Total Number Of Axons Research Articles

Multichannel bridges and NSC synergize to enhance axon regeneration, myelination, synaptic reconnection, and recovery after SCI

Regeneration in the injured spinal cord is limited by physical and chemical barriers. Acute implantation of a multichannel poly(lactide-co-glycolide) (PLG) bridge mechanically stabilizes the injury, modulates inflammation, and provides a permissive environment for rapid cellularization and robust axonal regrowth through this otherwise inhibitory milieu. However, without additional intervention, regenerated axons remain largely unmyelinated (<10%), limiting functional repair. While transplanted human neural stem cells (hNSC) myelinate axons after spinal cord injury (SCI), hNSC fate is highly influenced by the SCI inflammatory microenvironment, also limiting functional repair. Accordingly, we investigated the combination of PLG scaffold bridges with hNSC to improve histological and functional outcome after SCI. In vitro, hNSC culture on a PLG scaffold increased oligodendroglial lineage selection after inflammatory challenge. In vivo, acute PLG bridge implantation followed by chronic hNSC transplantation demonstrated a robust capacity of donor human cells to migrate into PLG bridge channels along regenerating axons and integrate into the host spinal cord as myelinating oligodendrocytes and synaptically integrated neurons. Axons that regenerated through the PLG bridge formed synaptic circuits that connected the ipsilateral forelimb muscle to contralateral motor cortex. hNSC transplantation significantly enhanced the total number of regenerating and myelinated axons identified within the PLG bridge. Finally, the combination of acute bridge implantation and hNSC transplantation exhibited robust improvement in locomotor recovery. These data identify a successful strategy to enhance neurorepair through a temporally layered approach using acute bridge implantation and chronic cell transplantation to spare tissue, promote regeneration, and maximize the function of new axonal connections.

(067) How Many Nerve Fibers Innervate the Human Glans Penis: A Histomorphometric Analysis of the Human Dorsal Nerve of the Penis

Abstract Introduction The mainstream media has frequently quoted that the penis has “half as many” nerve fibers as the human clitoris. Recent work has demonstrated that the number of nerve fibers in the dorsal nerve of clitoris was under-estimated, and no study has yet quantified the number of axons in the human dorsal nerve of the penis (DNP). Improving our understanding of penile innervation and sexual response has potential implications for fields of medical and surgical practice. Several nerve transfers have recently emerged targeting the DNP for re-innervation in order to restore penile sensation and/or erectile function, demonstrating variability in outcomes. Understanding the axon counts of the DNP at the anatomic level that these nerve transfers are performed may inform technical refinements and improve our understanding of current outcomes. Comparing DNP axon counts to the recently reported axon counts of the dorsal nerve of the clitoris may also inform techniques in transgender genital surgery, anticipate sensory outcomes in penile allotransplantation and further our understanding of sexual responses across genitalia. Objective The objective of this study is to quantify the number of axons in the human dorsal nerve of the penis. Methods Bilateral DNP samples were obtained from 5 fresh frozen cadavers. Samples were collected at the base of the penis at the level of the pubic symphysis, a location commonly targeted for coaptation in nerve transfers. Specimens were placed in 3% glutaraldehyde, post-fixed in 1% osmium tetroxide and serially dehydrated in ethanol and toluene. They were embedded in araldite, sectioned on ultramicrotome into 1 μm cross-sections and counter-stained with 1% toluidine blue. Histomorphometric evaluation was performed at 1000x magnification using Leitz Laborlux S microscope and image analysis software (Clemex Vision Professional, Longueuil, Quebec) to obtain nerve fiber counts from each specimen (Figure). Results 10 DNP samples were analyzed. The mean number of axons in the human dorsal nerve of penis was 3,844 +/- 1,238 (range 1,915 to 5,494). Accounting for the bilaterality of the DNP, the mean total number of axons innervating the human glans penis was 7,688 +/- 1,762. Conclusions This study is the first to report the number of axons in the human dorsal nerve of the penis and approximate the number of axons innervating the human glans penis. At the level of the pubic symphysis, axon counts of the dorsal nerve of penis varied significantly and averaged 3,844. The variation in axon counts at this anatomic level was greater than seen in prior reports on the DNC and may be one factor contributing to variations in outcomes following nerves transfers for penile sensation and erection. This variation could also reflect the anatomic level of sample collection or differences in specimen origin (cadaver vs. live person). DNP axon counts were less than or equal to recently reported axon counts of the human glans clitoris, despite the much larger size of the glans penis. This finding may be important when considering clitoral construction in transgender genital surgery, penile allotransplantation and different in sexual responsiveness across genitalia. Disclosure No.

