The study was supported by grants from the National Natural Science Foundation of China (81960226,81760223); the Natural Science Foundation of Yunnan Province (202001AS070045,202301AY070001-011)

The experimental protocol was approved by the Animal Ethics and Use Committee of Kunming Medical University (kmmu20220945). Sprague-Dawley (SD) rats of both sexes, 300-350 g, were used for the present study.
1. Inducing the SAH model
<ol>
	<li>Anesthetize the rats using 2% isoflurane and 100% oxygen. Maintain anesthesia by supplying continuous inhalation anesthesia with isoflurane (1%-3%). Secure the rat&#39;s head using a stereotaxic apparatus (see Table of Materials).</li>
	<li>Create the SAH model following the steps below.
	<ol>
		<li>Insert a microinjection needle into the suprasellar cistern. Then, inject autologous blood from the rat&#39;s tail artery (without anticoagulant) into the suprasellar cistern using a syringe pump (see Table of Materials).</li>
		<li>Implant a microinjection needle into the right lateral cerebral ventricle using the mentioned coordinates: bregma, &#8722;0.8 mm; lateral, 1.4 mm; depth, 4 mm9. For SAH groups, inject 0.2 mL of rat tail artery blood. For sham groups, administer the same volume of isotonic saline (Figure 1A).</li>
	</ol>
	</li>
</ol>
2. Brain slice preparation and stabilization
<ol>
	<li>Deeply anesthetize the rats using 2% isoflurane inhalation. After decapitation, extract the entire brains and immerse them in ice-cold artificial cerebrospinal fluid (ACSF). 
	NOTE: Use freshly prepared ACSF solutions with the following composition: 134 mM NaCl, 2.8 mM KCl, 29 mM NaHCO3, 1.1 mM NaH2PO4, 1.5 mM MgSO4, 2.5 mM CaCl2, and 10.11 mM D-Glucose (see Table of Materials). Maintain a pH between 7.3 and 7.4.</li>
	<li>Use a vibratome (see Table of Materials) to prepare acute brain slices with a thickness of 200 &#181;m from the SD rats in ice-cold ACSF that&#39;s aerated with 5% CO2 and 95% O2 (Figure 2).</li>
	<li>Place the 200 &#181;m-thick acute brain slices in a storage chamber on a nylon mesh submerged in ACSF. Equilibrate the ACSF solution with 95% O2 and 5% CO2, maintaining a temperature range of 35-37 &#176;C. Allow brain slices to stabilize for 2 h, giving them time to adjust (Figure 3).</li>
</ol>
3. Labeling pericytes in acute brain slices with TO-PRO-3
NOTE: Pericytes from acute brain slices were fluorescently labeled using the tracer TO-PRO-310.
<ol>
	<li>Add the fluorescent dye TO-PRO-3 to the ACSF, achieving a final concentration of 1 &#181;M. Incubate the acute brain slices at room temperature in a dark environment with the TO-PRO-3-containing ACSF for 20 min. 
	NOTE: Remember to wear latex gloves while handling TO-PRO-3 for protection.</li>
	<li>Transfer the nylon mesh strainer, carrying the brain slices, from the loading chamber to a 6-well plate rinsing chamber (see Table of Materials). Allow the brain slices to stay in the rinsing chamber for 10 min (Figure 4D). 
	NOTE: This rinsing step terminates the staining process, decreases background labeling, and prevents nonspecific staining.</li>
	<li>Rinse the preparations for a total of 15 min using ACSF solution that&#39;s equilibrated with a mixture of 5% CO2 and 95% O2. This rinsing step halts dye uptake and minimizes background labeling (Figure 4C).</li>
</ol>
4. Staining non-vital pericytes of cerebral microcirculation in acute brain slices
<ol>
	<li>Incubate brain slices preloaded with TO-PRO-3 at 37 &#176;C with isolectin B4 conjugated to Alexa Fluor 488 (FITC-ISOB4; 5 &#181;g/mL, see Table of Materials) for 30 min in a dark environment. After incubation, rinse the brain slices for 15 min in ACSF (Figure 4E).</li>
	<li>Incubate the brain slices in ACSF gassed with 5% CO2 and 95% O2 as usual. Add propidium iodide (PI) at a concentration of 37 &#181;M to both solutions at 37 &#176;C. This will label non-vital brain pericytes. Incubate the preparations in this ACSF solution for 60 min in the dark (Figure 4F).</li>
	<li>Next, rinse the preparations for 15 min with ACSF solutions to halt dye uptake and minimize background labeling.</li>
</ol>
5. Imaging of vital and non-vital brain pericytes in acute brain slices
<ol>
	<li>Gently transfer brain slices to glass bottom confocal dishes (see Table of Materials) using plastic Pasteur pipettes. Fill the dishes with ACSF solution previously equilibrated with 5% CO2 and 95% O2. Use an iron mesh to secure rat brain slices in place.</li>
	<li>Transfer the glass bottom confocal dishes to the stage of a confocal microscope. Position the acute brain slice at the bottom of the dish and perfuse9 it with ACSF solution equilibrated with a mixture of 95% O2 and 5% CO2 during confocal microscopy imaging (Figure 5A and Figure 5Ab&#39;).</li>
	<li>Visualize the wall cells of the cerebral cortical microvasculature using a 40x objective. Capture image stacks using compatible software (see Table of Materials). Use appropriate filters for IB4 (excitation/emission 460 nm/520 nm), PI (excitation/emission 545 nm/595 nm), and TO-PRO-3 (excitation/emission 606 nm/666 nm) (Figure 5D). 
	NOTE: Capture images with the following details: 40&#215; DIC N1 objective lens, 3 &#215; 12 bit: 512 &#215; 512 pixels (0.22 &#215; 0.22 mm), calibration: 0.42 &#181;m/px.</li>
	<li>Identify cerebral microvasculature and pericytes based on their network and morphology. Locate a specific region containing a cerebral microvasculature network on each brain slice and capture images.</li>
	<li>Carefully note the imaging location to ensure consistency in subsequent captures (Figure 5B,C). For further processing and analysis, use image analysis software (ImageJ) and photo editing software (see Table of Materials).</li>
</ol>

