Name: uptake of fluorescent labeled small extracellular vesicles in vitro and in spinal cord
Uploaded: 2021-05-23T14:00:00
Description: Watch this Scientific Journal Video about Uptake of Fluorescent Labeled Small Extracellular Vesicles In Vitro and in Spinal Cord at JoVE.com

This study was supported by grants from NIH NINDS R01NS102836 and the Pennsylvania Department of Health Commonwealth Universal Research Enhancement (CURE) awarded to Seena K. Ajit. We thank Dr. Bradley Nash for critical reading of the manuscript.

NOTE: All procedures were performed in compliance with the NIH Guide for the Care and Use of Laboratory Animals and approved by the Institutional Animal Care &#38; Use Committee of Drexel University College of Medicine. Timed-pregnant CD-1 mice were used for astrocytic culture, and all dams were received 15 days after impregnation. Ten-twelve weeks old C57BL/6 mice were used for in vivo uptake experiments.
1. Isolation of sEVs from RAW 264.7 macrophage cells
<ol>
	<li>Culture RAW 26...

<ol>
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In this protocol, we showed the labeling of sEVs with PKH dyes and the visualization of their uptake in the spinal cord. PKH lipophilic fluorescent dyes are widely used for labeling cells by flow cytometry and fluorescent microscopy3,5,6,12,24,25. Due to their relatively long half-life and low cytotoxicity, PKH dyes can be us...

