Axon Diameter Research Articles

The effect of pulsed radiofrequency application on nerve healing after sciatic nerve anastomosis in rats

ABSTRACT The Effect of Pulsed Radiofrequency Application on Nerve Healing After Sciatic Nerve Anastomosis in Rats. In this study, we aimed to evaluate the histomorphological and functional effect of Pulsed Radiofrequency (PRF) application on regeneration after experimental nerve damage in rats. Forty Sprague-Dawley male rats were used in the study. Sciatic nerve incision was applied to all rats and then anastomosis was performed. Twenty rats were separated as the control group, and the remaining 20 rats underwent PRF every day at 42oC, for 120 seconds. The groups were divided into two further subgroups to be sacrificed on the 15th and 30th days. Tissue samples were obtained from all groups at 24 hours and 72 hours after the injury. Sections of sciatic nerve samples were stained with hematoxylin-eosin for light microscopic investigation and prepared for evaluation of ultrastructural changes with transmission electron microscopy. In the evaluation of axon numbers and diameters were seen that the 30th-day RF group had an increase compared to the control group. In the electron microscopic examination, it was observed that myelinated and unmyelinated nerve fiber sheaths had borders that are more regular in the RF group, the nucleus structures of schwann cells were better preserved, mitochondrial damage was less, and the extensions of fibroblast and collagen fibers were smoother than the control group. The findings suggested that PRF application has a positive contribution histologically on nerve healing in the early period after full-layer incision nerve injury anastomosis surgery.

Long-Term Changes in Axon Calibers after Injury: Observations on the Mouse Corticospinal Tract.

White matter pathology is common across a wide spectrum of neurological diseases. Characterizing this pathology is important for both a mechanistic understanding of neurological diseases as well as for the development of neuroimaging biomarkers. Although axonal calibers can vary by orders of magnitude, they are tightly regulated and related to neuronal function, and changes in axon calibers have been reported in several diseases and their models. In this study, we utilize the impact acceleration model of traumatic brain injury (IA-TBI) to assess early and late changes in the axon diameter distribution (ADD) of the mouse corticospinal tract using Airyscan and electron microscopy. We find that axon calibers follow a lognormal distribution whose parameters significantly change after injury. While IA-TBI leads to 30% loss of corticospinal axons by day 7 with a bias for larger axons, at 21 days after injury we find a significant redistribution of axon frequencies that is driven by a reduction in large-caliber axons in the absence of detectable degeneration. We postulate that changes in ADD features may reflect a functional adaptation of injured neural systems. Moreover, we find that ADD features offer an accurate way to discriminate between injured and non-injured mice. Exploring injury-related ADD signatures by histology or new emerging neuroimaging modalities may offer a more nuanced and comprehensive way to characterize white matter pathology and may also have the potential to generate novel biomarkers of injury.

Role of stem cells-based in facial nerve reanimation: A meta-analysis of histological and neurophysiological outcomes.

BACKGROUNDTreatments involving stem cell (SC) usage represent novel and potentially interesting alternatives in facial nerve reanimation. Current literature includes the use of SC in animal model studies to promote graft survival by enhancing nerve fiber growth, spreading, myelinization, in addition to limiting fibrotic dege neration after surgery. However, the effectiveness of the clinical use of SC in facial nerve reanimation has not been clarified yet.AIMTo investigate the histological, neurophysiological, and functional outcomes in facial reanimation using SC, compared to autograft.METHODSOur study is a systematic review of the literature, consistently conducted according to the preferred reporting items for systematic reviews and meta-analyses statement guidelines. The review question was: In facial nerve reanimation on rats, has the use of stem cells revealed as effective when compared to autograft, in terms of histological, neurophysiological, and functional outcomes? Random-effect meta-analysis was conducted on histological and neurophysiological data from the included comparative studies.RESULTSAfter screening 148 manuscript, five papers were included in our study. 43 subjects were included in the SC group, while 40 in the autograft group. The meta-analysis showed no significative differences between the two groups in terms of myelin thickness [CI: -0.10 (-0.20, 0.00); I2 = 29%; P = 0.06], nerve fibers diameter [CI: 0.72 (-0.93, 3.36); I2 = 72%; P = 0.6], compound muscle action potential amplitude [CI: 1.59 (0.59, 3.77); I2 = 89%; P = 0.15] and latency [CI: 0.66 (-1.01, 2.32); I2 = 67%; P = 0.44]. The mean axonal diameter was higher in the autograft group [CI: 0.94 (0.60, 1.27); I2 = 0%; P ≤ 0.001].CONCLUSIONThe role of stem cells in facial reanimation is still relatively poorly studied, in animal models, and available results should not discourage their use in future studies on human subjects.

