Number Of Axons Research Articles

Rosmarinic acid Ameliorates neuronal regeneration in the bridging silicone rubber conduits of the sciatic nerve in taxol‐treated rats

Background and aimTaxol modulates local inflammatory conditions in peripheral nerves, which may impair their regeneration and recovery when injured. This study aimed to determine the effects of rosmarinic acid (RA, a polyphenol constituent of many culinary herbs) on the regeneration of the sciatic nerves in the bridging conduits. Experimental procedureIn the cell study, RA decreased nuclear factor (NF)-κB activity induced by taxol in a dose dependency. In the animal model, taxol-treated rats were divided into 3 groups (n = 10/group): taxol (2 mg/kg body weight for 4 times) and taxol + RA (3 times/week for 4 weeks at 20 and 40 mg/kg body weight) groups. Macrophage infiltration, calcitonin gene-related peptide (CGRP) expression levels, neuronal connectivity, animal behavior, and neuronal electrophysiology were evaluated. Results and conclusionAt the end of 4 weeks, macrophage density, CGRP expression level, and axon number significantly increased in the RA group compared with the taxol group. The RA administration unaffected heat, cold plate licking latencies, and motor coordination. Moreover, the 40 mg/kg RA group had significantly larger nerve conduction velocity and less latency compared to the taxol group. This study suggested that RA could ameliorate local inflammatory conditions to augment the recovery of regenerating nerves by accelerating their regrowth and improving electrophysiological function in taxol-treated peripheral nerve injury repaired with the silicone rubber conduit.

Peripheral neural interfaces: Skeletal muscles are hyper-reinnervated according to the axonal capacity of the surgically rewired nerves.

Advances in robotics have outpaced the capabilities of man-machine interfaces to decipher and transfer neural information to and from prosthetic devices. We emulated clinical scenarios where high- (facial) or low-neural capacity (ulnar) donor nerves were surgically rewired to the sternomastoid muscle, which is controlled by a very small number of motor axons. Using retrograde tracing and electrophysiological assessments, we observed a nearly 15-fold functional hyper-reinnervation of the muscle after high-capacity nerve transfer, demonstrating its capability of generating a multifold of neuromuscular junctions. Moreover, the surgically redirected axons influenced the muscle's physiological characteristics, by altering the expression of myosin heavy-chain types in alignment with the donor nerve. These findings highlight the remarkable capacity of skeletal muscles to act as biological amplifiers of neural information from the spinal cord for governing bionic prostheses, with the potential of expressing high-dimensional neural function for high-information transfer interfaces.

Dexamethasone and concentrated growth factors on peripheral nerve injury: A clinic-relevant animal study

BackgroundMandibular nerve injury is a common clinical condition that affects clinicians’ management and patients’ quality of life. In the literature, there are various effective treatments available. The primary purpose of this study was to determine and compare the effects of dexamethasone and concentrated growth factor (CGF) on regeneration in patients with nerve trauma that mimics clinical situations. MethodsIn this study, 36 rats were divided into 3 groups: the control, dexamethasone and CGF groups. The inferior alveolar nerve was traumatized through the extraction socket after mandibular molar tooth extraction in each group. ResultsThe data showed a decrease in the control (4.5–4), dexamethasone (3–2), and CGF (4–3) groups according to the histological injury severity score (HISS) results. Compared with those in the other groups, the number of degenerative axons and edematous areas observed via histological examination were significantly lower in the CGF groups. Similarly, compared with those in the control group, the nNOS and Neurofilament-H positivity in the dexamethasone group on the 30th day (2,2 to 1,1 respectively) was significantly lower. The positivity of all the primary antibodies in the 3rd and 30th day CGF groups was significant compared than that in the dexamethasone 30th day group. ConclusionAccording to the results of the analysis of the immunohistopathological and HISS data, the CGF groups exhibited greater regeneration than did the dexamethasone groups.

Pathologic classification of a late-onset peripheral neuropathy in a spontaneous Labrador retriever dog model.

