The authors thank Yoko Ishida (Juntendo University) for AAV vector production and Kisara Hoshino (Juntendo University) for technical assistance. This study was supported by JSPS KAKENHI (JP20K07231 to K.Y.; JP21H03529 to T.F.; JP20K07743 to M.K.; JP21H02592 to H.H.) and Scientific Research on Innovative Area &#8220;Resonance Bio&#8221; (JP18H04743 to H.H.). This study was also supported by the Japan Agency for Medical Research and Development (AMED) (JP21dm0207112 to T.F. and H.H.), Moonshot R&#38;D from the Japan Science and Technology Agency (JST) (JPMJMS2024 to H.H.), Fusion Oriented Research for disruptive Science and Technology (FOREST) from JST (JPMJFR204D to H.H.), Grants-in-Aid from the Research Institute for Diseases of Old Age at the Juntendo University School of Medicine (X2016 to K.Y.; X2001 to H.H.), and the Private School Branding Project.

All the experiments were approved by the Institutional Animal Care and Use Committees of Juntendo University (Approval No. 2021245, 2021246) and performed in accordance with Fundamental Guidelines for Proper Conduct of Animal Experiments by the Science Council of Japan (2006). Here, male C57BL/6J mice injected with AAV vector carrying enhanced green fluorescent protein (EGFP) gene and parvalbumin (PV)/myristoylation-EGFP-low-density lipoprotein receptor C-terminal bacterial artificial chromosome (BAC) transgenic mice (PV-FGL mice)9 were used. PV-FGL mice were maintained in C57BL/6J background. No sex-based differences were found with regard to this study.
1. Tissue preparation
<ol>
	<li>Perfusion fixation 
	NOTE: Perform steps 1.1.1 through 1.1.3 in a fume hood to limit the exposure to paraformaldehyde (PFA).
	<ol>
		<li>Anesthetize adult male mice (8&#8211;16 weeks old) by an intraperitoneal injection of overdose of sodium pentobarbital (200 mg/kg). Confirm adequacy of anesthesia by the absence of toe-pinch withdrawal and eye-blink reflexes.</li>
		<li>Open the thoracic cavity and cut the right atrial appendage with surgical scissors. Perfuse the mice with 20 mL of ice-cold phosphate buffer saline (PBS) using a 23 G needle attached to a 20 mL syringe, followed by perfusion of 20 mL of ice-cold 4% PFA in 0.1 M phosphate buffer (PB) using another 20 mL syringe. 
		CAUTION: PFA is toxic and teratogenic. Avoid inhalation or contact with skin, eyes, and mucous membrane.</li>
		<li>Remove brain tissues from the skull with tweezers. Transfer the brain tissues to a 15 mL tube containing 4% PFA in 0.1 M PB, protect the samples from light, and gently rock overnight at 4 &#176;C on a shaker at 50&#8211;100 rpm.</li>
		<li>NOTE: The harvested brain tissues can be stored for several weeks in 0.02% sodium azide (NaN3) in PBS at 4 &#176;C. 
		CAUTION: NaN3 is toxic. Avoid inhalation or contact with skin, eyes, and mucous membrane. Handle it inside a fume hood.</li>
	</ol>
	</li>
	<li>Brain slice preparation
	<ol>
		<li>Prepare 4% agar in PBS by adding 2 g of agar to 50 mL of PBS. Microwave the mixture until the agar is fully dissolved. Let the solution cool to 40-45 &#176;C. 
		NOTE: The viscous property provided by agaropectin, a major component of agar, improves ease of cutting of tissue slices.</li>
		<li>Add 10 mL of the agar solution to a 6-well culture plate. Submerge the brain tissue in the agar solution using forceps. Let the agar solidify on ice.</li>
		<li>Remove the embedded brain tissue from the well and trim the agar with a razor blade. Secure the agar block onto the bottom of the vibratome bath with superglue and pour 0.1 M PB in the buffer tray.</li>
		<li>Clean another razor blade using a lint-free tissue paper soaked in ethanol and attach the blade to the blade holder of the vibrating tissue slicer.</li>
		<li>Set the sectioning speed to 0.14 mm/s with 1.4 mm amplitude and the frequency to 75&#8211;77 Hz. Cut the brain tissue into 1-mm-thick slices and collect the slices in a 6-well cell culture plate containing PBS. 
		NOTE: The brain slices can be stored for several weeks in 0.02% NaN3 in PBS at 4 &#176;C.</li>
	</ol>
	</li>
</ol>
2. Tissue clarification
NOTE: The compositions of ScaleS solutions used are listed in Table 1. Samples should be protected from light by covering with a foil. The clearing steps is shown in Figure 1A.
<ol>
	<li>Add 8 mL of ScaleS0 solution to one well of a 6-well cell culture plate and add 8 mL of ScaleS4 solution to another well of the plate and pre-warm to 37 &#176;C in an incubator.</li>
	<li>Transfer the brain slices to the pre-warmed ScaleS0 solution with a spatula and incubate for 2 h at 37 &#176;C in a shaking incubator at 90 rpm.</li>
	<li>Transfer the permeabilized brain slices in 8 mL of PBS(&#8211;) in a 6-well cell culture plate with a spatula and wash for 15 min by keeping in an orbital shaker at 40&#8211;60 rpm. Repeat this twice.</li>
	<li>Transfer the brain slices in the pre-warmed 8 mL of ScaleS4 solution with a spatula and clear them by incubating in a shaking incubator at 90 rpm for 8&#8211;12 h at 37 &#176;C. A cleared brain slices can be seen in Figure 1.</li>