Visualization of Brain Pericyte Contractility Post-Subarachnoid Hemorrhage

<ol>
	<li>Dalkara, T., Gursoy-Ozdemir, Y., Yemisci, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Brain+microvascular+pericytes+in+health+and+disease.">Brain microvascular pericytes in health and disease.</a> Acta Neuropathologica. 122 (1), 1-9 (2011).</li><li>Dore-Duffy, P., Cleary, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Morphology+and+properties+of+pericytes.">Morphology and properties of pericytes.</a> Methods in Molecular Biology (Clifton, N.J). 686, 49-68 (2011).</li><li>Peppiatt, C. M., Howarth, C., Mobbs, P., Attwell, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bidirectional+control+of+CNS+capillary+diameter+by+pericytes.">Bidirectional control of CNS capillary diameter by pericytes.</a> Nature. 443 (7112), 700-704 (2006).</li><li>Attwell, D., Mishra, A., Hall, C. N., O'Farrell, F. M., Dalkara, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=What+is+a+pericyte.">What is a pericyte.</a> Journal of Cerebral Blood Flow and Metabolism: Official Journal of the International Society of Cerebral Blood Flow and Metabolism. 36 (2), 451-455 (2016).</li><li>Yemisci, M., Gursoy-Ozdemir, Y., Vural, A., Can, A., Topalkara, K., Dalkara, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pericyte+contraction+induced+by+oxidative-nitrative+stress+impairs+capillary+reflow+despite+successful+opening+of+an+occluded+cerebral+artery.">Pericyte contraction induced by oxidative-nitrative stress impairs capillary reflow despite successful opening of an occluded cerebral artery.</a> Nature Medicine. 15 (9), 1031-1037 (2009).</li><li>Korte, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Noradrenaline+released+from+locus+coeruleus+axons+contracts+cerebral+capillary+pericytes+via+&#945;2+adrenergic+receptors.">Noradrenaline released from locus coeruleus axons contracts cerebral capillary pericytes via &#945;2 adrenergic receptors.</a> Journal of Cerebral Blood Flow and Metabolism: Official Journal of the International Society of Cerebral Blood Flow and Metabolism. , (2023).</li><li>Hirunpattarasilp, C., Barkaway, A., Davis, H., Pfeiffer, T., Sethi, H., Attwell, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hyperoxia+evokes+pericyte-mediated+capillary+constriction.">Hyperoxia evokes pericyte-mediated capillary constriction.</a> Journal of Cerebral Blood Flow and Metabolism: Official Journal of the International Society of Cerebral Blood Flow and Metabolism. 42 (11), 2032-2047 (2022).</li><li>Neuhaus, A. A., Couch, Y., Sutherland, B. A., Buchan, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+method+to+study+pericyte+contractility+and+responses+to+ischaemia+in+vitro+using+electrical+impedance.">Novel method to study pericyte contractility and responses to ischaemia in vitro using electrical impedance.</a> Journal of Cerebral Blood Flow and Metabolism: Official Journal of the International Society of Cerebral Blood Flow and Metabolism. 37 (6), 2013-2024 (2017).</li><li>Gong, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increased+TRPM4+Activity+in+cerebral+artery+myocytes+contributes+to+cerebral+blood+flow+reduction+after+subarachnoid+hemorrhage+in+rats.">Increased TRPM4 Activity in cerebral artery myocytes contributes to cerebral blood flow reduction after subarachnoid hemorrhage in rats.