Small extracellular vesicles (sEVs) are nanosized, membrane-derived vesicles with a size range of 50-150 nm. They originate from multi-vesicular bodies (MVBs) and are released from cells upon fusion of the MVBs with the plasma membrane. sEVs contain miRNAs, mRNAs, proteins, and bioactive lipids, and these molecules are transferred between cells in the form of cell-to-cell communication. sEVs can be internalized by recipient cells by a variety of endocytic pathways, and this capture of sEVs by recipient cells is mediated by the recognition of surface molecules on both EVs and the target cells1.
sEVs have gained interest due to their capacity to trigger molecular and phenotypic changes in acceptor cells, their utility as a therapeutic agent, and their potential as carriers for cargo molecules or pharmacological agents. Due to their small size, the imaging and tracking of sEVs can be challenging, especially for in vivo studies and clinical settings. Therefore, many methods have been developed to label and image sEVs to assist their biodistribution and tracking in vitro and in vivo2.
The most common technique to study sEV biodistribution and target cell interactions involves labeling them with fluorescent dye molecules3,4,5,6,7. EVs were initially labeled with cell membrane dyes that were commonly used to image cells. These fluorescent dyes generally stain the lipid bilayer or proteins of interest on sEVs. Several lipophilic dyes display a strong fluorescent signal when incorporated into the cytosol, including DiR (1,1&#8242;-dioctadecyl-3,3,3&#8242;,3&#8242;-tetramethylindotricarbocyanine iodide), DiL (1, 1&#8242;-dioctadecyl-3, 3, 3&#8242;, 3&#8242;-tetramethyl indocarbocyanine perchlorate), and DiD (1, 1&#8242;-dioctadecyl-3, 3, 3&#8242;, 3&#8242;-tetramethyl indocarbocyanine 4-chlorobenzenesulfonate salt)8,9,10,11.
Other lipophilic dyes, such as PKH67 and PKH26, have a highly fluorescent polar head group and a long aliphatic hydrocarbon tail that readily intercalates into any lipid structure and leads to long-term dye retention and stable fluorescence12. PKH dyes can also label EVs, which allows the study of EV properties in vivo13. Many other dyes have been used to observe exosomes using fluorescence microscopy and flow cytometry, including lipid-labeling dyes14 and cell-permeable dyes such as carboxyfluorescein diacetate succinimidyl ester (CFDA-SE)15,16 and calcein acetoxymethyl (AM) ester17.
Studies of sEV-mediated crosstalk between different cells in the CNS have provided important insights on the pathogenesis of neuroinflammatory and neurodegenerative diseases18. For example, sEVs from neurons can spread beta-amyloid peptides and phosphorylated tau proteins and aid in the pathogenesis of Alzheimer&#39;s disease19. Additionally, EVs derived from erythrocytes contain large amounts of alpha-synuclein and can cross the blood-brain barrier and contribute to Parkinson&#39;s pathology20. The ability of sEVs to cross physiological barriers21 and transfer their biomolecules to target cells makes them convenient tools to deliver therapeutic drugs to the CNS22.
Visualizing sEV uptake by myriad CNS cells in the spinal cord will enable both mechanistic studies and the evaluation of the therapeutic benefits of exogenously administered sEVs from various cellular sources. This paper describes the methodology to label sEVs derived from macrophages and image their uptake in vitro and in vivo in the lumbar spinal cord by neurons, microglia, and astrocytes to qualitatively confirm sEV delivery by visualization.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Amicon Ultra 0.5 mL centrifugal filters</td>
			<td>MilliporeSigma</td>
			<td>Z677094</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-Alix Antibody</td>
			<td>Abcam</td>
			<td>ab186429</td>
			<td>1:1000</td>
		</tr>
		<tr>
			<td>Anti-Calnexin Antibody</td>
			<td>Abcam</td>
			<td>Ab10286</td>
			<td>1:1000</td>
		</tr>
		<tr>
			<td>Anti-CD81 Antibody</td>
			<td>Santa Cruz Biotechnology</td>
			<td>sc-166029</td>
			<td>1:1000</td>
		</tr>
		<tr>
			<td>Anti-GAPDH Monoclonal Antibody (14C10)</td>
			<td>Cell Signaling Technology</td>
			<td>2118</td>
			<td>1:1000</td>
		</tr>
		<tr>
			<td>Anti-Glial Fibrillary Acidic Protein Antibody</td>
			<td>Sigma-Aldrich</td>
			<td>MAB360</td>
			<td>1:500 for IF; 1:1000 for IHC</td>
		</tr>
		<tr>
			<td>Anti-Iba1 Antibody</td>
			<td>Wako</td>
			<td>019-19741</td>
			<td>1:2000</td>
		</tr>
		<tr>
			<td>Anti-MAP2A Antibody</td>
			<td>Sigma-Aldrich</td>
			<td>MAB378</td>
			<td>1:500</td>
		</tr>
		<tr>
			<td>Bovine Serum Albumin (BSA)</td>
			<td>VWR</td>
			<td>0332</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell Strainer, 40 &#956;m</td>
			<td>VWR</td>
			<td>15-1040-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge Tubes</td>
			<td>Thermo Scientific</td>
			<td>3118-0050</td>
			<td>12,000 x g</td>
		</tr>
		<tr>
			<td>Coverslip, 12-mm, #1.5</td>
			<td>Electron Microscopy Sciences</td>
			<td>72230-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Coverslip, 18-mm, #1.5</td>
			<td>Electron Microscopy Sciences</td>
			<td>72222-01</td>
			<td></td>
		</tr>
		<tr>
			<td>DAPI</td>
			<td>Sigma-Aldrich</td>
			<td>D9542-1MG</td>
			<td>1 &#181;g/mL</td>
		</tr>
		<tr>