Short- and Long-Term Effects of Chlorpyrifos on Thyroid Hormone Axis and Brain Development in Xenopus laevis

Introduction: The extensive use of the insecticide chlorpyrifos (CPF) throughout the world has brought increased scrutiny on its environmental and health impact. CPF is a cholinergic neurotoxicant; however, exposure to low noncholinergic doses is associated with numerous neurodevelopmental effects in animal models. In this study, we aimed to assess CPF for its potential to disrupt thyroid hormone signalling and investigate the short- and long-term effects on neurodevelopment by using Xenopus laevis. Methods: The thyroid hormone (TH) disrupting potential of CPF was assessed using TH-sensitive transgenic Tg(thibz:eGFP) tadpoles. The consequences of early embryonic exposure were examined by exposing fertilized eggs for 72 h to environmentally relevant CPF concentrations (10⁻¹⁰ M and 10⁻⁸ M). Three endpoints were evaluated: (1) gene expression in whole embryonic brains immediately after exposure, (2) mobility and brain morphology 1 week after exposure, and (3) brain morphology and axon diameters at the end of metamorphosis (2 months after the exposure). Results: CPF disrupted TH signalling in Tg(thibz:eGFP) tadpoles. The expression of genes klf9, cntn4, oatp1c1, and tubb2b was downregulated in response to CPF. Tadpoles exposed to CPF exhibited increased mobility and altered brain morphology compared to control tadpoles. Early embryonic exposure of CPF affected myelinated axon diameter, with exposed animals exhibiting shifted frequency distributions of myelinated axons diameters towards smaller diameters in the hindbrain of froglets. Discussion/Conclusion: This study provides more evidence of the endocrine and neurodevelopment disrupting activity of CPF. Further experimental and epidemiological studies are warranted to determine the long-term consequences of early CPF exposure on brain development.

Imaging peripheral nerve micro-anatomy with MUSE, 2D and 3D approaches

Understanding peripheral nerve micro-anatomy can assist in the development of safe and effective neuromodulation devices. However, current approaches for imaging nerve morphology at the fiber level are either cumbersome, require substantial instrumentation, have a limited volume of view, or are limited in resolution/contrast. We present alternative methods based on MUSE (Microscopy with Ultraviolet Surface Excitation) imaging to investigate peripheral nerve morphology, both in 2D and 3D. For 2D imaging, fixed samples are imaged on a conventional MUSE system either label free (via auto-fluorescence) or after staining with fluorescent dyes. This method provides a simple and rapid technique to visualize myelinated nerve fibers at specific locations along the length of the nerve and perform measurements of fiber morphology (e.g., axon diameter and g-ratio). For 3D imaging, a whole-mount staining and MUSE block-face imaging method is developed that can be used to characterize peripheral nerve micro-anatomy and improve the accuracy of computational models in neuromodulation. Images of rat sciatic and human cadaver tibial nerves are presented, illustrating the applicability of the method in different preclinical models.

Proteomic and functional analyses of the periodic membrane skeleton in neurons

Actin, spectrin, and associated molecules form a membrane-associated periodic skeleton (MPS) in neurons. The molecular composition and functions of the MPS remain incompletely understood. Here, using co-immunoprecipitation and mass spectrometry, we identified hundreds of potential candidate MPS-interacting proteins that span diverse functional categories. We examined representative proteins in several of these categories using super-resolution imaging, including previously unknown MPS structural components, as well as motor proteins, cell adhesion molecules, ion channels, and signaling proteins, and observed periodic distributions characteristic of the MPS along the neurites for ~20 proteins. Genetic perturbations of the MPS and its interacting proteins further suggested functional roles of the MPS in axon-axon and axon-dendrite interactions and in axon diameter regulation, and implicated the involvement of MPS interactions with cell adhesion molecules and non-muscle myosin in these roles. These results provide insights into the interactome of the MPS and suggest previously unknown functions of the MPS in neurons.