</a> Neurotherapeutics: The Journal of the American Society for Experimental NeuroTherapeutics. 16 (3), 901-911 (2019).</li><li>Mai-Morente, S. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pericyte+mapping+in+cerebral+slices+with+the+far-red+fluorophore+TO-PRO-3.">Pericyte mapping in cerebral slices with the far-red fluorophore TO-PRO-3.</a> Bio-protocol. 11 (22), e4222 (2021).</li><li>Mai-Morente, S. P., Marset, V. M., Blanco, F., Isasi, E. E., Abudara, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+nuclear+fluorescent+dye+identifies+pericytes+at+the+neurovascular+unit.">A nuclear fluorescent dye identifies pericytes at the neurovascular unit.</a> Journal of Neurochemistry. 157 (4), 1377-1391 (2021).</li><li>Zhao, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rationale+for+the+real-time+and+dynamic+cell+death+assays+using+propidium+iodide.">Rationale for the real-time and dynamic cell death assays using propidium iodide.</a> Cytometry. Part A: The Journal of the International Society for Analytical Cytology. 77 (4), 399-405 (2010).</li><li>Van Hooijdonk, C. A., Glade, C. P., Van Erp, P. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=TO-PRO-3+iodide:+A+novel+HeNe+laser-excitable+DNA+stain+as+an+alternative+for+propidium+iodide+in+multiparameter+flow+cytometry.">TO-PRO-3 iodide: A novel HeNe laser-excitable DNA stain as an alternative for propidium iodide in multiparameter flow cytometry.</a> Cytometry. 17 (2), 185-189 (1994).</li><li>Lacar, B., Herman, P., Platel, J. C., Kubera, C., Hyder, F., Bordey, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neural+progenitor+cells+regulate+capillary+blood+flow+in+the+postnatal+subventricular+zone.">Neural progenitor cells regulate capillary blood flow in the postnatal subventricular zone.</a> The Journal of Neuroscience: The Official Journal of the Society for Neuroscience. 32 (46), 16435-16448 (2012).</li><li>Mai-Morente, S. P., Marset, V. M., Blanco, F., Isasi, E. E., Abudara, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+nuclear+fluorescent+dye+identifies+pericytes+at+the+neurovascular+unit.">A nuclear fluorescent dye identifies pericytes at the neurovascular unit.</a> Journal of Neurochemistry. 157 (4), 1377-1391 (2021).</li><li>Hezel, M., Ebrahimi, F., Koch, M., Dehghani, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Propidium+iodide+staining:+a+new+application+in+fluorescence+microscopy+for+analysis+of+cytoarchitecture+in+adult+and+developing+rodent+brain.">Propidium iodide staining: a new application in fluorescence microscopy for analysis of cytoarchitecture in adult and developing rodent brain.</a> Micron (Oxford, England). 43 (10), 1031-1038 (2012).</li><li>Mathiisen, T. M., Lehre, K. P., Danbolt, N. C., Ottersen, O. 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The authors declare that they have no competing financial interests.

Developed are high-resolution confocal imaging techniques for visualizing vital brain pericytes, non-vital brain pericytes, and the microvasculature in brain slices. In acute rat brain slices, the process entails initial labeling of pericytes with TO-PRO-311, followed by microvascular endothelial cells with IB412; subsequently, identification of deceased pericytes is conducted using PI. This protocol is straightforward, reproducible, and highly applicable for functional res...