			<td>DC Protein Assay</td>
			<td>Bio-Rad</td>
			<td>500-0116</td>
			<td></td>
		</tr>
		<tr>
			<td>Deoxyribonuclease I (DNAse I)</td>
			<td>MilliporeSigma</td>
			<td>D4513-1VL</td>
			<td></td>
		</tr>
		<tr>
			<td>Donkey Anti-Rabbit IgG H&#38;L (HRP)</td>
			<td>Abcam</td>
			<td>ab16284</td>
			<td>1:10000</td>
		</tr>
		<tr>
			<td>Donkey Anti-Rabbit IgG H&#38;L, Alexa Fluor 488</td>
			<td>Invitrogen</td>
			<td>A-21206</td>
			<td>1:500</td>
		</tr>
		<tr>
			<td>Double Frosted Microscope Slides, #1</td>
			<td>Thermo Scientific</td>
			<td>12-552-5</td>
			<td></td>
		</tr>
		<tr>
			<td>DPBS without Calcium and Magnesium</td>
			<td>Corning</td>
			<td>21-031-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s Modified Eagle Medium (DMEM)</td>
			<td>Corning</td>
			<td>10-013-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>Exosome-Depleted Fetal Bovine Serum</td>
			<td>Gibco</td>
			<td>A27208-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum (FBS)</td>
			<td>Corning</td>
			<td>35-011-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>FluorChem M imaging system</td>
			<td>ProteinSimple</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>FV3000 Confocal Microscope</td>
			<td>Olympus</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Goat Anti-Mouse IgG H&#38;L (HRP)</td>
			<td>Abcam</td>
			<td>ab6789</td>
			<td>1:10000</td>
		</tr>
		<tr>
			<td>Goat Anti-Mouse IgG H&#38;L, Alexa Fluor 488</td>
			<td>Invitrogen</td>
			<td>A-11001</td>
			<td>1:500</td>
		</tr>
		<tr>
			<td>Goat Anti-Mouse IgG1, Alexa Fluor 594</td>
			<td>Invitrogen</td>
			<td>A-21125</td>
			<td></td>
		</tr>
		<tr>
			<td>Hank&#39;s Balanced Salt Solution (HBSS)</td>
			<td>VWR</td>
			<td>02-0121</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Gibco</td>
			<td>15630080</td>
			<td></td>
		</tr>
		<tr>
			<td>HRP Substrate</td>
			<td>Thermo Scientific</td>
			<td>34094</td>
			<td></td>
		</tr>
		<tr>
			<td>Intercept blocking buffer, TBS</td>
			<td>LI-COR Biosciences</td>
			<td>927-60001</td>
			<td></td>
		</tr>
		<tr>
			<td>Laemmli SDS Sample Buffer</td>
			<td>Alfa Aesar</td>
			<td>AAJ61337AC</td>
			<td></td>
		</tr>
		<tr>
			<td>Micro Cover Glass, #1</td>
			<td>VWR</td>
			<td>48404-454</td>
			<td></td>
		</tr>
		<tr>
			<td>Microm HM550</td>
			<td>Thermo Scientific</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>NanoSight NS300 system</td>
			<td>Malvern Panalytical</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>NanoSight NTA 3.2 software</td>
			<td>Malvern Panalytical</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Neuro-2a Cell Line</td>
			<td>ATCC</td>
			<td>CCL-131</td>
			<td></td>
		</tr>
		<tr>
			<td>Normal Goat Serum</td>
			<td>Vector Laboratories</td>
			<td>S-1000</td>
			<td></td>
		</tr>
		<tr>
			<td>O.C.T Compound</td>
			<td>Sakura Finetek</td>
			<td>4583</td>
			<td></td>
		</tr>
		<tr>
			<td>Papain</td>
			<td>Worthington Biochemical Corporation</td>
			<td>NC9597281</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Electron Microscopy Sciences</td>
			<td>19210</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin</td>
			<td>Gibco</td>
			<td>15140122</td>
			<td></td>
		</tr>
		<tr>
			<td>PKH26</td>
			<td>Sigma-Aldrich</td>
			<td>MINI26-1KT</td>
			<td></td>
		</tr>
		<tr>
			<td>PKH67</td>
			<td>Sigma-Aldrich</td>
			<td>MINI67-1KT</td>
			<td></td>
		</tr>
		<tr>
			<td>Protease Inhibitor Cocktail</td>
			<td>Thermo Scientific</td>
			<td>1862209</td>
			<td></td>
		</tr>
		<tr>
			<td>PVDF Transfer Membrane</td>
			<td>MDI</td>
			<td>SVFX8302XXXX101</td>
			<td></td>
		</tr>
		<tr>
			<td>RAW 267.4 Cell Line</td>
			<td>ATCC</td>
			<td>TIB-71</td>
			<td></td>
		</tr>
		<tr>
			<td>RIPA Buffer</td>
			<td>Sigma-Aldrich</td>
			<td>R0278</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Chloride</td>
			<td>AMRESCO</td>
			<td>0241-2.5KG</td>
			<td></td>
		</tr>
		<tr>
			<td>Superfrost Plus Gold Slides</td>
			<td>Thermo Scientific</td>
			<td>15-188-48</td>
			<td>adhesive slides</td>
		</tr>
		<tr>
			<td>T-75 Flasks</td>
			<td>Corning</td>
			<td>431464U</td>
			<td></td>
		</tr>
		<tr>
			<td>Tecnai 12 Digital Transmission Electron Microscope</td>
			<td>FEI Company</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>TEM Grids</td>
			<td>Electron Microscopy Sciences</td>
			<td>FSF300-cu</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris-Glycine Protein Gel, 12%</td>
			<td>Invitrogen</td>
			<td>XP00120BOX</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris-Glycine SDS Running Buffer</td>
			<td>Invitrogen</td>
			<td>LC26755</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris-Glycine Transfer Buffer</td>
			<td>Invitrogen</td>
			<td>LC3675</td>
			<td></td>
		</tr>
		<tr>
			<td>TrypLE Express</td>
			<td></td>
			<td>cell dissociation enzyme</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Acros Organics</td>
			<td>327371000</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin, 0.25%</td>
			<td>Corning</td>
			<td>25-053-CL</td>
			<td></td>
		</tr>
		<tr>
			<td>Tween 20</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Ultracentrifuge Tubes</td>
			<td>Beckman</td>
			<td>344058</td>
			<td>110,000 x g</td>
		</tr>
	</tbody>
</table>

