Toluidine Blue Staining of Resin-Embedded Sections for Evaluation of Peripheral Nerve Morphology

The effects of graft source and orientation on outcomes after ablation of a branched peripheral nerve

Segmental peripheral nerve injuries (PNI) are the most common cause of enduring nervous system dysfunction. The peripheral nervous system (PNS) has an extensive and highly branching organization. While much is known about the factors that affect regeneration through sharp bisections and linear ablations of peripheral nerves, very little has been investigated or documented about PNIs that ablate branch points. Such injuries present additional complexity compared to linear segmental defects. This study compared outcomes following ablation of a branch point with branched grafts, specifically examining how graft source and orientation of the branched graft contributed to regeneration. The model system was Lewis rats that underwent a 2.5 cm ablation that started in the sciatic nerve trunk and included the peroneal/tibial branch point. Rats received grafts that were rat sciatic autograft, inbred sciatic allograft, and inbred femoral allograft, each of which was a branched graft of 2.5 cm. Allografts were obtained from Lewis rats, which is an inbred strain. Both branches of the sciatic grafts were mixed motor and sensory while the femoral grafts were smaller in diameter than sciatic grafts and one branch of the femoral graft is sensory and the other motor. All branched grafts were sutured into the defect in two orientations dictated by which branch in the graft was sutured to the tibial vs peroneal stumps in recipients. Outcome measures include compound muscle action potentials (CMAPs) and CatWalk gait analysis throughout the recovery period, with toluidine blue for intrinsic nerve morphometry and retrograde labeling conducted at the 36-week experimental end point. Results indicate that graft source and orientation does play a significant role earlier in the regenerative process but by 36 weeks all groups showed very similar indications of regeneration across multiple outcomes.

Oral Administration of Glutathione Trisulfide Increases Reactive Sulfur Levels in Dorsal Root Ganglion and Ameliorates Paclitaxel-Induced Peripheral Neuropathy in Mice

Peripheral neuropathy is a dose-limiting side effect of chemotherapy with paclitaxel. Paclitaxel-induced peripheral neuropathy (PIPN) is typically characterized by a predominantly sensory neuropathy presenting with allodynia, hyperalgesia and spontaneous pain. Oxidative mitochondrial damage in peripheral sensory neurons is implicated in the pathogenesis of PIPN. Reactive sulfur species, including persulfides (RSSH) and polysulfides (RSnH), are strong nucleophilic and electrophilic compounds that exert antioxidant effects and protect mitochondria. Here, we examined the potential neuroprotective effects of glutathione trisulfide (GSSSG) in a mouse model of PIPN. Intraperitoneal administration of paclitaxel at 4 mg/kg/day for 4 days induced mechanical allodynia and thermal hyperalgesia in mice. Oral administration of GSSSG at 50 mg/kg/day for 28 days ameliorated mechanical allodynia, but not thermal hyperalgesia. Two hours after oral administration, 34S-labeled GSSSG was detected in lumber dorsal root ganglia (DRG) and in the lumber spinal cord. In mice treated with paclitaxel, GSSSG upregulated expression of genes encoding antioxidant proteins in lumber DRG, prevented loss of unmyelinated axons and inhibited degeneration of mitochondria in the sciatic nerve. In cultured primary neurons from cortex and DRG, GSSSG mitigated paclitaxel-induced superoxide production, loss of axonal mitochondria, and axonal degeneration. These results indicate that oral administration of GSSSG mitigates PIPN by preventing axonal degeneration and mitochondria damage in peripheral sensory nerves. The findings suggest that administration of GSSSG may be an approach to the treatment or prevention of PIPN and other peripheral neuropathies.

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.

A pathological perspective to painful inguinal hernia: Report of two cases

Introduction

Preoperative inguinal pain (painful inguinal hernia) is a well-known factor associated with chronic postoperative inguinal pain (CPIP). However, it remains unclear what preventive measures should be taken in such patients.

Case presentation

We report two patients with painful inguinal hernia who underwent pragmatic ilioinguinal nerve neurectomy during open anterior repair. The nerve was compressed by bulky spermatic cord lipoma in case 1 and by the hernia sac presenting over a few decades in case 2. Hematoxylin and eosin staining of the resected nerves revealed mucoid degeneration. Toluidine blue staining of resin-embedded nerve sections demonstrated that fully-myelinated axons had significantly decreased in case 1 and almost disappeared in case 2, indicating the development of massive demyelination of the ilioinguinal nerve in both cases.