Brain pericytes, distinguished by their slender protuberances and protruding cell bodies, encircle the microcirculation1,2. While cerebral blood flow augmentation is predominantly driven by capillary dilation, smaller arteries exhibit slower rates of dilation3. Pericyte contractility exerts influence over capillary diameter and pericyte morphology, impacting vascular dynamics4. Contraction of brain pericytes leads to capillary constriction, and in pathological scenarios, excessive contraction may impede erythrocyte flow5. Various factors, including norepinephrine released from the locus coeruleus, can induce brain pericyte contraction within capillaries6. With a regulatory role in cerebral blood flow, pericytes exhibit 20-HETE synthesis, serving as an oxygen sensor during hyperoxia7. Oxidative-nitrative stress-triggered contraction of brain pericytes detrimentally affects capillaries5. Despite both in vivo and ex vivo investigations into brain pericyte contraction8, limited knowledge persists regarding the imaging of viable and non-viable brain pericytes within brain slices.
Crucially, post-tissue fixation imaging of brain pericytes compromises their vitality and subsequent contractility assessment. Moreover, in scenarios such as neurological disorders (e.g., subarachnoid hemorrhage - SAH), transgenic labeling of brain pericytes fails to differentiate between viable and non-viable pericytes, as confirmed by our preliminary SAH-induced brain pericyte death study9. 
To surmount these challenges, we employed TO-PRO-3 to label live pericytes, while deceased ones were stained with propidium iodide (PI). We used high-resolution confocal imaging technologies to visualize viable and non-viable brain pericytes in brain slices while preserving slice activity during imaging. This article aims to present a reproducible method for imaging viable and non-viable brain pericytes in brain slices, serving as a valuable tool to probe the impact of brain pericytes on cerebral microcirculation post SAH.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>6-well plate</td>
			<td>ABC biochemistry</td>
			<td>ABC703006</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Adobe Photoshop</td>
			<td>Adobe</td>
			<td>Adobe Illustrator CS6 16.0.0</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Aluminium foil</td>
			<td>MIAOJIE</td>
			<td>225 mm x 273 mm</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>CaCl2&#183;2H2O</td>
			<td>Sigma-Aldrich</td>
			<td>C3881</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Confocal imaging software</td>
			<td>Nikon</td>
			<td>NIS-Elements 4.10.00</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Confocal Laser Scanning Microscope</td>
			<td>Nikon</td>
			<td>N-SIM/C2si</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Gas tank (5% CO2, 95% O2)</td>
			<td>PENGYIDA</td>
			<td>40L</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Glass Bottom Confocal Dishes</td>
			<td>Beyotime</td>
			<td>FCFC020-10pcs</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td>Sigma-Aldrich</td>
			<td>G5767</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Glue</td>
			<td>EVOBOND</td>
			<td>KH-502</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Ice machine</td>
			<td>XUEKE</td>
			<td>IMS-20</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Image analysis software</td>
			<td>National Institutes of Health</td>
			<td>Image J</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Inhalation anesthesia system</td>
			<td>SCIENCE</td>
			<td>QAF700</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Isolectin B 4-FITC</td>
			<td>SIGMA</td>
			<td>L2895&#8211;2MG</td>
			<td>Store aliquots at &#8211;20 &#176;C</td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Sigma-Aldrich</td>
			<td>7447&#8211;40&#8211;7</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>KH2PO4</td>
			<td>Sigma-Aldrich</td>
			<td>P0662</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>MgSO4</td>
			<td>Sigma-Aldrich</td>
			<td>M7506</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Sigma-Aldrich</td>
			<td>7647&#8211;14&#8211;5</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>NaH2PO4&#183;H2O</td>
			<td>Sigma-Aldrich</td>
			<td>10049&#8211;21&#8211;5</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>NaHCO3</td>
			<td>Sigma-Aldrich</td>
			<td>S5761</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Pasteur pipette</td>
			<td>NEST Biotechnology</td>
			<td>318314</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Peristaltic Pump</td>
			<td>Scientific Industries Inc</td>
			<td>Model 203</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Propidium (Iodide)</td>
			<td>Med Chem Express</td>
			<td>HY-D0815/CS-7538</td>
			<td>Store aliquots at &#8211;20 &#176;C</td>
		</tr>
		<tr>
			<td>Stereotaxic apparatus</td>
			<td>SCIENCE</td>
			<td>QA</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Syringe pump</td>
			<td>Harvard PUMP</td>
			<td>PUMP 11 ELITE Nanomite</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Thermostatic water bath</td>
			<td>OLABO</td>
			<td>HH-2</td>
			<td>RT</td>
		</tr>
		<tr>
			<td>Vibrating microtome</td>
			<td>Leica</td>
			<td>VT1200</td>
			<td>RT</td>
		</tr>
	</tbody>
</table>

imaging vital and non-vital brain pericytes in brain slices following subarachnoid hemorrhage