uptake of fluorescent labeled small extracellular vesicles in vitro and in spinal cord

Small extracellular vesicles (sEVs) are 50-150 nm vesicles secreted by all cells and present in bodily fluids. sEVs transfer biomolecules such as RNA, proteins, and lipids from donor to acceptor cells, making them key signaling mediators between cells. In the central nervous system (CNS), sEVs can mediate intercellular signaling, including neuroimmune interactions. sEV functions can be studied by tracking the uptake of labeled sEVs in recipient cells both in vitro and in vivo. This paper describes the labeling of sEVs from the conditioned media of RAW 264.7 macrophage cells using a PKH membrane dye. It shows the uptake of different concentrations of labeled sEVs at multiple time points by Neuro-2a cells and primary astrocytes in vitro. Also shown is the uptake of sEVs delivered intrathecally in mouse spinal cord neurons, astrocytes, and microglia visualized by confocal microscopy. The representative results demonstrate time-dependent variation in the uptake of sEVs by different cells, which can help confirm successful sEVs delivery into the spinal cord.

After the isolation of sEVs from RAW 264.7 conditioned media via centrifugation, NTA was used to determine the concentration and size distribution of the purified sEVs. The average mean size of RAW 264.7-derived sEVs was 140 nm, and the peak particle size was 121.8 nm, confirming that most detectable particles in the light scattering measurement fell within the size range of exosomes or sEVs at 50-150 nm (Figure 1A). As suggested in the minimal information for studies of extracellular vesicl...

Watch this Scientific Journal Video about Uptake of Fluorescent Labeled Small Extracellular Vesicles In Vitro and in Spinal Cord at JoVE.com

Uptake of Fluorescent Labeled Small Extracellular Vesicles In Vitro and in Spinal Cord

We describe a protocol to label macrophage-derived small extracellular vesicles with PKH dyes and observe their uptake in vitro and in the spinal cord after intrathecal delivery.

Uptake of Fluorescent Labeled Small Extracellular Vesicles In Vitro and in Spinal Cord

Small extracellular vesicles (sEVs) are 50-150 nm vesicles secreted by all cells and present in bodily fluids. sEVs transfer biomolecules such as RNA, ...

Visualizing uptake of small extracellular vesicles, also known as sEVs, by different cells in the spinal cord, can confirm a successful delivery of sEVs. This enables both mechanistic and therapeutic studies of intrathecally administered sEVs from various sources in roden models. This protocol can be used to visualize sEVs uptake by cells in a mild spinal cord, and can help evaluate the role of sEVs and its cargo molecules in spinal disorders, pain and inflammation.This procedure will be demonstrated by me, along with and Xuan Luo a nd Zhucheng Lin, the two graduate students in Dr Seena Ajit's lab. Begin by placing 18 millimeter cover slips in the 12 well plate, then plate neuro-2a cells in each well with a total of 1 milliliter of complete DMEM containing 10%FBS and 1%pen strep. When the cell count fluency has reached 80 to 90%change the medium to DMEM exosome depleted medium in each well add one, 5 or 10 micrograms of labeled sEVs.For 1, 4 and 24 hours. For dose and time dependent uptake to the rest of the wells at an equal volume of dye control. Collect the brains of postnatal pups in a 60 millimeter, Petri dish containing ice cold Hanks balanced salt solution supplemented with 10 millimolar hepes, dissect both the cortical lobes and remove the meninges.Then mince the tissues with a sterilized blade. Transfer the tissues into a 15 milliliter conical tube containing Pepane or deoxyribonucleus one dissociation buffer and incubate for 20 minutes at 37 degrees Celsius, swirling the tube every 5 minutes, aspirate the supernatant and add 5 milliliters of complete DMEM to the tube. To inactivate the enzyme activity, try to rate carefully to dissociate the tissues with a 5 milliliter glass serological pipette, and a flame polished pasture pipette.Pass the cell suspension through a 40 micrometer cell strainer, and then centrifuge the cells at 250 times G for 5 minutes at 4 degrees Celsius, aspirate the medium and see the cells in 10 milliliters of complete DMEM in a 75 square centimeter flask. After 4 hours of plating, replace the supernate and medium with 15 milliliters of fresh DMEM medium. After 14 days in vitro to detach the microglia and oligodendrocytes, transfer the flask to an orbital shaker at 320 RPM for 6 hours.Use 5 milliliters of the cell dissociation enzyme for 10 minutes at 37 degrees Celsius. To tripsinize, the remaining astrocytes, to inactivate the enzymatic action, add a 5 milliliters of complete DMEM and then pellet the cells at 250 times G for 5 minutes at 4 degrees Celsius. Resuspend the cells in complete DMEM and see the cells on the 12 millimeter number 1.5 cover slips in a 24 well plate.Using PBS rinse the cells 3 times and then fix them with 4%power formaldehyde or PFA in PBS for 10 minutes at room temperature. Wash the fixed cells 3 times for 5 minutes with PBS and permeabilize them using 0.1%Triton X 100 in PBS for 10 to 15 minutes. Then repeat the washes with PBS.Use 5%normal goat serum or NGS in PBS for 1 hour at room temperature to block the cells, incubate the neuro-2a cells with map two-way antibodies and the primary astrocytes with GFAP antibodies at a 1 to 500 ratio in fresh 5%NGS or PBS overnight at 4 degrees Celsius with gentle shaking. After washing the cells 3 times in PBS, add the fluorophore conjugated secondary antibodies in 5%NGS. Incubate for 2 hours at room temperature protected from light on a rocker.Repeat the washing with PBS and incubate the cell with 1 microgram per milliliter of DAPI for 10 minutes at room temperature. Once again, wash the cells 3 times with PBS. Using an anti fade mounting medium, mount the cover slips on number 1 slides, let them dry overnight in the dark and store the prepared glass slides at 4 degrees Celsius until imaging on a confocal microscope.Dissect the spinal cord and fix it in 4%PFA in PBS at 4 degrees Celsius for 24 hours. Prior protect the tissues in 30%sucrose in PBS at 4 degrees Celsius for 24 hours or until the tissues sink and then store the tissues at 4 degrees Celsius until immunohistochemistry, imbed the L4 L5 spinal cord in OCT compound, then freeze it on dry ice until it is completely solidified. Use a cryostat to section the tissues at 30 micrometres and the collect the sections in a 24 well plate containing PBS.Wash the sections 3 times for 5 minutes each with 0.3%Triton in PBS, Block the non-specific binding sites using 5%MGS in 0.3%Triton PBS for 2 hours at room temperature. Incubate the sections overnight at 4 degrees Celsius on a shaker. Wash the sections 3 times for 5 minutes with 0.3%Triton in Pbs.Then add the appropriate concentration of the secondary antibodies. According to the text manuscript, incubate at room temperature for two hours, wash the sections using only PBS and incubate them in 1 microgram per milliliter of DAPI for 10 minutes at room temperature. Then repeat the PBS washes under a light microscope, mount the sections on a clear adhesive slide with a fine paint brush.Wet the cover slip with the mounting medium and cure overnight in the dark at room temperature, acquire images under a confocal microscope with the respective lasers, The average mean size of RA 2 6 4 0.7 derived sEVs was 140 nanometers and the peak particle size was 121.8 nanometers. With the most detectable particles falling within the size range of exosomes or sEVS. At 50 to 150 nanometers, western blotting of sEVs, Cell Lysate and exodepleted Media, demonstrated that sEV derived protein samples contained the sEV marker proteins Alix CD81 and GAPDH.The cell lysate was enriched with endoplasmic reticulum, resident protein Calnexin thus Calnexin served as a negative marker for cellular contamination as it was absent in the sEVs. It was observed that the uptake of sEVs occurred at 1 hour and for the 1, 5 and 10 microgram sEVs, post incubation fluorescence could be detected at 4 hours, for 4, 5, and 10 micrograms of sEVs. The uptake of PKH 26 labeled sEVs by primary astrocytes was examined and maximum fluorescence from sEVS uptake in primary cortical astrocytes occurred at 24 hours PKH26-labeled sEVs were taken up and maximum fluorescence was observed at 6 hours, post-injection in neurons astrocytes and microglial cells.The inclusion of controls, unlabeled sEVs, and dye control it create code to a wind false positive recent signals due to now specific labeling Opry dance of Unbound dye patch coasts. The uptake of seVs can be confirmed by investigating biomolecular cargo transfer to recipe and cells and tissues and determining the changes in expression levels of biomolecules or target genes. Behavior studies can also be performed, to investigate the functional impact of sEV delivery.