Discussion

In cases where the injured nerve is left in situ, CPIP may occur since demyelinating neuropathy sometimes becomes irreversible.

Conclusion

Planned nerve resection via open anterior inguinal hernia repair may be an option to prevent CPIP in patients with painful inguinal hernia.

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Painful inguinal hernia is a known risk factor for CPIP; however, preventive measures remains unclear.

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Ilioinguinal nerves were massively demyelinated in two patients with painful inguinal hernia.

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Severe neuropathy induced by chronic compression of the ilioinguinal nerve may be associated with painful inguinal hernia.

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Planned nerve resection via anterior hernia repair is an option to prevent CPIP in patients with painful inguinal hernia.

GRHL3 activates FSCN1 to relax cell-cell adhesions between migrating keratinocytes during wound reepithelialization

The migrating keratinocyte wound front is required for skin wound closure. Despite significant advances in wound healing research, we do not fully understand the molecular mechanisms that orchestrate collective keratinocyte migration. Here, we show that, in the wound front, the epidermal transcription factor Grainyhead like-3 (GRHL3) mediates decreased expression of the adherens junction protein E-cadherin; this results in relaxed adhesions between suprabasal keratinocytes, thus promoting collective cell migration and wound closure. Wound fronts from mice lacking GRHL3 in epithelial cells (Grhl3-cKO) have lower expression of Fascin-1 (FSCN1), a known negative regulator of E-cadherin. Assay for Transposase-Accessible Chromatin using sequencing (ATAC-seq) on wounded keratinocytes shows decreased wound-induced chromatin accessibility near the Fscn1 gene in Grhl3-cKO mice, a region enriched for GRHL3 motifs. These data reveal a wound-induced GRHL3/FSCN1/E-cadherin pathway that regulates keratinocyte-keratinocyte adhesion during wound-front migration; this pathway is activated in acute human wounds and is altered in diabetic wounds in mice, suggesting translational relevance.

Preclinical study of peripheral nerve regeneration using nerve guidance conduits based on polyhydroxyalkanaotes

Nerve guidance conduits (NGCs) are used as an alternative to the "gold standard" nerve autografting, preventing the need for surgical intervention required to harvest autologous nerves. However, the regeneration outcomes achieved with the current NGCs are only comparable with autografting when the gap is short (less than 10 mm). In the present study, we have developed NGCs made from a blend of polyhydroxyalkanoates, a family of natural resorbable polymers. Hollow NGCs made from a 75:25 poly(3-hydroxyoctanoate)/poly(3-hydroxybutyrate) blend (PHA-NGCs) were manufactured using dip-molding. These PHA-NGCs showed appropriate flexibility for peripheral nerve regeneration. In vitro cell studies performed using RT4-D6P2T rat Schwann cell line confirmed that the material is capable of sustaining cell proliferation and adhesion. PHA-NGCs were then implanted in vivo to repair 10 mm gaps of the median nerve of female Wistar rats for 12 weeks. Functional evaluation of the regenerated nerve using the grasping test showed that PHA-NGCs displayed similar motor recovery as the autograft, starting from week 7. Additionally, nerve cross-sectional area, density and number of myelinated cells, as well as axon diameter, fiber diameter, myelin thickness and g-ratio obtained using the PHA-NGCs were found comparable to an autograft. This preclinical data confirmed that the PHA-NGCs are indeed highly promising candidates for peripheral nerve regeneration.

Rostro-caudal different energy metabolism leading to differences in degeneration in spinal cord injury

Spinal cord injury gradually spreads away from the epicentre of injury. The rate of degeneration on the rostral side of the injury differs from that on the caudal side. Rostral degeneration is an immediate process, while caudal degeneration is delayed. In this study, we demonstrated that the rostro-caudal differences in energy metabolism led to differences in the spread of degeneration in early thoracic cord injury using in vivo imaging. The blood flow at the rostral side of the injury showed ischaemia-reperfusion, while the caudal side presented stable perfusion. The rostral side had an ATP shortage 20 min after spinal cord injury, while the ATP levels were maintained on the caudal side. Breakdown products of purine nucleotides were accumulated at both sides of injury 18 h after spinal cord injury, but the principal metabolites in the tricarboxylic acid cycle and glycolytic pathway were elevated on the caudal side. Although the low-ATP regions expanded at the rostral side of injury until 24 h after spinal cord injury, the caudal-side ATP levels were preserved. The low-ATP regions on the rostral side showed mitochondrial reactive oxygen species production. Administration of 2-deoxy-d-glucose as a glycolysis inhibitor decreased the caudal ATP levels and expanded the low-ATP regions to the caudal side until 24 h after spinal cord injury. These results suggest that deficits in the glycolytic pathway accelerate the caudal degeneration, while immediate rostral degeneration is exacerbated by oxidative stress in early thoracic cord injury.