Low-intensity low-frequency pulsed ultrasound ameliorates sciatic nerve dysfunction in a rat model of cisplatin-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy is a neurological complication that frequently occurs during chemotherapeutic intervention, resulting in damaged myelin sheath, motor weakness and/or sensory impairment. This study aims to investigate the therapeutic efficiency of low-intensity pulsed low-frequency ultrasound on cisplatin-induced peripheral neuropathy. Rats were randomly divided into five experimental groups as control, cisplatin administration, 10 mg/kg melatonin treatment after cisplatin administration, 1 MHz frequency 0.5 W/cm2 pulsed ultrasound treatment after cisplatin administration and 1 MHz frequency 1.5 W/cm2 pulsed ultrasound treatment after cisplatin administration. Chemical neuropathy was induced by the injection of 3 mg/kg/week of cisplatin (i.p.) for 5 weeks. Afterwards, melatonin and pulsed ultrasound treatments were applied for 15 consecutive days. Cisplatin administration resulted in a decrease in nociceptive pain perception and nerve conduction velocities together with a decrease in myelin thickness and diameters of axons and myelinated fibers, indicating a dysfunction and degeneration in sciatic nerves. In addition, cisplatin administration led to a decrease, in superoxide dismutase activity, and an increase in malondialdehyde and IL-1β levels together with an increase in caspase-3 protein expression levels and a decrease in Bcl-2 and Parkin levels. The ultrasound treatments resulted in an increase in nociceptive pain perception and sciatic nerve conduction; led to a decrease in oxidative stress and inflammation, restored nerve degeneration and regulated apoptosis and mitophagy. Taken together, low-intensity pulsed low-frequency ultrasound was efficient in restoring the alterations attributable to cisplatin-induced peripheral neuropathy, and warrants further investigations.

Modelling the effect of ephaptic coupling on spike propagation in peripheral nerve fibres

Experimental and theoretical studies have shown that ephaptic coupling leads to the synchronisation and slowing down of spikes propagating along the axons within peripheral nerve bundles. However, the main focus thus far has been on a small number of identical axons, whereas realistic peripheral nerve bundles contain numerous axons with different diameters. Here, we present a computationally efficient spike propagation model, which captures the essential features of propagating spikes and their ephaptic interaction, and facilitates the theoretical investigation of spike volleys in large, heterogeneous fibre bundles. We first lay out the theoretical basis to describe how the spike in an active axon changes the membrane potential of a passive axon. These insights are then incorporated into the spike propagation model, which is calibrated with a biophysically realistic model based on Hodgkin–Huxley dynamics. The fully calibrated model is then applied to fibre bundles with a large number of axons and different types of axon diameter distributions. One key insight of this study is that the heterogeneity of the axonal diameters has a dispersive effect, and that a higher level of heterogeneity requires stronger ephaptic coupling to achieve full synchronisation between spikes.

Electromagnetic modeling and simulation of the biophoton propagation in myelinated axon waveguide.

Biophotons in the nervous system are a potential carrier of neural signals. Previous experiments and studies indicated that biophotons are closely related to the neuronal activity and can propagate along myelinated axons. We establish a multilayer electromagnetic simulation model and demonstrate that the myelinated axon waveguide has low attenuation and low dispersion and operates in a narrow bandwidth on the order of 10 nm. We also find that the operating wavelength of the waveguide is almost linearly related to the axon diameter and the number of myelin layers. Each additional layer of the myelin sheath causes the operating wavelength of the myelinated axon waveguide to shift 52.3 nm to the long-wave direction, while an increase in the axon diameter of 1.0 µm causes the operating wavelength to shift 94.5 nm to the short-wave direction. These findings well explain the tendency of the spectral redshift among different species and the spectral blueshift during the aging process of mice. Via the analysis method in this paper, we can predict the wavelength of the propagating biophotons based on the neural structure.