</ol>
3. Brain slice mounting
NOTE: A customizable imaging chamber is used for reliable mounting of cleared brain slices (Figure 2)6. The chamber consists of the chamber frame and bottom coverslip. The microscope stage adaptors are also designed to mount the imaging chamber on microscope stages directly (Figure 2A,B). The chamber frame and microscope stage adaptors can be 3D-printed using in-house or outsourced 3D-printing services. 3D computer-aided design (CAD) data of the imaging chamber are provided in Furuta et al. 20226.
<ol>
	<li>For chamber preparation, attach the chamber frame to a coverslip using a pressure-sensitive adhesive.</li>
	<li>Prepare 1.5% agarose in ScaleS4D25(0) solution (ScaleS4 gel) by adding 1.5 g of agarose to 100 mL of the solution in a bottle. Mix the solution well by stirring and microwave the solution until the agarose is fully dissolved. Once done, allow the solution to cool to 37 &#176;C.</li>
	<li>Mount the cleared brain slice onto the bottom coverslip of the imaging chamber with a spatula. Wipe away the excess solution from the cleared slice using a clean lint-free tissue paper.</li>
	<li>Add the ScaleS4 gel on the brain slice using a micropipette to fill the imaging chamber. Place another coverslip on top with forceps and place a piece of lint-free tissue paper and a glass slide on the coverslip in this order.</li>
	<li>Transfer the imaging chamber to a refrigerator at 4 &#176;C. Place metal weights on the glass slide and leave them for 30 min.</li>
	<li>Remove the metal weights, glass slide, lint-free tissue paper, and coverslip from the imaging chamber, and wipe the excess gel away (Figure 2A,B).</li>
	<li>Place the imaging chamber in a 60 mm glass Petri dish and attach the rim of the imaging chamber to the dish with a putty-like pressure sensitive adhesive. Attach the chamber at multiple points to the Petri dish.</li>
	<li>Pour ScaleS4 solution in the dish and shake gently for 1 h at 20-25 &#176;C on an orbital shaker at 40-60 rpm. Substitute with fresh solution and remove air bubbles on the gel surface by gently scraping the surface using a 200 &#181;L pipette tip. Mount the immersed imaging chamber on a microscope stage (Figure 2C).</li>
</ol>
4. CLSM imaging
<ol>
	<li>Acquire images using a CLSM equipped with a multi-immersion objective lens of a long working distance (WD) (16x/0.60 numerical aperture [NA], WD = 2.5 mm). 
	NOTE: High NA objective lenses can provide high diffraction-limited resolution.</li>
	<li>Turn on all the relevant imaging equipment (workstation, microscope, scanner, lasers, and mercury lamp) and launch a CLSM imaging software.</li>
	<li>Set the correction collar of the multi-immersion objective lens to 1.47. ScaleS4 solution has a refractive index (RI) of around 1.475,7. RI mismatch-induced aberrations can disturb the image formation (Figure 3).</li>
	<li>Immerse the objective lens in the solution, and let it approach the slice slowly. Remove any air bubbles trapped on the tip of the objective lens. Find regions of interest (ROIs) in the cleared tissues using epifluorescence.</li>
	<li>Set image acquisition parameters by testing appropriate settings.
	<ol>
		<li>Determine the bit depth for image acquisition. The data size of the image increases with the bit depth.</li>
		<li>Set the&#160;detection wavelength. Adjust the appropriate gate for the detector according to the emission spectrum. Ensure that the detection wavelength does not cover any laser lines.</li>
		<li>Set the xy resolution. Larger formats provide better xy resolutions, but it takes longer time to collect the images.</li>
		<li>Set the scan speed. A slower scan speed provides a high signal-to-noise ratio. However, it also increases the pixel dwell time and the risk of photobleaching. Choose accordingly.</li>
		<li>Adjust the pinhole size. The pinhole size controls optical section thickness. A smaller pinhole size creates a thinner optical section, and thus better z resolution, but reduces fluorescence signal. Making the pinhole size larger provides a thicker optical section with stronger fluorescence signal.</li>
		<li>Set the laser power, the detector/amplifier gain, and offset. Gradually increase the laser power and detector/amplifier gain until a suitable image is obtained. A high laser power carries the risk of photobleaching. Adjust the offset (contrast) appropriately to obtain a high signal-to-noise ratio.</li>
		<li>Determine the tilling area needed based on the size of ROI. Ensure that the entire length and width of the ROI is captured.</li>
		<li>Navigate the cleared tissues in all planes, and set the start and end points of the stack. Set the z-step size according to the desired z-resolution.</li>
	</ol>
	</li>
	<li>Collect images when satisfied with the image acquisition settings, and record captured images. Process the images using an image analysis software.</li>
</ol>