Pericytes are crucial mural cells situated within cerebral microcirculation, pivotal in actively modulating cerebral blood flow via contractility adjustments. Conventionally, their contractility is gauged by observing morphological shifts and nearby capillary diameter changes under specific circumstances. Yet, post-tissue fixation, evaluating vitality and ensuing pericyte contractility of imaged brain pericytes becomes compromised. Similarly, genetically labeling brain pericytes falls short in distinguishing between viable and non-viable pericytes, particularly in neurologic conditions like subarachnoid hemorrhage (SAH), where our preliminary investigation validates brain pericyte demise. A reliable protocol has been devised to surmount these constraints, enabling simultaneous fluorescent tagging of both functional and non-functional brain pericytes in brain sections. This labeling method allows high-resolution confocal microscope visualization, concurrently marking the brain slice microvasculature. This innovative protocol offers a means to appraise brain pericyte contractility, its impact on capillary diameter, and pericyte structure. Investigating brain pericyte contractility within the SAH context yields insightful comprehension of its effects on cerebral microcirculation.

Under normal physiological conditions, brain pericytes generally do not undergo cell death. Figure 6 illustrates this phenomenon, with yellow indicating the presence of vital brain pericytes; brain pericytes show no staining with PI, indicating their viability. To further investigate whether pericytes remain attached to the microvasculature following cell death, methods were employed in a SAH rat model, and subsequent imaging was conducted.
Methods for imaging bot...

Watch this Scientific Journal Video about Imaging Pericytes Post-Subarachnoid Hemorrhaging in Rodents at JoVE.com

Author Spotlight: Imaging Pericytes Post-Subarachnoid Hemorrhaging in Rodents 

The preliminary inquiry confirms that subarachnoid hemorrhage (SAH) causes brain pericyte demise. Evaluating pericyte contractility post-SAH requires differentiation between viable and non-viable brain pericytes. Hence, a procedure has been developed to label viable and non-viable brain pericytes concurrently in brain sections, facilitating observation using a high-resolution confocal microscope.

Imaging Vital and Non-vital Brain Pericytes in Brain Slices following Subarachnoid Hemorrhage

Pericytes are crucial mural cells situated within cerebral microcirculation, pivotal in actively modulating cerebral blood flow via contractility ...

imaging-vital-non-vital-brain-pericytes-brain-slices-following

Research

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Neuroscience

988 Views.  The First Affiliated Hospital of Kunming Medical University. The preliminary inquiry confirms that subarachnoid hemorrhage (SAH) causes brain pericyte demise. Evaluating pericyte contractility post-SAH requires differentiation between viable and non-viable brain pericytes. Hence, a procedure has been developed to label viable and non-viable brain pericytes concurrently in brain sections, facilitating observation using a high-resolution confocal microscope.

Video: Author Spotlight: Imaging Pericytes Post-Subarachnoid Hemorrhaging in Rodents 

Imaging Calcium Responses in GFP-tagged Neurons of Hypothalamic Mouse Brain Slices

Despite an enormous increase in our knowledge about the mechanisms underlying the encoding of information in the brain, a central question concerning the precise molecular steps as well as the activity of specific neurons in multi-functional nuclei of brain areas such as the hypothalamus remain. This problem includes identification of the molecular components involved in the regulation of various neurohormone signal transduction cascades. Elevations of intracellular Ca2+ play an important role in regulating the sensitivity of neurons, both at the level of signal transduction and at synaptic sites.
New tools have emerged to help identify neurons in the myriad of brain neurons by expressing green fluorescent protein (GFP) under the control of a particular promoter. To monitor both spatially and temporally stimulus-induced Ca2+ responses in GFP-tagged neurons, a non-green fluorescent Ca2+ indicator dye needs to be used. In addition, confocal microscopy is a favorite method of imaging individual neurons in tissue slices due to its ability to visualize neurons in distinct planes of depth within the tissue and to limit out-of-focus fluorescence. The ratiometric Ca2+ indicator fura-2 has been used in combination with GFP-tagged neurons1. However, the dye is excited by ultraviolet (UV) light. The cost of the laser and the limited optical penetration depth of UV light hindered its use in many laboratories. Moreover, GFP fluorescence may interfere with the fura-2 signals2. Therefore, we decided to use a red fluorescent Ca2+ indicator dye. The huge Stokes shift of fura-red permits multicolor analysis of the red fluorescence in combination with GFP using a single excitation wavelength. We had previously good results using fura-red in combination with GFP-tagged olfactory neurons3. The protocols for olfactory tissue slices seemed to work equally well in hypothalamic neurons4. Fura-red based Ca2+ imaging was also successfully combined with GFP-tagged pancreatic &beta;-cells and GFP-tagged receptors expressed in HEK cells5,6. A little quirk of fura-red is that its fluorescence intensity at 650 nm decreases once the indicator binds calcium7. Therefore, the fluorescence of resting neurons with low Ca2+ concentration has relatively high intensity. It should be noted, that other red Ca2+-indicator dyes exist or are currently being developed, that might give better or improved results in different neurons and brain areas.

