The authors would like to acknowledge Lynn Opdenaker at the University of Delaware Center for Translational Research at the Helen F. Graham Cancer Center for technical assistance, as well as Nancy Martin from the Duke University Cancer Institute Flow Cytometry Shared Resource, and Dr. Susan H. Smith for guidance in methods and data collection.

1. Preparation for Tissue Collection (15 &#8211; 30 min)
<ol>
	<li>Fire polish three sets of glass Pasteur pipettes in decreasing diameters and number them &#8220;1&#8221; = approximately 1 mm diameter, &#8220;2&#8221; = approximately 0.75 mm diameter, and &#8220;3&#8221; = approximately 0.50 mm diameter.</li>
	<li>Resuspend lyophilized Enzyme A with all of Buffer A according to the protocol provided with the Neural Dissociation Kit (see Table of Materials). Do not vortex. Aliquot the solution into 50 &#181;l&#160;aliquots and store at -20 &#186;C for later use.</li>
	<li>Make 1 L of myelin removal buffer and vacuum filter for sterilization [myelin removal buffer = 1,000 ml of 0.1 M phosphate-buffered saline (PBS), 2 ml of 500 mM Ethylenediaminetetraacetic acid (EDTA), and 10 g of Bovine Serum Albumin (BSA)].</li>
	<li>Cut nylon mesh sheet into small 1&#160; x 1 inch (2.5 x 2.5 cm) squares that will be used for filtering cellular debris and autoclave in a small beaker covered with aluminum foil.</li>
	<li>Prepare 1 L of wash buffer [wash buffer = 1,000 ml of 0.1 M PBS, 2 ml of 500 mM EDTA, and 10 g BSA].</li>
</ol>
2. Tissue Collection
<ol>
	<li>Turn on water bath to 37 &#186;C.</li>
	<li>Prepare Buffer X from the Neural Dissociation Kit by adding beta-mercaptoethanol to Buffer X to a final concentration of 0.067 mM (for 4 samples, add 13.5 &#181;l of 50 mM beta-mercaptoethanol to 10 ml of Buffer X).</li>
	<li>Prepare Enzyme Mix 1 by mixing 50 &#181;l of Enzyme P with 1,900 &#181;l of Buffer X for each sample as described in the protocol for the Neural Dissociation Kit For Example, for 4 samples, mix 200 &#181;l of Enzyme P with 7,600 &#181;l of Buffer X.</li>
	<li>Place Buffer X in the water bath at 37 &#186;C.</li>
	<li>Place 2 ml of cold Hank&#8217;s Buffered Salt Solution (HBSS) (without Ca++ and Mg++) into one well of a sterile 6-well culture plate for each sample that will be collected and keep on ice for tissue dissection.</li>
</ol>
3. Tissue Dissection (45 min &#8211; 1 hr)
<ol>
	<li>Inject the animal with appropriate volume of euthanasia solution (commercial barbiturate solution, e.g., Euthasol), according to Institutional Animal Care and Use Committee (IACUC) guidelines, and perfuse out all blood with cold 0.9% saline solution.
	<ol>
		<li>Administer Rats with an overdose of euthanasia solution.</li>
		<li>Monitor anesthesia via breathing and via toe-pinch. When the animal is sufficiently anesthetized (no response to the toe-pinch and deep, slow breathing), the rat can be perfused.</li>
		<li>To perfuse the rat, cut the chest cavity open with a pair of heavy-duty scissors. Cut the diaphragm to allow access up to the heart. Cut the ribs along both sides up to towards the top of the chest, to allow full access to the heart. At that point, the rib cage can be held off to the side using a pair of hemostats.</li>
		<li>Perform cardiac perfusion by inserting an 18 G needle (for adult rats) attached to an electric pump into the left ventricle of the heart. The pump is drawing up cold 0.9% saline solution.</li>
		<li>Then cut open the right atrium with a small pair of scissors to allow for the blood and liquid perfusate to drain from the body.</li>
		<li>Perfuse rats with approximately 10 ml (for adult rats) of 0.9% saline to remove all peripheral immune cells and factors.</li>
	</ol>
	</li>
	<li>Dissect the desired part of the brain region using sterile razor blades and appropriate dissection, then place the tissue pieces into the cold HBSS without Ca2+ and Mg2+. 
	NOTE: The protocol requires HBSS without Ca2+ and Mg2+ in the early steps of the protocol as these ions may interfere with the enzymes required for neural dissociation.</li>
	<li>After all tissue samples have been collected, return to the clean bench or sterile culture hood for tissue processing.</li>
</ol>
4. Neural Dissociation (1 hr)
<ol>
	<li>Dice each tissue sample into small pieces using sterile razor blades on the lid of the 6-well culture plate. This protocol has been used for tissue samples of approximately 30 - 100 mg, but is approved for tissue samples of up to 400 mg. For tissue samples larger than 400 mg, the reagent volumes must be scaled up appropriately.</li>
	<li>Use 1 ml of fresh HBSS without Ca2+ and Mg2+ to transfer the diced pieces of tissue with a pipette into a sterile 2 ml centrifuge tube. Repeat steps 4.1 and 4.2 for all sample until all samples have been transferred into a 2ml centrifuge tube.</li>
	<li>Centrifuge the samples at 300 x g for 2 min at RT and aspirate supernatant.</li>
	<li>Add 1,900 &#181;l of warm Enzyme Mix 1, as prepared in Steps 2.2 and 2.3, to each sample and close the tubes.</li>
	<li>Incubate the samples for 15 min in the 37 &#186;C water bath, inverting the tubes several times every 5 min to re-suspend the settled pieces of tissue.</li>
	<li>Meanwhile, prepare Enzyme Mix 2 by mixing 20 &#181;l of Buffer Y with 10 &#181;l of thawed Enzyme A (for 4 samples, mix 80 &#181;l of Buffer Y with 40 &#181;l of thawed Enzyme A).</li>
	<li>Add 30 &#181;l of Enzyme Mix 2 to each sample and invert gently. Do not vortex.</li>
	<li>Dissociate each tissue sample with Pasteur pipette &#8220;1&#8221;, triturating up and down 30 times.</li>
	<li>Incubate the samples for 15 min in the 37 &#186;C water bath; invert the tubes several times every 5 min to re-suspend the settled pieces of tissue.</li>
	<li>Dissociate each tissue sample with Pasteur pipette &#8220;2&#8221;, triturating up and down 30 times. Avoid generating bubbles.</li>
	<li>Dissociate each tissue sample with Pasteur pipette &#8220;3&#8221;, triturating up and down 30 times. Avoid generating bubbles.</li>
	<li>Incubate the samples for 10 min in the 37 &#186;C water bath; invert the tubes several times every 5 min to re-suspend the settled cells.</li>
	<li>Apply single-cell suspension to an 80 micron cell strain placed on top of a 15 ml falcon tube to remove any large pieces of debris and wash the filter and cells with 10 ml of HBSS (with Ca2+ and Mg2+) to stop the enzyme reactions. Repeat until each sample is transferred into a clean 15 ml falcon tube.</li>
	<li>Centrifuge the samples at 300 x g for 10 min at RT and aspirate off the supernatant.</li>
</ol>
5. Myelin Depletion (45 min)
<ol>
	<li>Thoroughly re-suspend the pellet of cells with 400 &#181;l of myelin removal buffer.</li>
	<li>Add specified amount of the myelin removal beads and pipette up and down to thoroughly mix. 
	NOTE: The volume of myelin removal beads that is used will depend upon the size of the tissue, the age of the animal, and the amount of myelin expected in that particular brain region. e.g.,&#160;for an adult rat hippocampus sample (approximately 300 mg), incubate the sample with 100 &#181;l of myelin removal beads.
	
