A rapid method for semi-quantitative analysis of neurite outgrowth from chick DRG explants using image analysis

A tacrolimus-eluting nerve guidance conduit enhances regeneration in a critical-sized peripheral nerve injury rat model

Critical-sized peripheral nerve injuries pose a significant clinical challenge and lead to functional loss and disability. Current regeneration strategies, including autografts, synthetic nerve conduits, and biologic treatments, encounter challenges such as limited availability, donor site morbidity, suboptimal recovery, potential immune responses, and sustained stability and bioactivity. An obstacle in peripheral nerve regeneration is the immune response that can lead to inflammation and scarring that impede the regenerative process. Addressing both the immunological and regenerative needs is crucial for successful nerve recovery. Here, we introduce a novel biodegradable tacrolimus-eluting nerve guidance conduit engineered from a blend of poly (L-lactide-co-caprolactone) to facilitate peripheral nerve regeneration and report the testing of this conduit in 15-mm critical-sized gaps in the sciatic nerve of rats. The conduit's diffusion holes enable the local release of tacrolimus, a potent immunosuppressant with neuro-regenerative properties, directly into the injury site. A series of in vitro experiments were conducted to assess the ability of the conduit to maintain a controlled tacrolimus release profile that could promote neurite outgrowth. Subsequent in vivo assessments in rat models of sciatic nerve injury revealed significant enhancements in nerve regeneration, as evidenced by improved axonal growth and functional recovery compared to controls using placebo conduits. These findings indicate the synergistic effects of combining a biodegradable conduit with localized, sustained delivery of tacrolimus, suggesting a promising approach for treating peripheral nerve injuries. Further optimization of the design and long-term efficacy studies and clinical trials are needed before the potential for clinical translation in humans can be considered.

Systematic investigation and comparison of US FDA-approved immunosuppressive drugs FK506, cyclosporine and rapamycin for neuromuscular regeneration following chronic nerve compression injury

Aim: To compare therapeutic benefits of different immunophilin ligands for treating nerve injuries. Materials & methods: Cyclosporine, FK506 and rapamycin, were evaluated first in vitro on a serum-free culture of embryonic dorsal root ganglia followed by a new in vivo model of chronic nerve compression. Results: Outcomes of the in vitro study have shown a potent effect of cyclosporine and FK506, on dorsal root ganglia axonal outgrowth, comparable to the effect of nerve growth factor. Rapamycin exhibited only a moderate effect. The in vivo study revealed the beneficial effects of cyclosporine, FK506 and rapamycin for neuromuscular regeneration. Cyclosporine showed the better maintenance of the tissues and function. Conclusion: Cyclosporine, FK506 and rapamycin drugs showed potential for treating peripheral nerve chronic compression injuries.

Engineering Silk Fibroin-Based Nerve Conduit with Neurotrophic Factors for Proximal Protection after Peripheral Nerve Injury

Artificial nerve conduits capable of adequately releasing neurotrophic factors are extensively studied to bridge nerve defects. However, the lack of neurotrophic factors in the proximal area and their visible effects in axonal retrograde transport following nerve injury is one of the factors causing an incomplete nerve regeneration. Herein, an advanced conduit made of silk fibroin is produced, which can incorporate growth factors and promote an effective regeneration after injury. For that, enzymatically crosslinked silk fibroin-based conduits are developed to be used as a platform for the controlled delivery of neurotrophic factors. Nerve growth factor and glial-cell line derived neurotrophic factor (GDNF) are incorporated using two different methodologies: i) crosslinking and ii) absorption method. The release profile is measured by ELISA technique. The bioactivity of the neurotrophic factors is evaluated in vitro by using primary dorsal root ganglia. When implanted in a 10 mm sciatic nerve defect in rats, GDNF-loaded silk fibroin conduits reveal retrograde neuroprotection as compared to autografts and plain silk fibroin conduit. Therefore, the novel design presents a substantial improvement of retrograde trafficking, neurons' protection, and motor nerve reinnervation.

Chemotherapy-Induced Peripheral Neuropathy and Changes in Cytoskeleton

Despite the different antineoplastic mechanisms of action, peripheral neurotoxicity induced by all chemotherapy drugs (anti-tubulin agents, platinum compounds, proteasome inhibitors, thalidomide) is associated with neuron morphological changes ascribable to cytoskeleton modifications. The "dying back" degeneration of distal terminals (sensory nerves) of dorsal root ganglia sensory neurons, observed in animal models, in in vitro cultures and biopsies of patients is the most evident hallmark of the perturbation of the cytoskeleton. On the other hand, in highly polarized cells like neurons, the cytoskeleton carries out its role not only in axons but also has a fundamental role in dendrite plasticity and in the organization of soma. In the literature, there are many studies focused on the antineoplastic-induced alteration of microtubule organization (and consequently, fast axonal transport defects) while very few studies have investigated the effect of the different classes of drugs on microfilaments, intermediate filaments and associated proteins. Therefore, in this review, we will focus on: (1) Highlighting the fundamental role of the crosstalk among the three filamentous subsystems and (2) investigating pivotal cytoskeleton-associated proteins.

Drug-delivering nerve conduit improves regeneration in a critical-sized gap

Autologous nerve grafts are the current "gold standard" for repairing large nerve gaps. However, they cause morbidity at the donor nerve site and only a limited amount of nerve can be harvested. Nerve conduits are a promising alternative to autografts and can act as guidance cues for the regenerating axons, without the need to harvest donor nerve. Separately, it has been shown that localized delivery of GDNF can enhance axon growth and motor recovery. FK506, an FDA approved small molecule, has also been shown to enhance peripheral nerve regeneration. This paper describes the design of a novel hole-based drug delivery apparatus integrated with a polytetrafluoroethylene (PTFE) nerve conduit for controlled local delivery of a protein such as GDNF or a small molecule such as FK506. The PTFE devices were tested in a diffusion chamber, and the bioactivity of the released media was evaluated by measuring neurite growth of dorsal root ganglions (DRGs) exposed to the released drugs. The drug delivering nerve guide was able to release bioactive concentrations of FK506 or GDNF. Following these tests, optimized drug releasing nerve conduits were implanted across 10 mm sciatic nerve gaps in a BL6 yellow fluorescent protein (YFP) mouse model, where they demonstrated significant improvement in muscle mass, compound muscle action potential, and axon myelination in vivo as compared with nerve conduits without the drug. The drug delivery nerve guide could release drug for extended periods of time and enhance axon growth in vitro and in vivo.