A method to prepare large resin sections for counting myelinated axons in rodent CNS and PNS structures

We present a method that allows preparing histological sections from large blocks of nervous tissue embedded in epoxy resin. Resin-embedding provides excellent resolution especially for the myelin-rich white matter and is often being used for visualizing the myelinated axons in peripheral nerves. However, because of the limited penetration of the reagents, only very small tissue specimens can be processed in this way. Here, we describe a method that enables to embed large specimens and their sectioning on a standard sliding microtome. To process the large specimens, modifications in several steps of the processing technique had to be made. In this paper we demonstrate, that with this technique 1-3 μm thick transversal sections can be prepared from the resin-embedded specimens as large as rat brain hemisphere. Such a large section allows simultaneously: 1.) overviewing and delineating the gross anatomical structures, and 2.) observing the subcellular details at the highest possible optical magnifications. Such a large section with excellent resolution allows application of unbiased stereological methods and reliable quantification of very small objects within the area of interest.

Establishment of hematopoietic tissue primary cell cultures from the giant freshwater prawn Macrobrachium rosenbergii

The giant freshwater prawn Macrobrachium rosenbergii is one of the most important aquaculture species in Southeast Asia. In this study, in vitro culture of its hematopoietic tissue cells was achieved and characterized for use as a tool to study its pathogens that cause major farm losses. By transmission electron microscopy, the ultrastructure of the primary culture cells was similar to that of cells lining intact hematopoietic tissue lobes. Proliferating cell nuclear antigen (PCNA) (a marker for hematopoietic stem cell proliferation) was detected in some of the cultured cells by polymerase chain reaction (PCR) testing and flow cytometry. Using a specific staining method to detect phenoloxidase activity and using PCR to detect expression markers for semigranular and granular hemocytes (e.g., prophenoloxidase activating enzyme and prophenoloxidase) revealed that some of the primary cells were able to differentiate into mature hemocytes within 24 h. These results showed that some cells in the cultures were hematopoietic stem cells that could be used to study other interesting research topics (e.g. host pathogen interactions and development of an immortal hematopoietic stem cell line).

No effect of prior Dengue virus 1 infection in mouse dams on long-term behavioral profiles in offspring infected with Zika virus during gestation

Zika virus (ZIKV) is a mosquito-borne Flavivirus structurally and antigenically related to Dengue virus (DENV). Zika virus has been associated with congenital anomalies and most ZIKV outbreaks have occurred in endemic areas of DENV. The present study investigated the effects of prior DENV serotype 1 (DENV1) immunity in immunocompetent female Swiss mice on gestational ZIKV infection in offspring. Physical/reflex development, locomotor activity, anxiety, visual acuity, and brain-derived neurotrophic factor (BDNF) levels were evaluated in offspring during infancy and adolescence. Anti-DENV1 and anti-ZIKV antibodies were detected in sera of the progenitors, whereas no ZIKV genomes were detected in the offspring brain. Pups from dams with only DENV1 immunity presented alterations of physical/reflex development. Pups from all infected dams exhibited time-related impairments in locomotor activity and anxiolytic-like behavior. Offspring from DENV/ZIKV-infected dams exhibited impairments in visual acuity during infancy but not during adolescence, which was consistent with morphometric analysis of the optic nerve. Pups from DENV1-, ZIKV-, and DENV/ZIKV-infected dams exhibited a decrease in BDNF levels during infancy and an increase during adolescence in distinct brain regions. In summary, we found no influence of prior DENV1 immunity on gestational ZIKV infection in offspring, with the exception of alterations of early visual parameters, and an increase in BDNF levels in the hippocampus during adolescence.