	</li>
	<li>Incubate for 15 min in the refrigerator at 4 &#186;C.</li>
	<li>Wash each sample with 5 ml of myelin removal buffer.</li>
	<li>Centrifuge the samples at 300 x g for 10 min at RT.</li>
	<li>While centrifuging the samples, place 1 column for each sample in the magnetic field of the magnetic sorter and place a clean 80 micron filter on top of each column.</li>
	<li>Prepare the columns and filter by rinsing each column with 1 ml of myelin removal buffer, 3 times (3 ml total). Collect all flow-through in a waste container such as the bottom of an empty tip box.</li>
	<li>Position 5 ml polystyrene round bottom tube directly underneath each column in preparation of sample collection.</li>
	<li>When cells have finished centrifugation, aspirate supernatant and thoroughly re-suspend in 500 &#181;l of myelin removal buffer. Immediately apply cell suspension to the column and collect the cells in the tube below.</li>
	<li>Wash the filter and column with 1 ml myelin removal buffer, 4 times (4 ml total).</li>
	<li>Centrifuge the cell collection at 300 x g for 10 min at RT.</li>
	<li>Aspirate the supernatant and the cells are now ready for staining.</li>
</ol>
6. Staining Live Cells for FACS (1 hr for staining)
<ol>
	<li>Briefly vortex (2 sec) the cells to separate the pellet and immediately add 5 &#181;l of Fc block (anti- clusters of differentiation 32, CD32), vortex again, and incubate in the refrigerator at 4 &#186;C for 5 min.</li>
	<li>Meanwhile, prepare the primary antibody mixture by adding the three primary antibodies in wash buffer as follows: 0.125 &#181;l of allophycocyanin (APC) -conjugated CD11b antibody (1:800), 1 &#181;l of anti-GLT1 antibody (1:100), and 0.4 &#181;l of Fluorescein isothiocyanate (FITC) &#8211; conjugated Thy1 antibody (1:250) for every 100 &#181;l of wash buffer. Each sample will receive 100 &#181;l of primary antibody mixture for incubation; however, if your sample is much larger than 400 mg of tissue, you may want to consider increasing the volume of your primary antibody mixture accordingly</li>
	<li>Prepare tubes for single staining controls by removing just 2 &#181;l of cells from each sample tube and adding it to each single stain control tube. The &#8220;single stain&#8221; controls include: APC-CD11b only, GLT1 only, FITC-Thy1 only, PE secondary antibody only, and the &#8220;blank&#8221; or unstained control. 
	NOTE: All samples should be represented in all staining controls, thus 2 &#181;l of cells from each sample should be added to each staining control tube.</li>
	<li>Briefly vortex the tubes (2 sec) and add 100 &#181;l of primary antibody mixture to each sample tube and 100 &#181;l of appropriate primary antibody to each staining control tube, vortex the tubes again, cover the tubes with aluminum foil to protect the fluorescent antibodies from any light, and incubate the tubes in the refrigerator at 4 &#186;C for 20 min. The samples should be kept cool (at 4 &#186;C) for the remainder of the procedure to maintain the integrity of the samples and the antibodies.</li>
	<li>Briefly vortex the tubes and add 2 ml of wash buffer to each tube.</li>
	<li>Centrifuge tubes at 350 x g for 5 min at 4 &#186;C.</li>
	<li>Meanwhile, prepare the secondary antibody mixture by adding 0.2 &#181;l of PE-conjugated anti-rabbit secondary antibody for every 100 &#181;l of wash buffer. Each sample will get 100 &#181;l of secondary antibody mixture; however, if your sample is much larger than 400 mg of tissue, you may want to consider increasing the volume of your primary antibody mixture accordingly.</li>
	<li>When the centrifugation is complete, dump the supernatant off of each sample into the sink and blot the tubes upside-down on a paper towel.</li>
	<li>Briefly vortex the tubes and add 100 &#181;l of secondary antibody mixture to each sample tube and the appropriate secondary antibody to each staining control, vortex the tubes again, cover the tubes with aluminum foil, and incubate the tubes in the refrigerator at 4 &#186;C for 15 min. 
	NOTE: The GLT1-only staining control tube should get the secondary antibody mixture.
	
