We would like to thank Britta Kaltwasser for her excellent technical assistance and Mahesh Kumar Teli to organize the video filming preparation.

1. Animals
<ol>
	<li>Experiments were carried out according to the NIH guidelines for the care and use of laboratory animals and approved by local authorities. For all experiments, C57Bl6/J wild type mice, ApolipoproteinE-/- (ApoE KO) and SV129 mice (12-16 weeks old, 26-30 g body weight, 5-6 animals per experimental group) were used.</li>
</ol>
2. Staining of Cerebral Vessels with Colored Latex
<ol>
	<li>Prepare a mixture of 25 &mu;l carbon black ink (Herlitz, Germany) with 0.5 ml of latex compound (Pebeo, France) at a 1:20 ratio in an EP tube and warm up the mixture at 37 &deg;C in a water bath. Collect the mixture in a 2 ml syringe with a needle of 28-30G before anaesthetizing the animal.</li>
	<li>Dissolve 50 mg of papavarine hydrochloride powder into 1 ml of sterile normal saline. Collect the solution in an insulin syringe. Break off the needle from another sterile insulin syringe. Place this needle at the end of a 20 cm long PE10 tube. Now attach this PE10 tube on the needle of the insulin syringe containing papavarine hydrochloride solution to be injected through the femoral vein to ensure vasodilatation and proper filling of vessels.</li>
	<li>Prepare another two insulin syringes each containing 1 ml of saline. Insulin syringes allow smooth delivery of the injected fluid at a precise location. However, due to high viscosity of latex, alternative 1 ml syringes with removable wider needles should be used.</li>
	<li>Take all the syringes and sterilized dissecting instruments close to the operating stage. Spread a surgical draper sheet around the operation stage. The operation stage should be sufficiently illuminated and an operating microscope may be used if necessary.</li>
	<li>Now measure the body weight of a C57Bl6/J mouse and then induce anesthesia with 5% vaporized isoflurane in 70% N2O and 30% O2. Continue anesthesia with 1% of vaporized isoflurane. After proper positioning of the mouse on its back and fixation of the limbs, assess the depth of anesthesia. Then cut the skin over the left femoral vein and locate the vein. Insert the sharp tip of the needle placed on PE10 tube and slowly inject papavarine hydrochloride solution at a rate of 100 &mu;l per min (50 mg/kg body weight).</li>
	<li>Following the injection, cut the abdominal cavity and pierce the diaphragm. Cut the ribs to expose the heart without damaging or bruising it. Clip the descending thoracic aorta with an artery forceps. Make a sharp cut over the right atrium to allow the venous blood drain out. Inject 2 ml of saline into the left ventricle, followed by injecting the colored latex manually with slight pressure over 18-20 sec. Use the pre-filled syringes one after another. Avoid injecting any bubbles.</li>
	<li>Following injection of latex, leave the animal for 5 min. Decapitate the animal and carefully remove the whole brain. Take good care not to injure the vessel architecture and cortex while removing the skull bone and meninges. Place the brain in a 60 mm cell culture dish containing 6-8 ml of 4% PFA to take a photo. Place a measuring ruler under the transparent dish. Take photos at a 25x magnification of the dorsal and the ventral surface of the brain with a camera attached to the operating microscope. Photos should be taken at 90&deg; angle between the Petri dish and the microscope objective in order to quantify the original distance.</li>
	<li>Repeat the procedure in another 4-5 animals.</li>
</ol>
3. Staining of Cerebral Vessels with Mixture of Carbon Black Inks
<ol>
	<li>To compare the outcome of latex based cerebral vascular staining with our protocol, prepare a mixture of 100 &mu;l of Herlitz Stempelfarbe ink (CB1) with 900 &mu;l of Pelican Scribtol Schwarz ink (CB2) in a 1.5 ml EP tube. Prepare two EP tubes to make a total volume of 2 ml mixture of CB1 and CB2 at a 1:9 ratio. Collect the mixture in two separate insulin syringes (1 ml each). Cap the syringes and place them in a water bath to warm up to 37 &deg;C. Collect 2 ml of saline in another two insulin syringes, and place them in a water bath as well.</li>
