BDNF contributes to animal model neuropathic pain after peripheral nerve transection

Strategies for Treating Traumatic Neuromas with Tissue-Engineered Materials

Neuroma, a pathological response to peripheral nerve injury, refers to the abnormal growth of nerve tissue characterized by disorganized axonal proliferation. Commonly occurring after nerve injuries, surgeries, or amputations, this condition leads to the formation of painful nodular structures. Traditional treatment options include surgical excision and pharmacological management, aiming to alleviate symptoms. However, these approaches often offer temporary relief without addressing the underlying regenerative challenges, necessitating the exploration of advanced strategies such as tissue-engineered materials for more comprehensive and effective solutions. In this study, we discussed the etiology, molecular mechanisms, and histological morphology of traumatic neuromas after peripheral nerve injury. Subsequently, we summarized and analyzed current nonsurgical and surgical treatment options, along with their advantages and disadvantages. Additionally, we emphasized recent advancements in treating traumatic neuromas with tissue-engineered material strategies. By integrating biomaterials, growth factors, cell-based approaches, and electrical stimulation, tissue engineering offers a comprehensive solution surpassing mere symptomatic relief, striving for the structural and functional restoration of damaged nerves. In conclusion, the utilization of tissue-engineered materials has the potential to significantly reduce the risk of neuroma recurrence after surgical treatment.

Ultrahigh frequency transcutaneous electrical nerve stimulation for neuropathic pain alleviation and neuromodulation

A challenging complication in patients with peripheral compressive neuropathy is neuropathic pain. Excessive neuroinflammation at the injury site worsens neuropathic pain and impairs function. Currently, non-invasive modulation techniques like transcutaneous electrical nerve stimulation (TENS) have shown therapeutic promise with positive results. However, the underlying regulatory molecular mechanism for pain relief remains complex and unexplored. This study aimed to validate the therapeutic effect of ultrahigh frequency (UHF)-TENS in chronic constriction injury of the rat sciatic nerve. Alleviation of mechanical allodynia was achieved through the application of UHF-TENS, lasting for 3 days after one session of therapy and 4 days after two sessions, without causing additional damage to the myelinated axon structure. The entire tissue collection schedule was divided into four time points: nerve exposure surgery, 7 days after nerve ligation, and 1 and 5 days after one session of UHF therapy. Significant reductions in pain-related neuropeptides, MEK, c-Myc, c-FOS, COX2, and substance P, were observed in the injured DRG neurons after UHF therapy. RNA sequencing of differential gene expression in sensory neurons revealed significant downregulation in Cables, Pik3r1, Vps4b, Tlr7, and Ezh2 after UHF therapy, while upregulation was observed in Nfkbie and Cln3. UHF-TENS effectively and safely relieved neuropathic pain without causing further nerve damage. The decreased production of pain-related neuropeptides within the DRG provided the therapeutic benefit. Possible molecular mechanisms behind UHF-TENS may result from the modulation of the NF-κB complex, toll-like receptor-7, and phosphoinositide 3-kinase/Akt signaling pathways. These results suggest the neuromodulatory effects of UHF-TENS in rat sciatic nerve chronic constriction injury, including alleviation of neuropathic pain, amelioration of pain-related neuropeptides, and regulation of neuroinflammatory gene expression. In combination with the regulation of related neuroinflammatory genes, UHF-TENS could become a new modality for enhancing the treatment of neuropathic pain in the future.

Biology and pathophysiology of symptomatic neuromas

ABSTRACT

Neuromas are a substantial cause of morbidity and reduction in quality of life. This is not only caused by a disruption in motor and sensory function from the underlying nerve injury but also by the debilitating effects of neuropathic pain resulting from symptomatic neuromas. A wide range of surgical and therapeutic modalities have been introduced to mitigate this pain. Nevertheless, no single treatment option has been successful in completely resolving the associated constellation of symptoms. While certain novel surgical techniques have shown promising results in reducing neuroma-derived and phantom limb pain, their effectiveness and the exact mechanism behind their pain-relieving capacities have not yet been defined. Furthermore, surgery has inherent risks, may not be suitable for many patients, and may yet still fail to relieve pain. Therefore, there remains a great clinical need for additional therapeutic modalities to further improve treatment for patients with devastating injuries that lead to symptomatic neuromas. However, the molecular mechanisms and genetic contributions behind the regulatory programs that drive neuroma formation-as well as the resulting neuropathic pain-remain incompletely understood. Here, we review the histopathological features of symptomatic neuromas, our current understanding of the mechanisms that favor neuroma formation, and the putative contributory signals and regulatory programs that facilitate somatic pain, including neurotrophic factors, neuroinflammatory peptides, cytokines, along with transient receptor potential, and ionotropic channels that suggest possible approaches and innovations to identify novel clinical therapeutics.

