The support of the Lions Eye Bank of Delaware Valley was invaluable for this work. Primary mouse monoclonal antibody against ICP8 was a kind gift from Dr. David Knipe (Harvard Medical School). We also thank Dr. Stephen Jennings (Drexel University College of Medicine) and Dr. Peter Laibson (Wills Eye Institute) for helpful discussions and expertise.

All reagents and equipment were purchased sterile or were sterilized prior to the procedure. This article describes the steps of setting up the ex vivo model beginning with a pre-enucleated eye. In our experiments, we use fresh whole eyeballs from young (8-12 wks) albino rabbits (Pel-Freez Biologicals, Rogers, AR). In addition, we use human corneas obtained from the local eye bank. If performing enucleation yourself, take care to avoid damaging the cornea or the limbus during the procedure. Rabbit enucleation protocols can be found elsewhere 2.
Part 1: Excision of the Corneoscleral Button
<ol>
 <li> Wet a narrow strip of gauze with PBS and wrap it around the eyeball to facilitate holding it during the procedure. </li>
 <li> Use a sharp scalpel to make a tangential incision in the sclera, about 0.5 cm away from the limbus. </li>
 <li> Use sharp scissors to extend the incision and completely excise the corneoscleral button. </li>
 <li> Once the corneoscleral button is isolated, tease away the iris while holding the scleral rim with forceps. Avoid damaging the endothelium or exerting excessive stress on the cornea. </li>
</ol>
Part 2: Introduction of Cornea into Organotypic Culture
<ol>
 <li> Explanted corneas are cultured in Minimum Essential Medium (MEM) supplemented with Non-Essential Amino Acids (1X), L-Glutamine (2 mM), Penicillin (200 U/ml), and Streptomycin (200 &mu;g/ml). An antifungal agent, such as amphotericin, may also be added if necessary. </li>
 <li> Prepare a 1% agarose solution in culture medium and keep it ready at 55 &deg;C. </li>
 <li> Thoroughly rinse the cornea in sterile PBS containing Penicillin (200 U/ml) and Streptomycin (200 &mu;g/ml).</li>
 <li> Place the cornea epithelial side down into a well of a sterile spot plate. </li>
 <li> Add the agarose-containing medium to the endothelial concavity of the cornea just enough to fill it completely. Allow ~1 min for the agarose to solidify. </li>
 <li> Place the cornea with the supporting gel scaffold epithelial side up into a 35 mm tissue culture dish and add culture medium to cover the epithelial surface. </li>
 <li> The cornea may be cultured in this way for over a week, with medium changes every 48 hr. </li>
</ol>
Part 3: Infection with HSV-1 and Treatment with Experimental Drugs
<ol>
 <li> Add 1 ml of medium containing the desired amount of virus into a 35 mm tissue culture dish. We usually infect with 1x104 PFU of strain KOS HSV-1 per cornea. Our stock titers are determined by performing plaque assays on CV-1 monolayers. </li>
 <li> Place the cornea together with the agarose scaffold epithelial side down into the virus-containing medium. </li>
 <li> Place the cornea into a tissue culture incubator to infect for 1 hr with intermittent rocking every 10-15 min. </li>
 <li> After 1 hr, aspirate the virus-containing medium and rinse 2-3 times with PBS to remove any residual viral particles. </li>
 <li> Place the cornea back into its previous position and add fresh culture medium to cover the epithelial surface. </li>
 <li> Experimental treatments may be started before or after infection, depending on the nature of the experiment. </li>
 <li> Culture medium is changed every 48 hr. </li>
</ol>
Part 4: Sample Collection
<ol class="lalpha">
 <li> Medium for plaque assay analysis. Mix the medium well and use it immediately for a plaque assay or store at -80 &deg;C for later use if collecting samples at different time points.</li>
 <li> DNA, RNA, protein, or cells from corneal epithelium 
 <ol>
 <li> Remove the agarose scaffold and rinse the cornea well with PBS. </li>
 <li> Excise the ring of scleral tissue from the cornea to ensure that only corneal epithelial material is collected. </li>
 <li> Using a scalpel, scrape off the corneal epithelial cells into the appropriate buffer, depending on the type of material to be isolated. For isolation of DNA and RNA, we use the DNeasy Blood &amp; Tissue Kit and the RNeasy Mini Kit, respectively (QIAGEN, Hilden, Germany). For collection of protein lysates, we use Laemmli buffer. For flow cytometry analysis of corneal epithelial cells, we pre-incubate the corneas in a small amount of trypsin to loosen the cells, and then dislodge them into trypsin with a scalpel. Since scraping the corneal epithelium does not yield equal amounts of tissue, it is important to include appropriate controls when analyzing the samples. We use 18S rRNA as a reference transcript in qRT-PCRs, GAPDH as a reference gene in qPCRs, and nucleolin as a loading control for Western blots. </li>
 </ol>
 </li>
 <li>Tissue samples for immunohistochemistry or immunofluorescence
 