SPARC: Intersectional labeling of vagal afferent nerve subsets using Cre and FLP dependent dual reporter strain

Respiratory reflexes are tightly controlled by distinct types of vagal sensory afferent nerves. Afferent nerves can be categorized by their conduction velocity, axon diameter, myelination, responses to stimuli, ion channels/receptor expression, and embryological origin. Some airway vagal afferent nerves are sensitive to noxious stimuli (i.e. nociceptive). TRPV1, the capsaicin receptor, is selectively expressed on most vagal nociceptors. Vagal ganglia are comprised of jugular ganglia (neural crest origin) and nodose ganglia (placodal origin). Tac1 encodes Tachykinin1, the substance P precursor protein, and is mainly expressed in the jugular ganglia. P2X2, a purinergic receptor, is exclusively expressed in nodose ganglia. Previous data suggests that activation of jugular nociceptors and nodose nociceptors causes distinct reflexes. Here, we used intersectional genetics to simultaneously visualize nodose and jugular nociceptors. We generated a transgenic mouse model with dual recombinase responsive allele using Cre‐Lox and Flp‐FRT (Flippase‐Flp recognition target) systems. With the ROSA26‐RC::FLTG allele, cells with only Flp show tdTomato expression (by excising of FRT‐flanked STOP cassette) while cells with both Flp and Cre have GFP expression (by excising of both FRT‐flanked STOP cassette and loxP‐flanked tdTomato). We generated TRPV1‐FLP:Tac1‐Cre:ROSA and TRPV1‐FLP:P2X2‐Cre:ROSA strains. Offspring (6 to 8 weeks old) were used for characterization. Vagal ganglia, lung and brainstem were collected and fixed with 4% paraformaldehyde. Tissue were cryosectioned for immunohistochemistry. In TRPV1‐FLP:Tac1‐Cre:ROSA, the majority of tdTomato expressing cells were in nodose ganglia and GFP expressing neurons were in jugular ganglia. In TRPV1‐FLP:P2X2‐Cre:ROSA, as expected, GFP expressing neurons were only observed in nodose ganglia while tdTomato expressing neurons were observed in both nodose and jugular ganglia. Reporter expressing neurons in both strains overlapped with anti‐TRPV1 antibody staining indicating they were all nociceptive. In the brainstem, reporter expression was mainly in the nucleus of solitary tract (nTS) in both strains. In TRPV1‐FLP:Tac1‐Cre:ROSA strain, GFP expression (jugular nociceptors) was also observed in the paratrigeminal nucleus (Pa5). In the lung, most TRPV1+ fibers expressing Tac1 were found in close proximity to the epithelial layer of bronchi and bronchioles. Whereas TRPV1+ fibers expressing P2X2 often projected away from the conducting airways into the alveolar tissue. Taken together, we have developed cell type specific‐dual reporter mouse models using a combinatorial/intersectional Cre and FLP strategy to successfully identify distinct nociceptive subtypes of afferent nerves in vagal ganglia, brainstem, and lung.

Cyclin‐dependent kinase 7 contributes to myelin maintenance in the adult central nervous system and promotes myelin gene expression

Mechanisms regulating oligodendrocyte differentiation, developmental myelination and myelin maintenance in adulthood are complex and still not completely described. Their understanding is crucial for the development of new protective or therapeutic strategies in demyelinating pathologies such as multiple sclerosis. In this perspective, we have investigated the role of Cyclin-dependent kinase 7 (Cdk7), a kinase involved in cell-cycle progression and transcription regulation, in the oligodendroglial lineage. We generated a conditional knock-out mouse model in which Cdk7 is invalidated in post-mitotic oligodendrocytes. At the end of developmental myelination, the number and diameter of myelinated axons, as well as the myelin structure, thickness and protein composition, were normal. However, in young adult and in aged mice, there was a higher number of small caliber myelinated axons associated with a decreased mean axonal diameter, myelin sheaths of large caliber axons were thinner, and the level of some major myelin-associated proteins was reduced. These defects were accompanied by the appearance of an abnormal clasping phenotype. We also used an in vitro oligodendroglial model and showed that Cdk7 pharmacological inhibition led to an altered myelination-associated morphological modification combined with a decreased expression of myelin-specific genes. Altogether, we identified novel functions for Cdk7 in CNS myelination.

Refinement of axonal conduction and myelination in the mouse optic nerve indicate an extended period of postnatal developmental plasticity.