	<li>Anesthetize the animal and repeat the same procedure as described above except for injection of papavarine hydrochloride. Following injection of 2 ml salaine into the left ventricle, inject a 2 ml mixture of carbon black inks instead of the colored latex. Perform the injections by hand with slight pressure over 18-20 sec per ml. Clip the descending thoracic aorta prior to the injections.</li>
	<li>Sacrifice the animal, remove the brain and take photos.</li>
	<li>For long-term preservation of the brain, put the brain in 4% PFA overnight followed by incubation with sucrose with gradually increasing concentration until the floating brain submerges totally (5% followed by 15% and then 30%). Brains of the animals perfused with the colored latex can also be preserved in the same way.</li>
	<li>Perform the procedure in another 4-5 animals. To compare the difference in cerebral vascular anatomy due to different genetic background or strains, repeat the protocol in equal number of ApoE KO and SV129 mice, respectively.</li>
	<li>To study the vascular anatomy under ischemic conditions, induce transient focal cerebral ischemia for 45 min or 90 min according to a standard protocol of intraluminal occlusion of the MCA under deep anesthesia (a detailed description of the surgery is beyond the scope of this article; the reader is referred to Doeppner et al., 2010). At the end of the reperfusion period planned (1 day or 5 days), perform the vascular staining with CB1+CB2 inks only and stain the whole brain with 2% TTC solution at 37 &deg;C for 5-10 min to identify the infarct volume. TTC is reduced to red colored formazan by the mitochondrial enzymes (particularly succinate dehydrogenase). After TTC staining, the metabolically active tissue stains deep red while the infarcted tissue remains unstained and appears white due to dysfunctional and denatured mitochondrial enzyme. Collect images in the same way as described above.</li>
</ol>
4. Study of Cerebral Vascular Territories
<ol>
	<li>To analyze the gross anatomy of cerebral vessels, images of the dorsal surface of the brain either stained with colored latex or CB1+CB2 inks can be analyzed with ImageJ software (a Java based public domain software used for image processing and analysis). Brains perfused with colored latex may show variable degrees of vessel staining located on the dorsal surface, while CB1+CB2 perfusion will stain all the vessels on both the ventral and dorsal surfaces.</li>
	<li>Open an image file with ImageJ software. Identify all the anastomotic points between the ACA and the MCA. An anastomotic point is defined as the site where the vessel diameter is the narrowest or the half distance between the nearest branching points of the ACA and the MCA branches, respectively2. Draw an imaginary line (anastomotic line) by marking the anastomotic points with the help of drawing segmented line tool and the plugin "Dotted Line".</li>
	<li>Set the scale in mm. Measure the distance between the anastomotic line and the midline at 4 mm caudal to the frontal pole of the brain using straight line drawing tool and "measure" tool. Do the same at 6 mm caudally from the frontal pole. Analyze 3-4 images per animal and calculate the mean value. Compare the values among different groups of animals to identify the variation of cerebrovascular anatomy. In C57Bl6/J animals, the anastomotic line between the ACA and the MCA can be traced closer to the midline at 4 mm than at 6 mm caudally from the frontal pole. ApoE KO mice will present no significant difference in this respect. On the contrary, in SV129 mice the anastomotic line will lie further and parallel to the midline both at 4 mm and 6 mm caudally from the frontal pole.</li>
	<li>To analyze the vascular anatomy in ischemic conditions, perform the same calculations mentioned above. Identify the infarction border as the red and white colored tissue margin representing metabolically active tissue and necrotic unstained tissue, respectively. Measure the distance of the infarction border from the midline at 4 mm and at 6 mm caudal from the frontal pole of the brain. Collect the mean value from 3-4 images per animal. Compare the results between different ischemia and reperfusion periods.</li>
</ol>

