The development of peripheral nerves is an intriguing process. Neurons send out axons to innervate specific targets, which in humans are often more than 100 cm away from the soma of the neuron. Neuronal survival during development depends on target-derived growth factors but also on the support of Schwann cells (SCs). To this end SC ensheath axons from the region of the neuronal soma (or the transition from central to peripheral nervous system) to the synapse or neuromuscular junction. Schwann cells are derivatives of the neural crest and migrate as precursors along emerging axons until the entire axon is covered with SCs. This shows the importance of SC migration for the development of the peripheral nervous system and underlines the necessity to investigate this process. In order to analyze SC development, a setup is needed which next to the SCs also includes their physiological substrate for migration, the axon. Due to intrauterine development in vivo time-lapse imaging, however, is not feasible in placental vertebrates like mouse (mus musculus). To circumvent this, we adapted the superior cervical ganglion (SCG) explant technique. Upon treatment with nerve growth factor (NGF) SCG explants extend axons, followed by SC precursors migrating along the axons from the ganglion to the periphery. The beauty of this system is that the SC are derived from a pool of endogenous SC and that they migrate along their own physiological axons which are growing at the same time. This system is especially intriguing, because the SC development along axons can be analyzed by time-lapse imaging, opening further possibilities to gain insights into SC migration.
20 Related JoVE Articles!
Reproducible Mouse Sciatic Nerve Crush and Subsequent Assessment of Regeneration by Whole Mount Muscle Analysis
Institutions: Temple University .
Regeneration in the peripheral nervous system (PNS) is widely studied both for its relevance to human disease and to understand the robust regenerative response mounted by PNS neurons thereby possibly illuminating the failures of CNS regeneration1
. Sciatic nerve crush (axonotmesis) is one of the most common models of peripheral nerve injury in rodents2
. Crushing interrupts all axons but Schwann cell basal laminae are preserved so that regeneration is optimal3,4
. This allows the investigator to study precisely the ability of a growing axon to interact with both the Schwann cell and basal laminae4
. Rats have generally been the preferred animal models for experimental nerve crush. They are widely available and their lesioned sciatic nerve provides a reasonable approximation of human nerve lesions5,4
. Though smaller in size than rat nerve, the mouse nerve has many similar qualities. Most importantly though, mouse models are increasingly valuable because of the wide availability of transgenic lines now allows for a detailed dissection of the individual molecules critical for nerve regeneration6, 7
. Prior investigators have used multiple methods to produce a nerve crush or injury including simple angled forceps, chilled forceps, hemostatic forceps, vascular clamps, and investigator-designed clamps8,9,10,11,12
. Investigators have also used various methods of marking the injury site including suture, carbon particles and fluorescent beads13,14,1
. We describe our method to obtain a reproducibly complete sciatic nerve crush with accurate and persistent marking of the crush-site using a fine hemostatic forceps and subsequent carbon crush-site marking. As part of our description of the sciatic nerve crush procedure we have also included a relatively simple method of muscle whole mount we use to subsequently quantify regeneration.
Neuroscience, Issue 60, Sciatic nerve crush, regeneration, neuromuscular junction, muscle whole mount, mouse
Acute Dissociation of Lamprey Reticulospinal Axons to Enable Recording from the Release Face Membrane of Individual Functional Presynaptic Terminals
Institutions: University of Illinois at Chicago.
Synaptic transmission is an extremely rapid process. Action potential driven influx of Ca2+
into the presynaptic terminal, through voltage-gated calcium channels (VGCCs) located in the release face membrane, is the trigger for vesicle fusion and neurotransmitter release. Crucial to the rapidity of synaptic transmission is the spatial and temporal synchrony between the arrival of the action potential, VGCCs and the neurotransmitter release machinery. The ability to directly record Ca2+
currents from the release face membrane of individual presynaptic terminals is imperative for a precise understanding of the relationship between presynaptic Ca2+
and neurotransmitter release. Access to the presynaptic release face membrane for electrophysiological recording is not available in most preparations and presynaptic Ca2+
entry has been characterized using imaging techniques and macroscopic current measurements – techniques that do not have sufficient temporal resolution to visualize Ca2+
entry. The characterization of VGCCs directly at single presynaptic terminals has not been possible in central synapses and has thus far been successfully achieved only in the calyx-type synapse of the chick ciliary ganglion and in rat calyces. We have successfully addressed this problem in the giant reticulospinal synapse of the lamprey spinal cord by developing an acutely dissociated preparation of the spinal cord that yields isolated reticulospinal axons with functional presynaptic terminals devoid of postsynaptic structures. We can fluorescently label and identify individual presynaptic terminals and target them for recording. Using this preparation, we have characterized VGCCs directly at the release face of individual presynaptic terminals using immunohistochemistry and electrophysiology approaches. Ca2+
currents have been recorded directly at the release face membrane of individual presynaptic terminals, the first such recording to be carried out at central synapses.