Novel drug delivering conduit for peripheral nerve regeneration

OBJECTIVE

This paper describes the design of a novel drug delivery apparatus integrated with a poly lactic-co-glycolic acid (PLGA) based nerve guide conduit for controlled local delivery of nerve growth factor (NGF) and application in peripheral nerve gap injury.

APPROACH

An NGF dosage curve was acquired to determine the minimum in vitro concentration for optimal neurite outgrowth of dorsal root ganglion (DRG) cells; PLGA based drug delivery devices were then designed and tested in vitro and in vivo across 15 mm rat sciatic nerve gap injury model.

MAIN RESULTS

The drug delivery nerve guide was able to release NGF for 28 d at concentrations (0.1-10 ng ml^-1) that were shown to enhance DRG neurite growth. Furthermore, the released NGF was bioactive and able to enhance DRG neurite growth. Following these tests, optimized NGF-releasing nerve conduits were implanted across 15 mm sciatic nerve gaps in a rat model, where they demonstrated significant myelination and muscle innervation in vivo as compared to empty nerve conduits (p  <  0.05). This drug delivery nerve guide can release NGF for extended periods of time and enhance axon growth in vitro and in vivo and has the potential to improve nerve regeneration following a peripheral nerve injury.

SIGNIFICANCE

This integrated drug delivering nerve guide simplifies the design process and provides increased versatility for releasing a variety of different growth factors. This innovative device has the potential for broad applicability and allows for easier customization to change the type of drugs and dosage of individual drugs without devising a completely new biomaterial-drug conjugate each time.

Control of neurite growth and guidance by an inhibitory cell-body signal

The development of a functional nervous system requires tight control of neurite growth and guidance by extracellular chemical cues. Neurite growth is astonishingly sensitive to shallow concentration gradients, but a widely observed feature of both growth and guidance regulation, with important consequences for development and regeneration, is that both are only elicited over the same relatively narrow range of concentrations. Here we show that all these phenomena can be explained within one theoretical framework. We first test long-standing explanations for the suppression of the trophic effects of nerve growth factor at high concentrations, and find they are contradicted by experiment. Instead we propose a new hypothesis involving inhibitory signalling among the cell bodies, and then extend this hypothesis to show how both growth and guidance can be understood in terms of a common underlying signalling mechanism. This new model for the first time unifies several key features of neurite growth regulation, quantitatively explains many aspects of experimental data, and makes new predictions about unknown details of developmental signalling.

Nerve regeneration by human corneal stromal keratocytes and stromal fibroblasts

Laser refractive surgeries reshape corneal stroma to correct refractive errors, but unavoidably affect corneal nerves. Slow nerve regeneration and atypical neurite morphology cause desensitization and neuro-epitheliopathy. Following injury, surviving corneal stromal keratocytes (CSKs) are activated to stromal fibroblasts (SFs). How these two different cell types influence nerve regeneration is elusive. Our study evaluated the neuro-regulatory effects of human SFs versus CSKs derived from the same corneal stroma using an in vitro chick dorsal root ganglion model. The neurite growth was assessed by a validated concentric circle intersection count method. Serum-free conditioned media (CM) from SFs promoted neurite growth dose-dependently, compared to that from CSKs. We detected neurotrophic and pro-inflammatory factors (interleukin-8, interleukin-15, monocyte chemoattractant protein-1, eotaxin, RANTES) in SFCM by Bio-Plex Human Cytokine assay. More than 130 proteins in SFCM and 49 in CSKCM were identified by nanoLC-MS/MS. Proteins uniquely present in SFCM had reported neuro-regulatory activities and were predicted to regulate neurogenesis, focal adhesion and wound healing. Conclusively, this was the first study showing a physiological relationship between nerve growth and the metabolically active SFs versus quiescent CSKs from the same cornea source. The dose-dependent effect on neurite growth indicated that nerve regeneration could be influenced by SF density.

Syntaxin-4 and SNAP23 act as exocytic SNAREs to release NGF from cultured Schwann cells

Nowadays peripheral nerve (PN) injury occurs more frequently, the outcome is often poor because of the ineffective treatment. Once the PN was injured, Schwann cells (SCs) release neurotrophins to guide the regeneration of axons. Recent researches revealed the duration of NGF administration acts a positive role during the nerve regeneration, but the molecular mechanisms of NGF release from SCs are unknown. To investigate components of the exocytic machinery of NGF, we used RT-PCR, Western blot and immunocytochemistry to investigate expressions and locations of soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) in rat primary cultured SCs. We found that Syntaxin-4 and SNAP23 were co-localized with NGF by immunocytochemistry. Co-immunoprecipitation (Co-IP) and RNA interference (RNAi) confirmed Syntaxin-4 associated with SNAP23 to regulate the release of NGF from SCs. Knockdown of Syntaxin-4 and SNAP23 dramatically decreased the exocytosis of NGF and inhibited the neurite outgrowth of dorsal root ganglia (DRG). Syntaxin-4 and SNAP23 acted as exocytic SNAREs to release NGF from SCs.

Effect Of combining FK506 and neurotrophins on neurite branching and elongation

INTRODUCTION

There is a clinical need to improve the outcomes of peripheral nerve regeneration and repair after injury. In addition to its immunosuppressive effects, FK506 (tacrolimus) has been shown to have neuroregenerative properties. To determine biologically relevant local FK506 and growth factor concentrations, we performed an in vitro bioassay using dorsal root ganglion (DRG) from chicken embryos.

METHODS

Neurite elongation and neurite branching were analyzed microscopically after addition of FK506, glial cell line-derived neurotrophic factor (GDNF), and nerve growth factor (NGF), each alone and in combination.

RESULTS

FK506 induced modest neurite elongation (∼500-800 µm) without improving neurite branching significantly. The combination of FK506 with NGF, GDNF, or both, exerted a potentiating or competitive effect on neurite elongation (∼700-1100 µm) based on dosage and competitive effect on neurite branching (∼0.2-0.4).

CONCLUSIONS

These results strongly suggest that the interaction of FK506 with GDNF and NGF mediates distinct enhancement of neurite growth. Muscle Nerve 55: 570-581, 2017.