The Effect of Liraglutide on Axon Regeneration and Functional Recovery after Peripheral Nerve Lesion.

Peripheral nerve injuries inflict severe consequences, necessitating innovative therapeutic strategies. This study investigates the potential of liraglutide, a glucagon-like peptide-1 receptor agonist, in mitigating the consequences of peripheral nerve injury. The existing treatment methods for such injuries underscore the importance of ongoing translational research efforts. Thirty adult Wistar rats underwent sciatic nerve dissection and repair surgery. The nerves were surgically transected using micro scissors at a precise location located 1.5 cm proximal to the trifurcation site. The study included a control group and two experimental groups, one treated with saline (placebo group) and the other with liraglutide (experimental group) for 12 weeks. Motor function, electromyography (EMG), and biochemical and histopathological analyses were performed after 12 weeks of treatment. Electrophysiological assessments revealed that liraglutide improved the compound muscle action potential (CMAP) amplitude and motor function compared to the saline-treated group. Histological and immunohistochemical analyses demonstrated increased NGF expression, total axon number, and diameter and reduced fibrosis in the liraglutide group. Biochemical analyses illustrated liraglutide's antioxidative properties, evidenced by reduced malondialdehyde (MDA) levels. Galectin-3 levels were suppressed and GDF-11 levels were modulated by liraglutide, indicating anti-inflammatory and anti-apoptotic effects. Liraglutide is a promising therapeutic intervention for peripheral nerve injuries, promoting functional recovery and histopathological improvement. Its multifaceted positive impact, beyond glycemic control, suggests constructive effects on the acute and chronic inflammatory processes associated with peripheral neuropathy. These findings warrant further research to elucidate molecular mechanisms and facilitate clinical translation. The study contributes valuable insights to the growing understanding of GLP-1 receptor agonists' neuroprotective properties in the context of peripheral nerve injuries.

Impact of cerebral hypoperfusion–reperfusion on optic nerve integrity and visual function in the DBA/2J mouse model of glaucoma

ObjectiveOne of the most important risk factors for developing a glaucomatous optic neuropathy is elevated intraocular pressure. Moreover, mechanisms such as altered perfusion have been postulated to injure the optical...

Effect of glutaraldehyde-crosslinked cartilage acellular matrix film on anti-adhesion and nerve regeneration in a rat sciatic nerve injury model.

Decellularized extra-cellular matrix (ECM) has been studied as an alternative to anti-adhesive biomaterials and cartilage acellular matrix (CAM) has been shown to inhibit postoperative adhesion in several organs. This study aimed to evaluate the suitability of glutaraldehyde (GA) crosslinked CAM-films as anti-adhesion barriers for peripheral nerve injury. The films were successfully fabricated and showed improved physical properties such as mechanical strength, swelling ratio, and lengthened degradation period while maintaining the microstructure and chemical composition after GA crosslinking. In the in vitro study of CAM-film, the dsDNA content met the recommended limit of decellularization and more than 70% of the major ECM components were preserved after decellularization. The adhesion and proliferation of seeded human umbilical vein endothelial cells and fibroblasts were significantly lower in CAM-film than in control, but similar with Seprafilm. However, the CAM-film extract did not show cytotoxicity. In the in vivo study, the peri-neural fibrosis was thicker, adhesion score higher, and peri-neural collagen fibers more abundant in the control group than in the CAM-film group. The total number of myelinated axons was significantly higher in the CAM-film group than in the control group. The inflammatory marker decreased with time in the CAM-film group compared to that in the control group, whereas the nerve regenerative marker expression was maintained. Moreover, the ankle angles at contracture and toe-off were higher in the CAM film-treated rats than in the control rats. GA-crosslinked CAM films may be used during peripheral nerve surgery to prevent peri-neural adhesion and enhance nerve functional recovery.

Schwann cell delivery via a novel 3D collagen matrix conduit improves outcomes in critical length nerve gap repairs.