Neuroscience, Issue 92, reticulospinal synapse, reticulospinal axons, presynaptic terminal, presynaptic calcium, voltage-gated calcium channels, vesicle fusion, synaptic transmission, neurotransmitter release, spinal cord, lamprey, synaptic vesicles, acute dissociation
Genetic Study of Axon Regeneration with Cultured Adult Dorsal Root Ganglion Neurons
Institutions: Johns Hopkins University School of Medicine, Johns Hopkins University School of Medicine.
It is well known that mature neurons in the central nervous system (CNS) cannot regenerate their axons after injuries due to diminished intrinsic ability to support axon growth and a hostile environment in the mature CNS1,2
. In contrast, mature neurons in the peripheral nervous system (PNS) regenerate readily after injuries3
. Adult dorsal root ganglion (DRG) neurons are well known to regenerate robustly after peripheral nerve injuries. Each DRG neuron grows one axon from the cell soma, which branches into two axonal branches: a peripheral branch innervating peripheral targets and a central branch extending into the spinal cord. Injury of the DRG peripheral axons results in substantial axon regeneration, whereas central axons in the spinal cord regenerate poorly after the injury. However, if the peripheral axonal injury occurs prior to the spinal cord injury (a process called the conditioning lesion), regeneration of central axons is greatly improved4
. Moreover, the central axons of DRG neurons share the same hostile environment as descending corticospinal axons in the spinal cord. Together, it is hypothesized that the molecular mechanisms controlling axon regeneration of adult DRG neurons can be harnessed to enhance CNS axon regeneration. As a result, adult DRG neurons are now widely used as a model system to study regenerative axon growth5-7
Here we describe a method of adult DRG neuron culture that can be used for genetic study of axon regeneration in vitro
. In this model adult DRG neurons are genetically manipulated via electroporation-mediated gene transfection6,8
. By transfecting neurons with DNA plasmid or si/shRNA, this approach enables both gain- and loss-of-function experiments to investigate the role of any gene-of-interest in axon growth from adult DRG neurons. When neurons are transfected with si/shRNA, the targeted endogenous protein is usually depleted after 3-4 days in culture, during which time robust axon growth has already occurred, making the loss-of-function studies less effective. To solve this problem, the method described here includes a re-suspension and re-plating step after transfection, which allows axons to re-grow from neurons in the absence of the targeted protein. Finally, we provide an example of using this in vitro
model to study the role of an axon regeneration-associated gene, c-Jun, in mediating axon growth from adult DRG neurons9
Neuroscience, Issue 66, Physiology, Developmental Biology, cell culture, axon regeneration, axon growth, dorsal root ganglion, spinal cord injury
Dissection and Culture of Mouse Dopaminergic and Striatal Explants in Three-Dimensional Collagen Matrix Assays
Institutions: University Medical Center Utrecht.
Midbrain dopamine (mdDA) neurons project via the medial forebrain bundle towards several areas in the telencephalon, including the striatum1
. Reciprocally, medium spiny neurons in the striatum that give rise to the striatonigral (direct) pathway innervate the substantia nigra2
. The development of these axon tracts is dependent upon the combinatorial actions of a plethora of axon growth and guidance cues including molecules that are released by neurites or by (intermediate) target regions3,4
. These soluble factors can be studied in vitro
by culturing mdDA and/or striatal explants in a collagen matrix which provides a three-dimensional substrate for the axons mimicking the extracellular environment. In addition, the collagen matrix allows for the formation of relatively stable gradients of proteins released by other explants or cells placed in the vicinity (e.g. see references 5 and 6). Here we describe methods for the purification of rat tail collagen, microdissection of dopaminergic and striatal explants, their culture in collagen gels and subsequent immunohistochemical and quantitative analysis. First, the brains of E14.5 mouse embryos are isolated and dopaminergic and striatal explants are microdissected. These explants are then (co)cultured in collagen gels on coverslips for 48 to 72 hours in vitro
. Subsequently, axonal projections are visualized using neuronal markers (e.g. tyrosine hydroxylase, DARPP32, or βIII tubulin) and axon growth and attractive or repulsive axon responses are quantified. This neuronal preparation is a useful tool for in vitro
studies of the cellular and molecular mechanisms of mesostriatal and striatonigral axon growth and guidance during development. Using this assay, it is also possible to assess other (intermediate) targets for dopaminergic and striatal axons or to test specific molecular cues.