Characterization of dorsal root ganglion neurons cultured on silicon micro-pillar substrates

Our study focuses on characterization of dorsal root ganglion (DRG) neurons cultured on silicon micro-pillar substrates (MPS) with the ultimate goal of designing micro-electrode arrays (MEAs) for successful electrophysiological recordings of DRG neurons. Adult and neonatal DRG neurons were cultured on MPS and glass coverslips for 7 days in vitro. DRG neuronal distribution and morphometric analysis, including neurite alignment and length, was performed on MPS areas with different pillar width and spacing. We showed that MPS provide an environment for growth of adult and neonatal DRG neurons as permissive as control glass surfaces. Neonatal DRG neurons were present on MPS areas with narrow pillar spacing, while adult neurons preferred wider pillar spacing. Compared to the control glass surfaces the neonatal and adult DRG neurons in regions with narrow pillar spacing range developed a smaller number of longer neurites. In the same area, neurites were preferentially oriented along three directional axes at 30°, 90° and 150°. MPS architecture influenced growth directionality of all main DRG neuronal subtypes. We can conclude that specific micro-pillar substrate topography affects the morphology of DRG neurons. This knowledge can enable development of MEAs with precisely defined physical features for various neuroscience applications.

Inhibition of glial proliferation, promotion of axonal growth and myelin production by synthetic glycolipid: A new approach for spinal cord injury treatment

PURPOSE

After spinal cord injury (SCI) a glial scar is generated in the area affected that forms a barrier for axon growth and myelination, preventing functional recovery. Recently, we have described a synthetic glycolipid (IG20) that inhibited proliferation of human glioma cells. We show now that IG20 inhibited the proliferation of astrocytes and microglial cells, the principal cellular components of the glial scar, and promoting axonal outgrowth and myelin production in vitro.

METHODS

Glial cells were inhibited with IG20 (IC50≈10 μM) and studied by RT-PCR, Western Blotting, immunoprecipitation and fluorescence microscopy. Axonal outgrowth in dorsal root ganglia (DRG) and myelin production by oligodendrocytes were analyzed by immunocytochemistry. Adult rats were assayed in spinal cord contusion model and the recovery of treated animals (n = 6) and controls (n = 6) was followed.

RESULTS

The IG20 was localized in the cytosol of glial cells, forming a complex with RhoGDIα, a regulator of RhoGTPases. Treatment of astroglial cultures with IG20 increase the expression of BDNF receptor genes (TrkBT1, TrkB Full). IG20 reduced the astroglial marker GFAP, while increasing production of myelin basic protein in oligodendrocytes and promoted axonal outgrowth from DRG neurons. Local injection of IG20, near a spinal cord contusion, promoted the recovery of lesioned animals analyzed by BBB test (P <  0.05).

CONCLUSIONS

We propose that inhibition of astrocytes and microglia by IG20 could be diminished the glial scar formation, inducing the re-growth and myelination of axons, these elements constitute a new approach for SCI therapy.

The MAPK and PI3K pathways mediate CNTF-induced neuronal survival and process outgrowth in hypothalamic organotypic cultures

While collateral sprouting has been shown to occur in a variety of neuronal populations, the factor or factors responsible for mediating the sprouting response remain largely un-defined. There is evidence indicating that ciliary neurotrophic factor (CNTF) may play an important role in promoting neuronal survival and process outgrowth in neuronal phenotypes tested to date. We previously demonstrated that the astrocytic Jak-STAT pathway is necessary to mediate CNTF-induced oxytocinergic (OT) neuronal survival; however, the mechanism (s) of CNTF-mediated process outgrowth remain unknown. Our working hypothesis is that CNTF mediates differential neuroprotective responses via different intracellular signal transduction pathways. In order to test this hypothesis, we utilized stationary hypothalamic organotypic cultures to assess the contribution of the MAPK-ERK and PI3-AKT pathways to OT neuron survival and process outgrowth. Our results demonstrate that the MAPK-ERK½ pathway mediates CNTF-induced neuronal survival. Moreover, we show that inhibition of the p38-, JNK-MAPK, and mTOR pathways prevents loss OT neurons following axotomy. We also provide quantitative evidence indicating that CNTF promotes process outgrowth of OT neurons via the PI3K-AKT pathway. Together, these data indicate that distinct intracellular signaling pathways mediate diverse neuroprotective processes in response to CNTF.

The Achyranthes bidentata polypeptide k fraction enhances neuronal growth in vitro and promotes peripheral nerve regeneration after crush injury in vivo

We have previously shown that Achyranthes bidentata polypeptides (ABPP), isolated from Achyranthes bidentata Blume (a medicinal herb), exhibit neurotrophic and neuroprotective effects on the nervous system. To identify the major active component of ABPP, and thus optimize the use of ABPP, we used reverse-phase high performance liquid chromatography to separate ABPP. We obtained 12 fractions, among which the fraction of ABPPk demonstrated the strongest neuroactivity. Immunocytochemistry and western blot analysis showed that ABPPk promoted neurite growth in cultured dorsal root ganglion explant and dorsal root ganglion neurons, which might be associated with activation of Erk1/2. A combination of behavioral tests, electrophysiological assessment, and histomorphometric analysis indicated that ABPPk enhanced nerve regeneration and function restoration in a mouse model of crushed sciatic nerve. All the results suggest that ABPPk, as the key component of ABPP, can be used for peripheral nerve repair to yield better outcomes than ABPP.

Nanotechnology versus stem cell engineering: in vitro comparison of neurite inductive potentials

Purpose

Innovative nerve conduits for peripheral nerve reconstruction are needed in order to specifically support peripheral nerve regeneration (PNR) whenever nerve autotransplantation is not an option. Specific support of PNR could be achieved by neurotrophic factor delivery within the nerve conduits via nanotechnology or stem cell engineering and transplantation.

Methods

Here, we comparatively investigated the bioactivity of selected neurotrophic factors conjugated to iron oxide nanoparticles (np-NTFs) and of bone marrow-derived stem cells genetically engineered to overexpress those neurotrophic factors (NTF-BMSCs). The neurite outgrowth inductive activity was monitored in culture systems of adult and neonatal rat sensory dorsal root ganglion neurons as well as in the cell line from rat pheochromocytoma (PC-12) cell sympathetic culture model system.

Results

We demonstrate that np-NTFs reliably support numeric neurite outgrowth in all utilized culture models. In some aspects, especially with regard to their long-term bioactivity, np-NTFs are even superior to free NTFs. Engineered NTF-BMSCs proved to be less effective in induction of sensory neurite outgrowth but demonstrated an increased bioactivity in the PC-12 cell culture system. In contrast, primary nontransfected BMSCs were as effective as np-NTFs in sensory neurite induction and demonstrated an impairment of neuronal differentiation in the PC-12 cell system.