 <ol>
 <li> Remove the agarose scaffold and rinse the cornea well with PBS. </li>
 <li> Depending on your experimental goal, use the cornea to make a paraffin tissue block or a frozen tissue block, as shown in the video. We follow standard procedures when preparing corneal tissue sections.</li>
 </ol>
 </li>
</ol>
Representative Results
Most of the methods available for studying cells in tissue culture can be easily adapted for use in corneas infected with HSV-1 ex vivo. Shown here are representative results for a few of the most common techniques applicable to studying HSV-1 infection - qPCR (Figure 1D), qRT-PCR (Figure 1B), Western blot (Figure 1F), plaque assay (Figure 1C), and tissue immunofluorescence (Figure 1E). 
<img src="/files/ftp_upload/3631/3631fig1.jpg" alt="Figure 1" /> Figure 1. Analysis of corneas infected with HSV-1 ex vivo. (A) Schematic representation of the ex vivo model of acute corneal epithelial HSV-1 infection. (B-F) Analysis of corneas infected using the method outlined in this video article. Explanted rabbit corneas were infected with 1x104 PFU/cornea of strain KOS HSV-1 and cultured in the presence (PAA) or absence (Mock) of phosphonoacetic acid (400 &mu;g/ml), a known inhibitor of HSV replication. (B) Total RNA was collected at the indicated time points, and viral transcription was assessed by qRT-PCR with primers for HSV-1 polymerase. Primers against 18S rRNA were used as a reference. n=3. Error bars indicate &plusmn; SEM. (C) Culture medium was collected at 48 hpi, and infectious particle production was assessed by plaque assay on CV-1 monolayers. (D) Total DNA was collected at 48 hpi, and viral genome replication was assessed in a qPCR assay with primers for the HSV-1 genome. Primers against GAPDH were used as a reference. n=3. Error bars indicate &plusmn; SEM. (E) Mock-treated corneas were flash-frozen at 48 hpi, sectioned, and analyzed by indirect immunofluorescence for the presence of a viral early protein (ICP8) within the infected epithelium. Nuclei are counterstained with H&ouml;chst 33258. (F) Protein lysates were collected at 48 hpi, and expression of a viral protein (ICP0) was assessed by Western blot. BCA assay was used to ensure equal loading of samples. hpi = hours post infection.