In this protocol, we update recent progress in imaging Ca2+ signals of GFP-tagged neurons in brain tissue slices using a red fluorescent Ca2+ indicator dye.

Despite an enormous increase in our knowledge about the mechanisms underlying the encoding of information in the brain, a central question concerning the ...

In vivo Postnatal Electroporation and Time-lapse Imaging of Neuroblast Migration in Mouse Acute Brain Slices

The subventricular zone (SVZ) is one of the main neurogenic niches in the postnatal brain. Here, neural progenitors proliferate and give rise to neuroblasts able to move along the rostral migratory stream (RMS) towards the olfactory bulb (OB). This long-distance migration is required for the subsequent maturation of newborn neurons in the OB, but the molecular mechanisms regulating this process are still unclear. Investigating the signaling pathways controlling neuroblast motility may not only help understand a fundamental step in neurogenesis, but also have therapeutic regenerative potential, given the ability of these neuroblasts to target brain sites affected by injury, stroke, or degeneration.
In this manuscript we describe a detailed protocol for in vivo postnatal electroporation and subsequent time-lapse imaging of neuroblast migration in the mouse RMS. Postnatal electroporation can efficiently transfect SVZ progenitor cells, which in turn generate neuroblasts migrating along the RMS. Using confocal spinning disk time-lapse microscopy on acute brain slice cultures, neuroblast migration can be monitored in an environment closely resembling the in vivo condition. Moreover, neuroblast motility can be tracked and quantitatively analyzed. As an example, we describe how to use in vivo postnatal electroporation of a GFP-expressing plasmid to label and visualize neuroblasts migrating along the RMS. Electroporation of shRNA or CRE recombinase-expressing plasmids in conditional knockout mice employing the LoxP system can also be used to target genes of interest. Pharmacological manipulation of acute brain slice cultures can be performed to investigate the role of different signaling molecules in neuroblast migration. By coupling in vivo electroporation with time-lapse imaging, we hope to understand the molecular mechanisms controlling neuroblast motility and contribute to the development of novel approaches to promote brain repair.

In vivo Postnatal Electroporation and Time-lapse Imaging of Neuroblast Migration in Mouse Acute Brain Slices

Neuroblast migration is a fundamental event in postnatal neurogenesis. We describe a protocol for efficient labeling of neuroblasts by in vivo postnatal electroporation and subsequent visualization of their migration using time-lapse imaging of acute brain slices. We include a description for the quantitative analysis of neuroblast dynamics by video tracking.

The subventricular zone (SVZ) is one of the main neurogenic niches in the postnatal brain. Here, neural progenitors proliferate and give rise to ...

Paired Whole Cell Recordings in Organotypic Hippocampal Slices

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

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

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

Recording Synaptic Plasticity in Acute Hippocampal Slices Maintained in a Small-volume Recycling-, Perfusion-, and Submersion-type Chamber System

Even though experiments on brain slices have been in use since 1951, problems remain that reduce the probability of achieving a stable and successful analysis of synaptic transmission modulation when performing field potential or intracellular recordings. This manuscript describes methodological aspects that might be helpful in improving experimental conditions for the maintenance of acute brain slices and for recording field excitatory postsynaptic potentials in a commercially available submersion chamber with an outflow-carbogenation unit. The outflow-carbogenation helps to stabilize the oxygen level in experiments that rely on the recycling of a small buffer reservoir to enhance the cost-efficiency of drug experiments. In addition, the manuscript presents representative experiments that examine the effects of different carbogenation modes and stimulation paradigms on the activity-dependent synaptic plasticity of synaptic transmission.

This protocol describes the stabilization of the oxygen level in a small volume of recycled buffer and methodological aspects of recording activity-dependent synaptic plasticity in submerged acute hippocampal slices.

Even though experiments on brain slices have been in use since 1951, problems remain that reduce the probability of achieving a stable and successful ...