	</li>
	<li>After the incubation, briefly vortex the tubes and add 2 ml of wash buffer to each tube.</li>
	<li>Centrifuge the tubes at 350 x g for 5 min at 4 &#186;C.</li>
	<li>When the centrifugation is complete, dump the supernatant off of each sample into the sink and blot the tubes upside-down on a paper towel.</li>
	<li>Vortex the tubes and add 0.25 ml of sterile PBS to each tube. The samples are ready for sorting. 
	NOTE: More cells may require 0.5 ml of sterile PBS; however it is best to begin with a lower volume as the sample can always be diluted if it is too concentrated with cells. 
	NOTE: Optionally add DNase to the tube to prevent clumping of the cells and thus clogging of the sorter. Samples can also be filtered using a sterile 80 micron filter just prior to sorting in order to avoid clogging the sorter.
	
	</li>
	<li>Take cells to the sorter on ice. Collect the cell populations in 2 ml nuclease-free centrifuge tubes with 0.5 ml of sterile PBS in each tube.</li>
	<li>After the sort, spin the cells down at 300 x g for 2 min at 4 &#186;C. Aspirate off most of the PBS and flash freeze the cells in the -80 &#186;C freezer until further processing for either RNA extraction (see 1 for further protocol details), DNA extraction (see 2 for further protocol details) or cell lysis for protein analysis.</li>
</ol>

<ol><li>Schwarz, J. M., Smith, S. H., Bilbo, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((FACS+analysis+of+neuronal-glial+interactions+in+the+nucleus+accumbens+following+morphine+administration%5BTitle%5D)+AND+%22Psychopharmacology%22%5BJournal%5D)">FACS analysis of neuronal-glial interactions in the nucleus accumbens following morphine administration.</a> Psychopharmacology. 230 (4), 525-535 (2013).</li>
<li>Schwarz, J. M., Hutchinson, M. R., Bilbo, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Early-life+experience+decreases+drug-induced+reinstatement+of+morphine+CPP+in+adulthood+via+microglial-specific+epigenetic+programming+of+anti-inflammatory+IL-10+expression%5BTitle%5D)+AND+%22J+Neurosci%22%5BJournal%5D)">Early-life experience decreases drug-induced reinstatement of morphine CPP in adulthood via microglial-specific epigenetic programming of anti-inflammatory IL-10 expression.</a> J Neurosci. 31 (49), 17835-1523 (2011).</li>
<li>Herzenberg, L. A., Tung, J., Moore, W. A., Herzenberg, L. A., Parks, D. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Interpreting+flow+cytometry+data%3A+a+guide+for+the+perplexed%5BTitle%5D)+AND+%22Nature+Immunology%22%5BJournal%5D)">Interpreting flow cytometry data: a guide for the perplexed.</a> Nature Immunology. 7 (7), 681-685 (2006).</li>
<li>Guez-Barber, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((FACS+identifies+unique+cocaine-induced+gene+regulation+in+selectively+activated+adult+striatal+neurons%5BTitle%5D)+AND+%22J+Neurosci%22%5BJournal%5D)">FACS identifies unique cocaine-induced gene regulation in selectively activated adult striatal neurons.</a> J Neurosci. 31 (11), 4251-4259 (2011).</li>
<li>Fanous, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Unique+gene+alterations+are+induced+in+FACS-purified+Fos-positive+neurons+activated+during+cue-induced+relapse+to+heroin+seeking%5BTitle%5D)+AND+%22J+Neurochem%22%5BJournal%5D)">Unique gene alterations are induced in FACS-purified Fos-positive neurons activated during cue-induced relapse to heroin seeking.</a> J Neurochem. 124 (1), 100-108 (2013).</li>
<li>Liu, Q. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Detection+of+molecular+alterations+in+methamphetamine-activated+Fos-expressing+neurons+from+single+rat+dorsal+striatum+using+fluorescence-activated+cell+sorting+%28FACS%29%5BTitle%5D)+AND+%22J+Neurochem%22%5BJournal%5D)">Detection of molecular alterations in methamphetamine-activated Fos-expressing neurons from single rat dorsal striatum using fluorescence-activated cell sorting (FACS).</a> J Neurochem. 128 (1), 173-185 (2013).</li>
<li>Guez-Barber, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((FACS+purification+of+immunolabeled+cell+types+from+adult+rat+brain%5BTitle%5D)+AND+%22J+Neurosci+Methods%22%5BJournal%5D)">FACS purification of immunolabeled cell types from adult rat brain.</a> J Neurosci Methods. 203 (1), 10-18 (2012).</li>
<li>Nolte, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((GFAP+promoter-controlled+EGFP-expressing+transgenic+mice%3A+a+tool+to+visualize+astrocytes+and+astrogliosis+in+living+brain+tissue%5BTitle%5D)+AND+%22Glia%22%5BJournal%5D)">GFAP promoter-controlled EGFP-expressing transgenic mice: a tool to visualize astrocytes and astrogliosis in living brain tissue.</a> Glia. 33 (1), 72-86 (2000).</li>
<li>Okana, M., Bell, D. W., Haber, D. A., Li, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((DNA+methyltransferases+Dnmt3a+and+Dnmt3b+are+essential+for+de+novo+methylation+and+mammalian+development%5BTitle%5D)+AND+%22Cell%22%5BJournal%5D)">DNA methyltransferases Dnmt3a and Dnmt3b are essential for de novo methylation and mammalian development.</a> Cell. 99 (3), 247-257 (1999).</li>
<li>Bogdanović, O., Veenstra, G. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((DNA+methylation+and+methyl-CpG+binding+proteins%3A+developmental+requirements+and+function%5BTitle%5D)+AND+%22Chromosoma%22%5BJournal%5D)">DNA methylation and methyl-CpG binding proteins: developmental requirements and function.</a> Chromosoma. 118 (5), 549-565 (2009).</li>
<li>Iwamoto, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Neurons+show+distinctive+DNA+methylation+profile+and+higher+inter-individual+variations+compared+with+non-neurons%5BTitle%5D)+AND+%22Genome+Res%22%5BJournal%5D)">Neurons show distinctive DNA methylation profile and higher inter-individual variations compared with non-neurons.</a> Genome Res. 21 (5), 688-696 (2011).</li>
<li>Nishioka, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Neuronal+cell-type+specific+DNA+methylation+patterns+of+the+Cacna1c+gene%5BTitle%5D)+AND+%22Int+J+Dev+Neurosci%22%5BJournal%5D)">Neuronal cell-type specific DNA methylation patterns of the Cacna1c gene.</a> Int J Dev Neurosci. 31 (2), 89-95 (2013).</li>
<li>Kozlenkov, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Differences+in+DNA+methylation+between+human+neuronal+and+glial+cells+are+concentrated+in+enhancers+and+non-CpG+sites%5BTitle%5D)+AND+%22Nucleic+Acid+Res%22%5BJournal%5D)">Differences in DNA methylation between human neuronal and glial cells are concentrated in enhancers and non-CpG sites.</a> Nucleic Acid Res. 42 (1), 109-127 (2014).</li>
<li>Russo, S. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Nuclear+factor+kappa+B+signaling+regulates+neuronal+morphology+and+cocaine+reward%5BTitle%5D)+AND+%22J+Neurosci%22%5BJournal%5D)">Nuclear factor kappa B signaling regulates neuronal morphology and cocaine reward.</a> J Neurosci. 29 (11), 3529-3537 (2009).</li>
<li>Bhatt, D., Ghosh, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Regulation+of+the+NF-%CE%BAB-Mediated+Transcription+of+Inflammatory+Genes%5BTitle%5D)+AND+%22Front+Immunol%22%5BJournal%5D)">Regulation of the NF-κB-Mediated Transcription of Inflammatory Genes.</a> Front Immunol. 5, 71(2014).</li>
<li>Okada, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Flow+cytometric+sorting+of+neuronal+and+glial+nuclei+from+central+nervous+system+tissue%5BTitle%5D)+AND+%22J+Cell+Physiol%22%5BJournal%5D)">Flow cytometric sorting of neuronal and glial nuclei from central nervous system tissue.</a> J Cell Physiol. 226 (2), 552-558 (2011).</li>
</ol>