<ol>
	<li>Meng, H., Peng, 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=Nuclear+contrast+angiography:+A+simple+method+for+morphological+characterization+of+cerebral+arteries.">Nuclear contrast angiography: A simple method for morphological characterization of cerebral arteries.</a> Brain Research. 1261, 75-81 (2009).</li><li>Maeda, K., Hata, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differences+in+the+cerebrovascular+anatomy+of+C57black/6+and+SV129+mice.">Differences in the cerebrovascular anatomy of C57black/6 and SV129 mice.</a> Neuroreport. 9 (7), 1317-1319 (1998).</li><li>Coyle, P., Jokelainen, P. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dorsal+cerebral+arterial+collaterals+of+the+rat.">Dorsal cerebral arterial collaterals of the rat.</a> The Anatomical Record. 203, 397-404 (1982).</li><li>Coyle, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dorsal+cerebral+collaterals+of+stroke-prone+spontaneously+hypertensive+rats+(SHRSP)+and+Wistar+Kyoto+rats+(WKY).">Dorsal cerebral collaterals of stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar Kyoto rats (WKY).</a> The Anatomical Record. 218, 40-44 (1987).</li><li>Hasan, M. R., Herz, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visualization+of+macroscopic+cerebral+vessel+anatomy&#8212;A+new+and+reliable+technique+in+mice.">Visualization of macroscopic cerebral vessel anatomy&#8212;A new and reliable technique in mice.</a> Journal of Neuroscience Methods. 204, 249-253 (2012).</li><li>Doeppner, T. R., Nagel, F., 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=TAT-Hsp70-mediated+neuroprotection+and+increased+survival+of+neuronal+precursor+cells+after+focal+cerebral+ischemia+in+mice.">TAT-Hsp70-mediated neuroprotection and increased survival of neuronal precursor cells after focal cerebral ischemia in mice.</a> Journal of Cerebral Blood Flow &amp; Metabolism. 29, 1187-1196 (2009).</li><li>Todo, K., Kitagawa, K., 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=Granulocyte-macrophage+colony-stimulating+factor+enhances+leptomeningeal+collateral+growth+induced+by+common+carotid+artery+occlusion.">Granulocyte-macrophage colony-stimulating factor enhances leptomeningeal collateral growth induced by common carotid artery occlusion.</a> Stroke. 39 (6), 1875-1882 (2008).</li><li>Sugiyama, Y., Yagita, 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=Granulocyte+colony-stimulating+factor+enhances+arteriogenesis+and+ameliorates+cerebral+damage+in+a+mouse+model+of+ischemic+stroke.">Granulocyte colony-stimulating factor enhances arteriogenesis and ameliorates cerebral damage in a mouse model of ischemic stroke.</a> Stroke. 42 (3), 770-775 (2011).</li><li>Busch, H. J., Buschmann, I. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Arteriogenesis+in+hypoperfused+rat+brain.">Arteriogenesis in hypoperfused rat brain.</a> Journal of Cerebral Blood Flow &amp; Metabolism. 23 (5), 621-628 (2003).</li><li>Maeda, K., Hata, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regional+metabolic+disturbances+and+cerebrovascular+anatomy+after+permanent+middle+cerebral+artery+occlusion.">Regional metabolic disturbances and cerebrovascular anatomy after permanent middle cerebral artery occlusion.</a> in C57black/6 and SV129 mice. Neurobiology of Diseases. 6, 101-108 (1999).</li><li>Wang, Y., Kilic, E., 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=VEGF+overexpression+induces+post-ischaemic+neuroprotection,+but+facilitates+haemodynamic+steal+phenomena.">VEGF overexpression induces post-ischaemic neuroprotection, but facilitates haemodynamic steal phenomena.</a> Brain. 128 (1), 52-63 (2005).</li><li>ElAli, A., Doeppner, T. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increased+blood-brain+barrier+permeability+and+brain+edema+after+focal+cerebral+ischemia+induced+by+hyperlipidemia:+Role+of+lipid+peroxidation+and+calpain+1/2,+matrix+metalloproteinase-2/9,+and+RhoA+overoxidation.">Increased blood-brain barrier permeability and brain edema after focal cerebral ischemia induced by hyperlipidemia: Role of lipid peroxidation and calpain 1/2, matrix metalloproteinase-2/9, and RhoA overoxidation.</a> Stroke. 42, (2011).</li><li>Coyle, P., Jokelainen, P. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differential+outcome+to+middle+cerebral+artery+occlusion+in+spontaneously+hypertensive+stroke-prone+rats+(SHRSP)+and+Wistar+Kyoto+(WKY)+rats.">Differential outcome to middle cerebral artery occlusion in spontaneously hypertensive stroke-prone rats (SHRSP) and Wistar Kyoto (WKY) rats.</a> Stroke. 14, 605-611 (1983).</li><li>Coyle, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diameter+and+length+changes+in+cerebral+collaterals+after+middle+cerebral+artery+occlusion+in+the+young+rat.">Diameter and length changes in cerebral collaterals after middle cerebral artery occlusion in the young rat.</a> The Anatomical Record. 210 (2), 357-364 (1984).</li></ol>