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	<li>Susaki, E. A., Ueda, H. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Whole-body+and+whole-organ+clearing+and+imaging+techniques+with+single-cell+resolution:+Toward+organism-level+systems+biology+in+mammals.">Whole-body and whole-organ clearing and imaging techniques with single-cell resolution: Toward organism-level systems biology in mammals.</a> Cell Chemical Biology. 23 (1), 137-157 (2016).</li><li>Tainaka, K., Kuno, A., Kubota, S. I., Murakami, T., Ueda, H. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemical+principles+in+tissue+clearing+and+staining+protocols+for+whole-body+cell+profiling.">Chemical principles in tissue clearing and staining protocols for whole-body cell profiling.</a> Annual Reviews of Cell and Developmental Biology. 32, 713-741 (2016).</li><li>Ueda, H. R., 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=Whole-brain+profiling+of+cells+and+circuits+in+mammals+by+tissue+clearing+and+light-sheet+microscopy.">Whole-brain profiling of cells and circuits in mammals by tissue clearing and light-sheet microscopy.</a> Neuron. 106 (3), 369-387 (2020).</li><li>Ueda, H. R., 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=Tissue+clearing+and+its+applications+in+neuroscience.">Tissue clearing and its applications in neuroscience.</a> Nature Reviews. Neuroscience. 21 (2), 61-79 (2020).</li><li>Hama, H., 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=ScaleS:+an+optical+clearing+palette+for+biological+imaging.">ScaleS: an optical clearing palette for biological imaging.</a> Nature Neuroscience. 18 (10), 1518-1529 (2015).</li><li>Furuta, T., 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=Multi-scale+light+microscopy/electron+microscopy+neuronal+imaging+from+brain+to+synapse+with+a+tissue+clearing+method,+ScaleSF.">Multi-scale light microscopy/electron microscopy neuronal imaging from brain to synapse with a tissue clearing method, ScaleSF.</a> iScience. 25 (1), 103601 (2022).</li><li>Miyawaki, 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=Deep+imaging+of+cleared+brain+by+confocal+laser-scanning+microscopy.">Deep imaging of cleared brain by confocal laser-scanning microscopy.</a> Protocol Exchange. , (2016).</li><li>Okamoto, 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=Exclusive+labeling+of+direct+and+indirect+pathway+neurons+in+the+mouse+neostriatum+by+an+adeno-associated+virus+vector+with+Cre/lox+system.">Exclusive labeling of direct and indirect pathway neurons in the mouse neostriatum by an adeno-associated virus vector with Cre/lox system.</a> STAR Protocols. 2 (1), 100230 (2021).</li><li>Kameda, H., 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=Parvalbumin-producing+cortical+interneurons+receive+inhibitory+inputs+on+proximal+portions+and+cortical+excitatory+inputs+on+distal+dendrites.">Parvalbumin-producing cortical interneurons receive inhibitory inputs on proximal portions and cortical excitatory inputs on distal dendrites.</a> The European Journal of Neuroscience. 35 (6), 838-854 (2012).</li><li>Sohn, J., 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=A+single+vector+platform+for+high-level+gene+transduction+of+central+neurons:+Adeno-associated+virus+vector+equipped+with+the+Tet-off+system.">A single vector platform for high-level gene transduction of central neurons: Adeno-associated virus vector equipped with the Tet-off system.</a> PLoS One. 12 (1), 0169611 (2017).</li><li>Hama, H., 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=Scale:+a+chemical+approach+for+fluorescence+imaging+and+reconstruction+of+transparent+mouse+brain.">Scale: a chemical approach for fluorescence imaging and reconstruction of transparent mouse brain.</a> Nature Neuroscience. 14 (11), 1481-1488 (2011).</li><li>Stepanyants, A., Martinez, L. M., Ferecsko, A. S., Kisvarday, Z. 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The authors have nothing to disclose.

Critical steps within the protocol 
There are a few critical steps in the protocol that should be conducted with utmost caution to obtain meaningful results. Uniform fixation of samples is imperative for 3D imaging within large-scale tissues. The objective lens, sample, and immersion fluid should have matching RI. RI-mismatch among them will lead to highly disturbed imaging of EGFP-expressing cells within the cleared brain slices (Figure 3). The correction collar adjustment of the o...