<ol>
	<li>Kaye, S., Choudhary, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Herpes+simplex+keratitis.">Herpes simplex keratitis.</a> Prog. Retin. Eye Res. 25, 355-380 (2006).</li><li>Holmberg, B. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enucleation+of+exotic+pets.">Enucleation of exotic pets.</a> Journal of Exotic Pet Medicine. 16, 88-94 (2007).</li><li>Remeijer, L., Osterhaus, A., Verjans, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+herpes+simplex+virus+keratitis:+the+pathogenesis+revisited.">Human herpes simplex virus keratitis: the pathogenesis revisited.</a> Ocul. Immunol. Inflamm. 12, 255-285 (2004).</li><li>Foreman, D. M., Pancholi, S., Jarvis-Evans, J., McLeod, D., Boulton, M. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simple+organ+culture+model+for+assessing+the+effects+of+growth+factors+on+corneal+re-epithelialization.">A simple organ culture model for assessing the effects of growth factors on corneal re-epithelialization.</a> Exp. Eye Res. 62, 555-564 (1996).</li><li>Xu, K. P., Li, X. F., Yu, F. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Corneal+organ+culture+model+for+assessing+epithelial+responses+to+surfactants.">Corneal organ culture model for assessing epithelial responses to surfactants.</a> Toxicol. Sci. 58, 306-314 (2000).</li><li>Klausner, E. A., Peer, D., Chapman, R. L., Multack, R. F., Andurkar, S. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Corneal+gene+therapy.">Corneal gene therapy.</a> J. Control Release. 124, 107-133 (2007).</li><li>Halford, W. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ICP0+antagonizes+Stat+1-dependent+repression+of+herpes+simplex+virus:+implications+for+the+regulation+of+viral+latency.">ICP0 antagonizes Stat 1-dependent repression of herpes simplex virus: implications for the regulation of viral latency.</a> Virol. J. 3, 44 (2006).</li><li>Bhattacharjee, P. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effective+treatment+of+ocular+HSK+with+a+human+apolipoprotein+E+mimetic+peptide+in+a+mouse+eye+model.">Effective treatment of ocular HSK with a human apolipoprotein E mimetic peptide in a mouse eye model.</a> Invest Ophthalmol Vis. Sci. 49, 4263-4268 (2008).</li><li>Novitskaya, E. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Difficulties+imaging+herpes+simplex+keratitis+with+fluorescein+isothiocynate-labeled+anti-HSV-1+antibodies+in+an+ex+vivo+model.">Difficulties imaging herpes simplex keratitis with fluorescein isothiocynate-labeled anti-HSV-1 antibodies in an ex vivo model.</a> Cornea. 28, 421-425 (2009).</li><li>Sharma, A., Shimeld, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+immunofluorescence+to+diagnose+herpes+simplex+virus+keratitis+in+mice.">In vivo immunofluorescence to diagnose herpes simplex virus keratitis in mice.</a> Br. J. Ophthalmol. 81, 785-788 (1997).</li></ol>

No conflicts of interest declared.

In this video article we describe a method for studying acute corneal epithelial HSV-1 infection in an ex vivo model. This model is a useful stepping stone between the in vitro and the in vivo models, because it allows for physiologically-accurate validation of cell culture results and, thereby, limits the amount of animal experimentation that must be performed. In addition, the ex vivo model provides a unique and invaluable opportunity to study epithelial herpes infection in intact ...

<table border="1">
 <tbody>
 <tr>
 <td>Reagents/Supplies</td>
 <td>Company</td>
 <td>Catalogue 				#</td>
 </tr>
 <tr>
 <td>Minimum 				Essential Medium (MEM)</td>
 <td>Mediatech</td>
 <td>10-010-CV</td>
 </tr>
 <tr>
 <td>Non-Essential 				Amino Acids (100x solution)</td>
 <td>Mediatech</td>
 <td>25-025-CI</td>
 </tr>
 <tr>
 <td>L-Glutamine</td>
 <td>Mediatech</td>
 <td>25-005-CI</td>
 </tr>
 <tr>
 <td>Penicillin G 				Sodium Salt</td>
 <td>Sigma</td>
 <td>P3032</td>
 </tr>
 <tr>
 <td>Streptomycin 				Sulfate Salt</td>
 <td>Sigma</td>
 <td>S9137</td>
 </tr>
 <tr>
 <td>Agarose</td>
 <td>Invitrogen</td>
 <td>15510-027</td>
 </tr>
 <tr>
 <td>Phosphate 				Buffered Saline (PBS)</td>
 <td>Prepared in 				lab</td>
 <td>N/A</td>
 </tr>
 <tr>
 <td>Trypsin EDTA 				(1x)</td>
 <td>Mediatech</td>
 <td>25-053-CI</td>
 </tr>
 <tr>
 <td>DNeasy Blood 				&amp; Tissue Kit</td>
 <td>QIAGEN</td>
 <td>69504</td>
 </tr>
 <tr>
 <td>RNeasy Mini 				Kit</td>
 <td>QIAGEN</td>
 <td>74104</td>
 </tr>
 <tr>
 <td>Laemmli 				Buffer</td>
 <td>Prepared in 				lab</td>
 <td>N/A</td>
 </tr>
 <tr>
 <td>Optimal 				Cutting Temperature (OCT) Compound</td>
 <td>Tissue-Tek</td>
 <td>4583</td>
 </tr>
 <tr>
 <td>Whole Rabbit 				Eyes (Young)</td>
 <td>Pel-Freez</td>
 <td>41211-2</td>
 </tr>
 <tr>
 <td>Human 				Corneas and Whole Eyes</td>
 <td>Local Eye 				Bank</td>
 <td>N/A</td>
 </tr>
 <tr>
 <td>12 Well 				Porcelain Spot Plate</td>
 <td>Avogadro's 				Lab Supply</td>
 <td>1877</td>
 </tr>
 <tr>
 <td>35 mm Tissue 				Culture Dish</td>
 <td>Falcon</td>
 <td>353001</td>
 </tr>
 <tr>
 <td>6 Well Cell 				Culture Plate</td>
 <td>Greiner 				Bio-One</td>
 <td>657160</td>
 </tr>
 <tr>
 <td>Cryomold 				Intermediate</td>
 <td>Tissue-Tek</td>
 <td>4566</td>
 </tr>
 </tbody>
</table>