The current clinical standard of harvesting a nerve autograft for repair of long-segment peripheral nerve injuries (PNIs) is associated with many potential complications. Guidance channels offer an alternative therapy. The authors investigate whether autologous Schwann cells (SCs) implanted within a novel collagen-glycosaminoglycan conduit will improve axonal regeneration in a long-segment PNI model. Novel NeuraGen 3D collagen matrix conduits were implanted with autologous SCs to investigate axonal regeneration across a critical size defect (13 mm) in male Fischer rat sciatic nerve. Reversed sciatic nerve autografts served as positive controls, and conduits filled with serum only as negative controls. Electrophysiological assessments were made in vivo. Animals were killed at 4 or 16 weeks postinjury, muscle weights were measured, and grafts underwent immunohistochemical and morphometric analysis. SC survival was confirmed by the presence of green fluorescent protein-labeled SCs within regenerated fibers. Regeneration and elongation of myelinated axons in all segments of the graft were significantly enhanced at 16 weeks in the SC-filled conduits compared to the conduit alone and were statistically similar to those of the autograft. Nerves repaired with SC-filled conduits exhibited onset latencies and nerve conduction amplitudes similar to those of the contralateral controls and autograft (p < 0.05). Adding SCs to the conduit also significantly reduced muscle atrophy compared to conduit alone (p < 0.0001). Repair of long-segment PNI of rat sciatic nerve is significantly enhanced by SC-filled NeuraGen 3D conduits. Improvements in the total number of myelinated axons, axon diameter, and myelin thickness throughout SC-filled conduits allow for significant recovery in nerve conduction and a decrease in muscle atrophy.

3: IGF-1 Hydrogel-based Nanofiber Drug Delivery System to Improve Nerve Regeneration and Functional Recovery After Peripheral Nerve Repair

Purpose:Insulin-like growth factor 1 (IGF-1) is a potent mitogen with the potential to enhance axonal regeneration and minimize muscle atrophy and Schwann cell senescence following prolonged denervation after peripheral nerve injury. IGF-1 is a small protein with a half-life of 5 min, making local delivery a challenge. Our group has demonstrated over 6 weeks of sustained release of bioactive IGF-1 encapsulated within biodegradable nanoparticles (NP) and subsequently developed a nanofiber fiber hydrogel composite (NHC) carrier to retain IGF-1 NPs at target tissue locally for the duration of drug release. The aim of this study was to further characterize and refine the IGF-1 NP-NHC drug delivery and then investigate its efficacy in both rodent and non-human primate (NHP) median nerve injury models.Methods:IGF-1 was encapsulated in biodegradable PCL NPs and then embedded within the NHC composed of hyaluronic acid and PCL nanofibers. Release kinetics and biocompatibility were evaluated and optimized both in vitro and in vivo. The drug delivery system was assessed using a chronic denervation median nerve injury rat model and an acute median nerve repair NHP model. IGF-1NP/NHC was injected along the median nerve and within denervated muscle. In rodents, a range of IGF-1 doses (300, 900 and 1500 μg/mL) were investigated to evaluate dose-response relationships. Axonal regeneration, muscle atrophy, neuromuscular junction reinnervation and recovery of grip strength were assessed.Results:The refined NP-NHC delivery system provided sustained release of bioactive IGF-1, in vivo, for at least 42 days by serial ELISA. IGF-1 treated rodents demonstrated a 35% increase in functional recovery (stimulated grip strength) compared to untreated rodents, with no differences observed between the different concentrations of IGF-1 that were evaluated. Median nerve histomorphometry demonstrated a significantly greater total number of axons at each concentration of IGF-1 compared to untreated rodents (p<0.0001). IGF-1 treated rodents also demonstrated a greater percentage of reinnervation of neuromuscular junctions by 17% (from 14% to 31%). In addition, the IGF-1 treated non-human primate demonstrated a 31% increase in functional recovery compared to the untreated animal (N=1 per group).Conclusion:The IGF-1 NP/NHC delivery system provided sustained delivery for over 42 days in rodents and NHP. IGF-1 improves motor functional recovery by enhancing axonal regeneration and neuromuscular junction reinnervation while limiting denervation-induced muscle and Schwann cell atrophy in rodents. Our NHP pilot study has established a used pre-clinical model with robust functional analysis that will serve as a platform for a formal NHP study prior to clinical testing. The components of the NP-NHC delivery system are already used in FDA approved formulations, which will facilitate clinical translation.