Conclusion

Our results evidence that nanotechnology as used in our setup is superior over stem cell engineering when it comes to in vitro models for PNR. Furthermore, np-NTFs can easily be suspended in regenerative hydrogel matrix and could be delivered that way to nerve conduits for future in vivo studies and medical application.

The behavior of neuronal cells on tendon-derived collagen sheets as potential substrates for nerve regeneration

Peripheral nervous system injuries result in a decreased quality of life, and generally require surgical intervention for repair. Currently, the gold standard of nerve autografting, based on the use of host tissue such as sensory nerves is suboptimal as it results in donor-site loss of function and requires a secondary surgery. Nerve guidance conduits fabricated from natural polymers such as collagen are a common alternative to bridge nerve defects. In the present work, tendon sections derived through a process named bioskiving were studied for their potential for use as a substrate to fabricate nerve guidance conduits. We show that cells such as rat Schwann cells adhere, proliferate, and align along the fibrous tendon substrate which has been shown to result in a more mature phenotype. Additionally we demonstrate that chick dorsal root ganglia explants cultured on the tendon grow to similar lengths compared to dorsal root ganglia cultured on collagen gels, but also grow in a more oriented manner on the tendon sections. These results show that tendon sections produced through bioskiving can support directional nerve growth and may be of use as a substrate for the fabrication of nerve guidance conduits.

Delayed post-injury administration of C5a improves regeneration and functional recovery after spinal cord injury in mice

The activation of a complement system can aggravate the secondary injury after spinal cord injury (SCI). However, it was reported recently that the activation of a complement could have both a secondary injury and a neuroprotective effect, in which C5a is the most important factor, but there is no direct evidence for this dual effect of C5a after SCI. In order to investigate the potential neuroprotective effect of C5a after SCI, in this study ectogenic C5a was injected intraperitoneally before/after SCI in vivo, or administrated to mechanically injured neurones in vitro; following this, neurone apoptosis, neurite outgrowth, axonal regeneration and functional recovery were investigated. The in-vivo experiments indicated that, following treatment with C5a 24 h before or immediately after injury, locomotor function was impaired significantly. However, when treatment with C5a took place 24 h after injury, locomotor function improved significantly. In-vitro experiments indicated that a certain concentration of C5a (50-100 nM) could inhibit caspase-3-mediated neurone apoptosis by binding to its receptor CD88, and that it could even promote the neurite outgrowth of uninjured neurones. In conclusion, delayed post-injury administration of C5a within a certain concentration could exert its neuroprotective effect through inhibiting caspase-3-mediated neurone apoptosis and promoting neurite outgrowth of uninjured neurones as well. These data suggest that C5a may have opposite functions in a time- and concentration-dependent manner after SCI. The dual roles of C5a have to be taken into account when measures are taken to inhibit complement activation in order to promote regeneration after SCI.

Automated Analysis of Neurite Outgrowth in Mouse Retinal Explants

Despite intensive research efforts over the past years, regeneration of injured axons in the central nervous system remains elusive. In the quest for neurostimulatory agents that promote regeneration, well-defined models and analysis methods are required. Tissue explant cultures closely resemble the in vivo situation, making them ideal to study the effect of compounds on the neuro-glial network. This study reports the optimization of an explant culture technique using retinas of neonatal mice and the development of an analysis script that allows for rapid and automated analysis of neurite outgrowth from these explants. The key features of this script (i.e., local thresholding and form selection) allow for swift and unbiased detection of neurite outgrowth. The novel analysis method is compared with two commonly used manual methods and successfully validated by performing dose-response studies with molecules known to either inhibit (anti–β1-integrin antibody) or stimulate (brain-derived neurotrophic factor and ciliary neurotrophic factor) neurite outgrowth from retinal explants. Finally, the new analysis script is used to study whether retinal explant origin has any effect on neurite outgrowth.

Surface microstructures on planar substrates and textile fibers guide neurite outgrowth: a scaffold solution to push limits of critical nerve defect regeneration?

The treatment of critical size peripheral nerve defects represents one of the most serious problems in neurosurgery. If the gap size exceeds a certain limit, healing can't be achieved. Connection mismatching may further reduce the clinical success. The present study investigates how far specific surface structures support neurite outgrowth and by that may represent one possibility to push distance limits that can be bridged. For this purpose, growth cone displacement of fluorescent embryonic chicken spinal cord neurons was monitored using time-lapse video. In a first series of experiments, parallel patterns of polyimide ridges of different geometry were created on planar silicon oxide surfaces. These channel-like structures were evaluated with and without amorphous hydrogenated carbon (a-C:H) coating. In a next step, structured and unstructured textile fibers were investigated. All planar surface materials (polyimide, silicon oxide and a-C:H) proved to be biocompatible, i.e. had no adverse effect on nerve cultures and supported neurite outgrowth. Mean growth cone migration velocity measured on 5 minute base was marginally affected by surface structuring. However, surface structure variability, i.e. ridge height, width and inter-ridge spacing, significantly enhanced the resulting net velocity by guiding the growth cone movement. Ridge height and inter-ridge distance affected the frequency of neurites crossing over ridges. Of the evaluated dimensions ridge height, width, and inter-ridge distance of respectively 3, 10, and 10 µm maximally supported net axon growth. Comparable artificial grooves, fabricated onto the surface of PET fibers by using an excimer laser, showed similar positive effects. Our data may help to further optimize surface characteristics of artificial nerve conduits and bioelectronic interfaces.

In vitro beneficial activation of microglial cells by mechanically-injured astrocytes enhances the synthesis and secretion of BDNF through p38MAPK

It has long been promulgated that microglial cells serve beneficial roles in the central nervous system (CNS). The beneficial role of microglial cells is considered to be linked with microglial activation and consequent up-regulation of various trophic factors. However, what triggers microglial activation and consequent elevated level of trophic factors, especially brain-derived neurotrophic factor (BDNF), following traumatic CNS injury has become a crucial but elusive issue. Furthermore, an effort still remains in understanding of the cellular and molecular mechanisms underlying the endogenous neuroprotection of activated microglial cells. In this study, we demonstrated that mechanically-injured astrocyte conditioned medium (ACM) could provoke beneficial activation of microglial cells and thus promote the transcription, synthesis and release of BDNF in cultured microglial cells. The microglia-derived BDNF can exerted a demonstrable biological role in promoting neurite outgrowth and intimate terminal contacts of dorsal root ganglion (DRG) neurons co-cultured with microglial cells. Moreover, ACM induced remarkable p38MAPK phosphorylation in cultured microglial cells that preceded the burst of BDNF. Activating p38-MAPK by anisomycin resulted in salutary effects similar to those seen with ACM, whereas specific inhibition of the p38MAPK by SB203580 abrogated all the positive effects of ACM, including BDNF promotion and subsequent neurite outgrowth of DRG neurite outgrowth of DRG neurons and their intimate terminal contacts with microglial cells. Together, our results indicated that the neuroprotection of the microglial source is mainly caused by micro-environmental soluble molecules released from injured astrocytes, and ACM-induced BDNF production and release from microglial cells may be mediated through p38-MAPK signaling pathway. Therefore, these findings may lay a foundation to further investigations on the microglial beneficial activation role in the repair of traumatic CNS injury and neurodegenerative diseases.