Evaluation of Synapse Density in Hippocampal Rodent Brain Slices

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

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

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

Two-photon Calcium Imaging in Neuronal Dendrites in Brain Slices

Calcium (Ca2+) imaging is a powerful tool to investigate the spatiotemporal dynamics of intracellular Ca2+ signals in neuronal dendrites. Ca2+ fluctuations can occur through a variety of membrane and intracellular mechanisms and play a crucial role in the induction of synaptic plasticity and regulation of dendritic excitability. Hence, the ability to record different types of Ca2+ signals in dendritic branches is valuable for groups studying how dendrites integrate information. The advent of two-photon microscopy has made such studies significantly easier by solving the problems inherent to imaging in live tissue, such as light scattering and photodamage. Moreover, through combination of conventional electrophysiological techniques with two-photon Ca2+ imaging, it is possible to investigate local Ca2+ fluctuations in neuronal dendrites in parallel with recordings of synaptic activity in soma. Here, we describe how to use this method to study the dynamics of local Ca2+ transients (CaTs) in dendrites of GABAergic inhibitory interneurons. The method can be also applied to studying dendritic Ca2+ signaling in different neuronal types in acute brain slices.

We present a method combining whole-cell patch-clamp recordings and two-photon imaging to record Ca2+ transients in neuronal dendrites in acute brain slices.

Calcium (Ca2+) imaging is a powerful tool to investigate the spatiotemporal dynamics of intracellular Ca2+ signals in neuronal dendrites. Ca2+ ...

Recording and Modulation of Epileptiform Activity in Rodent Brain Slices Coupled to Microelectrode Arrays

Temporal lobe epilepsy (TLE) is the most common partial complex epileptic syndrome and the least responsive to medications. Deep brain stimulation (DBS) is a promising approach when pharmacological treatment fails or neurosurgery is not recommended. Acute brain slices coupled to microelectrode arrays (MEAs) represent a valuable tool to study neuronal network interactions and their modulation by electrical stimulation. As compared to conventional extracellular recording techniques, they provide the added advantages of a greater number of observation points and a known inter-electrode distance, which allow studying the propagation path and speed of electrophysiological signals. However, tissue oxygenation may be greatly impaired during MEA recording, requiring a high perfusion rate, which comes at the cost of decreased signal-to-noise ratio and higher oscillations in the experimental temperature. Electrical stimulation further stresses the brain tissue, making it difficult to pursue prolonged recording/stimulation epochs. Moreover, electrical modulation of brain slice activity needs to target specific structures/pathways within the brain slice, requiring that electrode mapping be easily and quickly performed live during the experiment. Here, we illustrate how to perform the recording and electrical modulation of 4-aminopyridine (4AP)-induced epileptiform activity in rodent brain slices using planar MEAs. We show that the brain tissue obtained from mice outperforms rat brain tissue and is thus better suited for MEA experiments. This protocol guarantees the generation and maintenance of a stable epileptiform pattern that faithfully reproduces the electrophysiological features observed with conventional field potential recording, persists for several hours, and outlasts sustained electrical stimulation for prolonged epochs. Tissue viability throughout the experiment is achieved thanks to the use of a small-volume custom recording chamber allowing for laminar flow and quick solution exchange even at low (1 mL/min) perfusion rates. Quick MEA mapping for real-time monitoring and selection of stimulating electrodes is performed by a custom graphic user interface (GUI).

We illustrate how to perform recording and electrical modulation of 4-aminopyridine-induced epileptiform activity in rodent brain slices using microelectrode arrays. A custom recording chamber maintains tissue viability throughout prolonged experimental sessions. Live electrode mapping and selection of stimulating pairs are performed by a custom graphical user interface.

Temporal lobe epilepsy (TLE) is the most common partial complex epileptic syndrome and the least responsive to medications. Deep brain stimulation (DBS) ...

Assessment of Long-term Depression Induction in Adult Cerebellar Slices

Synaptic plasticity provides a mechanism for learning and memory. For cerebellar motor learning, long-term depression (LTD) of synaptic transmissions from parallel fibers (PF) to Purkinje cells (PC) is considered the basis for motor learning, and deficiencies of both LTD and motor learning are observed in various gene-manipulated animals. Common motor learning sets, such as adaptation of the optokinetic reflex (OKR), the vestibular-ocular reflex (VOR), and rotarod test were used for evaluation of motor learning ability. However, results obtained from the GluA2-carboxy terminus modified knock-in mice demonstrated normal adaptation of the VOR and the OKR, despite lacking PF-LTD. In that report, induction of LTD was only attempted using one type of stimulation protocol at room temperature. Thus, conditions to induce cerebellar LTD were explored in the same knock-in mutants using various protocols at near physiological temperature. Finally, we found stimulation protocols, by which LTD could be induced in these gene-manipulated mice. In this study, a set of protocols are proposed to evaluate LTD-induction, which will more accurately allow examination of the causal relationship between LTD and motor learning. In conclusion, experimental conditions are crucial when evaluating LTD in gene-manipulated mice.