Neurobiological substrates underlying corpus callosum hypoconnectivity and brain metabolic patterns in the valproic acid rat model of autism spectrum disorder.

Atypical connectivity between brain regions and altered structure of the corpus callosum (CC) in imaging studies supports the long-distance hypoconnectivity hypothesis proposed for autism spectrum disorder (ASD). The aim of this study was to unveil the CC ultrastructural and cellular changes employing the valproic acid (VPA) rat model of ASD. Male Wistar rats were exposed to VPA (450mg/kg i.p.) or saline (control) during gestation (embryonic day 10.5), and maturation, exploration, and social behavior were subsequently tested. Myelin content, ultrastructure, and oligodendroglial lineage were studied in the CC at post-natal days 15 (infant) and 36 (juvenile). As a functional outcome, brain metabolic activity was determined by positron emission tomography. Concomitantly with behavioral deficits in juvenile VPA rats, the CC showed reduced myelin basic protein, conserved total number of axons, reduced percentage of myelinated axons, and aberrant and less compact arrangements of myelin sheath ultrastructure. Mature oligodendrocytes decreased and oligodendrocyte precursors increased in the absence of astrogliosis or microgliosis. In medial prefrontal and somatosensory cortices of juvenile VPA rats, myelin ultrastructure and oligodendroglial lineage were preserved. VPA animals exhibited global brain hypometabolism and local hypermetabolism in brain regions relevant for ASD. In turn, the CC of infant VPA rats showed reduced myelin content but preserved oligodendroglial lineage. Our findings indicate that CC hypomyelination is established during infancy and prior to oligodendroglial pattern alterations, which suggests that axon-oligodendroglia communication could be compromised in VPA animals. Thus, CC hypomyelination may underlie white matter alterations and contribute to atypical patterns of connectivity and metabolism found in ASD.

Functional and electron-microscopic changes after differential traction injury in the sciatic nerve of a rat

BackgroundDuring maxillofacial trauma or oral cancer surgery, peripheral nerve might be damaged by traction injury. The purpose of this study was to evaluate functional and histomorphometric changes after traction nerve injury in the sciatic nerve of a rat model.MethodsA total of 24 Sprague-Dawley rats were equally divided into three groups: unstretched (sham/control, group A), stretched with 0.7N (group B) and 1.5N (group C). Traction injury was performed for 10 min in B and C groups. Functional recovery of the sciatic nerve was evaluated by walking track analysis, toe spread test, and pinprick test 2 weeks after injury. The weight of gastrocnemius muscles of both sides was measured to evaluate weight ratio (ipsilateral/contralateral). Total number of axons, axon fiber size, myelin thickness, G-ratio, axon number/mm2, diameter of fiber, changes of longitudinal width, and formation of the edema and hematoma were evaluated by transmission electron microscopy.ResultsThe sciatic function indexes were −11.48±4.0, −15.11±14.84, and −49.12±35.42 for groups A, B, and C, respectively. Pinprick test showed 3.0, 2.86±0.38, and 1.38±0.52 for A, B, and group C. Muscle weight ratios were 0.98±0.13 for group A, 0.70±0.10 for group B, and 0.54±0.05 for group C. There were significant differences in toe spread test, pinprick test, and muscle weight ratio between control group and experimental group (p<0.001). In the experimental group, fiber number, fiber size, G-ratio, fiber number/mm2, myelin thickness, diameter of fiber, and longitudinal width were decreased with statistical significance.ConclusionThe present study demonstrated that the nerve traction injury in the rat sciatic nerve damaged the motor and sensory function and axonal integrity. The amount of functional nerve damage was proportional to the amount of traction power and dependent on the initial tensile strengths (0.7N and 1.5N).

