization in the Mouse Neocortex

Here we describe a procedure for tissue clearing, fluorescent labeling, and large-scale imaging of mouse brain tissue which, thereby, enables visualization of the three-dimensional organization of cell types in the neocortex.

The mammalian neocortex is composed of many types of excitatory and inhibitory neurons, each with specific electrophysiological and biochemical ...

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JoVE Journal

Neuroscience

8.3K Views.  RIKEN Brain Science Institute. Here we describe a procedure for tissue clearing, fluorescent labeling, and large-scale imaging of mouse brain tissue which, thereby, enables visualization of the three-dimensional organization of cell types in the neocortex.

Video: Large-scale Three-dimensional Imaging of Cellular Organization in the Mouse Neocortex

Multiple-mouse Neuroanatomical Magnetic Resonance Imaging

The field of mouse phenotyping with magnetic resonance imaging (MRI) is rapidly growing, motivated by the need for improved tools for characterizing and evaluating mouse models of human disease. MRI is an excellent modality for investigating genetically altered animals. It is capable of whole brain coverage, can be used in vivo, and provides multiple contrast mechanisms for investigating different aspects of neuranatomy and physiology. The advent of high-field scanners along with the ability to scan multiple mice simultaneously allows for rapid phenotyping of novel mutations.
Effective mouse MRI studies require attention to many aspects of experiment design. In this article, we will describe general methods to acquire quality images for mouse phenotyping using a system that images mice concurrently in shielded transmit/receive radio frequency (RF) coils in a common magnet (Bock et al., 2003). We focus particularly on anatomical phenotyping, an important and accessible application that has shown a high potential for impact in many mouse models at our imaging centre. Before we can provide the detailed steps to acquire such images, there are important practical considerations for both in vivo brain imaging (Dazai et al., 2004) and ex vivo brain imaging (Spring et al., 2007) that should be noted. These are discussed below.

Magnetic resonance imaging (MRI) has become an increasingly popular tool for examining the phenotype of genetically altered mice. This article illustrates the methods necessary to achieve high-throughput phenotyping of genetically altered mice using multiple-mouse MRI.

The field of mouse phenotyping with magnetic resonance imaging (MRI) is rapidly growing, motivated by the need for improved tools for characterizing and ...

Recording Large-scale Neuronal Ensembles with Silicon Probes in the Anesthetized Rat

Large scale electrophysiological recordings from neuronal ensembles offer the opportunity to investigate how the brain orchestrates the wide variety of behaviors from the spiking activity of its neurons. One of the most effective methods to monitor spiking activity from a large number of neurons in multiple local neuronal circuits simultaneously is by using silicon electrode arrays1-3.
Action potentials produce large transmembrane voltage changes in the vicinity of cell somata. These output signals can be measured by placing a conductor in close proximity of a neuron. If there are many active (spiking) neurons in the vicinity of the tip, the electrode records combined signal from all of them, where contribution of a single neuron is weighted by its 'electrical distance'. Silicon probes are ideal recording electrodes to monitor multiple neurons because of a large number of recording sites (+64) and a small volume. Furthermore, multiple sites can be arranged over a distance of millimeters, thus allowing for the simultaneous recordings of neuronal activity in the various cortical layers or in multiple cortical columns (Fig. 1). Importantly, the geometrically precise distribution of the recording sites also allows for the determination of the spatial relationship of the isolated single neurons4. Here, we describe an acute, large-scale neuronal recording from the left and right forelimb somatosensory cortex simultaneously in an anesthetized rat with silicon probes (Fig. 2).

Extracellular recordings of neuronal activity using silicon probes in the anesthetized rat will be described. This technique allows information to be obtained across multiple brain areas from more than 100 neurons simultaneously. It provides information with single cell resolution about neuronal ensembles dynamics in multiple local circuits.

Large scale electrophysiological recordings from neuronal ensembles offer the opportunity to investigate how the brain orchestrates the wide variety of ...