No conflicts of interest declared.

Perfusion of CB1+CB2 by manual injection can be carried out successfully by without intensive training as it does not involve any specific device to imply certain pressure2,3. The heterogeneity of perfusion outcomes in our protocol is also negligible. Only 1 animal out of 16 non-ischemic animals and 3 out of 20 ischemic animals have showed incomplete perfusion. In these cases, incorporation of bubbles during saline perfusion leading to occlusion of vessels was most likely the reason of the unsuccessful outcome...

<table border="1">
 <tbody>
 <tr>
 <td>Name of reagent</td>
 <td>Company Name</td>
 <td>Catalog No.</td>
 </tr>
 <tr>
 <td>Scribtol Schwarz (CB2)</td>
 <td>Pelican, Germany </td>
 <td>221 135</td>
 </tr>
 <tr>
 <td>Stempelfarbe (CB1)</td>
 <td>Herlitz PBS AG, Germany</td>
 <td>10417202</td>
 </tr>
 <tr>
 <td>Gedeo Latex </td>
 <td>Pebeo, France</td>
 <td>13042B</td>
 </tr>
 </tbody>
</table>

intravascular perfusion of carbon black ink allows reliable visualization of cerebral vessels

The anatomical structure of cerebral vessels is a key determinant for brain hemodynamics as well as the severity of injury following ischemic insults. The cerebral vasculature dynamically responds to various pathophysiological states and it exhibits considerable differences between strains and under conditions of genetic manipulations. Essentially, a reliable technique for intracranial vessel staining is essential in order to study the pathogenesis of ischemic stroke. Until recently, a set of different techniques has been employed to visualize the cerebral vasculature including injection of low viscosity resin, araldite F, gelatin mixed with various dyes1 (i.e. carmine red, India ink) or latex with2 or without3 carbon black. Perfusion of white latex compound through the ascending aorta has been first reported by Coyle and Jokelainen3. Maeda et al.2 have modified the protocol by adding carbon black ink to the latex compound for improved contrast visualization of the vessels after saline perfusion of the brain. However, inefficient perfusion and inadequate filling of the vessels are frequently experienced due to high viscosity of the latex compound4. Therefore, we have described a simple and cost-effective technique using a mixture of two commercially available carbon black inks (CB1 and CB2) to visualize the cerebral vasculature in a reproducible manner5. We have shown that perfusion with CB1+CB2 in mice results in staining of significantly smaller cerebral vessels at a higher density in comparison to latex perfusion5. Here, we describe our protocol to identify the anastomotic points between the anterior (ACA) and middle cerebral arteries (MCA) to study vessel variations in mice with different genetic backgrounds. Finally, we demonstrate the feasibility of our technique in a transient focal cerebral ischemia model in mice by combining CB1+CB2-mediated vessel staining with TTC staining in various degrees of ischemic injuries.

The protocol described here overcomes the technical limitations of conventional latex based visualization of rodent cerebral vasculature. Figure 1A shows that following perfusion of the colored latex, only the large vessels on the ventral surface are stained, leaving the entire dorsal surface unstained. The outcome is also highly variable. Only one animal out of six shows partial staining of the ACA and the MCA visible on the dorsal surface of the brain (data not shown). Conversely, CB1+CB2 perfusion res...

Watch this Scientific Journal Video about Intravascular Perfusion of Carbon Black Ink Allows Reliable Visualization of Cerebral Vessels at JoVE.com

Intravascular Perfusion of Carbon Black Ink Allows Reliable Visualization of Cerebral Vessels

Analysis of rodent cerebrovascular anatomy plays an important role in experimental stroke research. In this context, intravascular perfusion with colored latex has been considered as a standard tool for several years. However, this technique implies distinct technical limitations, which undermine its reproducibility. Here, we describe a simple method to visualize cerebral vessels in a reproducible manner. Injection of a mixture of two commercially available carbon black inks through the left myocardial ventricle results in adequate filling of cerebral vessels with high contrast visualization. We have successfully applied this technique to identify anastomotic points between cerebral vascular territories of mice with different genetic backgrounds. We finally give evidence that this novel and simple method for vessel staining can be combined with triphenyltetrazolium chloride (TTC) staining - a widely used tool to observe and analyze infarct volumes in mice.