The bone marrow-derived mesenchymal stem cells (BMSCs) alleviate diabetic peripheral neuropathy induced by STZ via activating GSK-3β/β-catenin signaling pathway

BACKGROUND

Diabetic peripheral neuropathy, a common complication of diabetic mellitus, has brought a threaten on patients' health. The bone marrow-derived mesenchymal stem cells (BMSCs) were reported to play an important role in diverse diseases. Nevertheless, the specific function of BMSCs in diabetic peripheral neuropathy remained uncharacterized.

METHODS

A wide range of experiments including RT-qPCR, western blot, H&E staining, oxidative stress assessment, measurement of thermal sensitivity, ELISA, urine protein and CCK-8 assays were implemented to explore the function and mechanism of BMSCs in vivo and vitro.

RESULTS

The experimental results displayed that BMSCs improve STZ-induced diabetes symptoms in rats by decreasing blood glucose and urinary protein. Functionally, BMSCs ameliorate oxidative stress, painful diabetic neuropathy, neurotrophic status and angiogenesis in STZ-induced rats. Moreover, BMSCs participate in the regulation of sciatic neuro morphology in diabetic neuropathy rat model. In mechanism, BMSCs alleviate diabetic peripheral neuropathy via activating GSK-3β/β-catenin signaling pathway in rats and improve Schwann's cells viability by activating GSK-3β/β-catenin signaling pathway under high glucose.

CONCLUSIONS

We verified that BMSCs alleviate diabetic peripheral neuropathy of rats induced by STZ via activating GSK-3β/β-catenin signaling pathway, which implied a novel biomarker for diabetic peripheral neuropathy treatment.

Duloxetine hydrochloride loaded film forming dermal gel enriched with methylcobalamin and geranium oil attenuates paclitaxel-induced peripheral neuropathy in rats

Objective

In attempt to conquer the major concerns of oral duloxetine hydrochloride (like low bioavailability, intolerable side-effects and no regeneration of demyelinated nerve fibres) for the management of chemotherapy-induced peripheral neuropathy (CIPN), an alternative delivery of duloxetine hydrochloride was aimed for in-vivo optimization.

Methods

A film forming dermal gel consisting of duloxetine hydrochloride was formulated and enriched with methylcobalamin and geranium oil. The formulated gel successfully qualified the various pharmaceutical characteristics of gel. Administration of paclitaxel (8 mg/kg/i.p. in four divided doses) for 4 alternate days induced the symptoms of peripheral neuropathy in rats. On 14th day, the responses to noxious stimulus (mechanical hyperalgesia, cold allodynia, and heat hyperalgesia) were increased and reached to its maximum. Thereafter, drug treatment with formulated dermal gel and oral duloxetine hydrochloride (30 mg/kg, once daily) was initiated for 2 weeks in different group of animals. On the 28th day animals were sacrificed to isolate sciatic nerve, to assess biochemical changes (TBARS, reduced GSH, total protein, TNF-α, IL-6) and for histopathological examinations of nerve sections using Hematoxylin-Eosin and Toludine blue staining methods.

Results

Application of formulated dermal gel to paclitaxel-treated rats significantly improved paw-withdrawal latency responses during noxious stimulus testing, reduced the levels of TBARS, TNF-α, IL-6 and elevated the levels of reduced GSH as compared to paclitaxel treated rats. Histographs also indicated marked regeneration of the damaged nerve fibers. Topical delivery of duloxetine hydrochloride produced similar results in disparity to oral route. However, no significant disparity in responses was obtained with twice application of formulated dermal gel when compared to once daily application.

Conclusion

Tremendous recovery from nociception, oxidation and inflammation in addition to nerve degeneration was achieved through dermal application of duloxetine hydrochloride in peripheral neuropathy.

Design-Based stereology and binary image histomorphometry in nerve assessment

BACKGROUND

Stereology and histomorphometry are widely used by investigators to quantify nerve characteristics in normal and pathological states, including nerve injury and regeneration. While these methods of analysis are complementary, no study to date has systematically compared both approaches in peripheral nerve. This study investigated the reliability of design-based stereology versus semi-automated binary imaging histomorphometry for assessing healthy peripheral nerve characteristics.

NEW METHOD

Stereological analysis was compared to histomorphometry with binary image analysis on uninjured sciatic nerves to determine nerve fiber number, nerve area, neural density, and fiber distribution.