Neurotrophin-3 (NT-3) as a Potential Biomarker of the Peripheral Nervous System Damage Following Breast Cancer Treatment

Damage to the peripheral nervous system (PNS) is a common complication of breast cancer (BC) treatment, with 60 to 80% of breast cancer survivors experiencing symptoms of PNS damage. In the current study, the levels of brain-derived neurotrophic factor (BDNF), galectin-3 (Gal-3), and neurotrophin-3 (NT-3) were measured in the blood serum of BC patients by ELISA as potential biomarkers that might indicate the PNS damage. Sixty-seven patients were enrolled in this multi-center trial and compared to the aged-matched healthy female volunteers (control group) (n = 25). Intergroup comparison of biomarker levels (i.e., Gal-3 and BDNF) did not show significant differences in any of the studied subgroups. However, intriguingly, NT-3 levels were significantly higher in BC patients as compared to healthy volunteers, constituting 14.85 [10.3; 18.0] and 5.74 [4.56; 13.7] pg/mL, respectively (p < 0.001). In conclusion, NT-3 might be employed as a potential biomarker in BC patients with clinical manifestations of PNS damage. However, further studies to validate its correlation to the degree of peripheral nervous system lesions are of high value.

Intrathecal dexmedetomidine attenuates mechanical allodynia through the downregulation of brain-derived neurotrophic factor in a mild traumatic brain injury rat model

BACKGROUND

This study evaluated the effects of dexmedetomidine and propofol on brain-derived neurotrophic factor level in the cerebrospinal fluid (c-BDNF) and mechanical allodynia in a mild traumatic brain injury (TBI) rat model.

METHODS

After fixing the rat's skull on a stereotactic frame under general anesthesia, craniotomy was performed. After impact, 10 µl of drug was injected into the cisterna magna (group S: sham, group D: dexmedetomidine 5 μg/kg, group P: propofol 500 μg/kg, and group T: untreated TBI). The 50% mechanical withdrawal threshold (50% MWT) and c-BDNF level were measured on postoperative days (PODs) 1, 7, and 14.

RESULTS

The 50% MWT measured on PODs 1, 7, and 14 was lower and the c-BDNF level on POD 1 was higher in group T than in group S. In group D, the c-BDNF level on POD 1 was lower than that in group T and was comparable with that in group S during the whole study period. The 50% MWT of group D was higher than that of group T throughout the postoperative period. In group P, there were no significant differences in the 50% MWT during the entire postoperative period compared with group T; the c-BDNF level was higher than that in group T on POD 1.

CONCLUSIONS

Intrathecal administration of dexmedetomidine may attenuate TBI-induced mechanical allodynia for up to two weeks post-injury through immediate suppression of c-BDNF in mild TBI rats. The inhibition of c-BDNF expression in the acute phase reduced the occurrence of TBI-induced chronic neuropathic pain.

Traumatic neuromas of peripheral nerves: Diagnosis, management and future perspectives

Traumatic neuromas are infrequent in clinical settings but are prevalent following trauma or surgery. A traumatic neuroma is not a true malignancy, rather, it is a hyperplastic, reparative nerve reaction after injury and typically manifests as a nodular mass. The most common clinical manifestations include painful hypersensitivity and the presence of a trigger point that causes neuralgic pain, which could seriously decrease the living standards of patients. While various studies are conducted aiming to improve current diagnosis and management strategies via the induction of emerging imaging tools and surgical or conservative treatment. However, researchers and clinicians have yet to reach a consensus regarding traumatic neuromas. In this review, we aim to start with the possible underlying mechanisms of traumatic neuromas, elaborate on the diagnosis, treatment, and prevention schemes, and discuss the current experiment models and advances in research for the future management of traumatic neuromas.

Involvement of GABAergic, glutamatergic, opioidergic, and brain-derived neurotrophic factor systems in the trigeminal neuropathic pain process

Trigeminal neuropathic pain (TNP) is an intense pain condition characterized by hyperalgesia and allodynia; however, its neural mechanisms are not completely understood. Its management is complex, and studies that investigate its biochemical mechanisms are important for improving clinical approaches. This study aimed to evaluate the involvement of GABAergic, glutamatergic, and opioidergic systems and brain-derived neurotrophic factor (BDNF) levels in the TNP process in rats. TNP is induced by chronic constriction injury of the infraorbital nerve (CCI-ION). Nociceptive responses were evaluated using the facial von Frey test before and after the administration of GABAergic and opioidergic agonists and glutamatergic antagonists. The rats were divided into vehicle-treated control (C), sham-surgery (SS), and CCI-ION groups, and then subdivided into the vehicle (V)-treated SS-V and CCI-ION-V groups, SS-MK801 and CCI-ION-MK801, treated with the N-methyl-d-aspartate receptor selective antagonist MK801; SS-PB and CCI-ION-PB, treated with phenobarbital; SS-BZD and CCI-ION-BZD, treated with diazepam; SS-MOR and CCI-ION-MOR, treated with morphine. BDNF levels were evaluated in the cerebral cortex, brainstem, trigeminal ganglion, infraorbital branch of the trigeminal nerve, and serum. CCI-ION induced facial mechanical hyperalgesia. Phenobarbital and morphine reversed the hyperalgesia induced by CCI-ION, and the CCI-BZD group had an increased nociceptive threshold until 60 min. CCI-ION-GLU increased the nociceptive threshold at 60 min. Cerebral cortex and brainstem BDNF levels increased in the CCI-ION and SS groups. Only the CCI group presented high levels of BDNF in the trigeminal ganglion. Our data suggest the involvement of GABAergic, glutamatergic, and opioidergic systems and peripheral BDNF in the TNP process.