Imbalance between sympathetic and sensory innervation in peritoneal endometriosis

To investigate possible mechanisms of pain pathophysiology in patients with peritoneal endometriosis, a clinical study on sensory and sympathetic nerve fibre sprouting in endometriosis was performed. Peritoneal lesions (n=40) and healthy peritoneum (n=12) were immunostained and analysed with anti-protein gene product 9.5 (PGP 9.5), anti-substance P (SP) and anti-tyrosine hydroxylase (TH), specific markers for intact nerve fibres, sensory nerve fibres and sympathetic nerve fibres, respectively, to identify the ratio of sympathetic and sensory nerve fibres. In addition, immune cell infiltrates in peritoneal endometriotic lesions were analysed and the nerve growth factor (NGF) and interleukin (IL)-1β expression was correlate with the nerve fibre density. Peritoneal fluids from patients with endometriosis (n=40) and without endometriosis (n=20) were used for the in vitro neuronal growth assay. Cultured chicken dorsal root ganglia (DRG) and sympathetic ganglia were stained with anti-growth associated protein 43 (anti-GAP 43), anti-SP and anti-TH. We could detect an increased sensory and decreased sympathetic nerve fibres density in peritoneal lesions compared to healthy peritoneum. Peritoneal fluids of patients with endometriosis compared to patients without endometriosis induced an increased sprouting of sensory neurites from DRG and decreased neurite outgrowth from sympathetic ganglia. In conclusion, this study demonstrates an imbalance between sympathetic and sensory nerve fibres in peritoneal endometriosis, as well as an altered modulation of peritoneal fluids from patients with endometriosis on sympathetic and sensory innervation which might directly be involved in the maintenance of inflammation and pain.

Effects of intervertebral disc cells on neurite outgrowth from dorsal root ganglion explants in culture

STUDY DESIGN

An experimental study investigating the effect of disc cells on neurite outgrowth in a rat dorsal root ganglion (DRG) culture system.

OBJECTIVE

To examine the effects of the 2 nucleus pulposus (NP) cell populations, notochordal cells (NC) and chondrocyte-like cells (CC) on neurite outgrowth from DRGs.

SUMMARY OF BACKGROUND DATA

NP consists of at least 2 cell populations, NC and CC. The cells in NP have been shown to be responsible for negative effects on neurite outgrowth in vitro and on nerve tissue in vivo. It is unknown whether 1 cell type or combinations of the 2 cell types are responsible for the reported effects.

METHODS

A total of 939 DRGs from newborn Sprague Dawley rats were harvested and placed in culture dishes. After 24 hours, the neurite outgrowth was measured. NP was harvested from tail discs of adult rats and the NP cells were separated into 2 populations, NC and CC. The cell populations were applied to the DRG culture in different cell concentrations and combinations, and compared to medium. After 24 hours of exposure, the neurite outgrowth was reassessed and expressed as the ratio between the outgrowth at 48 and 24 hours culture.

RESULTS

NC in intermediate and high concentration and CC in high concentration induced a significant inhibition of the neurite outgrowth compared to culture medium. Further, one of the combinations (low NC and high CC concentration) resulted in a significant inhibition of the neurite outgrowth.

CONCLUSION

The present study demonstrated negative effects of NP cells on nerve tissue culture explants. The combination of low NC and high CC concentrations may mimic the situation in humans, where we have an increased proportion of chondrocyte-like cells with age. The results from this study may provide a biologic explanation for the large variation of symptoms in disc herniation patients despite similar mechanical influence on nerve tissue.

A rapid, inexpensive high throughput screen method for neurite outgrowth

Neurite outgrowth assays are the most common phenotypic screen to assess chemical effects on neuronal cells. Current automated assays involve expensive equipment, lengthy sample preparation and handling, costly reagents and slow rates of data acquisition and analysis. We have developed a high throughput screen (HTS) for neurite outgrowth using a robust neuronal cell model coupled to fast and inexpensive visualization methods, reduced data volume and rapid data analysis. Neuroscreen-1 (NS-1) cell, a subclone of PC12, possessing rapid growth and enhanced sensitivity to NGF was used as a model neuron. This method reduces preparation time by using cells expressing GFP or native cells stained with HCS CellMask(™) Red in a multiplexed 30 min fixation and staining step. A 2x2 camera binning process reduced both image data files and analysis times by 75% and 60% respectively, compared to current protocols. In addition, eliminating autofocus steps during montage generation reduced data collection time. Pharmacological profiles for stimulation and inhibition of neurite outgrowth by NGF and SU6656 were comparable to current standard method utilizing immunofluorescence detection of tubulin. Potentiation of NGF-induced neurite outgrowth by members of a 1,120-member Prestwick compound library as assayed using this method identified six molecules, including etoposide, isoflupredone acetate, fludrocortisone acetate, thioguanosine, oxyphenbutazone and gibberellic acid, that more than doubled the neurite mass primed by 2 ng/ml NGF. This simple procedure represents an important routine approach in high throughput screening of large chemical libraries using the neurite outgrowth phenotype as a measure of the effects of chemical molecules on neuronal cells.

Neuron tracing in perspective

The study of the structure and function of neuronal cells and networks is of crucial importance in the endeavor to understand how the brain works. A key component in this process is the extraction of neuronal morphology from microscopic imaging data. In the past four decades, many computational methods and tools have been developed for digital reconstruction of neurons from images, with limited success. As witnessed by the growing body of literature on the subject, as well as the organization of challenging competitions in the field, the quest for a robust and fully automated system of more general applicability still continues. The aim of this work, is to contribute by surveying recent developments in the field for anyone interested in taking up the challenge. Relevant aspects discussed in the article include proposed image segmentation methods, quantitative measures of neuronal morphology, currently available software tools for various related purposes, and morphology databases. (c) 2010 International Society for Advancement of Cytometry.