ex vivo organotypic corneal model of acute epithelial herpes simplex virus type i infection

Herpes keratitis is one of the most severe pathologies associated with the herpes simplex virus-type 1 (HSV-1). Herpes keratitis is currently the leading cause of both cornea-derived and infection-associated blindness in the developed world. Typical presentation of herpes keratitis includes infection of the corneal epithelium and sometimes the deeper corneal stroma and endothelium, leading to such permanent corneal pathologies as scarring, thinning, and opacity 1.
Corneal HSV-1 infection is traditionally studied in two types of experimental models. The in vitro model, in which cultured monolayers of corneal epithelial cells are infected in a Petri dish, offers simplicity, high level of replicability, fast experiments, and relatively low costs. On the other hand, the in vivo model, in which animals such as rabbits or mice are inoculated directly in the cornea, offers a highly sophisticated physiological system, but has higher costs, longer experiments, necessary animal care, and a greater degree of variability. 
In this video article, we provide a detailed demonstration of a new ex vivo model of corneal epithelial HSV-1 infection, which combines the strengths of both the in vitro and the in vivo models. The ex vivo model utilizes intact corneas organotypically maintained in culture and infected with HSV-1. The use of the ex vivo model allows for highly physiologically-based conclusions, yet it is rather inexpensive and requires time commitment comparable to that of the in vitro model.

Watch this Scientific Journal Video about Ex Vivo Organotypic Corneal Model of Acute Epithelial Herpes Simplex Virus Type I Infection at JoVE.com

Ex Vivo Organotypic Corneal Model of Acute Epithelial Herpes Simplex Virus Type I Infection

In this video article we describe the use of a new ex vivo model of acute herpes simplex virus type I corneal epithelial infection.

Ex Vivo Organotypic Corneal Model of Acute Epithelial Herpes Simplex Virus Type I Infection

Herpes keratitis is one of the most severe pathologies associated with the herpes simplex virus-type 1 (HSV-1).  Herpes keratitis is currently the leading ...

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12.6K Views.  Drexel University College of Medicine. In this video article we describe the use of a new ex vivo model of acute herpes simplex virus type I corneal epithelial infection.

Video: Ex Vivo Organotypic Corneal Model of Acute Epithelial Herpes Simplex Virus Type I Infection