In some gene-manipulated animals, using a single protocol may fail to induce LTD in cerebellar Purkinje cells, and there may be a discrepancy between LTD and motor learning. Multiple protocols are necessary to assess LTD-induction in gene-manipulated animals. Standard protocols are shown.

Synaptic plasticity provides a mechanism for learning and memory. For cerebellar motor learning, long-term depression (LTD) of synaptic transmissions from ...

Ballistic Labeling of Pyramidal Neurons in Brain Slices and in Primary Cell Culture

It has been reported that the size and shape of dendritic spines is related to their structural plasticity. To identify the morphological structure of pyramidal neurons and dendritic spines, a ballistic labeling technique can be utilized. In the present protocol, pyramidal neurons are labeled with DilC18(3) dye and analyzed using neuronal reconstruction software to assess neuronal morphology and dendritic spines. To investigate neuronal structure, dendritic branching analysis and Sholl analysis are performed, allowing researchers to draw inferences about dendritic branching complexity and neuronal arbor complexity, respectively. The evaluation of dendritic spines is conducted using an automatic assisted classification algorithm integral to the reconstruction software, which classifies spines into four categories (i.e., thin, mushroom, stubby, filopodia). Furthermore, an additional three parameters (i.e., length, head diameter, and volume) are also chosen to assess alterations in dendritic spine morphology. To validate the potential of wide application of the ballistic labeling technique, pyramidal neurons from in vitro cell culture were successfully labeled. Overall, the ballistic labeling method is unique and useful for visualizing neurons in different brain regions in rats, which in combination with sophisticated reconstruction software, allows researchers to elucidate the possible mechanisms underlying neurocognitive dysfunction.

We present a protocol to label and analyze pyramidal neurons, which is critical for evaluating potential morphological alterations in neurons and dendritic spines that may underlie neurochemical and behavioral abnormalities.

It has been reported that the size and shape of dendritic spines is related to their structural plasticity. To identify the morphological structure of ...

Culture of Brain Capillary Pericytes for Cytosolic Calcium Measurements and Calcium Imaging Studies

Pericytes are associated with endothelial cells and astrocytic endfeet in a structure known as the neurovascular unit (NVU). Brain capillary pericyte function is not fully known. Pericytes have been suggested to be involved in capillary development, regulation of endothelial barrier tightness and trancytosis activity, regulation of capillary tone and to play crucial roles in certain brain pathologies.
Pericytes are challenging to investigate in the intact brain due to the difficulties in visualizing processes in the brain parenchyma, as well as the close proximity to the other cells of the NVU. The present protocol describes a method for isolation and culture of primary bovine brain capillary pericytes and their following usage in calcium imaging studies, where effects of agonists involved in brain signaling and pathologies can be investigated. Cortical capillary fragments are allowed to attach to the bottom of culture flasks and, after 6 days, endothelial cells and pericytes have grown out from the capillary fragments. The endothelial cells are removed by gentle trypsinization and pericytes are cultured for 5 additional days before passaging.
Isolated pericytes are seeded in 96-well culture plates and loaded with the calcium indicator dye (Fura-2 acetoxymethyl (AM)) to allow for measurements of intracellular calcium levels in a plate reader setup. Alternatively, pericytes are seeded on coverslips and mounted in cell chambers. Following loading with the calcium indicator (Cal-520 AM), calcium live-imaging can be performed using confocal microscopy at an excitation wavelength of 488 nm and emission wavelength of 510-520 nm.
The method described here has been used to obtain the first intracellular calcium measurements from primary brain capillary pericytes, demonstrating that pericytes are stimulated via ATP and are able to contract in vitro.

Brain capillary pericytes are essential players in the regulation of blood-brain barrier properties and blood flow. This protocol describes how brain capillary pericytes can be isolated, cultured, characterized with respect to cell type and applied for investigations of intracellular calcium signaling with fluorescent probes.

Pericytes are associated with endothelial cells and astrocytic endfeet in a structure known as the neurovascular unit (NVU). Brain capillary pericyte ...