Late-onset peripheral neuropathy (LPN) is a heritable canine neuropathy commonly found in Labrador retrievers and is characterized by laryngeal paralysis and pelvic limb paresis. Our objective was to establish canine LPN as a model for human hereditary peripheral neuropathy by classifying it as either an axonopathy or myelinopathy and evaluating length-dependent degeneration. We conducted a motor nerve conduction study of the sciatic and ulnar nerves, electromyography (EMG) of appendicular and epaxial musculature, and histologic analysis of sciatic and recurrent laryngeal nerves in LPN-affected and control dogs. LPN-affected dogs exhibited significant decreases in compound muscle action potential (CMAP) amplitude, CMAP area, and pelvic limb latencies. However, no differences were found in motor nerve conduction velocity, residual latencies, or CMAP duration. Distal limb musculature showed greater EMG changes in LPN-affected dogs. Histologically, LPN-affected dogs exhibited a reduction in the number of large-diameter axons, especially in distal nerve regions. In conclusion, LPN in Labrador retrievers is a common, spontaneous, length-dependent peripheral axonopathy that is a novel animal model of age-related peripheral neuropathy that could be used for fundamental research and clinical trials.

A mechanism for deviance detection and contextual routing in the thalamus: a review and theoretical proposal.

Predictive processing theories conceptualize neocortical feedback as conveying expectations and contextual attention signals derived from internal cortical models, playing an essential role in the perception and interpretation of sensory information. However, few predictive processing frameworks outline concrete mechanistic roles for the corticothalamic (CT) feedback from layer 6 (L6), despite the fact that the number of CT axons is an order of magnitude greater than that of feedforward thalamocortical (TC) axons. Here we review the functional architecture of CT circuits and propose a mechanism through which L6 could regulate thalamic firing modes (burst, tonic) to detect unexpected inputs. Using simulations in a model of a TC cell, we show how the CT feedback could support prediction-based input discrimination in TC cells by promoting burst firing. This type of CT control can enable the thalamic circuit to implement spatial and context selective attention mechanisms. The proposed mechanism generates specific experimentally testable hypotheses. We suggest that the L6 CT feedback allows the thalamus to detect deviance from predictions of internal cortical models, thereby supporting contextual attention and routing operations, a far more powerful role than traditionally assumed.

A7 CANNABINOID 1 AND 2 RECEPTOR AGONISTS AND MU-OPIOID RECEPTOR AGONISTS SYNERGISTICALLY INHIBIT COLONIC NOCICEPTION DURING ACUTE COLITIS

Abstract Background Abdominal pain is a debilitating symptom in patients with inflammatory bowel disease. Previously we have shown that combining sub-analgesic doses of cannabinoid 1 receptor (CB1R), but not cannabinoid 2 receptor (CB2R), and mu-opioid receptor (MOR) agonists synergistically inhibits colonic nociception in healthy mice. However, it is unknown whether this combination has analgesic efficacy in a pre-clinical model of colitis. Aims To determine the effects of combining sub-analgesic doses of CBR and MOR agonists on colonic nociception during acute colitis. Methods Colitis was induced in male and female C57BL/6 mice with 2.5% dextran sulfate sodium in drinking water. Extracellular afferent nerve recordings were obtained from ex vivo flat sheet preparations of mouse distal colon. Mechanosensitivity of single afferent axons was assessed via probing of the colon with a 1g von Frey hair before and after superfusion of agonists of CB1R or CB2R plus MOR. To examine effects in vivo, visceromotor response (VMR) to colorectal distention (volume range 20-80 µL) was measured via electromyography. Mice were injected intraperitoneally with vehicle, or a combination of CB1R or CB2R agonist plus morphine 30-minutes prior to VMR experiment. Data were analyzed using a one or two-way ANOVA with Bonferroni test. N denotes number of mice; n denotes number of single afferent axons. Results In afferent nerve recordings, in contrast to healthy mice, the CB2R agonist HU-308 (1 µM and 3 µM) inhibited colonic mechanosensitivity in mice with colitis (1 µM: p<0.01, N=5, n=12; 3 µM: p<0.01, N=7, n=10); a lower concentration (300 nM) had no effect (p=0.52, N=6, n=10). The CB1R agonist ACEA (10 µM) reduced mechanosensitivity during acute colitis (p<0.05, n=11, N=6), whereas 100 nM (p>0.99, n=7, N=5) and 1 µM (p=0.25, n=10, N=6) had no effect. A combination of sub-analgesic concentrations of ACEA (100 nM) and DAMGO (MOR agonist, 1 nM) inhibited colonic mechanosensitivity in healthy mice (p<0.01, N=4, n=8) and during acute colitis (p<0.05, N=6, n=8). While a combination of sub-analgesic concentrations of HU-308 (300 nM) and DAMGO (1 nM) had no effect in healthy mice (p=0.70, N=4, n=8), it inhibited colonic mechanosensitivity during acute colitis (p<0.01, N=8, n=15). In VMR experiments, a combination of a sub-analgesic dose of ACEA (0.3 mg/kg) with morphine (0.3 mg/kg) reduced VMR (p<0.01, N=7) during acute colitis. Similarly, a combination of a sub-analgesic dose of HU-308 (1 mg/kg) and morphine (0.3 mg/kg) reduced VMR (p<0.01, N=6) during acute colitis. Conclusions A CB2R agonist inhibits colonic nociception during acute colitis, but not in healthy mice. A sub-analgesic combination of CB1R and MOR agonists can inhibit pain in healthy and inflamed mice, while combining sub-analgesic CB2R and MOR agonists is only inhibitory during acute colitis. Funding Agencies NRC