Ex vivo Culturing of Whole, Developing Drosophila Brains

We describe a method for ex vivo culturing of whole Drosophila brains. This can be used as a counterpoint to chronic genetic manipulations for investigating the cell biology and development of central brain structures by allowing acute pharmacological interventions and live imaging of cellular processes. As an example of the technique, prior work from our lab1 has shown that a previously unrecognized subcellular compartment lies between the axonal and somatodendritic compartments of axons of the Drosophila central brain. The development of this compartment, referred to as the axon initial segment (AIS)2, was shown genetically to depend on the neuron-specific cyclin-dependent kinase, Cdk5. We show here that ex vivo treatment of wild-type Drosophila larval brains with the Cdk5-specific pharmacological inhibitors roscovitine and olomoucine3 causes acute changes in actin organization, and in localization of the cell-surface protein Fasciclin 2, that mimic the changes seen in mutants that lack Cdk5 activity genetically.
A second example of the ex vivo culture technique is provided for remodeling of the connections of embryonic mushroom body (MB) gamma neurons during metamorphosis from larva to adult. The mushroom body is the center of olfactory learning and memory in the fly4, and these gamma neurons prune their axonal and dendritic branches during pupal development and then re-extend branches at a later timepoint to establish the adult innervation pattern5. Pruning of these neurons of the MB has been shown to occur via local degeneration of neurite branches6, by a mechanism that is triggered by ecdysone, a steroid hormone, acting at the ecdysone receptor B17, and that is dependent on the activity of the ubiquitin-proteasome system6. Our method of ex vivo culturing can be used to interrogate further the mechanism of developmental remodeling. We found that in the ex vivo culture setting, gamma neurons of the MB recapitulated the process of developmental pruning with a time course similar to that in vivo. It was essential, however, to wait until 1.5 hours after puparium formation before explanting the tissue in order for the cells to commit irreversibly to metamorphosis; dissection of animals at the onset of pupariation led to little or no metamorphosis in culture. Thus, with appropriate modification, the ex vivo culture approach can be applied to study dynamic as well as steady state aspects of central brain biology.

Ex vivo Culturing of Whole, Developing Drosophila Brains

This article describes a method by which one can mimic in vivo development of the Drosophila mushroom body in an ex vivo culture system.

We describe a method for ex vivo culturing of whole Drosophila brains. This can be used as a counterpoint to chronic genetic manipulations for ...

Ex Vivo Preparations of the Intact Vomeronasal Organ and Accessory Olfactory Bulb

The mouse accessory olfactory system (AOS) is a specialized sensory pathway for detecting nonvolatile social odors, pheromones, and kairomones. The first neural circuit in the AOS pathway, called the accessory olfactory bulb (AOB), plays an important role in establishing sex-typical behaviors such as territorial aggression and mating. This small (&#60;1 mm3) circuit possesses the capacity to distinguish unique behavioral states, such as sex, strain, and stress from chemosensory cues in the secretions and excretions of conspecifics. While the compact organization of this system presents unique opportunities for recording from large portions of the circuit simultaneously, investigation of sensory processing in the AOB remains challenging, largely due to its experimentally disadvantageous location in the brain. Here, we demonstrate a multi-stage dissection that removes the intact AOB inside a single hemisphere of the anterior mouse skull, leaving connections to both the peripheral vomeronasal sensory neurons (VSNs) and local neuronal circuitry intact. The procedure exposes the AOB surface to direct visual inspection, facilitating electrophysiological and optical recordings from AOB circuit elements in the absence of anesthetics. Upon inserting a thin cannula into the vomeronasal organ (VNO), which houses the VSNs, one can directly expose the periphery to social odors and pheromones while recording downstream activity in the AOB. This procedure enables controlled inquiries into AOS information processing, which can shed light on mechanisms linking pheromone exposure to changes in behavior.

Ex Vivo Preparations of the Intact Vomeronasal Organ and Accessory Olfactory Bulb

The mouse accessory olfactory bulb (AOB) has been difficult to study in the context of sensory coding. Here, we demonstrate a dissection that produces an ex vivo preparation in which AOB neurons remain functionally connected to their peripheral inputs, facilitating research into information processing of mouse pheromones and kairomones.

The mouse accessory olfactory system (AOS) is a specialized sensory pathway for detecting nonvolatile social odors, pheromones, and kairomones. The first ...

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 ...

Simultaneous ex vivo Functional Testing of Two Retinas by in vivo Electroretinogram System

An In vivo electroretinogram (ERG) signal is composed of several overlapping components originating from different retinal cell types, as well as noise from extra-retinal sources. Ex vivo ERG provides an efficient method to dissect the function of retinal cells directly from an intact isolated retina of animals or donor eyes. In addition, ex vivo ERG can be used to test the efficacy and safety of potential therapeutic agents on retina tissue from animals or humans. We show here how commercially available in vivo ERG systems can be used to conduct ex vivo ERG recordings from isolated mouse retinas. We combine the light stimulation, electronic and heating units of a standard in vivo system with custom-designed specimen holder, gravity-controlled perfusion system and electromagnetic noise shielding to record low-noise ex vivo ERG signals simultaneously from two retinas with the acquisition software included in commercial in vivo systems. Further, we demonstrate how to use this method in combination with pharmacological treatments that remove specific ERG components in order to dissect the function of certain retinal cell types.