A rapid, quantitative method for assessing axonal extension on biomaterial platforms

Measuring outgrowth of neuronal explants is critical in evaluating the ability of a biomaterial to act as a permissive substrate for neuronal adhesion and growth. Previous methods lack the ability to quantify robust outgrowth, or lack the capacity to quantify growth on opaque substrates because they exploit the transparent nature of culture dishes to segregate neuronal processes from an image background based on color intensity. In this study, we sought to investigate the ability of opaque silica sol-gel materials to facilitate axonal outgrowth; therefore, a method was developed for quantifying outgrowth of neurites from dorsal root ganglion explants on these unique surfaces. Dorsal root ganglia were isolated from stage-nine chick embryos and cultured for 48 h on sol-gel materials presenting agarose and chitosan polysaccharides individually or in combination. Explants were then imaged, and basic image analysis software was used by three independent observers to obtain axonal length and axonal area measurements. Robust axon length and axonal spread measurements for ganglia cultured on agarose-chitosan sol-gel matrices yield an estimate of strong neural compatibility for these substrates over silica matrices presenting no polysaccharides, or silica matrices presenting chitosan or agarose individually. We suggest that this simple protocol for quantifying material biocompatibility offers an analysis strategy that can be used universally to the same end.

Twenty-First Century Challenges for In Vitro Neurotoxicity

During the last 40 years, studies incorporating in vitro methodologies have greatly advanced our understanding of human nerve cell biology. Attempts have been made to apply these to investigations of neurotoxicity. Due to the complexity of the nervous system, underpinned by an array of integrated interactions between a host of cell types, it is concluded that, at present, alternative neural models are most successful in determining the underlying mechanisms which can cause perturbation of normal functioning of the nervous system, both in adults and during the embryonic period. The use of tiered batteries of test models has been proposed in screening programmes for neurotoxicity, with the generation of much encouraging data in laboratories across the globe. This review aims to discuss the development of neural alternatives, considers the various model systems available, and highlights specific neuronal endpoints which can be tested, in addition to the cytotoxic evaluation of neuronal viability. Developments in molecular and stem cell biology, which are appropriate to neural tissue, and which offer the prospect of exciting advances for the next decade, are cited.

Synergistic effect of GDNF and NGF on axonal branching and elongation in vitro

There is a clinical need to enhance functional recovery of injured peripheral nerves. Local administration of neurotrophic factors (NTFs) after surgical repair has been proposed for this purpose. Little is known, however, on the optimal local dose and dosing frequency of NTFs in a peripheral nerve defect. For increasing our knowledge on biologically relevant local NTFs concentrations and for making available an in vitro assay for assessing the bioactivity of NTFs in connection with implantable localized delivery systems, we developed in this study a bioassay for NTFs, which is based on dorsal root ganglion (DRG) explants from E9 (9 days old) chicken embryos. Axonal elongation and extent of axonal branching was analyzed microscopically after addition of glial cell line-derived neurotrophic factor (GDNF) and nerve growth factor (NGF), each alone and in combination. GDNF significantly promoted axonal elongation, but only little axonal branching, whereas NGF induced extensive axonal branching with modest axonal elongation. The combination of GDNF and NGF exerted a synergistic effect on the axonal elongation, axonal branching and growth kinetics. GDNF and NGF also enhanced the expression of their respective functional receptors Ret and TrkA on the DRG neurons. This information should be relevant for the development of implants containing NTFs and on drug therapy of damaged peripheral nerves.

Creation of highly aligned electrospun poly-L-lactic acid fibers for nerve regeneration applications

Aligned, electrospun polymer fibers have shown considerable promise in directing regenerating axons in vitro and in vivo. However, in several studies, final electrospinning parameters are presented for producing aligned fiber scaffolds, and alignment where minimal fiber crossing occurs is not achieved. Highly aligned species are necessary for neural tissue engineering applications to ensure that axonal extension occurs through a regenerating environment efficiently. Axonal outgrowth on fibers that deviate from the natural axis of growth may delay axonal extension from one end of a scaffold to the other. Therefore, producing aligned fiber scaffolds with little fiber crossing is essential. In this study, the contributions of four electrospinning parameters (collection disk rotation speed, needle size, needle tip shape and syringe pump flow rate) were investigated thoroughly with the goal of finding parameters to obtain highly aligned electrospun fibers made from poly-L-lactic acid (PLLA). Using an 8 wt% PLLA solution in chloroform, a collection disk rotation speed of 1000 revolutions per minute (rpm), a 22 gauge, sharp-tip needle and a syringe pump rate of 2 ml h(-1) produced highly aligned fiber (1.2-1.6 microm in diameter) scaffolds verified using a fast Fourier transform and a fiber alignment quantification technique. Additionally, the application of an insulating sheath around the needle tip improved the rate of fiber deposition (electrospinning efficiency). Optimized scaffolds were then evaluated in vitro using embryonic stage nine (E9) chick dorsal root ganglia (DRGs) and rat Schwann cells (SCs). To demonstrate the importance of creating highly aligned scaffolds to direct neurite outgrowth, scaffolds were created that contained crossing fibers. Neurites on these scaffolds were directed down the axis of the aligned fibers, but neurites also grew along the crossed fibers. At times, these crossed fibers even stopped further axonal extension. Highly aligned PLLA fibers generated under optimized electrospinning conditions guided neurite and SC growth along the aligned fibers. Schwann cells demonstrated the bipolar phenotype seen along the fibers. Using a novel technique to determine fiber density, an increase in fiber density correlated to an increase in the number of neurites, but average neurite length was not statistically different between the two different fiber densities. Together, this work presents methods by which to produce highly aligned fiber scaffolds efficiently and techniques for assessing neurite outgrowth on different fiber scaffolds, while suggesting that crossing fibers may be detrimental in fostering efficient, directed axonal outgrowth.