Neuroscience, Issue 61, Axon guidance, collagen matrix, development, dissection, dopamine, medium spiny neuron, rat tail collagen, striatum, striatonigral, mesostriatal
Assaying the Ability of Diffusible Signaling Molecules to Reorient Embryonic Spinal Commissural Axons
Institutions: University of Southern California, University of Southern California.
Dorsal commissural axons in the vertebrate spinal cord1
have been an invaluable model system in which to identify axon guidance signals. Here, we describe an in vitro
assay, "the reorientation assay", that has been used extensively to study the effect of extrinsic and intrinsic signals on the orientation of commissural axons2
. This assay was developed by numerous people in the laboratories of Jane Dodd, Thomas Jessell and Andrew Lumsden (see acknowledgements for more details) and versions of this assay were used to demonstrate the reorientation activities of key axon guidance molecules, including the BMP chemorepellent in the roof plate3,4
and the chemoattractive activities of Netrin15
and Sonic Hedgehog (Shh)6
in the floor plate in the spinal cord.
Explants comprising 2-3 segments of the dorsal two-thirds of spinal cord are dissected from embryonic day (E) 11 rats and cultured in three dimensional collagen gels7
. E11 dorsal spinal explants contain newly born commissural neurons, which can be identified by their axonal expression of the glycoprotein, Tag18
. Over the course of 30-40 hours in culture, the commissural axon trajectory is recapitulated in these dorsal explants with a time course similar to that seen in vivo
. This axonal trajectory can be challenged by placing either test tissues or a COS cell aggregate expressing a candidate signaling molecule in contact with one of the lateral edges of the dorsal explant. Commissural axons extending in the vicinity of the appended tissue will grow under the influence of both the endogenous roof plate and signals from the ectopic lateral tissue. The degree to which commissural axons are reoriented under these circumstances can be quantified. Using this assay, it is possible both to examine the sufficiency of a particular signal to reorient commissural axons3,4
as well the necessity for this signal to direct the commissural trajectory9
Neuroscience, Issue 37, commissural axons, spinal cord, rat, explant, collagen, COS cells, bone morphogenetic proteins (BMPs)
Protocol for Culturing Sympathetic Neurons from Rat Superior Cervical Ganglia (SCG)
Institutions: Columbia University, Columbia University.
The superior cervical ganglia (SCG) in rats are small, glossy, almond-shaped structures that contain sympathetic neurons. These neurons provide sympathetic innervations for the head and neck regions and they constitute a well-characterized and relatively homogeneous population (4). Sympathetic neurons are dependent on nerve growth factor (NGF) for survival, differentiation and axonal growth and the wide-spread availability of NGF facilitates their culture and experimental manipulation (2, 3, 6). For these reasons, cultured sympathetic neurons have been used in a wide variety of studies including neuronal development and differentiation, mechanisms of programmed and pathological cell death, and signal transduction (1, 2, 5, and 6). Dissecting out the SCG from newborn rats and culturing sympathetic neurons is not very complicated and can be mastered fairly quickly. In this article, we will describe in detail how to dissect out the SCG from newborn rat pups and to use them to establish cultures of sympathetic neurons. The article will also describe the preparatory steps and the various reagents and equipment that are needed to achieve this.
Neuroscience, Issue 23, SCG, sympathetic neurons, primary neuronal culture, NGF, trophic factor, apoptosis, programmed cell death
Inhibitory Synapse Formation in a Co-culture Model Incorporating GABAergic Medium Spiny Neurons and HEK293 Cells Stably Expressing GABAA Receptors
Institutions: University College London.
Inhibitory neurons act in the central nervous system to regulate the dynamics and spatio-temporal co-ordination of neuronal networks. GABA (γ-aminobutyric acid) is the predominant inhibitory neurotransmitter in the brain. It is released from the presynaptic terminals of inhibitory neurons within highly specialized intercellular junctions known as synapses, where it binds to GABAA
Rs) present at the plasma membrane of the synapse-receiving, postsynaptic neurons. Activation of these GABA-gated ion channels leads to influx of chloride resulting in postsynaptic potential changes that decrease the probability that these neurons will generate action potentials.
During development, diverse types of inhibitory neurons with distinct morphological, electrophysiological and neurochemical characteristics have the ability to recognize their target neurons and form synapses which incorporate specific GABAA
Rs subtypes. This principle of selective innervation of neuronal targets raises the question as to how the appropriate synaptic partners identify each other.