Simultaneous ex vivo Functional Testing of Two Retinas by in vivo Electroretinogram System

Ex vivo ERG can be used to record electrical activity of retinal cells directly from isolated intact retinas of animals or humans. We demonstrate here how common in vivo ERG systems can be adapted for ex vivo ERG recordings in order to dissect the electrical activity of retinal cells.

An In vivo electroretinogram (ERG) signal is composed of several overlapping components originating from different retinal cell types, as well as noise ...

Observation of the Ciliary Movement of Choroid Plexus Epithelial Cells Ex Vivo

The choroid plexus is located in the ventricular wall of the brain, the main function of which is believed to be production of cerebrospinal fluid. Choroid plexus epithelial cells (CPECs) covering the surface of choroid plexus tissue harbor multiple unique cilia, but most of the functions of these cilia remain to be investigated. To uncover the function of CPEC cilia with particular reference to their motility, an ex vivo observation system was developed to monitor ciliary motility during embryonic, perinatal and postnatal periods. The choroid plexus was dissected out of the brain ventricle and observed under a video-enhanced contrast microscope equipped with differential interference contrast optics. Under this condition, a simple and quantitative method was developed to analyze the motile profiles of CPEC cilia for several hours ex vivo. Next, the morphological changes of cilia during development were observed by scanning electron microscopy to elucidate the relationship between the morphological maturity of cilia and motility. Interestingly, this method could delineate changes in the number and length of cilia, which peaked at postnatal day (P) 2, while the beating frequency reached a maximum at P10, followed by abrupt cessation at P14. These techniques will enable elucidation of the functions of cilia in various tissues. While related techniques have been published in a previous report1, the current study focuses on detailed techniques to observe the motility and morphology of CPEC cilia ex vivo.

Observation of the Ciliary Movement of Choroid Plexus Epithelial Cells Ex Vivo

In this study, a detailed light microscopic technique was optimized for real-time observation and analysis of the motion of CPEC cilia ex vivo together with an electron microscopic method for ultrastructural analysis.

The choroid plexus is located in the ventricular wall of the brain, the main function of which is believed to be production of cerebrospinal fluid. ...

Ex Vivo Optogenetic Dissection of Fear Circuits in Brain Slices

Optogenetic approaches are now widely used to study the function of neural populations and circuits by combining targeted expression of light-activated proteins and subsequent manipulation of neural activity by light. Channelrhodopsins (ChRs) are light-gated cation-channels and when fused to a fluorescent protein their expression allows for visualization and concurrent activation of specific cell types and their axonal projections in defined areas of the brain. Via stereotactic injection of viral vectors, ChR fusion proteins can be constitutively or conditionally expressed in specific cells of a defined brain region, and their axonal projections can subsequently be studied anatomically and functionally via ex vivo optogenetic activation in brain slices. This is of particular importance when aiming to understand synaptic properties of connections that could not be addressed with conventional electrical stimulation approaches, or in identifying novel afferent and efferent connectivity that was previously poorly understood. Here, a few examples illustrate how this technique can be applied to investigate these questions to elucidating fear-related circuits in the amygdala. The amygdala is a key region for acquisition and expression of fear, and storage of fear and emotional memories. Many lines of evidence suggest that the medial prefrontal cortex (mPFC) participates in different aspects of fear acquisition and extinction, but its precise connectivity with the amygdala is just starting to be understood. First, it is shown how ex vivo optogenetic activation can be used to study aspects of synaptic communication between mPFC afferents and target cells in the basolateral amygdala (BLA). Furthermore, it is illustrated how this ex vivo optogenetic approach can be applied to assess novel connectivity patterns using a group of GABAergic neurons in the amygdala, the paracapsular intercalated cell cluster (mpITC), as an example.

Ex Vivo Optogenetic Dissection of Fear Circuits in Brain Slices

Optogenetic approaches are widely used to manipulate neural activity and assess the consequences for brain function. Here, a technique is outlined that&#160;upon in vivo expression of the optical activator Channelrhodopsin, allows for ex vivo analysis of synaptic properties of specific long range and local neural connections in fear-related circuits.