(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.

Induced Attenuation of Scleral TGF-β Signaling in Mutant Mice Increases Susceptibility to IOP-Induced Optic Nerve Damage.

Axonal optic nerve (ON) damage in glaucoma is characteristically associated with increased amounts of active transforming growth factor-beta 2 (TGF-β2) in the ON head. Here we investigated the functional role of scleral TGF-β signaling in glaucoma. A deficiency of Tgfbr2, which encodes for TGF-β receptor type II (TGF-βRII), the essential receptor for canonical TGF-β signaling, was induced in fibroblasts (including those of the sclera) of mutant mice. To this end, 5-week-old mice were treated with tamoxifen eye drops. Experimental glaucoma was induced in 8-week-old mice using a magnetic microbead (MB) model. After 6 weeks of high intraocular pressure (IOP), the ON axons and their somata in the retina were labeled by paraphenylenediamine (PPD) and RNA-binding protein with multiple splicing (RBPMS) immunohistochemistry, respectively, and quantified. Tamoxifen treatment resulted in a significant decrease of TGF-βRII and its mRNA in the sclera. After 6 weeks of high IOP, reduced numbers of PPD-stained ON axons were seen in MB-injected eyes in comparison with not-injected contralateral eyes. Moreover, MB injection also led to a decrease of retinal ganglion cell (RGC) somata as seen in RBPMS-stained retinal wholemounts. Axon loss and RGC loss were significantly higher in mice with a fibroblast specific deficiency of TGF-βRII in comparison with control animals. We conclude that the ablation of scleral TGF-β signaling increases the susceptibility to IOP-induced ON damage. Scleral TGF-β signaling in mutant mice appears to be beneficial for ON axon survival in experimentally induced glaucoma.

Dexamethasone release from hyaluronic acid microparticle and proanthocyanidin-gelatin hydrogel in sciatic tissue regeneration

Biodegradable microparticles are useful vehicles for the controlled release of bioactive molecules in drug delivery, tissue engineering and biopharmaceutical applications. We developed dexamethasone (Dex) encapsulation into tyramine-substituted hyaluronic acid microparticles (Dex-HA-Tyr Mp) mediated by horseradish peroxidase (HRP) crosslinking using a microfluidic device and infollowing crosslinked gelatin (Gela) with proanthocyanidin (PA) as a semi-confined bed hydrogel for the repair of sciatic tissue injury. It was found that the simultaneous use of Dex-HA-Tyr Mp and cross-linked Gela-PA hydrogel improved the physical properties of the hydrogel, including mechanical strength and degradability. The designed composite also provided a sustained release system for Dex delivery to the surrounding sites, demonstrating the applicability of the fabricated hydrogel composite for sciatic nerve tissue engineering and regeneration. The encapsulated cells were viable and showed adequate growth ability and morphogenesis during prolonged incubation in Gela-PA/HA-Tyr Mp hydrogel compared to control conditions. Interestingly, histological analysis revealed a significant increase in the number of axons in the injured sciatic nerve following treatment with Dex-HA-Tyr Mp and injectable Gela-PA hydrogel compared to other control groups. In conclusion, the results demonstrated that fabricated Dex-loaded MPs and injectable hydrogel from biomimetic components are suitable systems for sustained delivery of Dex with adequate biocompatibility and the approach may have potential therapeutic applications in peripheral nerve regeneration.Graphical