To elucidate the underlying molecular mechanisms, a novel in vitro
co-culture model system was established, in which medium spiny GABAergic neurons, a highly homogenous population of neurons isolated from the embryonic striatum, were cultured with stably transfected HEK293 cell lines that express different GABAA
R subtypes. Synapses form rapidly, efficiently and selectively in this system, and are easily accessible for quantification. Our results indicate that various GABAA
R subtypes differ in their ability to promote synapse formation, suggesting that this reduced in vitro
model system can be used to reproduce, at least in part, the in vivo
conditions required for the recognition of the appropriate synaptic partners and formation of specific synapses. Here the protocols for culturing the medium spiny neurons and generating HEK293 cells lines expressing GABAA
Rs are first described, followed by detailed instructions on how to combine these two cell types in co-culture and analyze the formation of synaptic contacts.
Neuroscience, Issue 93, Developmental neuroscience, synaptogenesis, synaptic inhibition, co-culture, stable cell lines, GABAergic, medium spiny neurons, HEK 293 cell line
Using Microfluidics Chips for Live Imaging and Study of Injury Responses in Drosophila Larvae
Institutions: University of Michigan, University of Michigan, University of Michigan, University of Michigan, University of Michigan.
Live imaging is an important technique for studying cell biological processes, however this can be challenging in live animals. The translucent cuticle of the Drosophila
larva makes it an attractive model organism for live imaging studies. However, an important challenge for live imaging techniques is to noninvasively immobilize and position an animal on the microscope. This protocol presents a simple and easy to use method for immobilizing and imaging Drosophila
larvae on a polydimethylsiloxane (PDMS) microfluidic device, which we call the 'larva chip'. The larva chip is comprised of a snug-fitting PDMS microchamber that is attached to a thin glass coverslip, which, upon application of a vacuum via a syringe, immobilizes the animal and brings ventral structures such as the nerve cord, segmental nerves, and body wall muscles, within close proximity to the coverslip. This allows for high-resolution imaging, and importantly, avoids the use of anesthetics and chemicals, which facilitates the study of a broad range of physiological processes. Since larvae recover easily from the immobilization, they can be readily subjected to multiple imaging sessions. This allows for longitudinal studies over time courses ranging from hours to days. This protocol describes step-by-step how to prepare the chip and how to utilize the chip for live imaging of neuronal events in 3rd
instar larvae. These events include the rapid transport of organelles in axons, calcium responses to injury, and time-lapse studies of the trafficking of photo-convertible proteins over long distances and time scales. Another application of the chip is to study regenerative and degenerative responses to axonal injury, so the second part of this protocol describes a new and simple procedure for injuring axons within peripheral nerves by a segmental nerve crush.
Bioengineering, Issue 84, Drosophila melanogaster, Live Imaging, Microfluidics, axonal injury, axonal degeneration, calcium imaging, photoconversion, laser microsurgery
Live Cell Imaging of Alphaherpes Virus Anterograde Transport and Spread
Institutions: Montana State University, Princeton University.
Advances in live cell fluorescence microscopy techniques, as well as the construction of recombinant viral strains that express fluorescent fusion proteins have enabled real-time visualization of transport and spread of alphaherpes virus infection of neurons. The utility of novel fluorescent fusion proteins to viral membrane, tegument, and capsids, in conjunction with live cell imaging, identified viral particle assemblies undergoing transport within axons. Similar tools have been successfully employed for analyses of cell-cell spread of viral particles to quantify the number and diversity of virions transmitted between cells. Importantly, the techniques of live cell imaging of anterograde transport and spread produce a wealth of information including particle transport velocities, distributions of particles, and temporal analyses of protein localization. Alongside classical viral genetic techniques, these methodologies have provided critical insights into important mechanistic questions. In this article we describe in detail the imaging methods that were developed to answer basic questions of alphaherpes virus transport and spread.
Virology, Issue 78, Infection, Immunology, Medicine, Molecular Biology, Cellular Biology, Microbiology, Genetics, Microscopy, Fluorescence, Neurobiology, Herpes virus, fluorescent protein, epifluorescent microscopy, neuronal culture, axon, virion, video microscopy, virus, live cell, imaging
In vivo Imaging of Optic Nerve Fiber Integrity by Contrast-Enhanced MRI in Mice
Institutions: Jena University Hospital, Fritz Lipmann Institute, Jena, Jena University Hospital.