Optogenetic approaches are now widely used to study the function of neural populations and circuits by combining targeted expression of light-activated ...

Ex Utero Electroporation and Organotypic Slice Cultures of Embryonic Mouse Brains for Live-Imaging of Migrating GABAergic Interneurons

GABAergic interneurons (INs) are critical components of neuronal networks that drive cognition and behavior. INs destined to populate the cortex migrate tangentially from their place of origin in the ventral telencephalon (including from the medial and caudal ganglionic eminences (MGE, CGE)) to the dorsal cortical plate in response to a variety of intrinsic and extrinsic cues. Different methodologies have been developed over the years to genetically manipulate specific pathways and investigate how they regulate the dynamic cytoskeletal changes required for proper IN migration. In utero electroporation has been extensively used to study the effect of gene repression or overexpression in specific IN subtypes while assessing the impact on morphology and final position. However, while this approach is readily used to modify radially migrating pyramidal cells, it is more technically challenging when targeting INs. In utero electroporation generates a low yield given the decreased survival rates of pups when electroporation is conducted before e14.5, as is customary when studying MGE-derived INs. In an alternative approach, MGE explants provide easy access to the MGE and facilitate the imaging of genetically modified INs. However, in these explants, INs migrate into an artificial matrix, devoid of endogenous guidance cues and thalamic inputs. This prompted us to optimize a method where INs can migrate in a more naturalistic environment, while circumventing the technical challenges of in utero approaches. In this paper, we describe the combination of ex utero electroporation of embryonic mouse brains followed by organotypic slice cultures to readily track, image and reconstruct genetically modified INs migrating along their natural paths in response to endogenous cues. This approach allows for both the quantification of the dynamic aspects of IN migration with time-lapse confocal imaging, as well as the detailed analysis of various morphological parameters using neuronal reconstructions on fixed immunolabeled tissue.

Ex Utero Electroporation and Organotypic Slice Cultures of Embryonic Mouse Brains for Live-Imaging of Migrating GABAergic Interneurons

Here, we provide a low-cost and reliable method to generate electroporated brain organotypic slice cultures from mouse embryos suitable for confocal microscopy and live-imaging techniques.

GABAergic interneurons (INs) are critical components of neuronal networks that drive cognition and behavior. INs destined to populate the cortex migrate ...

In Situ Visualization of Axon Growth and Growth Cone Dynamics in Acute Ex Vivo Embryonic Brain Slice Cultures

During neuronal development, axons navigate the cortical environment to reach their final destinations and establish synaptic connections. Growth cones -the sensory structures located at the distal tips of developing axons- execute this process. Studying the structure and dynamics of the growth cone is crucial to understanding axonal development and the interactions with the surrounding central nervous system (CNS) that enable it to form neural circuits. This is essential when devising methods to reintegrate axons into neural circuits following injury in fundamental research and pre-clinical contexts. Thus far, the general understanding of growth cone dynamics is primarily founded on studies of neurons cultured in two dimensions (2D). Although undoubtedly fundamental to the current knowledge of growth cone structural dynamics and response to stimuli, 2D studies misrepresent the physiological three-dimensional (3D) environment encountered by neuronal growth cones in intact CNS tissue. More recently, collagen gels were employed to overcome some of these limitations, enabling the investigation of neuronal development in 3D. However, both synthetic 2D and 3D environments lack signaling cues within CNS tissue, which direct the extension and pathfinding of developing axons. This protocol provides a method for studying axons and growth cones using organotypic brain slices, where developing axons encounter physiologically relevant physical and chemical cues. By combining fine-tuned in utero and ex utero electroporation to sparsely deliver fluorescent reporters along with super-resolution microscopy, this protocol presents a methodological pipeline for the visualization of axon and growth cone dynamics in situ. Furthermore, a detailed toolkit description of the analysis of long-term and live-cell imaging data is included.

In Situ Visualization of Axon Growth and Growth Cone Dynamics in Acute Ex Vivo Embryonic Brain Slice Cultures

This protocol demonstrates a straightforward and robust method to study in situ axon growth and growth cone dynamics. It describes how to prepare ex vivo physiologically relevant acute brain slices and provides a user-friendly analysis pipeline.