Oligodendrocyte calcium signaling promotes actin-dependent myelin sheath extension

Myelin is essential for rapid nerve signaling and is increasingly found to play important roles in learning and in diverse diseases of the CNS. Morphological parameters of myelin such as sheath length are thought to precisely tune conduction velocity, but the mechanisms controlling sheath morphology are poorly understood. Local calcium signaling has been observed in nascent myelin sheaths and can be modulated by neuronal activity. However, the role of calcium signaling in sheath formation remains incompletely understood. Here, we use genetic tools to attenuate oligodendrocyte calcium signaling during myelination in the developing mouse CNS. Surprisingly, genetic calcium attenuation does not grossly affect the number of myelinated axons or myelin thickness. Instead, calcium attenuation causes myelination defects resulting in shorter, dysmorphic sheaths. Mechanistically, calcium attenuation reduces actin filaments in oligodendrocytes, and an intact actin cytoskeleton is necessary and sufficient to achieve accurate myelin morphology. Together, our work reveals a cellular mechanism required for accurate CNS myelin formation and may provide mechanistic insight into how oligodendrocytes respond to neuronal activity to sculpt and refine myelin sheaths.

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.

Efficacy of collagen conduit wrapping with collagen fibers on nerve regeneration in sciatic nerve injury with partial transection: An experimental study in the rat model.

Peripheral nerve injuries (PNIs) include complete and partial transection, crushing, and chronic compression injuries. Hollow absorbable conduits are used to treat complete transection with short defects, while wrapping the injured part with an absorbent material promotes nerve recovery by inhibiting inflammatory cell infiltration and scar tissue formation in crush injuries. For treatment of partially transected nerve injuries (PTNIs), such as injection-related iatrogenic PNI, whether wrapping the entire nerve, including the injury site, or bridging the transected fascicle with an artificial nerve conduit (ANC) is beneficial remains to be verified. The purpose of this study was to investigate whether wrapping the injured nerve and placing collagen fibers as scaffolds at the nerve defect site contribute to neural recovery in PTNI. A unilateral 5-mm partial nerve defect was created at the mid-thigh level in a rat sciatic nerve injury model. Fifty-four Sprague-Dawley (SD) rats (150-250 g) were divided into three groups (n = 9 each): group 1, collagen fibers were placed in the nerve defect and the sciatic nerve was wrapped with collagen conduit; group 2, the sciatic nerve was wrapped by collagen conduit without collagen fibers; and group 3, nerve defect was reconstructed with collagen-filled conduit. Nerve regeneration was evaluated by analyses of gait, electrophysiology, wet muscle weight, and axon numbers with immunohistochemistry at 12 and 24 weeks. Dorsiflexion angles among all groups improved significantly from 12 to 24 weeks postoperatively. At 24 weeks postoperatively, compound muscle action potential amplitudes (CMAPs) of tibialis anterior were 5.26 ± 4.64, 1.31 ± 1.17, and 0.14 ± 0.24 mV (p < .05), CMAPs of gastrocnemius were 21.3 ± 5.98, 15.4 ± 5.46, and 13.11 ± 3.91 mV in groups 1, 2, and 3, respectively; and the value of group 1 was significantly higher than that of group 3 (p < .05). Axon numbers were 2194 ± 629; 1106 ± 645; and 805 ± 907 in groups 1, 2, and 3, respectively (p < .05). For PTNI reconstruction, artificial nerve wrap (ANW) was superior to ANC. Providing collagen scaffold at the nerve defect site enhanced nerve recovery during reconstruction with ANW.