Large-scale Recording of Neurons by Movable Silicon Probes in Behaving Rodents

A major challenge in neuroscience is linking behavior to the collective activity of neural assemblies. Understanding of input-output relationships of neurons and circuits requires methods with the spatial selectivity and temporal resolution appropriate for mechanistic analysis of neural ensembles in the behaving animal, i.e. recording of representatively large samples of isolated single neurons. Ensemble monitoring of neuronal activity has progressed remarkably in the past decade in both small and large-brained animals, including human subjects1-11. Multiple-site recording with silicon-based devices are particularly effective because of their scalability, small volume and geometric design.
Here, we describe methods for recording multiple single neurons and local field potential in behaving rodents, using commercially available micro-machined silicon probes with custom-made accessory components. There are two basic options for interfacing silicon probes to preamplifiers: printed circuit boards and flexible cables. Probe supplying companies (<a href="http://www.neuronexustech.com/" >http://www.neuronexustech.com/</a>; <a href="http://www.sbmicrosystems.com/">http://www.sbmicrosystems.com/</a>; <a href="http://www.acreo.se/">http://www.acreo.se/</a>) usually provide the bonding service and deliver probes bonded to printed circuit boards or flexible cables. Here, we describe the implantation of a 4-shank, 32-site probe attached to flexible polyimide cable, and mounted on a movable microdrive. Each step of the probe preparation, microdrive construction and surgery is illustrated so that the end user can easily replicate the process.

We describe methods for large-scale recording of multiple single units and local field potential in behaving rodents with silicon probes. Drive fabrication, probe attachment to the drive and probe implantation processes are illustrated in sufficient details for easy replication.

A major challenge in neuroscience is linking behavior to the collective activity of neural assemblies. Understanding of input-output relationships of ...

Dissection and Culture of Mouse Dopaminergic and Striatal Explants in Three-Dimensional Collagen Matrix Assays

Midbrain dopamine (mdDA) neurons project via the medial forebrain bundle towards several areas in the telencephalon, including the striatum1. Reciprocally, medium spiny neurons in the striatum that give rise to the striatonigral (direct) pathway innervate the substantia nigra2. The development of these axon tracts is dependent upon the combinatorial actions of a plethora of axon growth and guidance cues including molecules that are released by neurites or by (intermediate) target regions3,4. These soluble factors can be studied in vitro by culturing mdDA and/or striatal explants in a collagen matrix which provides a three-dimensional substrate for the axons mimicking the extracellular environment. In addition, the collagen matrix allows for the formation of relatively stable gradients of proteins released by other explants or cells placed in the vicinity (e.g. see references 5 and 6). Here we describe methods for the purification of rat tail collagen, microdissection of dopaminergic and striatal explants, their culture in collagen gels and subsequent immunohistochemical and quantitative analysis. First, the brains of E14.5 mouse embryos are isolated and dopaminergic and striatal explants are microdissected. These explants are then (co)cultured in collagen gels on coverslips for 48 to 72 hours in vitro. Subsequently, axonal projections are visualized using neuronal markers (e.g. tyrosine hydroxylase, DARPP32, or &beta;III tubulin) and axon growth and attractive or repulsive axon responses are quantified. This neuronal preparation is a useful tool for in vitro studies of the cellular and molecular mechanisms of mesostriatal and striatonigral axon growth and guidance during development. Using this assay, it is also possible to assess other (intermediate) targets for dopaminergic and striatal axons or to test specific molecular cues.

Explants from the midbrain dopamine system and striatum are used in a collagen matrix assay for the in vitro analysis of mesostriatal and striatonigral pathway development. In this assay axonal outgrowth and guidance can be manipulated and quantified. It can also be modified for assessing other regions or molecular cues.

Midbrain dopamine (mdDA) neurons project via the medial forebrain bundle towards several areas in the telencephalon, including the striatum1. ...

Time-lapse Imaging of Neuroblast Migration in Acute Slices of the Adult Mouse Forebrain

There is a substantial body of evidence indicating that new functional neurons are constitutively generated from an endogenous pool of neural stem cells in restricted areas of the adult mammalian brain. Newborn neuroblasts from the subventricular zone (SVZ) migrate along the rostral migratory stream (RMS) to their final destination in the olfactory bulb (OB)1. In the RMS, neuroblasts migrate tangentially in chains ensheathed by astrocytic processes2,3 using blood vessels as a structural support and a source of molecular factors required for migration4,5. In the OB, neuroblasts detach from the chains and migrate radially into the different bulbar layers where they differentiate into interneurons and integrate into the existing network1, 6.
In this manuscript we describe the procedure for monitoring cell migration in acute slices of the rodent brain. The use of acute slices allows the assessment of cell migration in the microenvironment that closely resembling to in vivo conditions and in brain regions that are difficult to access for in vivo imaging. In addition, it avoids long culturing condition as in the case of organotypic and cell cultures that may eventually alter the migration properties of the cells. Neuronal precursors in acute slices can be visualized using DIC optics or fluorescent proteins. Viral labeling of neuronal precursors in the SVZ, grafting neuroblasts from reporter mice into the SVZ of wild-type mice, and using transgenic mice that express fluorescent protein in neuroblasts are all suitable methods for visualizing neuroblasts and following their migration. The later method, however, does not allow individual cells to be tracked for long periods of time because of the high density of labeled cells. We used a wide-field fluorescent upright microscope equipped with a CCD camera to achieve a relatively rapid acquisition interval (one image every 15 or 30 sec) to reliably identify the stationary and migratory phases. A precise identification of the duration of the stationary and migratory phases is crucial for the unambiguous interpretation of results. We also performed multiple z-step acquisitions to monitor neuroblasts migration in 3D. Wide-field fluorescent imaging has been used extensively to visualize neuronal migration7-10. Here, we describe detailed protocol for labeling neuroblasts, performing real-time video-imaging of neuroblast migration in acute slices of the adult mouse forebrain, and analyzing cell migration. While the described protocol exemplified the migration of neuroblasts in the adult RMS, it can also be used to follow cell migration in embryonic and early postnatal brains.