Intravitreal injection worsens outcomes in a mouse model of indirect traumatic optic neuropathy from closed globe injury

It is well established that an intravitreal needle poke or injection of buffer is protective to the retina in models of photoreceptor degeneration due to release of endogenous neurotrophic factors. Here we assess the effect of intravitreal injection of buffer in a model of closed globe trauma that causes air-blast induced indirect traumatic optic neuropathy (bITON). We injected animals 1-day after the last bITON or sham procedure and performed assessments 1-month later. Surprisingly, we detected a lower electroretinogram (ERG), greater optic nerve damage, and increased levels of pro-inflammatory cytokines in animals given an intravitreal injection. The effect was sometimes independent of bITON and sometimes exacerbated by the injury. Retina histology appeared normal, however the total number of axons in the optic nerve was lower even in uninjured animals that were injected. The number of degenerative axons was further increased in injured animals that were injected. In contrast, we detected a decrease in the ERG a wave and b wave amplitudes, but no effect on the visual evoked potential. Levels of the pro-inflammatory cytokines, IL-1α and IL-1β were elevated in the mice that received an intravitreal injection. This increase was even greater in animals that also had a bITON. This suggests that intravitreal injections may be injurious to the optic nerve particularly during the acute stage of optic nerve injury. In addition, the data suggests a role for IL-1α and IL-1β in this response.

Convergence of Olfactory Inputs within the Central Nervous System of a Cartilaginous and a Bony Fish: An Anatomical Indicator of Olfactory Sensitivity

The volume of the olfactory bulbs (OBs) relative to the brain has been used previously as a proxy for olfactory capabilities in many vertebrate taxa, including fishes. Although this gross approach has predictive power, a more accurate assessment of the number of afferent olfactory inputs and the convergence of this information at the level of the telencephalon is critical to our understanding of the role of olfaction in the behaviour of fishes. In this study, we used transmission electron microscopy to assess the number of first-order axons within the olfactory nerve (ON) and the number of second-order axons in the olfactory peduncle (OP) in established model species within cartilaginous (brownbanded bamboo shark, Chiloscyllium punctatum [CP]) and bony (common goldfish, Carassius auratus [CA]) fishes. The total number of axons varied from a mean of 18.12 ± 7.50 million in the ON to a mean of 0.38 ± 0.21 million in the OP of CP, versus 0.48 ± 0.16 million in the ON and 0.09 ± 0.02 million in the OP of CA. This resulted in a convergence ratio of approximately 50:1 and 5:1, respectively, for these two species. Based on astroglial ensheathing, axon type (unmyelinated [UM] and myelinated [M]) and axon size, we found no differentiated tracts in the OP of CP, whereas a lateral and a medial tract (both of which could be subdivided into two bundles or areas) were identified for CA, as previously described. Linear regression analyses revealed significant differences not only in axon density between species and locations (nerves and peduncles), but also in axon type and axon diameter (p < 0.05). However, UM axon diameter was larger in the OPs than in the nerve in both species (p = 0.005), with no significant differences in UM axon diameter in the ON (p = 0.06) between species. This study provides an in-depth analysis of the neuroanatomical organisation of the ascending olfactory pathway in two fish taxa and a quantitative anatomical comparison of the summation of olfactory information. Our results support the assertion that relative OB volume is a good indicator of the level of olfactory input and thereby a proxy for olfactory capabilities.

A morphologic and histologic study of the radial nerve and its branches at potential compression sites

ObjectivesThis study examined variations in the termination level of the radial nerve (RN) and the morphometry of the RN and its branches at potential compression sites. Additionally, we digitally analysed histological sections of the RN, the superficial branch of the radial nerve (SBRN), and the posterior interosseous nerve (PIN). MethodsWe conducted this study on 14 formalin fixed adult cadavers. The lengths of the RN, SBRN, and PIN were measured up to potential compression sites, using appropriate surface skeletal landmarks as reference points. We histologically evaluated the fascicular and non-fascicular areas and the number of axons in each nerve. All parameters were statistically analysed using a paired t-test. ResultsWe found variations in the bifurcation of the RN with respect to the biepicondylar line (BEL). However, the course of RN terminal branches was constant in the forearm. There was a significant histological difference between the fascicular and non-fascicular areas of the PIN. There was no significant difference in the total number of axons in the SBRN and PIN. Finally, we observed that the intramuscular length of the PIN within the supinator muscle was variable and that the SBRN had more fascicles compared to the RN and PIN. ConclusionsIn our study, the RN and PIN had more variable morphometry compared to that of the SBRN. The histologic evaluation and quantification of these nerves at their potential compression sites could serve as a guide for surgeons planning nerve reconstruction procedures.