Regenerative Peripheral Nerve Interface (RPNI) Surgery for Mitigation of Neuroma and Postamputation Pain.

A neuroma occurs when a regenerating transected peripheral nerve has no distal target to reinnervate. Symptomatic neuromas are a common cause of postamputation pain that can lead to substantial disability1-3. Regenerative peripheral nerve interface (RPNI) surgery may benefit patients through the use of free nonvascularized muscle grafts as physiologic targets for peripheral nerve reinnervation for mitigation of neuroma and postamputation pain. An RPNI is constructed by implanting the distal end of a transected peripheral nerve into a free nonvascularized skeletal muscle graft. The neuroma or free end of the affected nerve is identified, transected, and skeletonized. A free muscle graft is then harvested from the donor thigh or from the existing amputation site, and the distal end of each transected nerve is implanted into the center of the free muscle graft with use of 6-0 nonabsorbable suture. This can be done acutely at the time of amputation or as an elective procedure at any time postoperatively. Nonsurgical treatments of neuromas include desensitization, chemical or anesthetic injections, biofeedback, transcutaneous electrical nerve stimulation, topical lidocaine, and/or other medications (e.g., antidepressants, anticonvulsants, and opioids). Surgical treatment of neuromas includes neuroma excision, nerve capping, excision with transposition into bone or muscle, nerve grafting, and targeted muscle reinnervation. Creation of an RPNI is a simple and reproducible surgical option to prevent neuroma formation that leverages several biologic processes and addresses many limitations of existing neuroma-treatment strategies. Given the understanding that neuromas will form when regenerating axons are not presented with end organs for reinnervation, any strategy that reduces the number of aimless axons within a residual limb should serve to reduce symptomatic neuromas. The use of free muscle grafts offers a vast supply of denervated muscle targets for regenerating nerve axons and facilitates the reestablishment of neuromuscular junctions without sacrificing denervation of any residual muscles. Articles describing RPNI surgery for postamputation pain have shown favorable outcomes, with significant reduction in neuroma pain and phantom pain scores at approximately 7 months postoperatively4,5. Neuroma pain scores were reduced by 71% and phantom pain scores were reduced by 53%4. Prophylactic RPNI surgery is also associated with substantially lower incidence of symptomatic neuromas (0% versus 13.3%) and a lower rate of phantom limb pain (51.1% versus 91.1%)5 compared with the rates in patients who did not undergo RPNI surgery. Ask the patient preoperatively to point at the site of maximal tenderness, as this can serve as a guide for where the symptomatic neuroma may be located. The incision can be made either through the previous site of the amputation or directly over the site of maximal tenderness longitudinally. The pitfall of incising directly over the site is creating another incision with its attendant risk of wound infection.Excise the terminal neuroma with a knife until healthy-appearing axons are visualized.The free nonvascularized skeletal muscle graft can be obtained from local muscle (preferred) or from a separate donor site. A separate donor site can introduce donor-site morbidity and complications, including hematoma and pain.The harvested skeletal muscle graft should ideally be approximately 35 mm long, 20 mm wide, and 5 mm thick in order to ensure survivability and to prevent central necrosis. The harvesting can be performed with curved Mayo scissors.The peripheral nerve should be implanted parallel to the direction of the muscle fibers, and the epineurium should be secured to the free muscle graft at 1 or 2 places. One suture should be utilized to tack the distal end of the epineurium to the middle of the bed of the muscle graft. Another suture should be utilized to start the wrapping of the muscle graft around the nerve using a bite through the muscle, a bite through the epineurium of the proximal end of the nerve, and another bite through the other muscle edge in order to form a cylindrical wrap around the nerve.Wrap the entire muscle graft by taking only bites of muscle graft around the nerve to secure the muscle graft in a cylindrical structure using 2 to 4 more sutures.Avoid locating the RPNI near weight-bearing surfaces of the residual limb when closing. The RPNI should be in the muscular tissue, deep to the subcutaneous tissue and dermis.Do perform intraneural dissection for large-caliber nerves to create several (normally 2 to 4) distinct RPNIs, to avoid too many regenerating axons in a single free muscle graft.