Tissue clearing methods have improved depth-independent imaging of biological and clinical samples with light microscopy, allowing for extraction of structural information on intact tissues1,2. Optical clearing techniques could also potentially speed up, and reduce the cost for histological analysis. Currently, three major clearing approaches are available: hydrophilic, hydrophobic, and hydrogel-based methods1,2. Hydrophilic approaches surpass in preserving fluorescence signals and tissue integrity and are less toxic compared to the other two approaches3,4.
A hydrophilic clearing method, ScaleS, holds a distinctive position with its preservation of structural and molecular integrity as well as potent clearing capability (clearing-preservation spectrum)5. In a previous study, we developed a rapid and isometric clearing protocol, ScaleSF, for tissue slices (~1-mm thickness) by modifying the clearing procedure of ScaleS6. This clearing protocol requires sequential incubations of brain slices in three solutions for 10.5-14.5 h. The method is featured with a high clearing-preservation spectrum, which is compatible even with electron microscopy (EM) analysis (Supplementary Figure 1), allowing for multi-scale high-resolution three dimensional (3D) imaging with accurate signal reconstruction6. Thus, ScaleSF should be effective especially in the brain, where neuronal cells elaborate exuberant processes of tremendous length, and arrange specialized fine subcellular structures for transmitting and receiving information. Extracting structural information with scales from circuit to subcellular levels on neuronal cells is quite useful toward better understanding of brain functions.
Here, we provide a detailed protocol to visualize neuronal structures with scales from the mesoscopic/circuit to microscopic/subcellular level using ScaleSF. The protocol includes tissue preparation, tissue clarification, handling of cleared tissues, and confocal laser scanning microscopy (CLSM) imaging of cleared tissues. Our protocol focuses on interrogating neuronal structures from circuit to subcellular component scales. For a detailed procedure for preparation of the solutions and stereotaxic injection of adeno-associated virus (AAV) vectors into mouse brains, refer to Miyawaki et al. 20167 and Okamoto et al. 20218, respectively.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>16x multi-immersion objective lens</td>
			<td>Leica Microsystems</td>
			<td>HC FLUOTAR 16x/0.60 IMM CORR VISIR</td>
			<td></td>
		</tr>
		<tr>
			<td>Agar</td>
			<td>Nacalai Tesque</td>
			<td>01028-85</td>
			<td></td>
		</tr>
		<tr>
			<td>Agarose</td>
			<td>TaKaRa Bio</td>
			<td>L03</td>
			<td></td>
		</tr>
		<tr>
			<td>Dimethyl sulfoxide</td>
			<td>Nacalai Tesque</td>
			<td>13407-45</td>
			<td></td>
		</tr>
		<tr>
			<td>D-Sorbitol</td>
			<td>Nacalai Tesque</td>
			<td>06286-55</td>
			<td></td>
		</tr>
		<tr>
			<td>&#947;-cyclodextrin</td>
			<td>Wako Pure Chemical Industries</td>
			<td>037-10643</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>Sigma-Aldrich</td>
			<td>G9012</td>
			<td></td>
		</tr>
		<tr>
			<td>Huygens Essential</td>
			<td>Scientific Volume Imaging</td>
			<td>ver. 18.10.0p8/21.10.1p0 64b</td>
			<td></td>
		</tr>
		<tr>
			<td>Imaris</td>
			<td>Bitplane</td>
			<td>ver. 9.0.0</td>
			<td></td>
		</tr>
		<tr>
			<td>Leica Application Suite X</td>
			<td>Leica Microsystems</td>
			<td>LAS X, ver. 3.5.5.19976</td>
			<td></td>
		</tr>
		<tr>
			<td>Methyl-&#946;-cyclodextrin</td>
			<td>Tokyo Chemical Industry</td>
			<td>M1356</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Merck Millipore</td>
			<td>1.04005.1000</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphate Buffered Saline (10x; pH 7.4)</td>
			<td>Nacalai Tesque</td>
			<td>27575-31</td>
			<td>10x PBS(&#8211;)</td>
		</tr>
		<tr>
			<td>Sodium azide</td>
			<td>Nacalai Tesque</td>
			<td>31233-55</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium pentobarbital</td>
			<td>Kyoritsu Seiyaku</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>TCS SP8</td>
			<td>Leica Microsystems</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Nacalai Tesque</td>
			<td>35501-15</td>
			<td></td>
		</tr>
		<tr>
			<td>Urea</td>
			<td>Nacalai Tesque</td>
			<td>35940-65</td>
			<td></td>
		</tr>
		<tr>
			<td>Vibrating tissue slicer</td>
			<td>Dosaka EM</td>
			<td>PRO7N</td>
			<td></td>
		</tr>
	</tbody>
</table>

a tissue clearing method for neuronal imaging from mesoscopic to microscopic scales

A detailed protocol is provided here to visualize neuronal structures from mesoscopic to microscopic levels in brain tissues. Neuronal structures ranging from neural circuits to subcellular neuronal structures are visualized in mouse brain slices optically cleared with ScaleSF. This clearing method is a modified version of ScaleS and is a hydrophilic tissue clearing method for tissue slices that achieves potent clearing capability as well as a high-level of preservation of fluorescence signals and structural integrity. A customizable three dimensional (3D)-printed imaging chamber is designed for reliable mounting of cleared brain tissues. Mouse brains injected with an adeno-associated virus vector carrying enhanced green fluorescent protein gene were fixed with 4% paraformaldehyde and cut into slices of 1-mm thickness with a vibrating tissue slicer. The brain slices were cleared by following the clearing protocol, which include sequential incubations in three solutions, namely, ScaleS0 solution, phosphate buffer saline (&#8211;), and ScaleS4 solution, for a total of 10.5&#8211;14.5 h. The cleared brain slices were mounted on the imaging chamber and embedded in 1.5% agarose gel dissolved in ScaleS4D25(0) solution. The 3D image acquisition of the slices was carried out using a confocal laser scanning microscope equipped with a multi-immersion objective lens of a long working distance. Beginning with mesoscopic neuronal imaging, we succeeded in visualizing fine subcellular neuronal structures, such as dendritic spines and axonal boutons, in the optically cleared brain slices. This protocol would facilitate understanding of neuronal structures from circuit to subcellular component scales.