Evaluation of neurite outgrowth anisotropy using a novel application of circular analysis

Precise axon growth is required for making proper connections in development and after injury. One method of studying axon guidance and growth is through in vitro outgrowth assays that present controlled microenvironments. In this study, we applied circular statistical methods to evaluate directional neurite response. Visualization of data on a circular scale allows more accurate representation of the data, as neurite angles are inherently expressed on a circle. Here, the direction of neurite outgrowth from dorsal root ganglia derived neurons on different substrate types was quantitatively measured. Further, simulations of datasets with known circular parameters reflecting expected neurite angle distributions from different substrate types were also generated. Circular statistical methods were utilized and compared to linear statistical models widely used in the neuroscience literature. For small samples, Rao's spacing test showed the smallest occurrence of Type I errors (false positives) when tested against simulated uniform distributions. V-test and Rayleigh's test showed highest statistical power when tested against a unimodal distribution with known and unknown mean direction, respectively. For bimodal samples, Watson's U(2)-test showed the highest statistical power. Overall, circular statistical uniformity tests showed higher statistical power than linear non-parametric tests, particularly for small samples (n=5). Circular analysis methods represent a useful tool for evaluation of directionality of neurite outgrowth with applications including: (1) assessment of neurite outgrowth potential; (2) determination of isotropy of cellular responses to single and multiple cues and (3) determination of the relative strengths of cues present in a complex environment.

Developmental neurotoxicity testing in vitro: models for assessing chemical effects on neurite outgrowth

In vitro models may be useful for the rapid toxicological screening of large numbers of chemicals for their potential to produce toxicity. Such screening could facilitate prioritization of resources needed for in vivo toxicity testing towards those chemicals most likely to result in adverse health effects. Cell cultures derived from nervous system tissue have proven to be powerful tools for elucidating cellular and molecular mechanisms of nervous system development and function, and have been used to understand the mechanism of action of neurotoxic chemicals. Recently, it has been suggested that in vitro models could be used to screen for chemical effects on critical cellular events of neurodevelopment, including differentiation and neurite growth. This review examines the use of neuronal cell cultures as an in vitro model of neurite outgrowth. Examples of the cell culture systems that are commonly used to examine the effects of chemicals on neurite outgrowth are provided, along with a description of the methods used to quantify this neurodevelopmental process in vitro. Issues relating to the relevance of the methods and models currently used to assess neurite outgrowth are discussed in the context of hazard identification and chemical screening. To demonstrate the utility of in vitro models of neurite outgrowth for the evaluation of large numbers of chemicals, efforts should be made to: (1) develop a set of reference chemicals that can be used as positive and negative controls for comparing neurite outgrowth between model systems, (2) focus on cell cultures of human origin, with emphasis on the emerging area of neural progenitor cells, and (3) use high-throughput methods to quantify endpoints of neurite outgrowth.

Effects of collagen 1, fibronectin, laminin and hyaluronic acid concentration in multi-component gels on neurite extension

Recovery after peripheral nerve injury remains a significant challenge. Extracellular matrix proteins and hydrogels of extracellular matrix components have been shown to improve regeneration in peripheral nerve entubulation models, especially over long distances. The chemical properties, ligand identity and density, and mechanical properties of the hydrogel can affect neurite extension. However, the importance of combinatorial effects between different components in co-gels of several extracellular matrix components is unclear. In this study, we investigated neurite extension from explanted dorsal root ganglia cultured within co-gels made from laminin, fibronectin, collagen 1 and hyaluronic acid. Laminin had a strong, dose-dependent effect on both neurite length and outgrowth. Fibronectin was slightly, but generally not significantly, inhibitory to neurite extension. The concentration of collagen 1 and hyaluronic acid did not have significant effects on neurite extension. The combinatorial effects among the four components were additive rather than synergistic. A co-gel made with 1.5 mg/ml collagen 1 and 1.5 mg/ml laminin was optimum in this study, resulting in an average neurite length of 1532 +/- 91 microm versus 976 +/- 32 microm for controls, and an increase in overall volume outgrowth (reflecting neurite length and branching) of 85.9+/-9.3% over controls. This co-gel provides a mechanically stable scaffold with high ligand density and biochemical affinity. The results of this study support the use of co-gels of laminin and collagen 1 for promoting regeneration in peripheral nerve injuries and suggest that interactions among hydrogel components are not significant.

Automated analysis of neurite branching in cultured cortical neurons using HCA-Vision

Manual neuron tracing is a very labor-intensive task. In the drug screening context, the sheer number of images to process means that this approach is unrealistic. Moreover, the lack of reproducibility, objectivity, and auditing capability of manual tracing is limiting even in the context of smaller studies. We have developed fast, sensitive, and reliable algorithms for the purpose of detecting and analyzing neurites in cell cultures, and we have integrated them in software called HCA-Vision, suitable for the research environment. We validate the software on images of cortical neurons by comparing results obtained using HCA-Vision with those obtained using an established semi-automated tracing solution (NeuronJ). The effect of the Sez-6 deletion was characterized in detail. Sez-6 null neurons exhibited a significant increase in neurite branching, although the neurite field area was unchanged due to a reduction in mean branch length. HCA-Vision delivered considerable speed benefits and reliable traces.

Interaction of Cochlear Nucleus Explants With Semiconductor Materials

OBJECTIVE/HYPOTHESIS

Implantable hearing devices such as cochlear implants and auditory brainstem implants deliver auditory information through electrical stimulation of auditory neurons. The combination of microelectronic electrodes with auditory nerve cells may lead to further improvement of the hearing quality with these devices. Whereas several kinds of neurons are known to grow on semiconductor substrates, interactions of cochlear nucleus (CN) neurons with such materials have yet to be described.

MATERIALS AND METHODS

To investigate survival and growth behavior of CN neurons on different semiconductor materials. CN explants from postnatal day 10 Sprague-Dawley rats were cultured for 96 hours in Neurobasal medium on polished and unpolished silicon wafers (p-type Si [100] and p-type Si3N4[100]) as well as plastic surface. These surfaces had been coated with poly-L-lysine and laminin. Neuronal outgrowth was examined using image analysis software after immunohistologic staining for neurofilament. Neurite length and directional changes were quantified. Additionally, neurite morphology and adhesion to the semiconductor material was evaluated by scanning electron microscopy.

RESULTS

Although proper adhesion of CN explants was seen, no neurite growth could be detected on unpolished silicon wafers (Si and Si3N4). Compared with the other test conditions, polished, laminin-coated Si3N4 wafers showed best biocompatibility regarding neurite length and number per explant. CN explants developed a mean of eight neurons with an average length of 236 mum in 96 hours of culture on these wafers.

CONCLUSION

The results of this study demonstrate the general possibility of CN neuron growth in culture on semiconductors in vitro. The differences in neuron length and number per explant indicate that the growth of CN neurons is influenced by the semiconductor substrate as well as extracellular matrix proteins, with laminin-coated p-type Si3N4[100] being a preferable material for future hybrid experiments on auditory-neuron semiconductor chips.