Delayed short-term tamoxifen treatment does not promote remyelination or neuron sparing after spinal cord injury.

The tamoxifen-dependent Cre/lox system in transgenic mice has become an important research tool across all scientific disciplines for manipulating gene expression in specific cell types. In these mouse models, Cre-recombination is not induced until tamoxifen is administered, which allows researchers to have temporal control of genetic modifications. Interestingly, tamoxifen has been identified as a potential therapy for spinal cord injury (SCI) and traumatic brain injury patients due to its neuroprotective properties. It is also reparative in that it stimulates oligodendrocyte differentiation and remyelination after toxin-induced demyelination. However, it is unknown whether tamoxifen is neuroprotective and neuroreparative when administration is delayed after SCI. To properly interpret data from transgenic mice in which tamoxifen treatment is delayed after SCI, it is necessary to identify the effects of tamoxifen alone on anatomical and functional recovery. In this study, female and male mice received a moderate mid-thoracic spinal cord contusion. Mice were then gavaged with corn oil or a high dose of tamoxifen from 19-22 days post-injury, and sacrificed 42 days post-injury. All mice underwent behavioral testing for the duration of the study, which revealed that tamoxifen treatment did not impact hindlimb motor recovery. Similarly, histological analyses revealed that tamoxifen had no effect on white matter sparing, total axon number, axon sprouting, glial reactivity, cell proliferation, oligodendrocyte number, or myelination, but tamoxifen did decrease the number of neurons in the dorsal and ventral horn. Semi-thin sections confirmed that axon demyelination and remyelination were unaffected by tamoxifen. Sex-specific responses to tamoxifen were also assessed, and there were no significant differences between female and male mice. These data suggest that delayed tamoxifen administration after SCI does not change functional recovery or improve tissue sparing in female or male mice.

Measurement-oriented deep-learning workflow for improved segmentation of myelin and axons in high-resolution images of human cerebral white matter

BackgroundStandard segmentation of high-contrast electron micrographs (EM) identifies myelin accurately but does not translate easily into measurements of individual axons and their myelin, even in cross-sections of parallel fibers. We describe automated segmentation and measurement of each myelinated axon and its sheath in EMs of arbitrarily oriented human white matter from autopsies. New methodsPreliminary segmentation of myelin, axons and background by machine learning, using selected filters, precedes automated correction of systematic errors. Final segmentation is done by a deep neural network (DNN). Automated measurement of each putative fiber rejects measures encountering pre-defined artifacts and excludes fibers failing to satisfy pre-defined conditions. ResultsImproved segmentation of three sets of 30 annotated images each (two sets from human prefrontal white matter and one from human optic nerve) is achieved with a DNN trained only with a subset of the first set from prefrontal white matter. Total number of myelinated axons identified by the DNN differed from expert segmentation by 0.2%, 2.9%, and -5.1%, respectively. G-ratios differed by 2.96%, 0.74% and 2.83%. Intraclass correlation coefficients between DNN and annotated segmentation were mostly >0.9, indicating nearly interchangeable performance. Comparison with existing method(s)Measurement-oriented studies of arbitrarily oriented fibers from central white matter are rare. Published methods are typically applied to cross-sections of fascicles and measure aggregated areas of myelin sheaths and axons, allowing estimation only of average g-ratio. ConclusionsAutomated segmentation and measurement of axons and myelin is complex. We report a feasible approach that has so far proven comparable to manual segmentation.

Efficient determination of axon number in the optic nerve: A stereological approach

Quantifying the number of axons in the optic nerve is of interest in many research questions. Here, we show that a stereological method allows simple, efficient, precise and unbiased determination of the total axon number in the murine optic nerve. Axons in semi-thin optic nerve cross sections from untreated eyes (n = 21) and eyes subjected to retinal damage by intravitreous NMDA injections (n = 32) or PBS controls (n = 5) were manually identified, counted and digitally labeled by hand. A stereological procedure was empirically tested with systematic combinations of different sampling methods (simple random sampling without replacement, systematic uniform random sampling, stratified random sampling) and sampling parameters. Extensive numerical Monte Carlo experiments were performed to evaluate their large-sample properties. Our results demonstrate reliable determination of total axon number and superior performance compared to other methods at a small fraction of the time required for a full manual count. We specify suitable sampling parameters for the adoption of an efficient stereological sampling scheme, give empirical estimates of the additionally introduced sampling variance to facilitate experimental planning, and offer AxonCounter, an easy-to-use plugin implementing these stereological methods for the multi-platform image processing application NIH ImageJ.