The rodent visual system encompasses retinal ganglion cells and their axons that form the optic nerve to enter thalamic and midbrain centers, and postsynaptic projections to the visual cortex. Based on its distinct anatomical structure and convenient accessibility, it has become the favored structure for studies on neuronal survival, axonal regeneration, and synaptic plasticity. Recent advancements in MR imaging have enabled the in vivo
visualization of the retino-tectal part of this projection using manganese mediated contrast enhancement (MEMRI). Here, we present a MEMRI protocol for illustration of the visual projection in mice, by which resolutions of (200 µm)3
can be achieved using common 3 Tesla scanners. We demonstrate how intravitreal injection of a single dosage of 15 nmol MnCl2
leads to a saturated enhancement of the intact projection within 24 hr. With exception of the retina, changes in signal intensity are independent of coincided visual stimulation or physiological aging. We further apply this technique to longitudinally monitor axonal degeneration in response to acute optic nerve injury, a paradigm by which Mn2+
transport completely arrests at the lesion site. Conversely, active Mn2+
transport is quantitatively proportionate to the viability, number, and electrical activity of axon fibers. For such an analysis, we exemplify Mn2+
transport kinetics along the visual path in a transgenic mouse model (NF-κB p50KO
) displaying spontaneous atrophy of sensory, including visual, projections. In these mice, MEMRI indicates reduced but not delayed Mn2+
transport as compared to wild type mice, thus revealing signs of structural and/or functional impairments by NF-κB mutations.
In summary, MEMRI conveniently bridges in vivo
assays and post mortem
histology for the characterization of nerve fiber integrity and activity. It is highly useful for longitudinal studies on axonal degeneration and regeneration, and investigations of mutant mice for genuine or inducible phenotypes.
Neuroscience, Issue 89, manganese-enhanced MRI, mouse retino-tectal projection, visual system, neurodegeneration, optic nerve injury, NF-κB
Sequential Photo-bleaching to Delineate Single Schwann Cells at the Neuromuscular Junction
Institutions: Technische Universität München, Technische Universität München, Technische Universität München, Technische Universität München.
Sequential photo-bleaching provides a non-invasive way to label individual SCs at the NMJ. The NMJ is the largest synapse of the mammalian nervous system and has served as guiding model to study synaptic structure and function. In mouse NMJs motor axon terminals form pretzel-like contact sites with muscle fibers. The motor axon and its terminal are sheathed by SCs. Over the past decades, several transgenic mice have been generated to visualize motor neurons and SCs, for example Thy1
Along motor axons, myelinating axonal SCs are arranged in non-overlapping internodes, separated by nodes of Ranvier, to enable saltatory action potential propagation. In contrast, terminal SCs at the synapse are specialized glial cells, which monitor and promote neurotransmission, digest debris and guide regenerating axons. NMJs are tightly covered by up to half a dozen non-myelinating terminal SCs - these, however, cannot be individually resolved by light microscopy, as they are in direct membrane contact3
Several approaches exist to individually visualize terminal SCs. None of these are flawless, though. For instance, dye filling, where single cells are impaled with a dye-filled microelectrode, requires destroying a labelled cell before filling a second one. This is not compatible with subsequent time-lapse recordings3
. Multi-spectral "Brainbow" labeling of SCs has been achieved by using combinatorial expression of fluorescent proteins4
. However, this technique requires combining several transgenes and is limited by the expression pattern of the promoters used. In the future, expression of "photo-switchable" proteins in SCs might be yet another alternative5
. Here we present sequential photo-bleaching, where single cells are bleached, and their image obtained by subtraction. We believe that this approach - due to its ease and versatility - represents a lasting addition to the neuroscientist's technology palette, especially as it can be used in vivo
and transferred to others cell types, anatomical sites or species6
In the following protocol, we detail the application of sequential bleaching and subsequent confocal time-lapse microscopy to terminal SCs in triangularis sterni muscle explants. This thin, superficial and easily dissected nerve-muscle preparation7,8
has proven useful for studies of NMJ development, physiology and pathology9
. Finally, we explain how the triangularis sterni muscle is prepared after fixation to perform correlated high-resolution confocal imaging, immunohistochemistry or ultrastructural examinations.
Neuroscience, Issue 71, Cellular Biology, Molecular Biology, Neurobiology, Immunology, Medicine, Anatomy, Physiology, Surgery, Triangularis sterni, explant, Schwann cells, imaging, neuromuscular junction, immunohistochemistry, bleaching, muscle, nerve, mouse, animal model
Production and Isolation of Axons from Sensory Neurons for Biochemical Analysis Using Porous Filters
Institutions: Montreal Neurological Institute, McGill University.
Neuronal axons use specific mechanisms to mediate extension, maintain integrity, and induce degeneration. An appropriate balance of these events is required to shape functional neuronal circuits. The protocol described here explains how to use cell culture inserts bearing a porous membrane (filter) to obtain large amounts of pure axonal preparations suitable for examination by conventional biochemical or immunocytochemical techniques. The functionality of these filter inserts will be demonstrated with models of developmental pruning and Wallerian degeneration, using explants of embryonic dorsal root ganglion. Axonal integrity and function is compromised in a wide variety of neurodegenerative pathologies. Indeed, it is now clear that axonal dysfunction appears much earlier in the course of the disease than neuronal soma loss in several neurodegenerative diseases, indicating that axonal-specific processes are primarily targeted in these disorders. By obtaining pure axonal samples for analysis by molecular and biochemical techniques, this technique has the potential to shed new light into mechanisms regulating the physiology and pathophysiology of axons. This in turn will have an impact in our understanding of the processes that drive degenerative diseases of the nervous system.