Clinical and Molecular Outcomes After Combined Intense Pulsed Light Therapy With Low-Level Light Therapy in Recalcitrant Evaporative Dry Eye Disease With Meibomian Gland Dysfunction

PURPOSE

Dry eye disease (DED) is a leading cause of ocular morbidity worldwide. This study evaluates the effects of combined light therapy [intense pulsed light (IPL) and low-level light therapy (LLLT)] on clinical and molecular outcomes in evaporative DED with meibomian gland dysfunction (MGD).

METHODS

This prospective study evaluated 94 eyes (47 subjects) with chronic MGD treated with combined light therapy. Patients underwent a detailed evaluation of MGD and DED using the Ocular Surface Disease Index, dry eye tests-tear breakup time and Schirmer test, ocular surface staining, meibomian gland expressibility scoring, and meibography. Patients underwent a single session of combined light therapy (IPL + LLLT treatment) using the Eye-light device. All these tests were repeated at 3 and 6 months after treatment. Tear fluid and ocular surface wash samples were collected from a subset of patients before and after treatment for cellular and secreted immune factor profiling by flow cytometry.

RESULTS

Combined light therapy (IPL + LLLT) demonstrated a marked improvement in the clinical metrics studied. Three months after treatment, Ocular Surface Disease Index showed a significant reduction in 95.6% ( P < 0.0001), tear breakup time increased in 72.3% ( P < 0.0001), and meibomian gland expressibility scoring increased in 80.8% ( P < 0.0001) of the eyes. These effects were observed to be sustained during the 6-month follow-up visit. Significant ( P < 0.05) reduction in tear fluid levels of interleukin-1β, interleukin-17F, and MMP9; MMP9/TIMP1 ratio; and ocular surface B-cell proportions was observed.

CONCLUSIONS

Combined light therapy shows promising results in patients with chronic MGD and DED, even in recalcitrant cases. Clinical and molecular factor alterations support the improved symptomatology and reduced inflammation.

Target Receptors of Regenerating Nerves: Neuroma Formation and Current Treatment Options

Neuromas form as a result of disorganized sensory axonal regeneration following nerve injury. Painful neuromas lead to poor quality of life for patients and place a burden on healthcare systems. Modern surgical interventions for neuromas entail guided regeneration of sensory nerve fibers into muscle tissue leading to muscle innervation and neuroma treatment or prevention. However, it is unclear how innervating denervated muscle targets prevents painful neuroma formation, as little is known about the fate of sensory fibers, and more specifically pain fiber, as they regenerate into muscle. Golgi tendon organs and muscle spindles have been proposed as possible receptor targets for the regenerating sensory fibers; however, these receptors are not typically innervated by pain fibers, as these free nerve endings do not synapse on receptors. The mechanisms by which pain fibers are signaled to cease regeneration therefore remain unknown. In this article, we review the physiology underlying nerve regeneration, the guiding molecular signals, and the target receptor specificity of regenerating sensory axons as it pertains to the development and prevention of painful neuroma formation while highlighting gaps in literature. We discuss management options for painful neuromas and the current supporting evidence for the various interventions.

Macrophage Activation in the Dorsal Root Ganglion in Rats Developing Autotomy after Peripheral Nerve Injury

Autotomy, self-mutilation of a denervated limb, is common in animals after peripheral nerve injury (PNI) and is a reliable proxy for neuropathic pain in humans. Understanding the occurrence and treatment of autotomy remains challenging. The objective of this study was to investigate the occurrence of autotomy in nude and Wistar rats and evaluate the differences in macrophage activation and fiber sensitization contributing to the understanding of autotomy behavior. Autotomy in nude and Wistar rats was observed and evaluated 6 and 12 weeks after sciatic nerve repair surgery. The numbers of macrophages and the types of neurons in the dorsal root ganglion (DRG) between the two groups were compared by immunofluorescence studies. Immunostaining of T cells in the DRG was also assessed. Nude rats engaged in autotomy with less frequency than Wistar rats. Autotomy symptoms were also relatively less severe in nude rats. Immunofluorescence studies revealed increased macrophage accumulation and activation in the DRG of Wistar rats. The percentage of NF200+ neurons was higher at 6 and 12 weeks in Wistar rats compared to nude rats, but the percentage of CGRP+ neurons did not differ between two groups. Additionally, macrophages were concentrated around NF200-labeled A fibers. At 6 and 12 weeks following PNI, CD4+ T cells were not found in the DRG of the two groups. The accumulation and activation of macrophages in the DRG may account for the increased frequency and severity of autotomy in Wistar rats. Our results also suggest that A fiber neurons in the DRG play an important role in autotomy.

Schwann cells and trigeminal neuralgia

Schwann cells are components of the peripheral nerve myelin sheath, which supports and nourishes axons. Upon injury of the trigeminal nerve, Schwann cells are activated and cause trigeminal neuralgia by engulfing the myelin sheath and secreting various neurotrophic factors. Further, Schwann cells can repair the damaged nerve and thus alleviate trigeminal neuralgia. Here, we briefly describe the development and activation of Schwann cells after nerve injury. Moreover, we expound on the occurrence, regulation, and treatment of trigeminal neuralgia; further, we point out the current research deficiencies and future research directions.