The authors declare that they have no competing financial interests.

Similar to many other tissues and systems, the brain is comprised of a heterogeneous cell population that functions together to impact behavior. The analysis of gene expression, protein expression, or epigenetic modifications from individual cells within that heterogeneous population has the potential to reveal information about the function of the system as a whole, to identify cellular processes regulating both normal behavior and disease processes, and to provide cell-type-specific targets for potential therapies. It ...

The purpose of the protocol described below is to isolate individual cell types from a heterogeneous population of neural tissue for the subsequent analysis of cell-type-specific gene expression, protein expression, or even epigenetic markers. The brain is comprised of many cell types that are derived from distinct progenitor cells and that have cell-type-specific properties and functions. Despite these differences, these distinct neural cell types can express similar receptors and intracellular signaling molecules which make the analysis of these more ubiquitous proteins difficult to measure or interpret in a cell-type-specific manner using conventional methods. Neuroscientists must identify the function and activation of these distinct cell types in the brain and how they can individually impact behavior as this will ultimately be the first step to identifying more specific drugs and therapeutic targets for neurological and neuropsychiatric diseases. Despite this overarching goal of neuroscience research, it can been difficult to isolate individual neural cell types from the brain for the analysis of gene or protein expression, the activation of signaling molecules, or the modification of epigenetic markers on DNA. Of the techniques that are currently used, immunohistochemistry can identify the expression of proteins in a cell-type-specific manner when combined with additional staining of a cell-type-specific marker, though this relies on specific antibodies that can properly stain for the proteins of interest and it can be difficult to quantify. In situ hybridization can identify the specific localization of messenger ribonucleic acid (mRNA) in individual cells in the brain, but this is a laborious process that also limits the co-analysis of specific cell types and only allows for the analysis of one or maybe a few genes of interest. Laser capture micro-dissection uses a laser to isolate subpopulations of cells that are visualized via microscopy; however the time-consuming nature of this process and the relatively low yield can significantly limit the subsequent analysis of proteins or mRNA levels, particularly if the expression of these molecules is low to begin with. Fluorescence activated cell sorting (FACS) is a relatively novel technique in the field of neuroscience to isolate individual cell types from the brain for subsequent analysis of gene expression1 and/or epigenetic targets2. This process can also be used to sort specific types of neural cells for subsequent analysis of cell-type-specific gene expression, protein expression, or epigenetic markers. FACS has been used in a number of medical research fields such as cancer and immunology for decades to count and sort different cells based on either physical or biochemical characteristics3. In addition, flow cytometry has classically been used to analyze protein expression on a per cell basis, using specific antibodies. The procedure described below, takes advantage of classical flow cytometry techniques to isolate individual cell types for subsequent analysis of molecular biology endpoints. The flow cytometer can analyze several thousand cells in a second, which makes it a quick and efficient alternative to the techniques described above. In addition, cells can be isolated based on the cellular expression of a specific protein (for example a neurotransmitter receptor) or a combination of two or more proteins (colocalization of multiple proteins in a specific cell type). This allows the user to isolate very selective neural cell types based on their molecular properties to identify their function in the brain.
To perform FACS, neural cells are prepared into a single-cell suspension which is passed through a flow cell that carries and aligns the cells so that they pass single-file through a light beam and lasers for analysis. A computer acquires the data from each cell and plots it on a histogram for analysis of specified parameters (size, granularity, and fluorescence). Based on these parameters, the cells can immediately be sorted into separate tubes for their recollection and subsequent analysis of any endpoint desired. The protocol described below utilizes three antibodies to sort neurons (using a Thymocyte antigen 1, Thy1 antibody), astrocytes (using a glial glutamate transporter, GLT1 antibody), and microglia (using a cluster of differentiation molecule 11B, CD11b antibody). This protocol can be used as described below or modified with different antibodies depending on the cell type that one would like to isolate for his own experiments.