Retinal ganglion cells generate a pattern of action potentials to communicate visual information from the retina to cortical areas. Myelin, an insulating sheath, wraps axonal segments to facilitate signal propagation and when deficient, can impair visual function. Optic nerve development and initial myelination has largely been considered completed by the fifth postnatal week. However, the relationship between the extent of myelination and axonal signaling in the maturing optic nerve is not well characterized. Here, we examine the relationship between axon conduction and elements of myelination using extracellular nerve recordings, immunohistochemistry, western blot analysis, scanning electron microscopy, and simulations of nerve responses. Comparing compound action potentials from mice aged 4-12weeks revealed five functional distinct axonal populations, an increase in the number of functional axons, and shifts toward fast-conducting axon populations at 5 and 8weeks postnatal. At these ages, our analysis revealed increased myelin thickness, lower g-ratios and changes in the 14kDa MBP isoform, while the density of axons and nodes of Ranvier remained constant. At 5 postnatal weeks, axon diameter increased, while at 8weeks, increased expression of a mature sodium ion channel subtype, Nav 1.6, was observed at nodes of Ranvier. A simulation model of nerve conduction suggests that ion channel subtype, axon diameter, and myelin thickness are more likely to be key regulators of nerve function than g-ratio. Such refinement of axonal function and myelin rearrangement identified an extended period of maturation in the normal optic nerve that may facilitate the development of visual signaling patterns.

A simple model considering spiking probability during extracellular axon stimulation.

The spiking probability of an electrically stimulated axon as a function of stimulus amplitude increases in a sigmoidal dependency from 0 to 1. However, most computer simulation studies for neuroprosthetic applications calculate thresholds for neural targets with a deterministic model and by reducing the sigmoid curve to a step function, they miss an important information about the control signal, namely how the spiking efficiency increases with stimulus intensity. Here, this spiking efficiency is taken into account in a compartment model of the Hodgkin Huxley type where a noise current is added in every compartment with an active membrane. A key parameter of the model is a common factor knoise which defines the ion current fluctuations across the cell membrane for every compartment by its maximum sodium ion conductance. In the standard model Gaussian signals are changed every 2.5 μs as a compromise of accuracy and computational costs. Additionally, a formula for other noise transmission times is presented and numerically tested. Spiking probability as a function of stimulus intensity can be approximated by the cumulative distribution function of the normal distribution with RS = σ/μ. Relative spread RS, introduced by Verveen, is a measure for the spread (normalized by the threshold intensity μ), that decreases inversely with axon diameter. Dynamic range, a related measure used in neuroprosthetic studies, defines the intensity range between 10% and 90% spiking probability. We show that (i) the dynamic range normalized by threshold is 2.56 times RS, (ii) RS increases with electrode-axon distance and (iii) we present knoise values for myelinated and unmyelinated axon models in agreement with recoded RS data. The presented method is applicable for other membrane models and can be extended to whole neurons that are described by multi-compartment models.

Measurement of Full Diffusion Tensor Distribution Using High-Gradient Diffusion MRI and Applications in Diffuse Gliomas

Diffusion MRI is widely used for the clinical examination of a variety of diseases of the nervous system. However, clinical MRI scanners are mostly capable of magnetic field gradients in the range of 20–80 mT/m and are thus limited in the detection of small tissue structures such as determining axon diameters. The availability of high gradient systems such as the Connectome MRI scanner with gradient strengths up to 300 mT/m enables quantification of the reduction of the apparent diffusion coefficient and thus resolution of a wider range of diffusion coefficients. In addition, biological tissues are heterogenous on many scales and the complexity of tissue microstructure may not be accurately captured by models based on pre-existing assumptions. Thus, it is important to analyze the diffusion distribution without prior assumptions of the underlying diffusion components and their symmetries. In this paper, we outline a framework for analyzing diffusion MRI data with b-values up to 17,800 s/mm2 to obtain a Full Diffusion Tensor Distribution (FDTD) with a wide variety of diffusion tensor structures and without prior assumption of the form of the distribution, and test it on a healthy subject. We then apply this method and use a machine learning method based on K-means classification to identify features in FDTD to visualize and characterize tissue heterogeneity in two subjects with diffuse gliomas.