A quantitative method for analysis of in vitro neurite outgrowth

The adult mammalian CNS is extremely limited in its ability to regenerate axons following injury. Glial scar, neuroinflammatory processes and molecules released from myelin impair axonal regrowth and contribute to the lack of neural regeneration. An in vitro assay that quantitates neurite outgrowth from cultured neurons as a model of neuronal regenerative potential is described. Specifically, the neurite outgrowth from primary neurons (rat cerebellar granule neurons; CGNs) and a neuronal cell line (NG108-15) were quantitatively measured after optimization of culture conditions. After cultures were fixed and immunostained to label neurons and nuclei, microscope images were captured and an image analysis algorithm was developed using Image-Pro Plus software to allow quantitative analysis. The algorithm allowed the determination of total neurite length, number of neurons, and number of neurons without neurites. The algorithm also allows for end-user control of thresholds for staining intensity and cell/nuclei size. This assay represents a useful tool for quantification of neurite outgrowth from a variety of neuronal sources with applications that include: (1) assessment of neurite outgrowth potential; (2) identification of molecules that can block or stimulate neurite outgrowth in conventional culture media; and (3) identification of agents that can overcome neurite outgrowth inhibition by inhibitory substrates.

The effect of polypyrrole with incorporated neurotrophin-3 on the promotion of neurite outgrowth from auditory neurons

This research aims to improve the nerve-electrode interface of the cochlear implant using polymer technology to encourage neuron survival, elongation and adhesion to the electrodes. Polypyrrole (Ppy) doped with p-toluene sulphonate (pTS) is an electroactive polymer into which neurotrophin-3 (NT3) can be incorporated. Ppy/pTS+/-NT3 was synthesised over gold electrodes and used as a surface for auditory neuron explant culture. Neurite outgrowth from explants grown on Ppy/pTS was equivalent to tissue culture plastic but improved with the incorporation of NT3 (Ppy/pTS/NT3). Electrical stimulation of Ppy/pTS/NT3 with a biphasic current pulse, as used in cochlear implants, significantly improved neurite outgrowth from explants. Using (125)I-NT3, it was shown that low levels of NT3 passively diffused from Ppy/pTS/NT3 during normal incubation and that electrical stimulation enhanced the release of biologically active NT3 in quantities adequate for neuron survival. Furthermore, Ppy/pTS/NT3 and its constituents were not toxic to auditory neurons and the Ppy/pTS/NT3 coating on gold electrodes did not alter impedance. If applied to the cochlear implant, Ppy/pTS/NT3 will provide a biocompatible, low-impedance substrate for storage and release of NT3 to help protect auditory neurons from degradation after sensorineural hearing loss and encourage neurite outgrowth towards the electrodes.

Optimizing neurotrophic factor combinations for neurite outgrowth

Most neurotrophic factors are members of one of three families: the neurotrophins, the glial cell-line derived neurotrophic factor family ligands (GFLs) and the neuropoietic cytokines. Each family activates distinct but overlapping cellular pathways. Several studies have shown additive or synergistic interactions between neurotrophic factors from different families, though generally only a single combination has been studied. Because of possible interactions between the neurotrophic factors, the optimum concentration of a factor in a mixture may differ from the optimum when applied individually. Additionally, the effect of combinations of neurotrophic factors from each of the three families on neurite extension is unclear. This study examines the effects of several combinations of the neurotrophin nerve growth factor (NGF), the GFL glial cell-line derived neurotrophic factor (GDNF) and the neuropoietic cytokine ciliary neurotrophic factor (CNTF) on neurite outgrowth from young rat dorsal root ganglion (DRG) explants. The combination of 50 ng ml(-1) NGF and 10 ng ml(-1) of each GDNF and CNTF induced the highest level of neurite outgrowth at a 752 +/- 53% increase over untreated DRGs and increased the longest neurite length to 2031 +/- 97 microm compared to 916 +/- 64 microm for untreated DRGs. The optimum concentrations of the three factors applied in combination corresponded to the optimum concentration of each factor when applied individually. These results indicate that the efficacy of future therapies for nerve repair would be enhanced by the controlled release of a combination of neurotrophins, GFLs and neuropoietic cytokines at higher concentrations than used in previous conduit designs.

Neurite outgrowth in dorsal root ganglia induced by islet neogenesis-associated protein peptide involves protein kinase A activation

Islet neogenesis-associated protein (INGAP) peptide is a candidate therapeutic for diabetes and corrects sensory dysfunction in experimental diabetes in mice. In this study, we investigated the mechanism of action by which INGAP peptide promotes neurite outgrowth in sensory neurons of the dorsal root ganglia. Treatment of dorsal root ganglia primary dispersed cultures with INGAP peptide led to the displacement of fluorescently labeled forskolin from adenylate cyclase, the cyclic AMP-generating enzyme that has been implicated in neuritogenesis. The addition of forskolin or dibutyryl cyclic AMP enhanced the effects of INGAP peptide on neurite outgrowth in dorsal root ganglia explant cultures. Furthermore, pharmacological inhibition of adenylate cyclase with SQ22,536 or of protein kinase A with H89 or KT5720 significantly reduced the neurite-promoting effects of INGAP peptide. These results suggest that INGAP peptide-induced neurite outgrowth in the dorsal root ganglia partially involves cyclic AMP-dependent activation of protein kinase A.

Automated identification of axonal growth cones in time-lapse image sequences

The isolation and purification of axon guidance molecules has enabled in vitro studies of the effects of axon guidance molecule gradients on numerous neuronal cell types. In a typical experiment, cultured neurons are exposed to a chemotactic gradient and their growth is recorded by manual identification of the axon tip position from two or more micrographs. Detailed and statistically valid quantification of axon growth requires evaluation of a large number of neurons at closely spaced time points (e.g. using a time-lapse microscopy setup). However, manual tracing becomes increasingly impractical for recording axon growth as the number of time points and/or neurons increases. We present a software tool that automatically identifies and records the axon tip position in each phase-contrast image of a time-lapse series with minimal user involvement. The software outputs several quantitative measures of axon growth, and allows users to develop custom measurements. For, example analysis of growth velocity for a dissociated E13 mouse cortical neuron revealed frequent extension and retraction events with an average growth velocity of 0.05 +/- 0.14 microm/min. Comparison of software-identified axon tip positions with manually identified axon tip positions shows that the software's performance is indistinguishable from that of skilled human users.