Covering the proximal nerve stump with chondroitin sulfate proteoglycans prevents traumatic painful neuroma formation by blocking axon regeneration after neurotomy in Sprague Dawley rats

OBJECTIVE

Neuropathic pain caused by traumatic neuromas is an extremely intractable clinical problem. Disorderly scar tissue accumulation and irregular and immature axon regeneration around the injury site mainly contribute to traumatic painful neuroma formation. Therefore, successfully preventing traumatic painful neuroma formation requires the effective inhibition of irregular axon regeneration and disorderly accumulation of scar tissue. Considering that chondroitin sulfate proteoglycans (CSPGs) can act on the growth cone and effectively inhibit axon regeneration, the authors designed and manufactured a CSPG-gelatin blocker to regulate the CSPGs' spatial distribution artificially and applied it in a rat model after sciatic nerve neurectomy to evaluate its effects in preventing traumatic painful neuroma formation.

METHODS

Sixty female Sprague Dawley rats were randomly divided into three groups (positive group: no covering; blank group: covering with gelatin blocker; and CSPG group: covering with the CSPG-gelatin blocker). Pain-related factors were evaluated 2 and 8 weeks postoperatively (n = 30). Neuroma growth, autotomy behavior, and histological features of the neuromas were assessed 8 weeks postoperatively (n = 30).

RESULTS

Eight weeks postoperatively, typical bulb-shaped neuromas did not form in the CSPG group, and autotomy behavior was obviously better in the CSPG group (p < 0.01) than in the other two groups. Also, in the CSPG group the regenerated axons showed a lower density and more regular and improved myelination (p < 0.01). Additionally, the distribution and density of collagenous fibers and the expression of α-smooth muscle actin were significantly lower in the CSPG group than in the positive group (p < 0.01). Regarding pain-related factors, c-fos, substance P, interleukin (IL)-17, and IL-1β levels were significantly lower in the CSPG group than those in the positive and blank groups 2 weeks postoperatively (p < 0.05), while substance P and IL-17 remained lower in the CSPG group 8 weeks postoperatively (p < 0.05).

CONCLUSIONS

The authors found that CSPGs loaded in a gelatin blocker can prevent traumatic neuroma formation and effectively relieve pain symptoms after sciatic nerve neurotomy by blocking irregular axon regeneration and disorderly collagenous fiber accumulation in the proximal nerve stump. These results indicate that covering the proximal nerve stump with CSPGs may be a new and promising strategy to prevent traumatic painful neuroma formation in the clinical setting.

Autologous fat grafting for nerve regeneration and neuropathic pain: current state from bench-to-bedside

Despite recent advances in microsurgical techniques, functional recovery following peripheral nerve injury remains slow and inadequate. Poor peripheral nerve regeneration not only leaves patients with significant impairments, but also commonly leads to the development of debilitating neuropathic pain. Recent research has demonstrated the potential therapeutic benefits of adipose-derived stem cells, to enhance nerve regeneration. However, clinical translation remains limited due to the current regulatory burdens of the US FDA. A reliable and immediately translatable alternative is autologous fat grafting, where native adipose-derived stem cells present in the transferred tissue can potentially act upon regenerating axons. This review presents the scope of adipose tissue-based therapies to enhance outcomes following peripheral nerve injury, specifically focusing on their role in regeneration and ameliorating neuropathic pain.

Pain Relief after Surgical Decompression of the Distal Brachial Plexus

Background  Brachial plexopathy causes pain and loss of function in the affected extremity. Entrapment of the brachial plexus terminal branches within the surrounding connective tissue, or medial brachial fascial compartment, may manifest in debilitating symptoms. Open fasciotomy and external neurolysis of the neurovascular bundle in the medial brachial fascial compartment were performed as a surgical treatment for pain and functional decline in the upper extremity. The aim of this study was to evaluate pain outcomes after surgery in patients diagnosed with brachial plexopathy.

Methods  We identified 21 patients who met inclusion criteria. Documents dated between 2005 and 2019 were reviewed from electronic medical records. Chart review was conducted to collect data on visual analog scale (VAS) for pain, Semmes-Weinstein monofilament test (SWMT), and Medical Research Council (MRC) scale for muscle strength. Pre- and postoperative data was obtained. A paired sample t -test was used to determine statistical significance of pain outcomes.

Results  Pain severity in the affected arm was significantly reduced after surgery (pre: 6.4 ± 2.5; post: 2.0 ± 2.5; p  < 0.01). Additionally, there was an increased response to SWMT after the procedure. More patients achieved an MRC rating score ≥3 and ≥4 in elbow flexion after surgery. This may be indicative of improved sensory and motor function.

Conclusion  Open fasciotomy and external neurolysis at the medial brachial fascial compartment is an effective treatment for pain when nerve continuity is preserved. These benefits were evident in patients with a prolonged duration elapsed since injury onset.