Optical clearing of a mouse brain slice of 1-mm thickness was achieved using this protocol. Figure 1B represents transmission images of a mouse brain slice before and after the clearing treatment. The tissue clearing method rendered a 1-mm-thick mouse brain slice transparent. A slight expansion in final sizes of brain slices was found after the incubation in the clearing solution for 12 h (linear expansion: 102.5% &#177; 1.3%).&#160;The preservation of fluorescence and structural integrity of the tissues...

Watch this Scientific Journal Video about A Tissue Clearing Method for Neuronal Imaging from Mesoscopic to Microscopic Scales at JoVE.com

A Tissue Clearing Method for Neuronal Imaging from Mesoscopic to Microscopic Scales

The protocol provides a detailed method of neuronal imaging in brain slice using a tissue clearing method, ScaleSF. The protocol includes brain tissue preparation, tissue clarification, handling of cleared slices and confocal laser scanning microscopy imaging of neuronal structures from mesoscopic to microscopic levels.

A detailed protocol is provided here to visualize neuronal structures from mesoscopic to microscopic levels in brain tissues. Neuronal structures ranging ...

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2.7K Views.  Juntendo University Graduate School of Medicine. The protocol provides a detailed method of neuronal imaging in brain slice using a tissue clearing method, ScaleSF. The protocol includes brain tissue preparation, tissue clarification, handling of cleared slices and confocal laser scanning microscopy imaging of neuronal structures from mesoscopic to microscopic levels.

Video: A Tissue Clearing Method for Neuronal Imaging from Mesoscopic to Microscopic Scales

DiOLISTIC Labeling of Neurons from Rodent and Non-human Primate Brain Slices

DiOLISTIC staining uses the gene gun to introduce fluorescent dyes, such as DiI, into neurons of brain slices (Gan et al., 2009; O'Brien and Lummis, 2007; Gan et al., 2000). Here we provide a detailed description of each step required together with exemplary images of good and bad outcomes that will help when setting up the technique. In our experience, a few steps proved critical for the successful application of DiOLISTICS. These considerations include the quality of the DiI-coated bullets, the extent of fixative exposure, and the concentration of detergent used in the incubation solutions. Tips and solutions for common problems are provided. This is a versatile labeling technique that can be applied to multiple animal species at a wide range of ages. Unlike other fluorescent labeling techniques that are limited to preparations from young animals or restricted to mice because they rely on the expression of a fluorescent transgene, DiOLISTIC labeling can be applied to animals of all ages, species and genotypes and it can be used in combination with immunostaining to identify a specific subpopulation of cells. Here we demonstrate the use of DiOLISTICS to label neurons in brain slices from adult mice and adult non-human primates with the purpose of quantifying dendrite branching and dendritic spine morphology.

We demonstrate the use of the gene gun to introduce fluorescent dyes, such as DiI, into neurons in brain slices from rodents and non-human primates of different ages. In this particular case, we use adult mice (3-6 months old) and adult cynomologus monkeys (9-15 years old). This technique, originally described by the laboratory of Dr. Lichtman (Gan et al., 2000), is well suited for the study of dendritic branching and dendritic spine morphology and can be combined with traditional immunostaining, if detergents are kept at a low concentration.

DiOLISTIC staining uses the gene gun to introduce fluorescent dyes, such as DiI, into neurons of brain slices (Gan et al., 2009; O'Brien and Lummis, 2007; ...