Identifying therapeutic compounds for autosomal dominant optic atrophy (ADOA) through screening in the nematode C. elegans.

Autosomal Dominant Optic Atrophy (ADOA) is a rare neurodegenerative condition, characterized by the bilateral loss of vision due to the degeneration of retinal ganglion cells. Its primary cause is linked to mutations in OPA1 gene, which ultimately affect mitochondrial structure and function. The current lack of successful treatments for ADOA emphasizes the need to investigate the mechanisms driving disease pathogenesis and exploit the potential of animal models for preclinical trials. Among such models, Caenorhabditis elegans stands out as a powerful tool, due its simplicity, its genetic tractability, and its relevance to human biology. Despite the lack of a visual system, the presence of mutated OPA1 in the nematode recapitulates ADOA pathology, by stimulating key pathogenic features of the human condition that can be studied in a fast and relatively non-laborious manner. Here, we provide a detailed guide on how to assess the therapeutic efficacy of chemical compounds, in either small or large scale, by evaluating three crucial phenotypes of humanized ADOA model nematodes, that express pathogenic human OPA1 in their GABAergic motor neurons: axonal mitochondria number, neuronal cell death and defecation cycle time. The described methods can deepen our understanding of ADOA pathogenesis and offer a practical framework for developing novel treatment schemes, providing hope for improved therapeutic outcomes and a better quality of life for individuals affected by this currently incurable condition.

Effects of exposure to 3,6-DBCZ on neurotoxicity and AhR pathway during early life stages of zebrafish (Danio rerio)

Polyhalogenated carbazoles (PHCZs) are emerging environmental pollutants, yet limited information is available on their embryotoxicity and neurotoxicity. Therefore, the current work was performed to investigate the adverse effects of 3,6-dibromocarbazole (3,6-DBCZ), a typical PHCZs homolog, on the early life stages of zebrafish larvae. It revealed that the 96-hour post-fertilization (hpf) median lethal concentration (LC50) value of 3,6-DBCZ in zebrafish larvae was determined to be 0.7988 mg/L. Besides, 3,6-DBCZ reduced survival rates at concentrations ≥ 1 mg/L and decreased hatching rates at ≥ 0.25 mg/L at 48 hpf. In behavior tests, it inhibited locomotor activities and reduced the frequency of recorded acceleration states in response to optesthesia (a sudden bright light stimulus) at concentrations ≥ 160 μg/L. Meanwhile, 3,6-DBCZ exposure decreased the frequency of recorded acceleration states in the startle response (tapping mode) at concentrations ≥ 6.4 μg/L. Pathologically, with the transgenic zebrafish model (hb9-eGFP), we observed a strikingly decreased axon length and number in motor neurons after 3,6-DBCZ treatment, which may be ascribed to the activation of the AhR signaling pathway, as evidenced by the molecular docking analysis and Microscale thermophoresis (MST) assay suggested that 3,6-DBCZ binding to AhR-ARNT2 compound proteins. Through interaction with AhR-ARNT, a striking reduction of the anti-oxidative stress (sod1/2, nqo1, nrf2) and neurodevelopment-related genes (elavl3, gfap, mbp, syn2a) were observed after 3,6-DBCZ challenge, accompanied by a marked increased inflammatory genes (TNFβ, IL1β, IL6). Collectively, our findings reveal a previously unrecognized adverse effect of 3,6-DBCZ on zebrafish neurodevelopment and locomotor behaviors, potentially mediated through the activation of the AhR pathway. Furthermore, it provides direct evidence for the toxic concentrations of 3,6-DBCZ and the potential target signaling in zebrafish larvae, which may be beneficial for the risk assessment of the aquatic ecosystems.

Increased fiber density of the fornix in patients with chronic tinnitus revealed by diffusion-weighted MRI.