Nanoscale Patterning of In Vitro Neuronal Circuits.

Methods for patterning neurons in vitro have gradually improved and are used to investigate questions that are difficult to address in or ex vivo. Though these techniques guide axons between groups of neurons, multiscale control of neuronal connectivity, from circuits to synapses, is yet to be achieved in vitro. As studying neuronal circuits with synaptic resolution in vivo poses significant challenges, we present an in vitro alternative to validate biophysical and computational models. In this work we use a combination of electron beam lithography and photolithography to create polydimethylsiloxane (PDMS) structures with features ranging from 150 nm to a few millimeters. Leveraging the difference between average axon and dendritic spine diameters, we restrict axon growth while allowing spines to pass through nanochannels to guide synapse formation between small groups of neurons (i.e., nodes). We show this technique can be used to generate large numbers of isolated feed-forward circuits where connections between nodes are restricted to regions connected by nanochannels. Using a genetically encoded calcium indicator in combination with fluorescently tagged postsynaptic protein, PSD-95, we demonstrate functional synapses can form in this region.

Individual variability in the nonlinear development of the corpus callosum during infancy and toddlerhood: a longitudinal MRI analysis.

The human brain spends several years bootstrapping itself through intrinsic and extrinsic modulation, thus gradually developing both spatial organization and functions. Based on previous studies on developmental patterns and inter-individual variability of the corpus callosum (CC), we hypothesized that inherent variations of CC shape among infants emerge, depending on the position within the CC, along the developmental timeline. Here we used longitudinal magnetic resonance imaging data from infancy to toddlerhood and investigated the area, thickness, and shape of the midsagittal plane of the CC by applying multilevel modeling. The shape characteristics were extracted using the Procrustes method. We found nonlinearity, region-dependency, and inter-individual variability, as well as intra-individual consistencies, in CC development. Overall, the growth rate is faster in the first year than in the second year, and the trajectory differs between infants; the direction of CC formation in individual infants was determined within six months and maintained to two years. The anterior and posterior subregions increase in area and thickness faster than other subregions. Moreover, we clarified that the growth rate of the middle part of the CC is faster in the second year than in the first year in some individuals. Since the division of regions exhibiting different tendencies coincides with previously reported divisions based on the diameter of axons that make up the region, our results suggest that subregion-dependent individual variability occurs due to the increase in the diameter of the axon caliber, myelination partly due to experience and axon elimination during the early developmental period.

Rapid, automated nerve histomorphometry through open-source artificial intelligence

We aimed to develop and validate a deep learning model for automated segmentation and histomorphometry of myelinated peripheral nerve fibers from light microscopic images. A convolutional neural network integrated in the AxonDeepSeg framework was trained for automated axon/myelin segmentation using a dataset of light-microscopic cross-sectional images of osmium tetroxide-stained rat nerves including various axonal regeneration stages. In a second dataset, accuracy of automated segmentation was determined against manual axon/myelin labels. Automated morphometry results, including axon diameter, myelin sheath thickness and g-ratio were compared against manual straight-line measurements and morphometrics extracted from manual labels with AxonDeepSeg as a reference standard. The neural network achieved high pixel-wise accuracy for nerve fiber segmentations with a mean (± standard deviation) ground truth overlap of 0.93 (± 0.03) for axons and 0.99 (± 0.01) for myelin sheaths, respectively. Nerve fibers were identified with a sensitivity of 0.99 and a precision of 0.97. For each nerve fiber, the myelin thickness, axon diameter, g-ratio, solidity, eccentricity, orientation, and individual x -and y-coordinates were determined automatically. Compared to manual morphometry, automated histomorphometry showed superior agreement with the reference standard while reducing the analysis time to below 2.5% of the time needed for manual morphometry. This open-source convolutional neural network provides rapid and accurate morphometry of entire peripheral nerve cross-sections. Given its easy applicability, it could contribute to significant time savings in biomedical research while extracting unprecedented amounts of objective morphologic information from large image datasets.