The anatomical structure of cerebral vessels is a key determinant for brain hemodynamics as well as the severity of injury following ischemic insults. The ...

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15.4K Views.  University of Duisburg-Essen Medical School. Analisi di anatomia roditore cerebrovascolari svolge un ruolo importante nella ricerca sperimentale ictus. In questo contesto, la perfusione intravascolare con lattice colorato è stato considerato come uno strumento standard per diversi anni. Tuttavia, questa tecnica comporta diverse limitazioni tecniche che mettono a repentaglio la sua riproducibilità. Qui, descriviamo un metodo semplice per visualizzare i vasi cerebrali in modo riproducibile. Iniezione di una miscela ...

Video: Intravascular Perfusion of Carbon Black Ink Allows Reliable Visualization of Cerebral Vessels

Focal Cerebral Ischemia Model by Endovascular Suture Occlusion of the Middle Cerebral Artery in the Rat

Stroke is the leading cause of disability and the third leading cause of death in adults worldwide1. In human stroke, there exists a highly variable clinical state; in the development of animal models of focal ischemia, however, achieving reproducibility of experimentally induced infarct volume is essential. The rat is a widely used animal model for stroke due to its relatively low animal husbandry costs and to the similarity of its cranial circulation to that of humans2,3. In humans, the middle cerebral artery (MCA) is most commonly affected in stroke syndromes and multiple methods of MCA occlusion (MCAO) have been described to mimic this clinical syndrome in animal models. Because recanalization commonly occurs following an acute stroke in the human, reperfusion after a period of occlusion has been included in many of these models. In this video, we demonstrate the transient endovascular suture MCAO model in the spontaneously hypertensive rat (SHR). A filament with a silicon tip coating is placed intraluminally at the MCA origin for 60 minutes, followed by reperfusion. Note that the optimal occlusion period may vary in other rat strains, such as Wistar or Sprague-Dawley. Several behavioral indicators of stroke in the rat are shown. Focal ischemia is confirmed using T2-weighted magnetic resonance images and by staining brain sections with 2,3,5-triphenyltetrazolium chloride (TTC) 24 hours after MCAO.

Surgical induction of ischemic brain damage in the rat is a widely used model for stroke research. Here we demonstrate the induction of focal cerebral ischemia by occlusion of the middle cerebral artery. Visualization of the resulting infarct by histological staining and magnetic resonance imaging is also shown.

Stroke is the leading cause of disability and the third leading cause of death in adults worldwide1. In human stroke, there exists a highly variable ...

Automated Interactive Video Playback for Studies of Animal Communication

Video playback is a widely-used technique for the controlled manipulation and presentation of visual signals in animal communication. In particular, parameter-based computer animation offers the opportunity to independently manipulate any number of behavioral, morphological, or spectral characteristics in the context of realistic, moving images of animals on screen. A major limitation of conventional playback, however, is that the visual stimulus lacks the ability to interact with the live animal. Borrowing from video-game technology, we have created an automated, interactive system for video playback that controls animations in response to real-time signals from a video tracking system. We demonstrated this method by conducting mate-choice trials on female swordtail fish, Xiphophorus birchmanni. Females were given a simultaneous choice between a courting male conspecific and a courting male heterospecific (X. malinche) on opposite sides of an aquarium. The virtual male stimulus was programmed to track the horizontal position of the female, as courting males do in the wild. Mate-choice trials on wild-caught X. birchmanni females were used to validate the prototype's ability to effectively generate a realistic visual stimulus.

Video playback is a widely used technique in animal behavior. We created and evaluated a program that applies rules-based, interactive playback of 3-D computer animations in response to real-time, automated data on subject behavior.

Video playback is a widely-used technique for the controlled manipulation and presentation of visual signals in animal communication. In particular, ...