uptake-fluorescent-labeled-small-extracellular-vesicles-vitro-spinal

Research

JoVE Journal

Neuroscience

Dissection and Culture of Commissural Neurons from Embryonic Spinal Cord

Commissural neurons have been widely used to investigate the mechanisms underlying axon guidance during embryonic spinal cord development. The cell bodies of these neurons are located in the dorsal spinal cord and their axons follow stereotyped trajectories during embryonic development. Commissural axons initially project ventrally towards the floorplate. After crossing the midline, these axons turn anteriorly and project towards the brain. Each of these steps is regulated by the action of several guidance cues. Cultures highly enriched in commissural neurons are ideally suited for many experiments addressing the mechanisms of axon pathfinding, including turning assays, immunochemistry and biochemistry. Here, we describe a method to dissect and culture commissural neurons from E13 rat dorsal spinal cord. First, the spinal cord is isolated and dorsal strips are dissected out. The dorsal tissue is then dissociated into a cell suspension by trypsinization and mechanical disruption. Neurons are plated onto poly-L-lysine-coated glass coverslips or tissue-culture dishes. After 30 hours in vitro, most neurons have extended an axon. The purity of the culture (Yam et al. 2009), typically over 90%, can be assessed by immunolabeling with the commissural neuron markers DCC, LH2 and TAG1 (Helms and Johnson, 1998). This neuronal preparation is a useful tool for in vitro studies of the cellular and molecular mechanisms of commissural axon growth and guidance during spinal cord development.

This video demonstrates a method to dissect and culture commissural neurons from E13 rat dorsal spinal cord. Dissociated commissural neurons are useful to study the cellular and molecular mechanisms of axon growth and guidance.

Commissural neurons have been widely used to investigate the mechanisms underlying axon guidance during embryonic spinal cord development. The cell bodies ...