Up to 45% of the elderly population suffer from chronic tinnitus - the phantom perception of sound that is often perceived as ringing, whistling, or hissing "in the ear" without external stimulation. Previous research investigated white matter changes in tinnitus patients using diffusion-weighted magnetic resonance imaging (DWI) to assess measures such as fractional anisotropy (a measure of microstructural integrity of fiber tracts) or mean diffusivity (a measure for general water diffusion). However, findings overlap only minimally and are sometimes even contradictory. We here present the first study encompassing higher diffusion data that allow to focus on changes in tissue microstructure, such as number of axons (fiber density) and macroscopic alterations, including axon diameter, and a combination of both. In order to deal with the crossing-fibers problem, we applied a fixel-based analysis using a constrained spherical deconvolution signal modeling approach. We investigated differences between tinnitus patients and control participants as well as how cognitive abilities and tinnitus distress are related to changes in white matter morphology in chronic tinnitus. For that aim, 20 tinnitus patients and 20 control participants, matched in age, sex and whether they had hearing loss or not, underwent DWI, audiometric and cognitive assessments, and filled in questionnaires targeting anxiety and depression. Our results showed increased fiber density in the fornix in tinnitus patients compared to control participants. The observed changes might, reflect compensatory structural alterations related to the processing of negative emotions or maladaptive changes related to the reinforced learning of the chronic tinnitus sensation. Due to the low sample size, the study should be seen as a pilot study that motivates further research to investigate underlying white matter morphology alterations in tinnitus.

Enhancement of nerve regeneration through schwann cell-mediated healing in a 3D printed polyacrylonitrile conduit incorporating hydrogel and graphene quantum dots: a study on rat sciatic nerve injury model

Despite recent technological advancements, effective healing from sciatic nerve damage remains inadequate. Cell-based therapies offer a promising alternative to autograft restoration for peripheral nerve injuries, and 3D printing techniques can be used to manufacture conduits with controlled diameter and size. In this study, we investigated the potential of Wharton’s jelly-derived mesenchymal stem cells (WJMSCs) differentiated into schwann cells, using a polyacrylonitrile (PAN) conduit filled with fibrin hydrogel and graphene quantum dots (GQDs) to promote nerve regeneration in a rat sciatic nerve injury model. We investigated the potential of WJMSCs, extracted from the umbilical cord, to differentiate into schwann cells and promote nerve regeneration in a rat sciatic nerve injury model. WJMSCs were 3D cultured and differentiated into schwann cells within fibrin gel for two weeks. A 3 mm defect was created in the sciatic nerve of the rat model, which was then regenerated using a conduit/fibrin, conduit covered with schwann cells in fibrin/GQDs, GQDs in fibrin, and a control group without any treatment (n = 6/group). At 10 weeks after transplantation, motor and sensory functions and histological improvement were assessed. The WJMSCs were extracted, identified, and differentiated. The differentiated cells expressed typical schwann cell markers, S100 and P75. In vivo investigations established the durability and efficacy of the conduit to resist the pressures over two months of implantation. Histological measurements showed conduit efficiency, schwann cell infiltration, and association within the fibrin gel and lumen. Rats treated with the composite hydrogel-filled PAN conduit with GQDs showed significantly higher sensorial recovery than the other groups. Histological results showed that this group had significantly more axon numbers and remyelination than others. Our findings suggest that the conduit/schwann approach has the potential to improve nerve regeneration in peripheral nerve injuries, with future therapeutic implications.

Potential of an artificial nerve graft containing Schwann cells for the treatment of a 20-mm nerve defect in rats.