Deficit of corpus callosum axons, reduced axon diameter and decreased area are markers of abnormal development of interhemispheric connections in autistic subjects

IntroductionIn autism spectrum disorder, lack of coherence and of complex information processing, and narrowly focused interests and repetitive behaviors are considered a sign of long-range underconnectivity and short-range overconnectivity. The goal of this morphometric study of five anatomically and functionally different segments of the corpus callosum (CC) was to establish patterns of differences between long-range interhemispheric connections in nine neurotypical and nine autistic subjects.ResultsElectron microscopy revealed a significant reduction in average axon diameter and axon cross-sectional area in autistic subjects, and reduction in CC segment–specific diversification of connections of functionally different cortical regions. The study shows an increase in the percentage of small diameter axons (< 0.651 μm) and a decrease in the percentage of axons with large diameter (> 1.051 μm). The total number of small-diameter axons is reduced in segment I and III by 43% on average. The number of medium- and large-diameter axons is reduced in all five CC segments by an average of 49 and 72%, respectively.ConclusionsThe detected pattern of pathology suggests a failure of mechanisms controlling guidance of axons during development leading to axonal deficit, and failure of mechanisms controlling axon structure. A reduction in axon diameter may affect the velocity and volume of signal transmission, and distort functional specialization of CC segments. Significant deficits in axon number and reduction in axon size in all five CC segments appear to be substantial components of brain connectome integrity distortion which may contribute to the autism phenotype.

Ontogenetic Shifts in the Number of Axons in the Olfactory Tract and Optic Nerve in Two Species of Deep-Sea Grenadier Fish (Gadiformes: Macrouridae: Coryphaenoides)

Neuroanatomical studies of the peripheral sense organs and brains of deep-sea fishes are particularly useful for predicting their sensory capabilities and ultimately their behaviour. Over the abyssal plane (between 2,000 and 6,000 m), communities of grenadiers (Gadiformes: Macrouridae) play an important ecological role as predator-scavengers. Previous studies suggest that these fishes rely heavily on chemosensation, especially olfaction. Furthermore, at least one species, Coryphaenoides armatus, undergoes an ontogenetic shift in the relative size of the optic tectum and the olfactory bulbs, suggesting. a shift from a reliance on vision to olfaction during ontogeny, apparently in association with a shift to a more scavenging lifestyle. Here, we compared the olfactory and visual sensory inputs to the brain in C. armatus, and in a second, closely-related species, Coryphaenoides profundicolus, by assessing the total number of axons (myelinated and unmyelinated) in the olfactory tract and optic nerve in a range of individuals from both species. In C. armatus, the numbers of axons in both tract and nerve increased with body size, with the total number of axons in the olfactory tract being far greater than the number of axons in the optic nerve. These differences became more pronounced in larger animals. In the two smaller C. profundicolus individuals (≤315 mm SL), there were more axons in the optic nerve than in the olfactory tract, but the opposite situation was found in larger individuals. As in C. armatus, the number of olfactory tract axons also increased with body size in C. profundicolus, but in contrast, the number of optic nerve axons decreased in this species. These results suggest that both C. armatus and C. profundicolus undergo an ontogenetic shift in sensory orientation, with olfaction becoming relatively more important than vision in larger animals. The differences in the ratio of olfactory tract to optic nerve axons in C. armatus indicate that olfaction is of particular importance to larger individuals of this species. In both species, the percentage of myelinated axons in the olfactory tract was relatively low, but we found evidence for interspecific and ontogenetic variation in the percentages of myelinated axons in the optic nerve.

Analysis of regeneration- and myelination-associated proteins in human neuroma in continuity and discontinuity.