Neuroscience, Issue 89, neuron, axon, filter inserts, culture system, dorsal root ganglion, axonal degeneration
An Ex Vivo Laser-induced Spinal Cord Injury Model to Assess Mechanisms of Axonal Degeneration in Real-time
Institutions: University of Louisville, University of Calgary.
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.
Neuroscience, Issue 93, spinal cord injury, axon, myelin, two-photon excitation microscopy, Nile Red, axonal degeneration, axonal dieback, axonal retraction
A Primary Neuron Culture System for the Study of Herpes Simplex Virus Latency and Reactivation
Institutions: New York University School of Medicine, New York University School of Medicine, New York University School of Medicine, New York University School of Medicine, New York University School of Medicine, New York University School of Medicine, New York University School of Medicine.
Herpes simplex virus type-1 (HSV-1) establishes a life-long latent infection in peripheral neurons. This latent reservoir is the source of recurrent reactivation events that ensure transmission and contribute to clinical disease. Current antivirals do not impact the latent reservoir and there are no vaccines. While the molecular details of lytic replication are well-characterized, mechanisms controlling latency in neurons remain elusive. Our present understanding of latency is derived from in vivo
studies using small animal models, which have been indispensable for defining viral gene requirements and the role of immune responses. However, it is impossible to distinguish specific effects on the virus-neuron relationship from more general consequences of infection mediated by immune or non-neuronal support cells in live animals. In addition, animal experimentation is costly, time-consuming, and limited in terms of available options for manipulating host processes. To overcome these limitations, a neuron-only system is desperately needed that reproduces the in vivo
characteristics of latency and reactivation but offers the benefits of tissue culture in terms of homogeneity and accessibility.
Here we present an in vitro
model utilizing cultured primary sympathetic neurons from rat superior cervical ganglia (SCG) (Figure 1
) to study HSV-1 latency and reactivation that fits most if not all of the desired criteria. After eliminating non-neuronal cells, near-homogeneous TrkA+
neuron cultures are infected with HSV-1 in the presence of acyclovir (ACV) to suppress lytic replication. Following ACV removal, non-productive HSV-1 infections that faithfully exhibit accepted hallmarks of latency are efficiently established. Notably, lytic mRNAs, proteins, and infectious virus become undetectable, even in the absence of selection, but latency-associated transcript (LAT) expression persists in neuronal nuclei. Viral genomes are maintained at an average copy number of 25 per neuron and can be induced to productively replicate by interfering with PI3-Kinase / Akt signaling or the simple withdrawal of nerve growth factor1
. A recombinant HSV-1 encoding EGFP fused to the viral lytic protein Us11 provides a functional, real-time marker for replication resulting from reactivation that is readily quantified. In addition to chemical treatments, genetic methodologies such as RNA-interference or gene delivery via lentiviral vectors can be successfully applied to the system permitting mechanistic studies that are very difficult, if not impossible, in animals. In summary, the SCG-based HSV-1 latency / reactivation system provides a powerful, necessary tool to unravel the molecular mechanisms controlling HSV1 latency and reactivation in neurons, a long standing puzzle in virology whose solution may offer fresh insights into developing new therapies that target the latent herpesvirus reservoir.
Immunology, Issue 62, neuron cell culture, Herpes Simplex Virus (HSV), molecular biology, virology
Motor Nerve Transection and Time-lapse Imaging of Glial Cell Behaviors in Live Zebrafish
Institutions: University of Virginia .
The nervous system is often described as a hard-wired component of the body even though it is a considerably fluid organ system that reacts to external stimuli in a consistent, stereotyped manner, while maintaining incredible flexibility and plasticity. Unlike the central nervous system (CNS), the peripheral nervous system (PNS) is capable of significant repair, but we have only just begun to understand the cellular and molecular mechanisms that govern this phenomenon. Using zebrafish as a model system, we have the unprecedented opportunity to couple regenerative studies with in vivo
imaging and genetic manipulation. Peripheral nerves are composed of axons surrounded by layers of glia and connective tissue. Axons are ensheathed by myelinating or non-myelinating Schwann cells, which are in turn wrapped into a fascicle by a cellular sheath called the perineurium. Following an injury, adult peripheral nerves have the remarkable capacity to remove damaged axonal debris and re-innervate targets. To investigate the roles of all peripheral glia in PNS regeneration, we describe here an axon transection assay that uses a commercially available nitrogen-pumped dye laser to axotomize motor nerves in live transgenic zebrafish. We further describe the methods to couple these experiments to time-lapse imaging of injured and control nerves. This experimental paradigm can be used to not only assess the role that glia play in nerve regeneration, but can also be the platform for elucidating the molecular mechanisms that govern nervous system repair.