In a previous study, the authors showed that the migration of Schwann cells (SCs) through end-to-side (ETS) neurorrhaphy promotes axonal regrowth within an acellular nerve graft. In the present study, the authors investigated whether a similar strategy using an artificial nerve (AN) would allow reconstruction of a long nerve gap (20 mm) in rats. Forty-eight 8- to 12-week-old Sprague Dawley rats were divided into control (AN) and experimental (SC migration-induced AN [SCiAN]) groups. Prior to the experiment, the ANs used in the SCiAN group were populated in vivo with SCs over a 4-week period by ETS neurorrhaphy onto the sciatic nerve. In both groups, a 20-mm sciatic nerve defect was reconstructed in an end-to-end fashion using 20-mm ANs. Sections from the nerve graft and distal sciatic nerve in both groups underwent assessments at 4 weeks for SC migration by immunohistochemical analysis and quantitative reverse transcription-polymerase chain reaction. At 16 weeks, axonal elongation was assessed by immunohistochemical analysis, histomorphometry, and electron microscopy. The number of myelinated fibers was counted, the g-ratio was calculated, and myelin sheath thickness and axon diameter were measured. Furthermore, functional recovery was evaluated at 16 weeks using the Von Frey filament test for sensory recovery and by calculating the muscle fiber area for motor recovery. The area occupied by SCs at 4 weeks and by axons at 16 weeks was significantly larger in the SCiAN group than in the AN group. Histomorphometric evaluation of the distal sciatic nerve revealed a significantly greater number of axons. At 16 weeks, plantar perception in the SCiAN group was significantly better, demonstrating improvement in sensory function. However, no tibialis anterior muscle motor improvement was observed in either group. The induction of SC migration into an AN by ETS neurorrhaphy is a useful technique for repairing 20-mm nerve defects in rats, with better nerve regeneration and sensory recovery. No motor recovery was observed in either group; however, motor recovery might require a longer period of time than the lifespan of the AN used in this study. Future studies should investigate whether structural and material reinforcement of the AN, to lower its decomposition rate, can improve functional recovery.

Peripheral nerve regeneration by bioabsorbable nerve conduits filled with platelet-rich fibrin

PurposeTo repair peripheral nerve defects and seek alternatives for autografts, nerve conduits with various growth factors and cells have been invented. Few pieces of literature report the effect of nerve conduits plus platelet-rich fibrin (PRF). This study aimed to investigate the effectiveness of nerve conduits filled with PRF. MethodsThe model of a 10 mm sciatic nerve gap in a rat was used to evaluate peripheral nerve regeneration. The thirty rats were randomly divided into one of the following three groups (n = 10 per group). Autogenous nerve grafts (autograft group), conduits filled with phosphate-buffered saline (PBS) (PBS group), or conduits filled with PRF group (PRF group). We assessed motor and sensory functions for the three groups at 4, 8, and 12 weeks postoperatively. In addition, axon numbers were measured 12 weeks after repair of the peripheral nerve gaps. ResultsSignificant differences in motor function were observed between the autograft group and the other two groups at 12 weeks postoperatively. In the test to evaluate the recovery of sensory function, there were significant differences between the PBS group and the other two groups at all time points. The most axon number was found in the autograft group. The axon number of the PRF group was significantly more extensive than that of the PBS group. ConclusionsThe nerve conduit filled with PRF promoted the axon regeneration of the sciatic nerve and improved sensory function.

Axonal mapping of motor and sensory components within the ulnar nerve and its branches.

Intrinsic function is indispensable for dexterous hand movements. Distal ulnar nerve defects can result in intrinsic muscle dysfunction and sensory deficits. Although the ulnar nerve's fascicular anatomy has been extensively studied, quantitative and topographic data on motor axons traveling within this nerve remain elusive. The ulnar nerves of 14 heart-beating organ donors were evaluated. The motor branches to the flexor carpi ulnaris (FCU) and flexor digitorum profundus (FDP) muscles and the dorsal branch (DoBUN) as well as 3 segments of the ulnar nerve were harvested in 2-cm increments. Samples were subjected to double immunofluorescence staining using antibodies against choline acetyltransferase and neurofilament. Samples revealed more than 25,000 axons in the ulnar nerve at the forearm level, with a motor axon proportion of only 5%. The superficial and DoBUN showed high axon numbers of more than 21,000 and 9300, respectively. The axonal mapping of more than 1300 motor axons revealed an increasing motor/sensory ratio from the proximal ulnar nerve (1:20) to the deep branch of the ulnar nerve (1:7). The motor branches (FDP and FCU) showed that sensory axons outnumber motor axons by a ratio of 10:1. Knowledge of the detailed axonal architecture of the motor and sensory components of the human ulnar nerve is of the utmost importance for surgeons considering fascicular grafting or nerve transfer surgery. The low number of efferent axons in motor branches of the ulnar nerve and their distinct topographical distribution along the distal course of the nerve is indispensable information for modern nerve surgery.