Automated Sholl Analysis of Digitized Neuronal Morphology at Multiple Scales

Neuronal morphology plays a significant role in determining how neurons function and communicate1-3. Specifically, it affects the ability of neurons to receive inputs from other cells2 and contributes to the propagation of action potentials4,5. The morphology of the neurites also affects how information is processed. The diversity of dendrite morphologies facilitate local and long range signaling and allow individual neurons or groups of neurons to carry out specialized functions within the neuronal network6,7. Alterations in dendrite morphology, including fragmentation of dendrites and changes in branching patterns, have been observed in a number of disease states, including Alzheimer's disease8, schizophrenia9,10, and mental retardation11. The ability to both understand the factors that shape dendrite morphologies and to identify changes in dendrite morphologies is essential in the understanding of nervous system function and dysfunction.
Neurite morphology is often analyzed by Sholl analysis and by counting the number of neurites and the number of branch tips. This analysis is generally applied to dendrites, but it can also be applied to axons. Performing this analysis by hand is both time consuming and inevitably introduces variability due to experimenter bias and inconsistency. The Bonfire program is a semi-automated approach to the analysis of dendrite and axon morphology that builds upon available open-source morphological analysis tools. Our program enables the detection of local changes in dendrite and axon branching behaviors by performing Sholl analysis on subregions of the neuritic arbor. For example, Sholl analysis is performed on both the neuron as a whole as well as on each subset of processes (primary, secondary, terminal, root, etc.) Dendrite and axon patterning is influenced by a number of intracellular and extracellular factors, many acting locally. Thus, the resulting arbor morphology is a result of specific processes acting on specific neurites, making it necessary to perform morphological analysis on a smaller scale in order to observe these local variations12.
The Bonfire program requires the use of two open-source analysis tools, the NeuronJ plugin to ImageJ and NeuronStudio. Neurons are traced in ImageJ, and NeuronStudio is used to define the connectivity between neurites. Bonfire contains a number of custom scripts written in MATLAB (MathWorks) that are used to convert the data into the appropriate format for further analysis, check for user errors, and ultimately perform Sholl analysis. Finally, data are exported into Excel for statistical analysis. A flow chart of the Bonfire program is shown in Figure 1.

We have developed a computer program to analyze neuronal morphology. In combination with two existing open source analysis tools, our program performs Sholl analysis and determines the number of neurites, branch points, and neurite tips. The analyses are performed so that local changes in neurite morphology can be observed.

Neuronal morphology plays a significant role in determining how neurons function and communicate1-3.  Specifically, it affects the ability of neurons to ...

Cryopreservation of Cortical Tissue Blocks for the Generation of Highly Enriched Neuronal Cultures

In this study, we outline a standardized protocol for the successful cryopreservation and thawing of cortical brain tissue blocks to generate highly enriched neuronal cultures. For this protocol the freezing medium used is 10% dimethyl sulfoxide (DMSO) diluted in Hank's Buffered Salt Solution (HBSS). Blocks of cortical tissue are transferred to cryovials containing the freezing medium and slowly frozen at -1&deg;C/min in a rate-controlled freezing container. Post-thaw processing and dissociation of frozen tissue blocks consistently produced neuronal-enriched cultures which exhibited rapid neuritic growth during the first 5 days in culture and significant expansion of the neuronal network within 10 days. Immunocytochemical staining with the astrocytic marker glial fibrillary acidic protein (GFAP) and the neuronal marker beta-tubulin class III, revealed high numbers of neurons and astrocytes in the cultures. Generation of neural precursor cell cultures after tissue block dissociation resulted in rapidly expanding neurospheres, which produced large numbers of neurons and astrocytes under differentiating conditions. This simple cryopreservation protocol allows for the rapid, efficient, and inexpensive preservation of cortical brain tissue blocks, which grants increased flexibility for later generation of neuronal, astrocyte, and neuronal precursor cell cultures.

Here, we describe a method for efficient cryopreservation and thawing of cortical brain tissue blocks to generate highly enriched neuronal cultures. This simple protocol provides flexibility for later generation of neuronal, astrocyte, and neuronal precursor cell cultures.

In this study, we outline a standardized protocol for the successful cryopreservation and thawing of cortical brain tissue blocks to generate highly ...

Super-resolution Imaging of Neuronal Dense-core Vesicles

Detection of fluorescence provides the foundation for many widely utilized and rapidly advancing microscopy techniques employed in modern biological and medical applications. Strengths of fluorescence include its sensitivity, specificity, and compatibility with live imaging. Unfortunately, conventional forms of fluorescence microscopy suffer from one major weakness, diffraction-limited resolution in the imaging plane, which hampers studies of structures with dimensions smaller than ~250 nm. Recently, this limitation has been overcome with the introduction of super-resolution fluorescence microscopy techniques, such as photoactivated localization microscopy (PALM). Unlike its conventional counterparts, PALM can produce images with a lateral resolution of tens of nanometers. It is thus now possible to use fluorescence, with its myriad strengths, to elucidate a spectrum of previously inaccessible attributes of cellular structure and organization.
Unfortunately, PALM is not trivial to implement, and successful strategies often must be tailored to the type of system under study. In this article, we show how to implement single-color PALM studies of vesicular structures in fixed, cultured neurons. PALM is ideally suited to the study of vesicles, which have dimensions that typically range from ~50-250 nm. Key steps in our approach include labeling neurons with photoconvertible (green to red) chimeras of vesicle cargo, collecting sparsely sampled raw images with a super-resolution microscopy system, and processing the raw images to produce a high-resolution PALM image. We also demonstrate the efficacy of our approach by presenting exceptionally well-resolved images of dense-core vesicles (DCVs) in cultured hippocampal neurons, which refute the hypothesis that extrasynaptic trafficking of DCVs is mediated largely by DCV clusters.

We describe how to implement photoactivated localization microscopy (PALM)-based studies of vesicles in fixed, cultured neurons. Key components of our protocol include labeling vesicles with photoconvertible chimeras, collecting sparsely sampled raw images with a super-resolution microscopy system, and processing the raw images to produce a super-resolution image.