Neuroscience, Issue 76, Neurobiology, Cellular Biology, Molecular Biology, Genetics, Developmental Biology, Neuroglia, Zebrafish, Danio rerio, Nerve Regeneration, laser transection, nerve injury, glia, glial cell, in vivo imaging, imaging, nerves, embryos, CNS, PNS, confocal microscopy, microdissection, animal model
Real-time Imaging of Axonal Transport of Quantum Dot-labeled BDNF in Primary Neurons
Institutions: University of California, San Diego, Shanghai Jiao Tong University, University of California, San Diego, VA San Diego Healthcare System.
BDNF plays an important role in several facets of neuronal survival, differentiation, and function. Structural and functional deficits in axons are increasingly viewed as an early feature of neurodegenerative diseases, including Alzheimer’s disease (AD) and Huntington’s disease (HD). As yet unclear is the mechanism(s) by which axonal injury is induced. We reported the development of a novel technique to produce biologically active, monobiotinylated BDNF (mBtBDNF) that can be used to trace axonal transport of BDNF. Quantum dot-labeled BDNF (QD-BDNF) was produced by conjugating quantum dot 655 to mBtBDNF. A microfluidic device was used to isolate axons from neuron cell bodies. Addition of QD-BDNF to the axonal compartment allowed live imaging of BDNF transport in axons. We demonstrated that QD-BDNF moved essentially exclusively retrogradely, with very few pauses, at a moving velocity of around 1.06 μm/sec. This system can be used to investigate mechanisms of disrupted axonal function in AD or HD, as well as other degenerative disorders.
Neuroscience, Issue 91, live imaging, brain-derived neurotrophic factor (BDNF), quantum dot, trafficking, axonal retrograde transport, microfluidic chamber
Analysis of Schwann-astrocyte Interactions Using In Vitro Assays
Institutions: University of Cambridge.
Schwann cells are one of the commonly used cells in repair strategies following spinal cord injuries. Schwann cells are capable of supporting axonal regeneration and sprouting by secreting growth factors 1,2
and providing growth promoting adhesion molecules 3
and extracellular matrix molecules 4
. In addition they myelinate the demyelinated axons at the site of injury 5
However following transplantation, Schwann cells do not migrate from the site of implant and do not intermingle with the host astrocytes 6,7
. This results in formation of a sharp boundary between the Schwann cells and astrocytes, creating an obstacle for growing axons trying to exit the graft back into the host tissue proximally and distally. Astrocytes in contact with Schwann cells also undergo hypertrophy and up-regulate the inhibitory molecules 8-13
assays have been used to model Schwann cell-astrocyte interactions and have been important in understanding the mechanism underlying the cellular behaviour.
These in vitro
assays include boundary assay, where a co-culture is made using two different cells with each cell type occupying different territories with only a small gap separating the two cell fronts. As the cells divide and migrate, the two cellular fronts get closer to each other and finally collide. This allows the behaviour of the two cellular populations to be analyzed at the boundary. Another variation of the same technique is to mix the two cellular populations in culture and over time the two cell types segregate with Schwann cells clumped together as islands in between astrocytes together creating multiple Schwann-astrocyte boundaries.
The second assay used in studying the interaction of two cell types is the migration assay where cellular movement can be tracked on the surface of the other cell type monolayer 14,15
. This assay is commonly known as inverted coverslip assay. Schwann cells are cultured on small glass fragments and they are inverted face down onto the surface of astrocyte monolayers and migration is assessed from the edge of coverslip.
Both assays have been instrumental in studying the underlying mechanisms involved in the cellular exclusion and boundary formation. Some of the molecules identified using these techniques include N-Cadherins 15, Chondroitin Sulphate proteoglycans(CSPGs) 16,17
, FGF/Heparin 18
This article intends to describe boundary assay and migration assay in stepwise fashion and elucidate the possible technical problems that might occur.
Cellular Biology, Issue 47, Schwann cell, astrocyte, boundary, migration, repulsion
Imaging Analysis of Neuron to Glia Interaction in Microfluidic Culture Platform (MCP)-based Neuronal Axon and Glia Co-culture System
Institutions: Tufts University, Tufts Sackler School of Graduate Biomedical Sciences.