Spinal Cord Electrophysiology II: Extracellular Suction Electrode Fabrication

Development of neural circuitries and locomotion can be studied using neonatal rodent spinal cord central pattern generator (CPG) behavior. We demonstrate a method to fabricate suction electrodes that are used to examine CPG activity, or fictive locomotion, in dissected rodent spinal cords. The rodent spinal cords are placed in artificial cerebrospinal fluid and the ventral roots are drawn into the suction electrode. The electrode is constructed by modifying a commercially available suction electrode. A heavier silver wire is used instead of the standard wire given by the commercially available electrode. The glass tip on the commercial electrode is replaced with a plastic tip for increased durability. We prepare hand drawn electrodes and electrodes made from specific sizes of tubing, allowing consistency and reproducibility. Data is collected using an amplifier and neurogram acquisition software. Recordings are performed on an air table within a Faraday cage to prevent mechanical and electrical interference, respectively.

A demonstration of the fabrication and use of an extracellular suction electrode used to measure electrophysiological recordings of neonatal rodent spinal cords in vitro

Development of neural circuitries and locomotion can be studied using neonatal rodent spinal cord central pattern generator (CPG) behavior. We demonstrate ...

Lateral Fluid Percussion: Model of Traumatic Brain Injury in Mice

Traumatic brain injury (TBI) research has attained renewed momentum due to the increasing awareness of head injuries, which result in morbidity and mortality. Based on the nature of primary injury following TBI, complex and heterogeneous secondary consequences result, which are followed by regenerative processes 1,2. Primary injury can be induced by a direct contusion to the brain from skull fracture or from shearing and stretching of tissue causing displacement of brain due to movement 3,4. The resulting hematomas and lacerations cause a vascular response 3,5, and the morphological and functional damage of the white matter leads to diffuse axonal injury 6-8. Additional secondary changes commonly seen in the brain are edema and increased intracranial pressure 9. Following TBI there are microscopic alterations in biochemical and physiological pathways involving the release of excitotoxic neurotransmitters, immune mediators and oxygen radicals 10-12, which ultimately result in long-term neurological disabilities 13,14. Thus choosing appropriate animal models of TBI that present similar cellular and molecular events in human and rodent TBI is critical for studying the mechanisms underlying injury and repair.
Various experimental models of TBI have been developed to reproduce aspects of TBI observed in humans, among them three specific models are widely adapted for rodents: fluid percussion, cortical impact and weight drop/impact acceleration 1. The fluid percussion device produces an injury through a craniectomy by applying a brief fluid pressure pulse on to the intact dura. The pulse is created by a pendulum striking the piston of a reservoir of fluid. The percussion produces brief displacement and deformation of neural tissue 1,15. Conversely, cortical impact injury delivers mechanical energy to the intact dura via a rigid impactor under pneumatic pressure 16,17. The weight drop/impact model is characterized by the fall of a rod with a specific mass on the closed skull 18. Among the TBI models, LFP is the most established and commonly used model to evaluate mixed focal and diffuse brain injury 19. It is reproducible and is standardized to allow for the manipulation of injury parameters. LFP recapitulates injuries observed in humans, thus rendering it clinically relevant, and allows for exploration of novel therapeutics for clinical translation 20.
We describe the detailed protocol to perform LFP procedure in mice. The injury inflicted is mild to moderate, with brain regions such as cortex, hippocampus and corpus callosum being most vulnerable. Hippocampal and motor learning tasks are explored following LFP.

Lateral fluid percussion (LFP), an established model of traumatic brain injury in mice, is demonstrated. LFP fulfills three major criteria for animal models: validity, reliability and clinical relevance. The procedure, consisting of surgical craniotomy, fixation of hub followed by induction of injury, resulting in focal and diffuse injuries, is described.

Traumatic brain injury (TBI) research has attained renewed momentum due to the increasing awareness of head injuries, which result in morbidity and ...

Retrograde Fluorescent Labeling Allows for Targeted Extracellular Single-unit Recording from Identified Neurons In vivo