GACSON software for automated segmentation and morphology analyses of myelinated axons in 3D electron microscopy

Background and ObjectiveAdvances in electron microscopy (EM) now allow three-dimensional (3D) imaging of hundreds of micrometers of tissue with nanometer-scale resolution, providing new opportunities to study the ultrastructure of the brain. In this work, we introduce a freely available Matlab-based gACSON software for visualization, segmentation, assessment, and morphology analysis of myelinated axons in 3D-EM volumes of brain tissue samples. MethodsThe software is equipped with a graphical user interface (GUI). It automatically segments the intra-axonal space of myelinated axons and their corresponding myelin sheaths and allows manual segmentation, proofreading, and interactive correction of the segmented components. gACSON analyzes the morphology of myelinated axons, such as axonal diameter, axonal eccentricity, myelin thickness, or g-ratio. ResultsWe illustrate the use of the software by segmenting and analyzing myelinated axons in six 3D-EM volumes of rat somatosensory cortex after sham surgery or traumatic brain injury (TBI). Our results suggest that the equivalent diameter of myelinated axons in somatosensory cortex was decreased in TBI animals five months after the injury. ConclusionOur results indicate that gACSON is a valuable tool for visualization, segmentation, assessment, and morphology analysis of myelinated axons in 3D-EM volumes. It is freely available at https://github.com/AndreaBehan/g-ACSON under the MIT license.

Polydendrocytes – undifferentiated cells of the nervous system

Oligodendrocyte progenitor cells (OPCs) were first described more than two decades ago. New marker techniques have revealed that they are independent cells with the high nerve tissue repair potential, and they have been classified as the fourth glial cell type in addition to astrocytes, oligodendrocytes and microglial cells. Another term used for this type of cells is polydendrocytes, this is due to both their morphology and developing knowledge of their diverse functions. OPCs play an important role in the development and myelinogenesis in adults giving rise to oligodendrocytes that cover axons providing signal isolation by the myelin sheath, thus accelerating action potential propagation and ensuring high transmission fidelity without the need for an increased axon diameter. Loss or absence of oligodendrocyte precursors and the resulting absence of differentiated oligodendrocytes are associated with lost myelination and subsequent impairment of neurological functions. Demyelination is a feature of various diseases such as multiple sclerosis, Alzheimer's disease, schizophrenia, infantile cerebral palsy and childhood cognitive impairment. Moreover, OPCs express receptors for various neurotransmitters and are exposed to membrane depolarisation to receive synaptic signals from neurons. Numerous research studies have been investigated polydendrocyte functionality and potential for use as target cells in the treatment and prevention of neural tissue diseases. There are no studies related to morphology, functionality and potential of oligodendrocyte precursors in our country. In this review we highlight issues of the polydendrocyte discovery, their localization and migration potential, possibilities of remyelination through OPCs in hypoxic injury in the embryonic and postnatal period.

369 Toward a Complete Mechanism of Action in Epidural Spinal Cord Stimulation - Including Threshold Accommodation

INTRODUCTION: Multiple waveform variations have been introduced for treating neuropathic pain with epidural spinal cord stimulation. These include higher frequencies (eg up to 10kHz) and different cadences of bursting signals. Prior understanding of mechansims of action for reducing pain have relied upon the reduction in WDR cell firing through retrograde stimulation of the largest Ab axons in the dorsal columns. However, prior models did not include details about diameter dependent threshold changes in the dorsal column axons. We sought to include this critical detail toward determining a deeper understand of how all of the waveform variations, including non-paresthetic stimuli, might also acheive pain relief. METHODS: Prior FEM and axonal models were used to achieve this analysis with additional adjustments of adding empirically-derived threshold accomodation to the axon membrane properties. These were calibrated based on axon diameter. Software was programmed in COMSOL and Mathematica, as well as proprietary programs using C++, Java, and JavaScript. RESULTS: Tonic stimulation above 100-300Hz and with increasing PW show accomodation changes and threshold inversions. Also, however, Burst and HF waveforms also showed threshold inversions and led to non-paresthetic activity within dorsal column fibers. Amplitudes were found to achive this phenomenon within typically-used clinical ranges. CONCLUSION: By accounting for known threshold accommodation, related to axon diameters within the dorsal coulmns, a clear mechnism of action could be ascribed to all known waveforms being used clinically. The results show that there would likely not be paresthesia experienced at clinically relevant amplitudes for many of these waveforms and a coherent complete mechanism of action for achieving pain relief is derived from this approach.