There are a few caveats to consider when determining whether this protocol is appropriate for specific experiments. One major caveat may concern the specific cell type that one would like to isolate. In this protocol, the three antibodies that are used are extracellular antibodies, which allow the experimenter to keep the cell types intact during the staining procedure, thus preserving the integrity of the RNA, DNA and proteins inside. It is possible that one may wish to isolate a specific neural cell type using an antibody that identifies a protein that is only expressed inside that particular cell. For example, one might want to isolate dopaminergic neurons using an antibody to tyrosine hydroxylase or isolate acetylcholine neurons using an antibody for choline acetyltransferase. These proteins are intracellular and thus would require fixation and permeabilization of the cell membrane for subsequent staining with the appropriate antibodies. While this has been done before 4,5, this process may significantly decrease the yield of RNA or DNA from these permeabilized cells. Another caveat may be that not all antibodies are appropriate for FACS. For example, one may currently use an antibody that works very well for western blot, a technique that requires the denaturation of proteins. This antibody may not necessarily be suitable for identification of these cell types using FACS given that the proteins are not denatured at any point in this protocol and thus the antibody may have no way to bind to its inherent antigen. Companies provide specification sheets which identify the applications for which an antibody has been approved. If an antibody has not been approved for flow cytometry, it should not discourage one from trying this protocol with a particular antibody; however, one should be aware that it isn&#8217;t guaranteed to work for FACS. A third caveat of this protocol has to do with the number of cells that one is trying to isolate. FACS is an excellent technique to yield the most cells possible from even a small piece of tissue, but it is also possible that if one would like to isolate a relatively sparse population of cells from a relatively small brain region, the yield from one animal will be inherently low. In this case, it may be necessary to pool the brain tissue from a few animals in the same treatment group in order to yield the number of cells necessary for subsequent analysis; however, a recent publication has used gene-targeted pre-amplification of cDNA for subsequent analysis of gene expression from a small number of activated neurons (5-6%) from a larger set sorted neurons, indicating that it is possible to analyze gene expression from even small subsets of neural cells without pooling large numbers of animals6A final caveat of this technique is that one should have access to a cell sorter that is not too far away. The cell sorter is a complicated machine that requires significant training in order to use it properly. Thus these machines are often run by a qualified technician in a core facility. In addition, the goal of this procedure is to dissociate the neural tissue, stain it for specific antibodies, and immediately take those samples to a sorter within a short period of time (perhaps a half day). This timeframe will help to increase the survival and yield of isolated cells and maintain the integrity of the cells for subsequent processing and analysis. If all of these parameters described above are met, FACS is an excellent method to analyze cell-type specific expression of genes and proteins from neural tissue.
All experiments were performed in accordance with the Institutional Animal Care and Use Committee (IACUC) of the University of Delaware and the National Institutes of Health Guide for the Care and Use of Laboratory Animals.

<table><tbody><tr><td>Neural Dissociation Kit (P)</td><td>Miltenyi Biotec</td><td>130-092-628</td><td></td></tr><tr><td>Myelin Removal Beads II</td><td>Miltenyi Biotec</td><td>130-096-733</td><td></td></tr><tr><td>LS Columns</td><td>Miltenyi Biotec</td><td>130-042-401</td><td></td></tr><tr><td>QuadroMACS Separator</td><td>Miltenyi Biotec</td><td>130-090-976</td><td></td></tr><tr><td>MACS MultiStand</td><td>Miltenyi Biotec</td><td>130-042-303</td><td></td></tr><tr><td>Nylon Mesh Sheet</td><td>Amazon</td><td>CMN-0074-10YD</td><td>40 inch width, 80 micron size mesh</td></tr><tr><td>Fc Block / anti-CD32</td><td>BD Biosciences</td><td>BDB550270</td><td>reactivity for rat</td></tr><tr><td>APC-conjugated CD11b antibody</td><td>Biolegend</td><td>201809</td><td>reactivity for rat</td></tr><tr><td>Rabbit anti-GLT1</td><td>Novus Biologicals</td><td>NBP1-20136</td><td>reactivity for rat or human</td></tr><tr><td>PE-conjugated anti-rabbit secondary antibody</td><td>eBioscience</td><td>1037259</td><td>secondary antibody for anti-GLT1</td></tr><tr><td>FITC-conjugated anti-rat CD90 (Thy1) mouse antibody</td><td>Biolegend</td><td>202504</td><td>reactivity for rat</td></tr></tbody></table>

using fluorescence activated cell sorting to examine cell-type-specific gene expression in rat brain tissue

The brain is comprised of four primary cell types including neurons, astrocytes, microglia and oligodendrocytes. Though they are not the most abundant cell type in the brain, neurons are the most widely studied of these cell types given their direct role in impacting behaviors. Other cell types in the brain also impact neuronal function and behavior via the signaling molecules they produce. Neuroscientists must understand the interactions between the cell types in the brain to better understand how these interactions impact neural function and disease. To date, the most common method of analyzing protein or gene expression utilizes the homogenization of whole tissue samples, usually with blood, and without regard for cell type. This approach is an informative approach for examining general changes in gene or protein expression that may influence neural function and behavior; however, this method of analysis does not lend itself to a greater understanding of cell-type-specific gene expression and the effect of cell-to-cell communication on neural function. Analysis of behavioral epigenetics has been an area of growing focus which examines how modifications of the deoxyribonucleic acid (DNA) structure impact long-term gene expression and behavior; however, this information may only be relevant if analyzed in a cell-type-specific manner given the differential lineage and thus epigenetic markers that may be present on certain genes of individual neural cell types. The Fluorescence Activated Cell Sorting (FACS) technique described below provides a simple and effective way to isolate individual neural cells for the subsequent analysis of gene expression, protein expression, or epigenetic modifications of DNA. This technique can also be modified to isolate more specific neural cell types in the brain for subsequent cell-type-specific analysis.