Detection of fluorescence provides the foundation for many widely utilized and rapidly advancing microscopy techniques employed in modern biological and ...

Prolonged Incubation of Acute Neuronal Tissue for Electrophysiology and Calcium-imaging

Acute neuronal tissue preparations, brain slices and retinal wholemount, can usually only be maintained for 6 - 8 h following dissection. This limits the experimental time, and increases the number of animals that are utilized per study. This limitation specifically impacts protocols such as calcium imaging that require prolonged pre-incubation with bath-applied dyes. Exponential bacterial growth within 3 - 4 h after slicing is tightly correlated with a decrease in tissue health. This study describes a method for&#160;limiting the proliferation of bacteria in acute preparations to maintain viable neuronal tissue for prolonged periods of time (&#62;24 h) without the need for antibiotics, sterile procedures, or tissue culture media containing growth factors. By cycling the extracellular fluid through UV irradiation and keeping the tissue in a custom holding chamber at 15 - 16 &#176;C, the tissue shows no difference in electrophysiological properties, or calcium signaling through intracellular calcium dyes at &#62;24 h postdissection. These methods will not only extend experimental time for those using acute neuronal tissue, but will reduce the number of animals required to complete experimental goals, and will set a gold standard for acute neuronal tissue incubation.

Once removed from the body, neuronal tissue is greatly affected by environmental conditions, leading to eventual degradation of the tissue after 6 - 8 h. Using a unique incubation method, which closely monitors and regulates the extracellular environment of the tissue, tissue viability can be significantly extended for &#62;24 h.

Acute neuronal tissue preparations, brain slices and retinal wholemount, can usually only be maintained for 6 - 8 h following dissection. This limits the ...

Rewiring Neuronal Circuits: A New Method for Fast Neurite Extension and Functional Neuronal Connection

Brain and spinal cord injury may lead to permanent disability and death because it is still not possible to regenerate neurons over long distances and accurately reconnect them with an appropriate target. Here a procedure is described to rapidly initiate, elongate, and precisely connect new functional neuronal circuits over long distances. The extension rates achieved reach over 1.2 mm/h, 30-60 times faster than the in vivo rates of the fastest growing axons from the peripheral nervous system (0.02 to 0.04 mm/h)28 and 10 times faster than previously reported for the same neuronal type at an earlier stage of development4. First, isolated populations of rat hippocampal neurons are grown for 2-3 weeks in microfluidic devices to precisely position the cells, enabling easy micromanipulation and experimental reproducibility. Next, beads coated with poly-D-lysine (PDL) are placed on neurites to form adhesive contacts and pipette micromanipulation is used to move the resulting bead-neurite complex. As the bead is moved, it pulls out a new neurite that can be extended over hundreds of micrometers and functionally connected to a target cell in less than 1 h. This process enables experimental reproducibility and ease of manipulation while bypassing slower chemical strategies to induce neurite growth. Preliminary measurements presented here demonstrate a neuronal growth rate far exceeding physiological ones. Combining these innovations allows for the precise establishment of neuronal networks in culture with an unprecedented degree of control. It is a novel method that opens the door to a plethora of information and insights into signal transmission and communication within the neuronal network as well as being a playground in which to explore the limits of neuronal growth. The potential applications and experiments are widespread with direct implications for therapies that aim to reconnect neuronal circuits after trauma or in neurodegenerative diseases.

This procedure describes how to rapidly initiate, extend and connect neurites organized in microfluidic chambers using poly-D-lysine-coated beads fixed to micropipettes that guide neurite elongation.

Brain and spinal cord injury may lead to permanent disability and death because it is still not possible to regenerate neurons over long distances and ...

A Hydrophobic Tissue Clearing Method for Rat Brain Tissue

Hydrophobic tissue clearing methods are easily adjustable, fast, and low-cost procedures that allows for the study of a molecule of interest in unaltered tissue samples. Traditional immunolabeling procedures require cutting the sample into thin sections, which restricts the ability to label and examine intact structures. However, if brain tissue can remain intact during processing, structures and circuits can remain intact for the analysis. Previously established clearing methods take significant time to completely clear the tissue, and the harsh chemicals can often damage sensitive antibodies. The iDISCO method quickly and completely clears tissue, is compatible with many antibodies, and requires no special lab equipment. This technique was initially validated for the use in mice tissue, but the current protocol adapts this method to image hemispheres of control and transgenic rat brains. In addition to this, the present protocol also makes several adjustments to preexisting protocol to provide clearer images with less background staining. Antibodies for Iba-1 and tyrosine hydroxylase were validated in the HIV-1 transgenic rat and in F344/N control rats using the present hydrophobic tissue clearing method. The brain is an interwoven network, where structures work together more often than separately of one another. Analyzing the brain as a whole system as opposed to a combination of individual pieces is the greatest benefit of this whole brain clearing method.

Here we present a hydrophobic tissue clearing method that allows for the viewing of target molecules as part of intact brain structures. This technique has now been validated for F344/N control and HIV-1 transgenic rats of both sexes.

Hydrophobic tissue clearing methods are easily adjustable, fast, and low-cost procedures that allows for the study of a molecule of interest in unaltered ...