Whole Animal Perfusion Fixation for Rodents

The goal of fixation is to rapidly and uniformly preserve tissue in a life-like state. While placing tissue directly in fixative works well for small pieces of tissue, larger specimens like the intact brain pose a problem for immersion fixation because the fixative does not reach all regions of the tissue at the same rate 5,7. Often, changes in response to hypoxia begin before the tissue can be preserved 12. The advantage of directly perfusing fixative through the circulatory system is that the chemical can quickly reach every corner of the organism using the natural vascular network. In order to utilize the circulatory system most effectively, care must be taken to match physiological pressures 3. It is important to note that physiological pressures are dependent on the species used. Techniques for perfusion fixation vary depending on the tissue to be fixed and how the tissue will be processed following fixation. In this video, we describe a low-cost, rapid, controlled and uniform fixation procedure using 4% paraformaldehyde perfused via the vascular system: through the heart of the rat to obtain the best possible preservation of the brain for immunohistochemistry. The main advantage of this technique (vs. gravity-fed systems) is that the circulatory system is utilized most effectively.

Here we describe a low-cost, rapid, controlled and uniform fixation procedure using 4% paraformaldehyde perfused via the vascular system: through the heart of the rat to obtain the best possible preservation of the brain.

The goal of fixation is to rapidly and uniformly preserve tissue in a life-like state. While placing tissue directly in fixative works well for small ...

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 ...

Visualization and Genetic Manipulation of Dendrites and Spines in the Mouse Cerebral Cortex and Hippocampus using In utero Electroporation

In utero electroporation (IUE) has become a powerful technique to study the development of different regions of the embryonic nervous system 1-5. To date this tool has been widely used to study the regulation of cellular proliferation, differentiation and neuronal migration especially in the developing cerebral cortex 6-8. Here we detail our protocol to electroporate in utero the cerebral cortex and the hippocampus and provide evidence that this approach can be used to study dendrites and spines in these two cerebral regions.
Visualization and manipulation of neurons in primary cultures have contributed to a better understanding of the processes involved in dendrite, spine and synapse development. However neurons growing in vitro are not exposed to all the physiological cues that can affect dendrite and/or spine formation and maintenance during normal development. Our knowledge of dendrite and spine structures in vivo in wild-type or mutant mice comes mostly from observations using the Golgi-Cox method 9. However, Golgi staining is considered to be unpredictable. Indeed, groups of nerve cells and fiber tracts are labeled randomly, with particular areas often appearing completely stained while adjacent areas are devoid of staining. Recent studies have shown that IUE of fluorescent constructs represents an attractive alternative method to study dendrites, spines as well as synapses in mutant / wild-type mice 10-11 (Figure 1A). Moreover in comparison to the generation of mouse knockouts, IUE represents a rapid approach to perform gain and loss of function studies in specific population of cells during a specific time window. In addition, IUE has been successfully used with inducible gene expression or inducible RNAi approaches to refine the temporal control over the expression of a gene or shRNA 12. These advantages of IUE have thus opened new dimensions to study the effect of gene expression/suppression on dendrites and spines not only in specific cerebral structures (Figure 1B) but also at a specific time point of development (Figure 1C).
Finally, IUE provides a useful tool to identify functional interactions between genes involved in dendrite, spine and/or synapse development. Indeed, in contrast to other gene transfer methods such as virus, it is straightforward to combine multiple RNAi or transgenes in the same population of cells. 
In summary, IUE is a powerful method that has already contributed to the characterization of molecular mechanisms underlying brain function and disease and it should also be useful in the study of dendrites and spines.

Visualization and Genetic Manipulation of Dendrites and Spines in the Mouse Cerebral Cortex and Hippocampus using In utero Electroporation

This article describes in detail a protocol to electroporate in utero the cerebral cortex and the hippocampus at E14.5 in mice. We also show that this is a valuable method to study dendrites and spines in these two cerebral regions.

In utero electroporation (IUE) has become a powerful technique to study the development of different regions of the embryonic nervous system 1-5. To date ...