During neuronal development, axons navigate the cortical environment to reach their final destinations and establish synaptic connections. Growth cones ...

Organotypic Cultures of Adult Human Cortex as an Ex vivo Model for Human Stem Cell Transplantation and Validation

Neurodegenerative disorders are common and heterogeneous in terms of their symptoms and cellular affectation, making their study complicated due to the lack of proper animal models that fully mimic human diseases and the poor availability of post-mortem human brain tissue. Adult human nervous tissue culture offers the possibility to study different aspects of neurological disorders. Molecular, cellular, and biochemical mechanisms could be easily addressed in this system, as well as testing and validating drugs or different treatments, such as cell-based therapies. This method combines long-term organotypic cultures of the adult human cortex, obtained from epileptic patients undergoing resective surgery, and ex vivo intracortical transplantation of induced pluripotent stem cell-derived cortical progenitors. This method will allow the study of cell survival, neuronal differentiation, the formation of synaptic inputs and outputs, and the electrophysiological properties of human-derived cells after transplantation into intact adult human cortical tissue. This approach is an important step prior to the development of a 3D human disease modeling platform that will bring basic research closer to the clinical translation of stem cell-based therapies for patients with different neurological disorders and allow the development of new tools for reconstructing damaged neural circuits.

Organotypic Cultures of Adult Human Cortex as an Ex vivo Model for Human Stem Cell Transplantation and Validation

This protocol describes long-term organotypic cultures of adult human cortex combined with ex vivo intracortical transplantation of induced pluripotent stem cell-derived cortical progenitors, which present a novel methodology to further test stem cell-based therapies for human neurodegenerative disorders.

Neurodegenerative disorders are common and heterogeneous in terms of their symptoms and cellular affectation, making their study complicated due to the ...

Using Chick Embryo Brain as a Model to Study Human Glioblastoma Cell Behavior

Using the Chick Embryo Brain as a Model for In Vivo and Ex Vivo Analyses of Human Glioblastoma Cell Behavior

The chick embryo has been an ideal model system for the study of vertebrate development, particularly for experimental manipulations. Use of the chick embryo has been extended for studying the formation of human glioblastoma (GBM) brain tumors in vivo and the invasiveness of tumor cells into surrounding brain tissue. GBM tumors can be formed by injection of a suspension of fluorescently labeled cells into the E5 midbrain (optic tectum) ventricle in ovo. 
Depending on the GBM cells, compact tumors randomly form in the ventricle and within the brain wall, and groups of cells invade the brain wall tissue. Thick tissue sections (350 &#181;m) of fixed E15 tecta with tumors can be immunostained to reveal that invading cells often migrate along blood vessels when analyzed by 3D reconstruction of confocal z-stack images. Live E15 midbrain and forebrain slices (250-350 &#181;m) can be cultured on membrane inserts, where fluorescently labeled GBM cells can be introduced into non-random locations to provide ex vivo co-cultures to analyze cell invasion, which also can occur along blood vessels, over a period of about 1 week. These ex vivo co-cultures can be monitored by widefield or confocal fluorescence time-lapse microscopy to observe live cell behavior. 
Co-cultured slices then can be fixed, immunostained, and analyzed by confocal microscopy to determine whether or not the invasion occurred along blood vessels or axons. Additionally, the co-culture system can be used for investigating potential cell-cell interactions by placing aggregates of different cell types and colors in different precise locations and observing cell movements. Drug treatments can be performed on ex vivo cultures, whereas these treatments are not compatible with the in ovo system. These two complementary approaches allow for detailed and precise analyses of human GBM cell behavior and tumor formation in a highly manipulatable vertebrate brain environment.

Author Spotlight: Using the Chick Embryo Brain as a Model for In Vivo and Ex Vivo Analyses of Human Glioblastoma Cell Behavior  

Chick embryos are used for studying human glioblastoma (GBM) brain tumors in ovo and in ex vivo brain slice co-cultures. GBM cell behavior can be recorded by time-lapse microscopy in ex vivo co-cultures, and both preparations can be analyzed at the experimental endpoint by detailed 3D confocal analysis.

The chick embryo has been an ideal model system for the study of vertebrate development, particularly for experimental manipulations. Use of the chick ...