Modulation of the Negative Affective Dimension of Pain: Focus on Selected Neuropeptidergic System Contributions

It is well known that emotions can interfere with the perception of physical pain, as well as with the development and maintenance of painful conditions. On the other hand, somatic pain can have significant consequences on an individual’s affective behavior. Indeed, pain is defined as a complex and multidimensional experience, which includes both sensory and emotional components, thus exhibiting the features of a highly subjective experience. Over the years, neural pathways involved in the modulation of the different components of pain have been identified, indicating the existence of medial and lateral pain systems, which, respectively, project from medial or lateral thalamic nuclei to reach distinct cortex regions relating to specific functions. However, owing to the limited information concerning how mood state and painful input affect each other, pain treatment is frequently unsatisfactory. Different neuromodulators, including endogenous neuropeptides, appear to be involved in pain-related emotion and in its affective influence on pain perception, thus playing key roles in vulnerability and clinical outcome. Hence, this review article focuses on evidence concerning the modulation of the sensory and affective dimensions of pain, with particular attention given to some selected neuropeptidergic system contributions.

Reduced gene expression of netrin family members in skin and sural nerve specimens of patients with painful peripheral neuropathies

OBJECTIVE

To investigate the expression of axon guidance cues in skin and sural nerve biopsies of patients with polyneuropathies (PNP) as potential markers of nerve de- and regeneration and inflammation.

METHODS

We prospectively recruited 88 patients with PNP and compared data between patient subgroups and healthy controls. All patients underwent skin punch and/or sural nerve biopsy at the lower leg and proximal thigh. We characterized gene expression profiles of netrin family members as target genes involved in neuronal de- and regeneration [netrin 1, deleted in colorectal cancer (DCC), uncoordinated5H2, neogenin 1 (NEO1), netrin G1, netrin G2] using quantitative real-time PCR.

RESULTS

Gene expression of netrin 1 (p < 0.05 in proximal skin), DCC (p < 0.001 in distal skin), NEO1 (p < 0.05 in distal skin), netrin G1 (p < 0.05 in proximal and p < 0.01 in distal skin), and netrin G2 (p < 0.001 in distal skin) was lower in skin biopsies of patients with neuropathy compared to healthy controls. Gene expression of NEO1 (p < 0.05 in distal skin), netrin G2 (p < 0.05 in distal skin), and DCC (p < 0.05 in sural nerve) was lower in samples of patients with painful compared to painless PNP and also correlated positively with intraepidermal nerve fiber density. Skin and sural nerve gene expression of the investigated target genes did not differ between neuropathies of different etiologies.

CONCLUSION

We show reduced cutaneous and neural axon guide expression, which may contribute to a dysregulation of nerve fiber de- and regeneration.

Time course of traumatic neuroma development

This study was designed to characterize morphologic stages during neuroma development post amputation with an eye toward developing better treatment strategies that intervene before neuromas are fully formed. Right forelimbs of 30 Sprague Dawley rats were amputated and limb stumps were collected at 3, 7, 28, 60 and 90 Days Post Amputation (DPA). Morphology of newly formed nerves and neuromas were assessed via general histology and neurofilament protein antibody staining. Analysis revealed six morphological characteristics during nerve and neuroma development; 1) normal nerve, 2) degenerating axons, 3) axonal sprouts, 4) unorganized bundles of axons, 5) unorganized axon growth into muscles, and 6) unorganized axon growth into fibrotic tissue (neuroma). At early stages (3 & 7 DPA) after amputation, normal nerves could be identified throughout the limb stump and small areas of axonal sprouts were present near the site of injury. Signs of degenerating axons were evident from 7 to 90 DPA. From day 28 on, variability of nerve characteristics with signs of unorganized axon growth into muscle and fibrotic tissue and neuroma formation became visible in multiple areas of stump tissue. These pathological features became more evident on days 60 and 90. At 90 DPA frank neuroma formation was present in all stump tissue. By following nerve regrowth and neuroma formation after amputation we were able to identify 6 separate histological stages of nerve regrowth and neuroma development. Axonal regrowth was observed as early as 3 DPA and signs of unorganized axonal growth and neuroma formation were evident by 28 DPA. Based on these observations we speculate that neuroma treatment and or prevention strategies might be more successful if targeted at the initial stages of development and not after 28 DPA.

Effect of local application of an antibody against brain-derived neurotrophic factor on neuroma formation after transection of the inferior alveolar nerve in the rat

This study aimed to examine the contributions of brain-derived neurotrophic factor (BDNF) at the injury site toward neuroma formation and nerve regeneration after inferior alveolar nerve transection. Histological analysis confirmed neuroma formation at 2 weeks after complete transection of the inferior alveolar nerve. A local administration of an antibody to BDNF inhibited connective tissue proliferation at the injury site and promoted nerve fiber integrity. Fluorogold labeling showed a significantly higher number of labeled cells in the trigeminal ganglion in the anti-BDNF-treated group compared with the vehicle control group. In-situ hybridization histochemistry showed intense signals for tropomyosin receptor kinase B mRNA in the area of the injury site containing fibrous or granular tissue in the anti-BDNF-treated group. In contrast, these signals were close to the detection limit in the area of the perineurium in intact nerve trunks, indicating that the signals were expressed by fibroblasts within the connective tissue. These findings suggest that antagonization of endogenous BDNF induced by nerve injury reduces neuroma formation, without inhibiting damaged axon regeneration.