The Importance of Myelin Depletion and Tissue Perfusion
Figure 1 depicts the importance of myelin depletion. Myelin depletion (Steps 5.1 through 5.12 of the protocol above) occurs when the single-cell suspension is incubated in the Myelin Removal Beads, washed, and subsequently passed through the column on the magnetic sorter. The purpose of these steps is to reduce the amount of cellular debris present in each sample. As neurons are dissociated and triturated, it can shear of...

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Using Fluorescence Activated Cell Sorting to Examine Cell-Type-Specific Gene Expression in Rat Brain Tissue

The goal of this protocol is to use the fluorescence activated cell sorting (FACS) technique to sort specific types of neural cells for subsequent analysis of cell-type-specific gene expression, epigenetic markers, and or protein expression.

The brain is comprised of four primary cell types including neurons, astrocytes, microglia and oligodendrocytes. Though they are not the most abundant ...

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Research

JoVE Journal

Neuroscience

16.9K Views.  University of Delaware. The goal of this protocol is to use the fluorescence activated cell sorting (FACS) technique to sort specific types of neural cells for subsequent analysis of cell-type-specific gene expression, epigenetic markers, and or protein expression.

Video: Using Fluorescence Activated Cell Sorting to Examine Cell-Type-Specific Gene Expression in Rat Brain Tissue

Generation of Topically Transgenic Rats by In utero Electroporation and In vivo Bioluminescence Screening

In utero electroporation (IUE) is a technique which allows genetic modification of cells in the brain for investigating neuronal development. So far, the use of IUE for investigating behavior or neuropathology in the adult brain has been limited by insufficient methods for monitoring of IUE transfection success by non-invasive techniques in postnatal animals. 
 For the present study, E16 rats were used for IUE. After intraventricular injection of the nucleic acids into the embryos, positioning of the tweezer electrodes was critical for targeting either the developing cortex or the hippocampus. 
 Ventricular co-injection and electroporation of a luciferase gene allowed monitoring of the transfected cells postnatally after intraperitoneal luciferin injection in the anesthetized live P7 pup by in vivo bioluminescence, using an IVIS Spectrum device with 3D quantification software. 
 Area definition by bioluminescence could clearly differentiate between cortical and hippocampal electroporations and detect a signal longitudinally over time up to 5 weeks after birth. This imaging technique allowed us to select pups with a sufficient number of transfected cells assumed necessary for triggering biological effects and, subsequently, to perform behavioral investigations at 3 month of age. As an example, this study demonstrates that IUE with the human full length DISC1 gene into the rat cortex led to amphetamine hypersensitivity. Co-transfected GFP could be detected in neurons by post mortem fluorescence microscopy in cryosections indicating gene expression present at &ge;6 months after birth.
 We conclude that postnatal bioluminescence imaging allows evaluating the success of transient transfections with IUE in rats. Investigations on the influence of topical gene manipulations during neurodevelopment on the adult brain and its connectivity are greatly facilitated. For many scientific questions, this technique can supplement or even replace the use of transgenic rats and provide a novel technology for behavioral neuroscience.

Generation of Topically Transgenic Rats by In utero Electroporation and In vivo Bioluminescence Screening

Genes can be manipulated during development of the cortex or the hippocampus of the rat via in utero electroporation (IUE) at E16, to enable fast and targeted modifications in neuronal connectivity for later studies of behavior or neuropathology in adult animals. Postnatal in vivo imaging for control of IUE success is performed by bioluminescence of activating co-transfected luciferase.

 In utero electroporation (IUE) is a technique which allows genetic modification of cells in the brain for investigating neuronal development. So far, the ...

Cell Sorting of Neural Stem and Progenitor Cells from the Adult Mouse Subventricular Zone and Live-imaging of their Cell Cycle Dynamics

Neural stem cells (NSCs) in the subventricular zone of the lateral ventricles (SVZ) sustain olfactory neurogenesis throughout life in the mammalian brain. They successively generate transit amplifying cells (TACs) and neuroblasts that differentiate into neurons once they integrate the olfactory bulbs. Emerging fluorescent activated cell sorting (FACS) techniques have allowed the isolation of NSCs as well as their progeny and have started to shed light on gene regulatory networks in adult neurogenic niches. We report here a cell sorting technique that allows to follow and distinguish the cell cycle dynamics of the above-mentioned cell populations from the adult SVZ with a LeX/EGFR/CD24 triple staining. Isolated cells are then plated as adherent cells to explore in details their cell cycle progression by time-lapse video microscopy. To this end, we use transgenic Fluorescence Ubiquitination Cell Cycle Indicator (FUCCI) mice in which cells are red-fluorescent during G1 phase due to a G1 specific red-Cdt1 reporter. This method has recently revealed that proliferating NSCs progressively lengthen their G1 phase during aging, leading to neurogenesis impairment. This method is easily transposable to other systems and could be of great interest for the study of the cell cycle dynamics of brain cells in the context of brain pathologies.

We report a Fluorescent Activated Cell Sorting (FACS)-based method to isolate neural stem cells (NSCs) and their progeny from the subventricular zone (SVZ) of the adult mouse brain. Applied to Fluorescence Ubiquitination Cell Cycle Indicator (FUCCI) transgenic mice, it allows the study of cell cycle progression by live imaging.