RESULTS

Sciatic nerves were harvested from 6 male Lewis rats, aged 8-12 weeks for comprehensive analysis of 6 nerve specimens. From each animal, sciatic nerve specimens were fixed, stained, and sectioned for analysis by light and electron microscopy. Both histomorphometry and stereological peripheral nerve analyses were performed on all specimens by two blinded and independent investigators who quantified nerve fiber count, fiber width, density, and related distribution parameters.

COMPARISON WITH EXISTING METHODS

Histomorphometry and stereological analysis provided similar outcomes in nerve fiber number and total nerve area. However, the light microscopy, but not electron microscopy, stereological analysis yielded higher nerve fiber area compared to histomorphometry or manual measurement.

CONCLUSION

Both methods measure similar fiber number and overall nerve fiber area; however, stereology with light microscopy quantified higher fiber area. Histomorphometry optimizes throughput and comprehensive analysis but requires user thresholding.

Methods for in vivo studies in rodents of chemotherapy induced peripheral neuropathy

Peripheral neuropathy is one of the most common, dose limiting, and long-lasting disabling adverse events of chemotherapy treatment. Unfortunately, no treatment has proven efficacy to prevent this adverse effect in patients or improve the nerve regeneration, once it is established. Experimental models, particularly using rats and mice, are useful to investigate the mechanisms related to axonal or neuronal degeneration and target loss of function induced by neurotoxic drugs, as well as to test new strategies to prevent the development of neuropathy and to improve functional restitution. Therefore, objective and reliable methods should be applied for the assessment of function and innervation in adequately designed in vivo studies of CIPN, taking into account the impact of age, sex and species/strains features. This review gives an overview of the most useful methods to assess sensory, motor and autonomic functions, electrophysiological and morphological tests in rodent models of peripheral neuropathy, focused on CIPN. We include as well a proposal of protocols that may improve the quality and comparability of studies undertaken in different laboratories. It is recommended to apply more than one functional method for each type of function, and to perform parallel morphological studies in the same targets and models.

Adipose-Derived Neural Stem Cells Combined with Acellular Dermal Matrix as a Neural Conduit Enhances Peripheral Nerve Repair

Reconstruction to close a peripheral nerve gap continues to be a challenge for clinical medicine, and much effort is being made to develop nerve conduits facilitate nerve gap closure. Acellular dermal matrix (ADM) is mainly used to aid wound healing, but its malleability and plasticity potentially enable it to be used in the treatment of nerve gaps. Adipose-derived stem cells (ADSCs) can be differentiated into three germ layer cells, including neurospheres. We tested the ability of ADSC-derived neural stem cells (NSCs) in combination with ADM or acellular sciatic nerve (ASN) to repair a transected sciatic nerve. We found that NSCs form neurospheres that express Nestin and Sox2, and could be co-cultured with ADM in vitro, where they express the survival marker Ki67. Following sciatic nerve transection in rats, treatment with ADM+NSC or ASN+NSC led to increases in relative gastrocnemius weight, cross-sectional muscle fiber area, and sciatic functional index as compared with untreated rats or rats treated with ADM or ASN alone. These findings suggest that ADM combined with NSCs can improve peripheral nerve gap repair after nerve transection and may also be useful for treating other types of neurological gaps.

Localized delivery of immunosuppressive regulatory T cells to peripheral nerve allografts promotes regeneration of branched segmental defects

Segmental injuries to peripheral nerves (PNs) too often result in lifelong disability or pain syndromes due to a lack of restorative treatment options. For injuries beyond a critical size, a bridging device must be inserted to direct regeneration. PN allografts from immunologically incompatible donors are highly effective bridging devices but are not a regular clinical option because of the expense and health risks of systemic immunosuppression (ISN). We have developed a method to deliver a single administration of ISN localized around a PN allograft that circumvents the risks of systemic ISN. Localized ISN was provided by regulatory T cells (Tregs), a potently immunosuppressive cell type, that was delivered around a PN allograft with a poly(ethylene glycol) norbornene (PEGNB) degradable hydrogel. Tregs are released from the hydrogel over 14 d, infiltrate the graft, suppress the host immune response and facilitate regeneration of the recipient rats equal to the autograft control. Furthermore, this method was effective in a segmental PN defect that included a branch point, for which there currently exist no treatment options. These results show that localized delivery of immunosuppressive cells for PN allografts is an effective new strategy for treating segmental PN defects that can also be used to regenerate complex nerve structures.