The anatomical relationship of the superficial radial nerve and the lateral antebrachial cutaneous nerve: A possible factor in persistent neuropathic pain

The superficial branch of the radial nerve (SBRN) is known for developing neuropathic pain syndromes after trauma. These pain syndromes can be hard to treat due to the involvement of other nerves in the forearm. When a nerve is cut, the Schwann cells, and also other cells in the distal segment of the transected nerve, produce the nerve growth factor (NGF) in the entire distal segment. If two nerves overlap anatomically, similar to the lateral antebrachial cutaneous nerve (LACN) and SBRN, the increase in secretion of NGF, which is mediated by the injured nerve, results in binding to the high-affinity NGF receptor, tyrosine kinase A (TrkA). This in turn leads to possible sprouting and morphological changes of uninjured fibers, which ultimately causes neuropathic pain. The aim of this study was to map the level of overlap between the SBRN and LACN. Twenty arms (five left and 15 right) were thoroughly dissected. Using a new analysis tool called CASAM (Computer Assisted Surgical Anatomy Mapping), the course of the SBRN and LACN could be compared visually. The distance between both nerves was measured at 5-mm increments, and the number of times they intersected was documented. In 81% of measurements, the distance between the nerves was >10 mm, and in 49% the distance was even <5 mm. In 95% of the dissected arms, the SBRN and LACN intersected. On average, they intersected 2.25 times. The close (anatomical) relationship between the LACN and the SBRN can be seen as a factor in the explanation of persistent neuropathic pain in patients with traumatic or iatrogenic lesion of the SBRN or the LACN.

Role of vitamin D3 in treatment of lumbar disc herniation--pain and sensory aspects: study protocol for a randomized controlled trial

BACKGROUND

Vitamin D receptors have been identified in the spinal cord, nerve roots, dorsal root ganglia and glial cells, and its genetic polymorphism association with the development of lumbar disc degeneration and herniation has been documented. Metabolic effects of active vitamin D metabolites in the nucleus pulposus and annulus fibrosus cells have been studied. Lumbar disc herniation is a process that involves immune and inflammatory cells and processes that are targets for immune regulatory actions of vitamin D as a neurosteroid hormone. In addition to vitamin D's immune modulatory properties, its receptors have been identified in skeletal muscles. It also affects sensory neurons to modulate pain. In this study, we aim to study the role of vitamin D3 in discogenic pain and related sensory deficits. Additionally, we will address how post-treatment 25-hydroxy vitamin D3 level influences pain and sensory deficits severity. The cut-off value for serum 25-hydroxy vitamin D3 that would be efficacious in improving pain and sensory deficits in lumbar disc herniation will also be studied.

METHODS/DESIGN

We will conduct a randomized, placebo-controlled, double-blind clinical trial. Our study population will include 380 cases with one-level and unilateral lumbar disc herniation with duration of discogenic pain less than 8 weeks. Individuals who do not have any contraindications, will be divided into three groups based on serum 25-hydroxy vitamin D3 level, and each group will be randomized to receive either a single-dose 300,000-IU intramuscular injection of vitamin D3 or placebo. All patients will be under conservative treatment. Pre-treatment and post-treatment assessments will be performed with the McGill Pain Questionnaire and a visual analogue scale. For the 15-day duration of this study, questionnaires will be filled out during telephone interviews every 3 days (a total of five times). The initial and final interviews will be scheduled at our clinic. After 15 days, serum 25-hydroxy vitamin D3 levels will be measured for those who have received vitamin D3 (190 individuals).

TRIAL REGISTRATION

Iranian Registry for Clinical Trials ID: IRCT2014050317534N1 (trial registration: 5 June 2014).

Brain-derived neurotrophic factor expression in dorsal root ganglia of a lumbar spinal stenosis model in rats

This study aimed to investigate the expression of brain-derived neurotrophic factor (BDNF) in dorsal root ganglia (DRG) of a rat model of lumbar spinal stenosis (LSS). Adult male rats were divided into the operation and sham operation groups. The operation group was comprised of the rat models of LSS. Walking distance and BDNF expression levels in DRG were measured in the two groups at different time points. The total BDNF protein levels and positive cell mean optical density (MOD) values in the operation group were significantly higher at each time point compared with that of the sham operation and preoperative control groups (P<0.05). The total BDNF protein levels and MOD values following sport in the operation group were significantly higher compared with those prior to sport (P<0.05). In the sham operation group, BDNF protein levels and MOD values before and after sport at each time point showed no significant differences than those of the operation group (P>0.05). Moreover, BDNF protein levels and MOD values in the operation group indicated a negative correlation with walking distance. The present study demonstrated that the expression of BDNF in rat models of LSS increased with time and was associated with a decrease in walking distance. BDNF was therefore important for the process of intermittent claudication caused by LSS.