We describe a protocol for real-time videoimaging of neuronal migration in the mouse forebrain. The migration of virally-labeled or grafted neuronal precursors was recorded in acute live slices using wide-field fluorescent imaging with a relatively rapid acquisition interval to study the different phases of cell migration, including the durations of the stationary and migration phases and the speed of migration.

There is a substantial body of evidence indicating that new functional neurons are constitutively generated from an endogenous pool of neural stem cells ...

Two-photon Imaging of Cellular Dynamics in the Mouse Spinal Cord

Two-photon (2P) microscopy is utilized to reveal cellular dynamics and interactions deep within living, intact tissues. Here, we present a method for live-cell imaging in the murine spinal cord. This technique is uniquely suited to analyze neural precursor cell (NPC) dynamics following transplantation into spinal cords undergoing neuroinflammatory demyelinating disorders. NPCs migrate to sites of axonal damage, proliferate, differentiate into oligodendrocytes, and participate in direct remyelination. NPCs are thereby a promising therapeutic treatment to ameliorate chronic demyelinating diseases. Because transplanted NPCs migrate to the damaged areas on the ventral side of the spinal cord, traditional intravital 2P imaging is impossible, and only information on static interactions was previously available using histochemical staining approaches. Although this method was generated to image transplanted NPCs in the ventral spinal cord, it can be applied to numerous studies of transplanted and endogenous cells throughout the entire spinal cord. In this article, we demonstrate the preparation and imaging of a spinal cord with enhanced yellow fluorescent protein-expressing axons and enhanced green fluorescent protein-expressing transplanted NPCs.

A new ex vivo preparation for imaging the mouse spinal cord. This protocol allows for two-photon imaging of live cellular interactions throughout the spinal cord.

Two-photon (2P) microscopy is utilized to reveal cellular dynamics and interactions deep within living, intact tissues. Here, we present a method for ...

Imaging Ca2+ Dynamics in Cone Photoreceptor Axon Terminals of the Mouse Retina

Retinal cone photoreceptors (cones) serve daylight vision and are the basis of color discrimination. They are subject to degeneration, often leading to blindness in many retinal diseases. Calcium (Ca2+), a key second messenger in photoreceptor signaling and metabolism, has been proposed to be indirectly linked with photoreceptor degeneration in various animal models. Systematically studying these aspects of cone physiology and pathophysiology has been hampered by the difficulties of electrically recording from these small cells, in particular in the mouse where the retina is dominated by rod photoreceptors. To circumvent this issue, we established a two-photon Ca2+ imaging protocol using a transgenic mouse line that expresses the genetically encoded Ca2+ biosensor TN-XL exclusively in cones and can be crossbred with mouse models for photoreceptor degeneration. The protocol described here involves preparing vertical sections (&#8220;slices&#8221;) of retinas from mice and optical imaging of light stimulus-evoked changes in cone Ca2+ level. The protocol also allows &#8220;in-slice measurement&#8221; of absolute Ca2+ concentrations; as the recordings can be followed by calibration. This protocol enables studies into functional cone properties and is expected to contribute to the understanding of cone Ca2+ signaling as well as the potential involvement of Ca2+ in photoreceptor death and retinal degeneration.

Imaging Ca2+ Dynamics in Cone Photoreceptor Axon Terminals of the Mouse Retina

We describe a protocol to monitor Ca2+ dynamics in the axon terminals of cone photoreceptors using an ex-vivo&#160;slice preparation of the mouse retina. This protocol allows comprehensive studies of cone Ca2+ signaling in an important mammalian model system, the mouse.