The overall goal of this method is to record single-unit responses from an identified population of neurons. In vivo electrophysiological recordings from individual neurons are critical for understanding how neural circuits function under natural conditions. Traditionally, these recordings have been performed 'blind', meaning the identity of the recorded cell is unknown at the start of the recording. Cellular identity can be subsequently determined via intracellular1, juxtacellular2 or loose-patch3 iontophoresis of dye, but these recordings cannot be pre-targeted to specific neurons in regions with functionally heterogeneous cell types. Fluorescent proteins can be expressed in a cell-type specific manner permitting visually-guided single-cell electrophysiology4-6. However, there are many model systems for which these genetic tools are not available. Even in genetically accessible model systems, the desired promoter may be unknown or genetically homogenous neurons may have varying projection patterns. Similarly, viral vectors have been used to label specific subgroups of projection neurons7, but use of this method is limited by toxicity and lack of trans-synaptic specificity. Thus, additional techniques that offer specific pre-visualization to record from identified single neurons in vivo are needed. Pre-visualization of the target neuron is particularly useful for challenging recording conditions, for which classical single-cell recordings are often prohibitively difficult8-11. The novel technique described in this paper uses retrograde transport of a fluorescent dye applied using tungsten needles to rapidly and selectively label a specific subset of cells within a particular brain region based on their unique axonal projections, thereby providing a visual cue to obtain targeted electrophysiological recordings from identified neurons in an intact circuit within a vertebrate CNS.
The most significant novel advancement of our method is the use of fluorescent labeling to target specific cell types in a non-genetically accessible model system. Weakly electric fish are an excellent model system for studying neural circuits in awake, behaving animals12. We utilized this technique to study sensory processing by "small cells" in the anterior exterolateral nucleus (ELa) of weakly electric mormyrid fish. "Small cells" are hypothesized to be time comparator neurons important for detecting submillisecond differences in the arrival times of presynaptic spikes13. However, anatomical features such as dense myelin, engulfing synapses, and small cell bodies have made it extremely difficult to record from these cells using traditional methods11, 14. Here we demonstrate that our novel method selectively labels these cells in 28% of preparations, allowing for reliable, robust recordings and characterization of responses to electrosensory stimulation.

Retrograde Fluorescent Labeling Allows for Targeted Extracellular Single-unit Recording from Identified Neurons In vivo

Retrograde transport of fluorescent dye labels a sub-population of neurons based on anatomical projection. Labeled axons can be visually targeted in vivo, permitting extracellular recording from identified axons. This technique facilitates recording when neurons cannot be labeled through genetic manipulation or are difficult to isolate using 'blind' in vivo approaches.

The overall goal of this method is to record single-unit responses from an identified population of neurons. In vivo electrophysiological recordings from ...

Spinal Cord Transection in the Larval Zebrafish

Mammals fail in sensory and motor recovery following spinal cord injury due to lack of axonal regrowth below the level of injury as well as an inability to reinitiate spinal neurogenesis. However, some anamniotes including the zebrafish Danio rerio exhibit both sensory and functional recovery even after complete transection of the spinal cord. The adult zebrafish is an established model organism for studying regeneration following spinal cord injury, with sensory and motor recovery by 6&#160;weeks post-injury. To take advantage of in vivo analysis of the regenerative process available in the transparent larval zebrafish as well as genetic tools not accessible in the adult, we use the larval zebrafish to study regeneration after spinal cord transection. Here we demonstrate a method for reproducibly and verifiably transecting the larval spinal cord. After transection, our data shows sensory recovery beginning at 2&#160;days post-injury (dpi), with the C-bend movement detectable by 3 dpi and resumption of free swimming by 5 dpi. Thus we propose the larval zebrafish as a companion tool to the adult zebrafish for the study of recovery after spinal cord injury.

After spinal transection, adult zebrafish have functional recovery by six weeks post-injury. To take advantage of larval transparency and faster recovery, we present a method for transecting the larval spinal cord. After transection, we observe sensory recovery beginning at 2&#160;days post-injury, and C-bend movement by 3 days post-injury.

Mammals fail in sensory and motor recovery following spinal cord injury due to lack of axonal regrowth below the level of injury as well as an inability ...

An Ex Vivo Laser-induced Spinal Cord Injury Model to Assess Mechanisms of Axonal Degeneration in Real-time

Injured CNS axons fail to regenerate and often retract away from the injury site. Axons spared from the initial injury may later undergo secondary axonal degeneration. Lack of growth cone formation, regeneration, and loss of additional myelinated axonal projections within the spinal cord greatly limits neurological recovery following injury. To assess how central myelinated axons of the spinal cord respond to injury, we developed an ex vivo living spinal cord model utilizing transgenic mice that express yellow fluorescent protein in axons and a focal and highly reproducible laser-induced spinal cord injury to document the fate of axons and myelin (lipophilic fluorescent dye Nile Red) over time using two-photon excitation time-lapse microscopy. Dynamic processes such as acute axonal injury, axonal retraction, and myelin degeneration are best studied in real-time. However, the non-focal nature of contusion-based injuries and movement artifacts encountered during in vivo spinal cord imaging make differentiating primary and secondary axonal injury responses using high resolution microscopy challenging. The ex vivo spinal cord model described here mimics several aspects of clinically relevant contusion/compression-induced axonal pathologies including axonal swelling, spheroid formation, axonal transection, and peri-axonal swelling providing a useful model to study these dynamic processes in real-time. Major advantages of this model are excellent spatiotemporal resolution that allows differentiation between the primary insult that directly injures axons and secondary injury mechanisms; controlled infusion of reagents directly to the perfusate bathing the cord; precise alterations of the environmental milieu (e.g., calcium, sodium ions, known contributors to axonal injury, but near impossible to manipulate in vivo); and murine models also offer an advantage as they provide an opportunity to visualize and manipulate genetically identified cell populations and subcellular structures. Here, we describe how to isolate and image the living spinal cord from mice to capture dynamics of acute axonal injury.