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

We present a method developed specifically to image the whole Drosophila brain during ongoing behavior such as walking. Head fixation and dissection are optimized to minimize their impact on behavior. This is first achieved by using a holder that minimizes movement hindrances. The back of the fly&#8217;s head is glued to this holder at an angle that allows optical access to the whole brain while retaining the fly&#8217;s ability to walk, groom, smell, taste and see. The back of the head is dissected to remove tissues in the optical path and muscles responsible for head movement artefacts. The fly brain can subsequently be imaged to record brain activity, for instance using calcium or voltage indicators, during specific behaviors such as walking or grooming, and in response to different stimuli. Once the challenging dissection, which requires considerable practice, has been mastered, this technique allows to record rich data sets relating whole brain activity to behavior and stimulus responses.

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

We present a method specifically tailored to image the whole brain of adult Drosophila during behavior and in response to stimuli. The head is positioned to allow optical access to the whole brain, while the fly can move its legs and the antennae, the tip of the proboscis, and the eyes can receive sensory stimuli.

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

In vitro Modeling for Neurological Diseases using Direct Conversion from Fibroblasts to Neuronal Progenitor Cells and Differentiation into Astrocytes

Research on neurological disorders focuses primarily on the impact of neurons on disease mechanisms. Limited availability of animal models severely impacts the study of cell type specific contributions to disease. Moreover, animal models usually do not reflect variability in mutations and disease courses seen in human patients. Reprogramming methods for generation of induced pluripotent stem cells (iPSCs) have revolutionized patient specific research and created valuable tools for studying disease mechanisms. However, iPSC technology has disadvantages such as time, labor commitment, clonal selectivity and loss of epigenetic markers. Recent modifications of these methods allow more direct generation of cell lineages or specific cell types, bypassing clonal isolation or a pluripotent stem cell state. We have developed a rapid direct conversion method to generate induced Neuronal Progenitor Cells (iNPCs) from skin fibroblasts utilizing retroviral vectors in combination with neuralizing media. The iNPCs can be differentiated into neurons (iNs) oligodendrocytes (iOs) and astrocytes (iAs). iAs production facilitates rapid drug and disease mechanism testing as differentiation from iNPCs only takes 5 days. Moreover, iAs are easy to work with and are generated in pure populations at large numbers. We developed a highly reproducible co-culture assay using mouse GFP+ neurons and patient derived iAs to evaluate potential therapeutic strategies for numerous neurological and neurodegenerative disorders. Importantly, the iA assays are scalable to 384-well format facilitating the evaluation of multiple small molecules in one plate. This approach allows simultaneous therapeutic evaluation of multiple patient cell lines with diverse genetic background. Easy production and storage of iAs and capacity to screen multiple compounds in one assay renders this methodology adaptable for personalized medicine.

We describe a protocol to reprogram human skin-derived fibroblasts into induced Neuronal Progenitor Cells (iNPCs), and their subsequent differentiation into induced Astrocytes (iAs). This method leads to fast and reproducible generation of iNPCs and iAs in large quantities.

Research on neurological disorders focuses primarily on the impact of neurons on disease mechanisms. Limited availability of animal models severely ...

Immunostaining of Whole-Mount Retinas with the CLARITY Tissue Clearing Method

The tissue hydrogel delipidation method (CLARITY), originally developed by the Deisseroth laboratory, has been modified and widely used for immunostaining and imaging of thick brain samples. However, this advanced technology has not yet been used for whole-mount retinas. Although the retina is partially transparent, its thickness of approximately 200 &#181;m (in mice) still limits the penetration of antibodies into the deep tissue as well as reducing light penetration for high-resolution imaging. Here, we adapted the CLARITY method for whole-mount mouse retinas by polymerizing them with an acrylamide monomer to form a nanoporous hydrogel and then clearing them in sodium dodecyl sulfate to minimize protein loss and avoid tissue damage. CLARITY-processed retinas were immunostained with antibodies for retinal neurons, glial cells, and synaptic proteins, mounted in a refractive index matching solution, and imaged. Our data demonstrate that CLARITY&#160;can improve the quality of standard immunohistochemical staining and imaging for retinal neurons and glial cells in whole-mount preparation. For instance, 3D resolution of fine axon-like and dendritic structures of dopaminergic amacrine cells were much improved by CLARITY. Compared to non-processed whole-mount retinas, CLARITY can reveal immunostaining for synaptic proteins such as postsynaptic density protein 95. Our results show that CLARITY renders the retina more optically transparent after the removal of lipids and preserves fine structures of retinal neurons and their proteins, which can be routinely used for obtaining high-resolution imaging of retinal neurons and their subcellular structures in whole-mount preparation.

Here we present a protocol to adapt the CLARITY method of the brain tissues for whole-mount retinas to improve the quality of standard immunohistochemical staining and high-resolution imaging of retinal neurons and their subcellular structures.

The tissue hydrogel delipidation method (CLARITY), originally developed by the Deisseroth laboratory, has been modified and widely used for immunostaining ...