Retinal cone photoreceptors (cones) serve daylight vision and are the basis of color discrimination. They are subject to degeneration, often leading to ...

Protocol for Three-dimensional Confocal Morphometric Analysis of Astrocytes

As glial cells in the brain, astrocytes have diverse functional roles in the central nervous system. In the presence of harmful stimuli, astrocytes modify their functional and structural properties, a condition called reactive astrogliosis. Here, a protocol for assessment of the morphological properties of astrocytes is presented. This protocol includes quantification of 12 different parameters i.e. the surface area and volume of the tissue covered by an astrocyte (astrocyte territory), the entire astrocyte including branches, cell body, and nucleus, as well as total length and number of branches, the intensity of fluorescence immunoreactivity of antibodies used for astrocyte detection, and astrocyte density (number/1,000 &#181;m2). For this purpose three-dimensional (3D) confocal microscopic images were created, and 3D image analysis software such as Volocity 6.3 was used for measurements. Rat brain tissue exposed to amyloid beta1-40 (A&#946;1-40) with or without a therapeutic&#160;intervention was used to present the method. This protocol can also be used for 3D morphometric analysis of other cells from either in vivo or in vitro conditions.

Astrocytes in the CNS change their functional and structural properties in response to harmful stimuli. This report presents a protocol for assessment of three-dimensional astrocyte morphology in diseased conditions or after therapeutic interventions.

As glial cells in the brain, astrocytes have diverse functional roles in the central nervous system. In the presence of harmful stimuli, astrocytes modify ...

Three-dimensional Imaging and Analysis of Mitochondria within Human Intraepidermal Nerve Fibers

The goal of this protocol is to study mitochondria within intraepidermal nerve fibers. Therefore, 3D imaging and analysis techniques were developed to isolate nerve-specific mitochondria and evaluate disease-induced alterations of mitochondria in the distal tip of sensory nerves. The protocol combines fluorescence immunohistochemistry, confocal microscopy and 3D image analysis techniques to visualize and quantify nerve-specific mitochondria. Detailed parameters are defined throughout the procedures in order to provide a concrete example of how to use these techniques to isolate nerve-specific mitochondria. Antibodies were used to label nerve and mitochondrial signals within tissue sections of skin punch biopsies, which was followed by indirect immunofluorescence to visualize nerves and mitochondria with a green and red fluorescent signal respectively. Z-series images were acquired with confocal microscopy and 3D analysis software was used to process and analyze the signals. It is not necessary to follow the exact parameters described within, but it is important to be consistent with the ones chosen throughout the staining, acquisition and analysis steps. The strength of this protocol is that it is applicable to a wide variety of circumstances where one fluorescent signal is used to isolate other signals that would otherwise be impossible to study alone.

This protocol uses three-dimensional (3D) imaging and analysis techniques to visualize and quantify nerve-specific mitochondria. The techniques are applicable to other situations where one fluorescent signal is used to isolate a subset of data from another fluorescent signal.

The goal of this protocol is to study mitochondria within intraepidermal nerve fibers. Therefore, 3D imaging and analysis techniques were developed to ...

Three-Dimensional Motor Nerve Organoid Generation

A fascicle of axons is one of the major structural motifs observed in the nervous system. Disruption of axon fascicles could cause developmental and neurodegenerative diseases. Although numerous studies of axons have been conducted, our understanding of formation and dysfunction of axon fascicles is still limited due to the lack of robust three-dimensional in vitro models. Here, we describe a step-by-step protocol for the rapid generation of a motor nerve organoid (MNO) from human induced pluripotent stem (iPS) cells in a microfluidic-based tissue culture chip. First, fabrication of chips used for the method is described. From human iPS cells, a motor neuron spheroid (MNS) is formed. Next, the differentiated MNS is transferred into the chip. Thereafter, axons spontaneously grow out of the spheroid and assemble into a fascicle within a microchannel equipped in the chip, which generates an MNO tissue carrying a bundle of axons extended from the spheroid. For the downstream analysis, MNOs can be taken out of the chip to be fixed for morphological analyses or dissected for biochemical analyses, as well as calcium imaging and multi-electrode array recordings. MNOs generated with this protocol can facilitate drug testing and screening and can contribute to understanding of mechanisms underlying development and diseases of axon fascicles.

This protocol provides a comprehensive procedure to fabricate human iPS cell-derived motor nerve organoid through spontaneous assembly of a robust bundle of axons extended from a spheroid in a tissue culture chip.

A fascicle of axons is one of the major structural motifs observed in the nervous system. Disruption of axon fascicles could cause developmental and ...