MOR is not enough: identification of novel mu-opioid receptor interacting proteins using traditional and modified membrane yeast two-hybrid screens

The mu-opioid receptor (MOR) is the G-protein coupled receptor primarily responsible for mediating the analgesic and rewarding properties of opioid agonist drugs such as morphine, fentanyl, and heroin. We have utilized a combination of traditional and modified membrane yeast two-hybrid screening methods to identify a cohort of novel MOR interacting proteins (MORIPs). The interaction between the MOR and a subset of MORIPs was validated in pulldown, co-immunoprecipitation, and co-localization studies using HEK293 cells stably expressing the MOR as well as rodent brain. Additionally, a subset of MORIPs was found capable of interaction with the delta and kappa opioid receptors, suggesting that they may represent general opioid receptor interacting proteins (ORIPS). Expression of several MORIPs was altered in specific mouse brain regions after chronic treatment with morphine, suggesting that these proteins may play a role in response to opioid agonist drugs. Based on the known function of these newly identified MORIPs, the interactions forming the MOR signalplex are hypothesized to be important for MOR signaling and intracellular trafficking. Understanding the molecular complexity of MOR/MORIP interactions provides a conceptual framework for defining the cellular mechanisms of MOR signaling in brain and may be critical for determining the physiological basis of opioid tolerance and addiction.

Laser therapy and pain-related behavior after injury of the inferior alveolar nerve: possible involvement of neurotrophins

Nerve-related complications have been frequently reported in dental procedures, and a very frequent type of occurrence involves the inferior alveolar nerve (IAN). The nerve injury in humans often results in persistent pain accompanied by allodynia and hyperalgesia. In this investigation, we used an experimental IAN injury in rats, which was induced by a Crile hemostatic clamp, to evaluate the effects of laser therapy on nerve repair. We also studied the nociceptive behavior (von Frey hair test) before and after the injury and the behavioral effects of treatment with laser therapy (emitting a wavelength of 904 nm, output power of 70 Wpk, a spot area of ∼0.1 cm², frequency of 9500 Hz, pulse time 60 ns and an energy density of 6 J/cm²). As neurotrophins are essential for the process of nerve regeneration, we used immunoblotting techniques to preliminarily examine the effects of laser therapy on the expression of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). The injured animals treated with laser exhibited an improved nociceptive behavior. In irradiated animals, there was an enhanced expression of NGF (53%) and a decreased BDNF expression (40%) after laser therapy. These results indicate that BDNF plays a locally crucial role in pain-related behavior development after IAN injury, increasing after lesions (in parallel to the installation of pain behavior) and decreasing with laser therapy (in parallel to the improvement of pain behavior). On the other hand, NGF probably contributes to the repair of nerve tissue, in addition to improving the pain-related behavior.

Double gene therapy with granulocyte colony-stimulating factor and vascular endothelial growth factor acts synergistically to improve nerve regeneration and functional outcome after sciatic nerve injury in mice

Peripheral-nerve injuries are a common clinical problem and often result in long-term functional deficits. Reconstruction of peripheral-nerve defects is currently undertaken with nerve autografts. However, there is a limited availability of nerves that can be sacrificed and the functional recovery is never 100% satisfactory. We have previously shown that gene therapy with vascular endothelial growth factor (VEGF) significantly improved nerve regeneration, neuronal survival, and muscle activity. Our hypothesis is that granulocyte colony-stimulating factor (G-CSF) synergizes with VEGF to improve the functional outcome after sciatic nerve transection. The left sciatic nerves and the adjacent muscle groups of adult mice were exposed, and 50 or 100 μg (in 50 μl PBS) of VEGF and/or G-CSF genes was injected locally, just below the sciatic nerve, and transferred by electroporation. The sciatic nerves were transected and placed in an empty polycaprolactone (PCL) nerve guide, leaving a 3-mm gap to challenge nerve regeneration. After 6 weeks, the mice were perfused and the sciatic nerve, the dorsal root ganglion (DRG), the spinal cord and the gastrocnemius muscle were processed for light and transmission electron microscopy. Treated animals showed significant improvement in functional and histological analyses compared with the control group. However, the best results were obtained with the G-CSF+VEGF-treated animals: quantitative analysis of regenerated nerves showed a significant increase in the number of myelinated fibers and blood vessels, and the number of neurons in the DRG and motoneurons in the spinal cord was significantly higher. Motor function also showed that functional recovery occurred earlier in animals receiving G-CSF+VEGF-treatment. The gastrocnemius muscle showed an increase in weight and in the levels of creatine phosphokinase, suggesting an improvement of reinnervation and muscle activity. These results suggest that these two factors acted synergistically and optimized the nerve repair potential, improving regeneration after a transection lesion.

Role of neurotrophins in neuropathic pain

Neurotrophins (NTs) belong to a family of structurally and functionally related proteins, they are the subsets of neurotrophic factors. Neurotrophins are responsible for diverse actions in the developing peripheral and central nervous systems. They are important regulators of neuronal function, affecting neuronal survival and growth. They are able to regulate cell death and survival in development as well as in pathophysiologic states. NTs and their receptors are expressed in areas of the brain that undergo plasticity, indicating that they are able to modulate synaptic plasticity.

Recently, neurotrophins have been shown to play significant roles in the development and transmission of neuropathic pain. Neuropathic pain is initiated by a primary lesion or dysfunction in the nervous system. It has a huge impact on the quality of life. It is debilitating and often has an associated degree of depression that contributes to decreasing human well being. Neuropathic pain ranks at the first place for sanitary costs.