An Ex Vivo Laser-induced Spinal Cord Injury Model to Assess Mechanisms of Axonal Degeneration in Real-time

We present a protocol utilizing two-photon excitation time-lapse microscopy to simultaneously visualize the dynamics of axon and myelin injuries in real time. This proposed protocol permits studies of both intrinsic and extrinsic factors which can influence central myelinated axon fate after injury and contribute to permanent clinical disability.

Injured CNS axons fail to regenerate and often retract away from the injury site. Axons spared from the initial injury may later undergo secondary axonal ...

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

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

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

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

Imaging Neural Activity in the Primary Somatosensory Cortex Using Thy1-GCaMP6s Transgenic Mice

The mammalian brain exhibits marked symmetry across the sagittal plane. However, detailed description of neural dynamics in symmetric brain regions in adult mammalian animals remains elusive. In this study, we describe an experimental procedure for measuring calcium dynamics through dual optical windows above bilateral primary somatosensory corticies (S1) in Thy1-GCaMP6s transgenic mice using 2-photon (2P) microscopy. This method enables recordings and quantifications of neural activity in bilateral mouse brain regions one at a time in the same experiment for a prolonged period in vivo. Key aspects of this method, which can be completed within an hour, include minimally invasive surgery procedures for creating dual optical windows, and the use of 2P imaging. Although we only demonstrate the technique in the S1 area, the method can be applied to other regions of the living brain facilitating the elucidation of structural and functional complexities of brain neural networks.

Imaging Neural Activity in the Primary Somatosensory Cortex Using Thy1-GCaMP6s Transgenic Mice

We describe an experimental procedure for measuring neuronal activity through dual optical windows above bilateral primary somatosensory corticies (S1) in Thy1-GCaMP6s transgenic mice using 2-photon (2P) microscopy in vivo.

The mammalian brain exhibits marked symmetry across the sagittal plane. However, detailed description of neural dynamics in symmetric brain regions in ...

Laminectomy and Spinal Cord Window Implantation in the Mouse

This protocol describes a method for spinal cord laminectomy and glass window implantation for in vivo imaging of the mouse spinal cord. An integrated digital vaporizer is utilized to achieve a stable plane of anesthesia at a low-flow rate of isoflurane. A single vertebral spine is removed, and a commercially available cover-glass is overlaid on a thin agarose bed. A 3D-printed plastic backplate is then affixed to the adjacent vertebral spines using tissue adhesive and dental cement. A stabilization platform is used to reduce motion artifact from respiration and heartbeat. This rapid and clamp-free method is well-suited for acute multi-photon fluorescence microscopy. Representative data are included for an application of this technique to two-photon microscopy of the spinal cord vasculature in transgenic mice expressing eGFP:Claudin-5 &#8212; a tight junction protein.

This protocol describes implantation of a glass window onto the spinal cord of a mouse to facilitate visualization by intravital microscopy.

This protocol describes a method for spinal cord laminectomy and glass window implantation for in vivo imaging of the mouse spinal cord. An integrated ...

Preparation of Rhythmically-active In Vitro Neonatal Rodent Brainstem-spinal Cord and Thin Slice

Mammalian inspiratory rhythm is generated from a neuronal network in a region of the medulla called the preB&#246;tzinger complex (pBC), which produces a signal driving the rhythmic contraction of inspiratory muscles. Rhythmic neural activity generated in the pBC and carried to other neuronal pools to drive the musculature of breathing may be studied using various approaches, including en bloc nerve recordings and transverse slice recordings. However, previously published methods have not extensively described the brainstem-spinal cord dissection process in a transparent and reproducible manner for future studies. Here, we present a comprehensive overview of a method used to reproducibly cut rhythmically-active brainstem slices containing the necessary and sufficient neuronal circuitry for generating and transmitting inspiratory drive. This work builds upon previous brainstem-spinal cord electrophysiology protocols to enhance the likelihood of reliably obtaining viable and rhythmically-active slices for recording neuronal output from the pBC, hypoglossal premotor neurons (XII pMN), and hypoglossal motor neurons (XII MN). The work presented expands upon previous published methods by providing detailed, step-by-step illustrations of the dissection, from whole rat pup, to in vitro slice containing the XII rootlets.

This protocol both visually communicates the brainstem-spinal cord preparation and clarifies the preparation of brainstem transverse slices in a comprehensive step-by-step manner. It was designed to increase reproducibility and enhance the likelihood of obtaining viable, long lasting, rhythmically-active slices for recording neural output from the respiratory regions of the brainstem.

Mammalian inspiratory rhythm is generated from a neuronal network in a region of the medulla called the preB&#246;tzinger complex (pBC), which produces a ...