Dual Electrophysiological Recordings of Synaptically-evoked Astroglial and Neuronal Responses in Acute Hippocampal Slices

Astrocytes form together with neurons tripartite synapses, where they integrate and modulate neuronal activity. Indeed, astrocytes sense neuronal inputs through activation of their ion channels and neurotransmitter receptors, and process information in part through activity-dependent release of gliotransmitters. Furthermore, astrocytes constitute the main uptake system for glutamate, contribute to potassium spatial buffering, as well as to GABA clearance. These cells therefore constantly monitor synaptic activity, and are thereby sensitive indicators for alterations in synaptically-released glutamate, GABA and extracellular potassium levels. Additionally, alterations in astroglial uptake activity or buffering capacity can have severe effects on neuronal functions, and might be overlooked when characterizing physiopathological situations or knockout mice. Dual recording of neuronal and astroglial activities is therefore an important method to study alterations in synaptic strength associated to concomitant changes in astroglial uptake and buffering capacities. Here we describe how to prepare hippocampal slices, how to identify stratum radiatum astrocytes, and how to record simultaneously neuronal and astroglial electrophysiological responses. Furthermore, we describe how to isolate pharmacologically the synaptically-evoked astroglial currents.

The preparation of acute brain slices from isolated hippocampi, as well as the simultaneous electrophysiological recordings of astrocytes and neurons in stratum radiatum during stimulation of schaffer collaterals is described. The pharmacological isolation of astroglial potassium and glutamate transporter currents is demonstrated.

Astrocytes form together with neurons tripartite synapses, where they integrate and modulate neuronal activity. Indeed, astrocytes sense neuronal inputs ...

Electrophysiology on Isolated Brainstem-spinal Cord Preparations from Newborn Rodents Allows Neural Respiratory Network Output Recording

While it is well known that the central respiratory drive is located in the brainstem, several aspects of its basic function, development, and response to stimuli remain to be fully understood. To overcome the difficulty of accessing the brainstem in the whole animal, isolation of the brainstem and part of the spinal cord is performed. This preparation is maintained in artificial cerebro-spinal fluid where gases, concentrations, and temperature are controlled and monitored. The output signal from the respiratory network is recorded by a suction electrode placed on the fourth ventral root. In this manner, stimuli can be directly applied onto the brainstem, and the effect can be recorded directly. The signal recorded is linked to the inspiratory signal sent to the diaphragm via the phrenic nerve, and can be described as bursts (around 8 bursts per minute). Analysis of these bursts (frequency, amplitude, length, and area under the curve) allows precise characterization of the stimulus effect on the respiratory network. The main limitation of this method is the viability of the preparation beyond the early post-natal stages. Thus, this method greatly focuses on the study of the whole network without the peripheral inputs in the newborn rat.

The central respiratory drive is located in the brainstem. Spontaneous respiratory motor output from an isolated brainstem-spinal cord is recorded by placing an electrode on the fourth ventral root. This experimental approach is valuable for pharmacological investigations or the assessment of respiratory challenges and genetic manipulations on rhythmic motor behavior.

While it is well known that the central respiratory drive is located in the brainstem, several aspects of its basic function, development, and response to ...

Purification of Mouse Brain Vessels

In the brain, most of the vascular system consists of a selective barrier, the blood-brain barrier (BBB) that regulates the exchange of molecules and immune cells between the brain and the blood. Moreover, the huge neuronal metabolic demand requires a moment-to-moment regulation of blood flow. Notably, abnormalities of these regulations are etiological hallmarks of most brain pathologies; including glioblastoma, stroke, edema, epilepsy, degenerative diseases (ex: Parkinson&#8217;s disease, Alzheimer&#8217;s disease), brain tumors, as well as inflammatory conditions such as multiple sclerosis, meningitis and sepsis-induced brain dysfunctions. Thus, understanding the signaling events modulating the cerebrovascular physiology is a major challenge. Much insight into the cellular and molecular properties of the various cell types that compose the cerebrovascular system can be gained from primary culture or cell sorting from freshly dissociated brain tissue. However, properties such as cell polarity, morphology and intercellular relationships are not maintained in such preparations. The protocol that we describe here is designed to purify brain vessel fragments, whilst maintaining structural integrity. We show that isolated vessels consist of endothelial cells sealed by tight junctions that are surrounded by a continuous basal lamina. Pericytes, smooth muscle cells as well as the perivascular astrocyte endfeet membranes remain attached to the endothelial layer. Finally, we describe how to perform immunostaining experiments on purified brain vessels.

We describe a protocol allowing the purification of the mouse brain's vascular compartment. Isolated brain vessels include endothelial cells linked by tight junctions and surrounded by a continuous basal lamina, pericytes, vascular smooth muscle cells, as well as perivascular astroglial membranes.