Neuromas are pathologic nerve distensions caused by a nerve's response to trauma, resulting in a dysfunctional to non-functional nerve. Depending on the severance of the affected nerve, the resulting neuroma can be differentiated into continuous and stump neuroma. While neuroma formation has been investigated in animal models with enormous regenerative capacity, the search for differences in human response to nerve trauma on a molecular level ultimately seeks to identify reasons for functionally successful versus unsuccessful regeneration after peripheral nerve trauma in man. In the present study, the regenerative potential of axons and the capability of Schwann cells (SC) to remyelinate regenerating axons was quantitatively and segmentally analyzed and compared within human neuroma in-continuity and discontinuity. For the stump neuroma and the neuroma in-continuity, there was a significant reduction of the total number of axons (86% stump neuroma and 91% neuroma in-continuity) from the proximal to the distal part of the neuroma, while the amount of fibrotic tissue increased, respectively. Labeling the myelin sheath of regenerating axons revealed a remyelination of regenerating axons by SCs in both neuroma types. The segmented analysis showed no distinct alterations in the number and spatial distribution of regenerating, mature, and myelinated axons between continuous and discontinuous neuroma. The quantitative and segmented analysis showed no distinct alterations in the number and spatial distribution of regenerating, mature, and myelinated axons between continuous and discontinuous neuroma, while the extensive expression of Gap43 in up to 55% of the human neuroma axons underlines their regenerative capacity independent of whether the neuroma is in continuity or discontinuity. Remyelination of Gap43-positive axons suggests that the capability of SCs to remyelinate regenerating axons is preserved in neuroma tissue.

End-to-end and end-to-side neurorrhaphy between thick donor nerves and thin recipient nerves: an axon regeneration study in a rat model.

During nerve reconstruction, nerves of different thicknesses are often sutured together using end-to-side neurorrhaphy and end-to-end neurorrhaphy techniques. In this study, the effect of the type of neurorrhaphy on the number and diameter of regenerated axon fibers was studied in a rat facial nerve repair model. An inflow-type end-to-side and end-to-end neurorrhaphy model with nerve stumps of different thicknesses (2:1 diameter ratio) was created in the facial nerve of 14 adult male Sprague-Dawley rats. After 6 and 12 weeks, nerve regeneration was evaluated in the rats using the following outcomes: total number of myelinated axons, average minor axis diameter of the myelinated axons in the central and peripheral sections, and axon regeneration rate. End-to-end neurorrhaphy resulted in a significantly greater number of regenerated myelinated axons and rate of regeneration after 6 weeks than end-to-side neurorrhaphy; however, no such differences were observed at 12 weeks. While the regenerated axons were thicker at 12 weeks than at 6 weeks, no significant differences in axon fiber thickness were detected between end-to-end and end-to-side neurorrhaphy. Thus, end-to-end neurorrhaphy resulted in greater numbers of regenerated axons and increased axon regeneration rate during the early postoperative period. As rapid reinnervation is one of the most important factors influencing the restoration of target muscle function, we conclude that end-to-end neurorrhaphy is desirable when suturing thick nerves to thin nerves.

The Effect of Carnitine on Peripheral Nerve Regeneration

Proximal and distal axons of the nerve body are subject to varying degrees of traumatic degeneration after an incision. The histologic structure of rat peripheral nerves cannot be distinguished from the human. Studies on systemic carnitine treatment following peripheral nerve injury and its positive results are available in the literature. There are no reported results of local administration. The authors used 50 rats. A total of 5 groups were created by randomly assigning the rats. In the first study group, the nerve was repaired following the incision. NaCl was locally administered to the repair region. In the second study group, the nerve was repaired following the incision. Carnitine was administered systemically. In the third study group, the nerve was repaired following the incision. The rats were administered Carnitine locally and additionally Carnitine was administered systemically. In the fourth study group, the nerve was repaired following the incision. Carnitine was administered locally. The fifth control group did not undergo any procedure. Although Sciatic function index of the groups that received carnitine was better than the group that received NaCl, no statistically significant difference was present. Nerve action potential amplitude values were calculated from the electrophysiological recordings obtained. All groups were compared among themselves, a statistically significant difference was found. A significant difference was found between first, second, third, fourth, control groups. The total nerve area and number of axons per mm was lower in the control group than all other groups. Local administration of carnitine was found to be as effective as systemic administration. The authors therefore conclude that carnitine can be used locally, systemically or systemically + locally to increase regeneration following peripheral nerve damage.