Neural stem cells (NSCs) in the subventricular zone of the lateral ventricles (SVZ) sustain olfactory neurogenesis throughout life in the mammalian brain. ...

Fluorescence Activated Cell Sorting (FACS) and Gene Expression Analysis of Fos-expressing Neurons from Fresh and Frozen Rat Brain Tissue

The study of neuroplasticity and molecular alterations in learned behaviors is switching from the study of whole brain regions to the study of specific sets of sparsely distributed activated neurons called neuronal ensembles that mediate learned associations. Fluorescence Activated Cell Sorting (FACS) has recently been optimized for adult rat brain tissue and allowed isolation of activated neurons using antibodies against the neuronal marker NeuN and Fos protein, a marker of strongly activated neurons. Until now, Fos-expressing neurons and other cell types were isolated from fresh tissue, which entailed long processing days and allowed very limited numbers of brain samples to be assessed after lengthy and complex behavioral procedures. Here we found that yields of Fos-expressing neurons and Fos mRNA from dorsal striatum were similar between freshly dissected tissue and tissue frozen at -80 &#186;C for 3 - 21 days. In addition, we confirmed the phenotype of the NeuN-positive and NeuN-negative sorted cells by assessing gene expression of neuronal (NeuN), astrocytic (GFAP), oligodendrocytic (Oligo2) and microgial (Iba1) markers, which indicates that frozen tissue can also be used for FACS isolation of glial cell types. Overall, it is possible to collect, dissect and freeze brain tissue for multiple FACS sessions. This maximizes the amount of data obtained from valuable animal subjects that have often undergone long and complex behavioral procedures.

Fluorescence Activated Cell Sorting FACS and Gene Expression Analysis of Fos-expressing Neurons from Fresh and Frozen Rat Brain Tissue

Here we present a Fluorescence Activated Cell Sorting (FACS) protocol to study molecular alterations in Fos-expressing neuronal ensembles from both fresh and frozen brain tissue. The use of frozen tissue allows FACS isolation of many brain areas over multiple sessions to maximize the use of valuable animal subjects.

The study of neuroplasticity and molecular alterations in learned behaviors is switching from the study of whole brain regions to the study of specific ...

Primary Cell Culture of Purified GABAergic or Glutamatergic Neurons Established through Fluorescence-activated Cell Sorting

The overall goal of this protocol is to generate purified neuronal cultures derived from either GABAergic or glutamatergic neurons. Purified neurons can be cultured in defined media for 16 days in vitro and are amenable to any analyses typically performed on dissociated cultures, including electrophysiological, morphological and survival analyses. The major advantage of these cultures is that specific cell types can be selectively studied in the absence of complex external influences, such as those arising from glial cells or other neuron types. When planning experiments with purified cells, however, it is important to note that neurons strongly depend on glia-conditioned media for their growth and survival. In addition, glutamatergic neurons further depend on glia-secreted factors for the establishment of synaptic transmission. We therefore also describe a method for co-culturing neurons and glial cells in a non-contact arrangement. Using these methods, we have identified major differences between the development of GABAergic and glutamatergic neuronal networks. Thus, studying cultures of purified neurons has great potential for furthering our understanding of how the nervous system develops and functions. Moreover, purified cultures may be useful for investigating the direct action of pharmacological agents, growth factors or for exploring the consequences of genetic manipulations on specific cell types. As more and more transgenic animals become available, labeling additional specific cell types of interest, we expect that the protocols described here will grow in their applicability and potential.

This protocol describes a cell sorting based method for the purification and culture of fluorescent GABAergic or glutamatergic neurons from the neocortex and hippocampus of postnatal mice or rats.

The overall goal of this protocol is to generate purified neuronal cultures derived from either GABAergic or glutamatergic neurons. Purified neurons can ...

Using Near-infrared Fluorescence and High-resolution Scanning to Measure Protein Expression in the Rodent Brain

Neuroscience is the study of how cells in the brain mediate various functions. Measuring protein expression in neurons and glia is critical for the study of neuroscience as cellular function is determined by the composition and activity of cellular proteins. In this article, we describe how immunocytochemistry can be combined with near-infrared high-resolution scanning to provide a semi-quantitative measure of protein expression in distinct brain regions. This technique can be used for single or double protein expression in the same brain region. Measuring proteins in this fashion can be used to obtain a relative change in protein expression with an experimental manipulation, molecular signature of learning and memory, activity in molecular pathways, and neural activity in multiple brain regions. Using the correct proteins and statistical analysis, functional connectivity among brain regions can be determined as well. Given the ease of implementing immunocytochemistry in a laboratory, using immunocytochemistry with near-infrared high-resolution scanning can expand the ability of the neuroscientist to examine neurobiological processes at a systems level.

Here, we present a protocol that uses near-infrared dyes in conjunction with immunohistochemistry and high-resolution scanning to assay proteins in brain regions.

Neuroscience is the study of how cells in the brain mediate various functions. Measuring protein expression in neurons and glia is critical for the study ...

Fluorescence-Activated Cell Sorting-Radioligand Treated Tissue (FACS-RTT) to Determine the Cellular Origin of Radioactive Signal

Glial cells probably have a considerable implication in the pathophysiology of neurodegenerative disorders, such as Alzheimer's disease (AD). Their alterations are perhaps associated with a pro-inflammatory state. The TgF344-AD rat strain has been designed to express human APP and human PS1&#916;E9 genes, encoding for amyloid proteins A&#946;-40 and A&#946;-42 and displays amyloid pathology and cognitive deficits with aging. The TgF344-AD rat model is used in this study to evaluate the cellular origin of the 18 kDa translocator protein (TSPO, a marker of glial cell activation) binding, and the 5HT2A-receptor (5HT2AR) serotonin receptor levels that are possibly disrupted in AD. The technique presented here is Fluorescence-Activated Cell Sorting to Radioligand Treated Tissue (FACS-RTT), a quantitative cell-type-specific technique complementary to in vivo PET or SPECT or ex vivo/in vitro autoradiography techniques. It quantifies the same radiolabeled tracer used prior for imaging, using a &#947; counter after cytometry cell sorting. This allows determining the cellular origin of the radiolabeled protein with high cellular specificity and sensitivity. For example, studies with FACS-RTT showed that (i) the increase in TSPO binding was associated with microglia in a rat model of lipopolysaccharide (LPS)-induced neuroinflammation, (ii) an increase in TSPO binding at 12- and 18-months was associated with astrocytes first, and then microglia in the TgF344-AD rats compared to wild type (WT) rats, and (iii) the striatal density of 5HT2AR decreases in astrocytes at 18 months in the same rat AD model. Interestingly, this technique can be extended to virtually all radiotracers.