Proper neuron to glia interaction is critical to physiological function of the central nervous system (CNS). This bidirectional communication is sophisticatedly mediated by specific signaling pathways between neuron and glia1,2
. Identification and characterization of these signaling pathways is essential to the understanding of how neuron to glia interaction shapes CNS physiology. Previously, neuron and glia mixed cultures have been widely utilized for testing and characterizing signaling pathways between neuron and glia. What we have learned from these preparations and other in vivo
tools, however, has suggested that mutual signaling between neuron and glia often occurred in specific compartments within neurons (i.e.
, axon, dendrite, or soma)3
. This makes it important to develop a new culture system that allows separation of neuronal compartments and specifically examines the interaction between glia and neuronal axons/dendrites. In addition, the conventional mixed culture system is not capable of differentiating the soluble factors and direct membrane contact signals between neuron and glia. Furthermore, the large quantity of neurons and glial cells in the conventional co-culture system lacks the resolution necessary to observe the interaction between a single axon and a glial cell.
In this study, we describe a novel axon and glia co-culture system with the use of a microfluidic culture platform (MCP). In this co-culture system, neurons and glial cells are cultured in two separate chambers that are connected through multiple central channels. In this microfluidic culture platform, only neuronal processes (especially axons) can enter the glial side through the central channels. In combination with powerful fluorescent protein labeling, this system allows direct examination of signaling pathways between axonal/dendritic and glial interactions, such as axon-mediated transcriptional regulation in glia, glia-mediated receptor trafficking in neuronal terminals, and glia-mediated axon growth. The narrow diameter of the chamber also significantly prohibits the flow of the neuron-enriched medium into the glial chamber, facilitating probing of the direct membrane-protein interaction between axons/dendrites and glial surfaces.
Neuroscience, Issue 68, Molecular Biology, Cellular Biology, Biophysics, Microfluidics, Microfluidic culture platform, Compartmented culture, Neuron to glia signaling, neurons, glia, cell culture
Retrograde Labeling of Retinal Ganglion Cells by Application of Fluoro-Gold on the Surface of Superior Colliculus
Institutions: The University of Hong Kong - HKU.
Retinal ganglion cell (RGC) counting is essential to evaluate retinal degeneration especially in glaucoma. Reliable RGC labeling is fundamental for evaluating the effects of any treatment. In rat, about 98% of RGCs is known to project to the contralateral superior colliculus (SC) (Forrester and Peters, 1967). Applying fluoro-gold (FG) on the surface of SC can label almost all the RGCs, so that we can focus on this most vulnerable retinal neuron in glaucoma. FG is taken up by the axon terminals of retinal ganglion cells and bilaterally transported retrogradely to its somas in the retina. Compare with retrograde labeling of RGC by putting FG at stump of transected optic nerve for 2 days, the interference of RGC survival is minimized. Compare with cresyl violet staining that stains RGCs, amacrine cells and endothelium of the blood vessel in the retinal ganglion cell layer, this labeling method is more specific to the RGC. This video describes the method of retrograde labeling of RGC by applying FG on the surface of SC. The surgical procedures include drilling the skull; aspirating the cortex to expose the SC and applying gelatin sponge over entire dorsal surface of SC are shown. Useful tips for avoiding massive intracranial bleeding and aspiration of the SC have been given.
Neuroscience, Issue 16, Retrograde labeling, retinal ganglion cells, ophthalmology research, superior colliculus, experimental glaucoma
Preparation and Maintenance of Dorsal Root Ganglia Neurons in Compartmented Cultures
Institutions: Dana Farber Cancer Institute, Harvard Medical School.
Neurons extend axonal processes that are far removed from the cell body to innervate target tissues, where target-derived growth factors are required for neuronal survival and function. Neurotrophins are specifically required to maintain the survival and differentiation of innervating sensory neurons but the question of how these target-derived neurotrophins communicate to the cell body of innervating neurons has been an area of active research for over 30 years. The most commonly accepted model of how neurotrophin signals reach the cell body proposes that signaling endosomes carry this signal retrogradely along the axon. In order to study retrograde transport, a culture system was originally devised by Robert Campenot, in which cell bodies are isolated from their axons. The technique of preparing these compartmented chambers for culturing sensory neurons recapitulates the selective stimulation of neuron terminals that occurs in vivo following release of target-derived neurotrophins. Retrograde signaling events that require long-range microtubule dependent retrograde transport have important implications for the treatment of neurodegenerative disorders.
Neuroscience, Issue 20, campenot cultures, cell culture, dorsal root ganglia (DRG) neurons, neuronal culture