In the brain, most of the vascular system consists of a selective barrier, the blood-brain barrier (BBB) that regulates the exchange of molecules and ...

Isolation and Cannulation of Cerebral Parenchymal Arterioles

Intracerebral parenchymal arterioles (PAs), which include parenchymal arterioles, penetrating arterioles and pre-capillary arterioles, are high resistance blood vessels branching out from pial arteries and arterioles and diving into the brain parenchyma. Individual PA perfuse a discrete cylindrical territory of the parenchyma and the neurons contained within. These arterioles are a central player in the regulation of cerebral blood flow both globally (cerebrovascular autoregulation) and locally (functional hyperemia). PAs are part of the neurovascular unit, a structure that matches regional blood flow to metabolic activity within the brain and also includes neurons, interneurons, and astrocytes. Perfusion through PAs is directly linked to the activity of neurons in that particular territory and increases in neuronal metabolism lead to an augmentation in local perfusion caused by dilation of the feed PA. Regulation of PAs differs from that of better-characterized pial arteries. Pressure-induced vasoconstriction is greater in PAs and vasodilatory mechanisms vary. In addition, PAs do not receive extrinsic innervation from perivascular nerves &#8212; innervation is intrinsic and indirect in nature through contact with astrocytic endfeet. Thus, data regarding contractile regulation accumulated by studies using pial arteries does not directly translate to understanding PA function. Further, it remains undetermined how pathological states, such as hypertension and diabetes, affect PA structure and reactivity. This knowledge gap is in part a consequence of the technical difficulties pertaining to PA isolation and cannulation. In this manuscript we present a protocol for isolation and cannulation of rodent PAs. Further, we show examples of experiments that can be performed with these arterioles, including agonist-induced constriction and myogenic reactivity. Although the focus of this manuscript is on PA cannulation and pressure myography, isolated PAs can also be used for biochemical, biophysical, molecular, and imaging studies.

This manuscript describes a simple and reproducible protocol for isolation of intracerebral arterioles (a group of blood vessels encompassing parenchymal arterioles, penetrating arterioles and pre-capillary arterioles) from mice, to be used in pressure myography, immunofluorescence, biochemistry, and molecular studies.

Intracerebral parenchymal arterioles (PAs), which include parenchymal arterioles, penetrating arterioles and pre-capillary arterioles, are high resistance ...

Intracerebroventricular and Intravascular Injection of Viral Particles and Fluorescent Microbeads into the Neonatal Brain

In the study on the pathogenesis of viral encephalitis, the infection method is critical. The first of the two main infectious routes to the brain is the hematogenous route, which involves infection of the endothelial cells and pericytes of the brain. The second is the intracerebroventricular (ICV) route. Once within the central nervous system (CNS), viruses may spread to the subarachnoid space, meninges, and choroid plexus via the cerebrospinal fluid. In experimental models, the earliest stages of CNS viral distribution are not well characterized, and it is unclear whether only certain cells are initially infected. Here, we have analyzed the distribution of cytomegalovirus (CMV) particles during the acute phase of infection, termed primary viremia, following ICV or intravascular (IV) injection into the neonatal mouse brain. In the ICV injection model, 5 &#181;l of murine CMV (MCMV) or fluorescent microbeads were injected into the lateral ventricle at the midpoint between the ear and eye using a 10-&#181;l syringe with a 27 G needle. In the IV injection model, a 1-ml syringe with a 35 G needle was used. A transilluminator was used to visualize the superficial temporal (facial) vein of the neonatal mouse. We infused 50 &#181;l of MCMV or fluorescent microbeads into the superficial temporal vein. Brains were harvested at different time points post-injection. MCMV genomes were detected using the in situ hybridization method. Fluorescent microbeads or green fluorescent protein expressing recombinant MCMV particles were observed by fluorescent microscopy. These techniques can be applied to many other pathogens to investigate the pathogenesis of encephalitis.

Here, we describe a simple method of intracerebroventricular and intravascular injection of viral particles or fluorescent microbeads into the neonatal mouse brain. The localization pattern of the virus and nanoparticles could be detected by microscopic evaluation or by in situ hybridization.

In the study on the pathogenesis of viral encephalitis, the infection method is critical. The first of the two main infectious routes to the brain is the ...