Fluorescence-Activated Cell Sorting-Radioligand Treated Tissue FACS-RTT to Determine the Cellular Origin of Radioactive Signal

Fluorescence-Activated Cell Sorting-Radioligand Treated Tissue (FACS-RTT) is a powerful tool to study the role of the 18 kDa translocator protein or Serotonin 5HT2A-receptor expression in Alzheimer&#39;s Disease at a cellular scale. This protocol describes the ex-vivo application of FACS-RTT in the TgF344-AD rat model.

Glial cells probably have a considerable implication in the pathophysiology of neurodegenerative disorders, such as Alzheimer's disease (AD). Their ...

RNA Isolation from Cell Specific Subpopulations Using Laser-capture Microdissection Combined with Rapid Immunolabeling

Laser capture microdissection (LCM) allows the isolation of specific cells from thin tissue sections with high spatial resolution. Effective LCM requires precise identification of cells subpopulations from a heterogeneous tissue. Identification of cells of interest for LCM is usually based on morphological criteria or on fluorescent protein reporters. The combination of LCM and rapid immunolabeling offers an alternative and efficient means to visualize specific cell types and to isolate them from surrounding tissue. High-quality RNA can then be extracted from a pure cell population and further processed for downstream applications, including RNA-sequencing, microarray or qRT-PCR. This approach has been previously performed and briefly described in few publications. The goal of this article is to illustrate how to perform rapid immunolabeling of a cell population while keeping RNA integrity, and how to isolate these specific cells using LCM. Herein, we illustrated this multi-step procedure by immunolabeling and capturing dopaminergic cells in brain tissue from one-day-old mice. We highlight key critical steps that deserve special consideration. This protocol can be adapted to a variety of tissues and cells of interest. Researchers from different fields will likely benefit from the demonstration of this approach.

Gene expression analysis of a subset of cells in a specific tissue represents a major challenge. This article describes how to isolate high-quality total RNA from a specific cell population by combining a rapid immunolabeling method with laser capture microdissection.

Laser capture microdissection (LCM) allows the isolation of specific cells from thin tissue sections with high spatial resolution. Effective LCM requires ...

Biology

Fluorescence-Guided Matrix-assisted Laser Desorption/Ionization with Laser-Induced Postionization Mass Spectrometry of Individual Rat Neural Cells

Single-cell measurements are critical to understanding the rich spatiochemical heterogeneity of the brain. Matrix-assisted laser/desorption ionization (MALDI) mass spectrometry (MS) is capable of label-free, high-throughput characterization of endogenous molecules in individual cells. The recent advances in the development of MALDI mass spectrometers with laser-induced post-ionization (MALDI-2) provide greatly enhanced sensitivity of detection for a variety of lipids and other small molecules. However, MS imaging of large samples with MALDI-2 at cellular resolution is prohibitively slow for most applications. In this protocol, primary cells are isolated and dispersed onto conductive slides. Relative cell locations are determined by whole-slide fluorescence microscopy, followed by accurate coregistration of the microscopy coordinates to the stage coordinates of the MALDI-2 mass spectrometer. Targeted MS analysis of only cell locations provides high-throughput, single-cell measurements with high analyte coverage and reduced data size as compared to MS imaging of the entire sample. We describe the critical steps necessary for single-cell preparation, whole-slide fluorescence imaging, matrix application, and MALDI-2 mass spectrometry.

This protocol outlines the use of microMS for fluorescence-guided, single-cell MALDI-2 mass spectrometry, enabling enhanced molecular profiling of primary rat neuronal cells.

Single-cell measurements are critical to understanding the rich spatiochemical heterogeneity of the brain. Matrix-assisted laser/desorption ionization ...

Isolating Fluorescently Labeled Neurons from a Murine Brain

Source: Paul, A., et al., <a href="https://app.jove.com/v/58690">Single-cell RNA Sequencing of Fluorescently Labeled Mouse Neurons Using Manual Sorting and Double In Vitro Transcription with Absolute Counts Sequencing (DIVA-Seq).</a> J. Vis. Exp. (2018)
This video demonstrates a method to isolate fluorescently labeled neurons from a mouse brain.

All procedures involving sample collection have been performed in accordance with the institute&#39;s IRB guidelines.
1. Manual Sorting of Fluorescently ...

JoVE Encyclopedia of Experiments

Neuronal Culture Techniques

Primary Neuronal Culture

Obtaining Various Neural Cell Populations from a Rat Hippocampus

Source: Schwarz, J. M. <a href="https://app.jove.com/v/52537">Using Fluorescence Activated Cell Sorting to Examine Cell-Type-Specific Gene Expression in Rat Brain Tissue.</a> J. Vis. Exp. (2015)
This video demonstrates a protocol to isolate cells from rat hippocampi, including neurons, astrocytes, and microglia.

All procedures involving sample collection have been performed in accordance with the institute&#39;s IRB guidelines.
1. Tissue Collection

	Prepare ...

Using Fluorescence Activated Cell Sorting to Examine Cell-Type-Specific Gene Expression in Rat Brain Tissue

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