Neuropathic pain treatment is extremely difficult. Several molecular pathways are involved, making it a very complex disease. Excitatory or inhibitory pathways controlling neuropathic pain development show altered gene expression, caused by peripheral nerve injury. At present there are no valid treatments over time and neuropathic pain can be classified as an incurable disease.

Nowadays, pain research is directing towards new molecular methods. By targeting neurotrophin molecules it may be possible to provide better pain control than currently available.

Refined sensory measures of neural repair in human spinal cord injury: bridging preclinical findings to clinical value

Sensory input from the periphery to the brain can be severely compromised or completely abolished after an injury to the spinal cord. Evidence from animal models suggests that endogenous repair processes in the spinal cord mediate extensive sprouting and that this might be further attenuated by targeted therapeutic interventions. However, the extent to which sprouting can contribute to spontaneous recovery after human spinal cord injury (SCI) remains largely unknown, in part because few measurement tools are available in order to non-invasively detect subtle changes in neurophysiology. The proposed application of segmental sensory evoked potentials (e.g., dermatomal contact heat evoked potentials and somatosensory evoked potentials) to assess conduction in ascending pathways (i.e., spinothalamic and dorsal column, respectively) differs from conventional approaches in that individual spinal segments adjacent to the level of lesion are examined. The adoption of these approaches into clinical research might provide improved resolution for measuring changes in sensory impairments and might determine the extent by which spontaneous recovery after SCI is mediated by similar endogenous repair mechanisms in humans as in animal models.

Comparison of central versus peripheral delivery of pregabalin in neuropathic pain states

Background

Although pregabalin therapy is beneficial for neuropathic pain (NeP) by targeting the CaVα₂δ-1 subunit, its site of action is uncertain. Direct targeting of the central nervous system may be beneficial for the avoidance of systemic side effects.

Results

We used intranasal, intrathecal, and near-nerve chamber forms of delivery of varying concentrations of pregabalin or saline delivered over 14 days in rat models of experimental diabetic peripheral neuropathy and spinal nerve ligation. As well, radiolabelled pregabalin was administered to determine localization with different deliveries. We evaluated tactile allodynia and thermal hyperalgesia at multiple time points, and then analyzed harvested nervous system tissues for molecular and immunohistochemical changes in CaVα₂δ-1 protein expression. Both intrathecal and intranasal pregabalin administration at high concentrations relieved NeP behaviors, while near-nerve pregabalin delivery had no effect. NeP was associated with upregulation of CACNA2D1 mRNA and CaVα₂δ-1 protein within peripheral nerve, dorsal root ganglia (DRG), and dorsal spinal cord, but not brain. Pregabalin's effect was limited to suppression of CaVα₂δ-1 protein (but not CACNA2D1 mRNA) expression at the spinal dorsal horn in neuropathic pain states. Dorsal root ligation prevented CaVα₂δ-1 protein trafficking anterograde from the dorsal root ganglia to the dorsal horn after neuropathic pain initiation.

Conclusions

Either intranasal or intrathecal pregabalin relieves neuropathic pain behaviours, perhaps due to pregabalin's effect upon anterograde CaVα₂δ-1 protein trafficking from the DRG to the dorsal horn. Intranasal delivery of agents such as pregabalin may be an attractive alternative to systemic therapy for management of neuropathic pain states.

Reduction of post-traumatic neuroma and epineural scar formation in rat sciatic nerve by application of microcrystallic chitosan

Injury of peripheral nerve is associated with the development of post-traumatic neuroma at the end of the proximal stump, often being the origin of neuropathic pain. This type of pain is therapy-resistant and therefore extremely nagging for patients. We examined the influence of the microcrystallic chitosan gel applied to the proximal stump of totally transected sciatic nerve on the neuroma formation and neuropathic pain development in rats. In 14 rats, right sciatic nerve was transected and the distal stump was removed to avoid spontaneous rejoining. In the chitosan (experimental) group (n = 7), the proximal stump was covered with a thin layer of the microcrystallic chitosan gel. In control animals (n = 7), the cut nerve was left unsecured. Autotomy, an animal model of neuropathic pain, was monitored daily for 20 weeks following surgery. Then, the animals were perfused transcardially and the proximal stumps of sciatic nerves were dissected and subjected to histologic evaluation. The presence, size, and characteristics of neuromas as well as extraneural fibrosis were examined. In chitosan group, the incidence and the size of the neuroma were markedly reduced, as compared with the control group; however, there was no difference in autotomy behavior between groups. In addition, extraneural fibrosis was significantly reduced in chitosan group when compared to the control group. The results demonstrate beneficial influence of microcrystallic chitosan applied to the site of nerve transection on the development of post-traumatic neuroma and reduction of extraneural fibrosis, however without reduction of neuropathic pain.

Stump rotation in a nerve autograft by 2 factors: cross-connection and difference in diameter

The aim of this study was to determine the influence of stump rotation (fascicular cross-connection) on nerve autograft functional recovery. Thirty rat sciatic nerves were transected and repaired by autograft. The rats were divided into 3 groups according to the number of stump rotations of the autograft: (1) plain graft (PG-g, with no change in fascicular orientation, no difference in diameter), (2) graft rotation (GR-g, with no change in fascicular orientation, and diameter difference between fascicles), (3) stump rotation (SR-g, with cross-connection and diameter difference between fascicles). Relative gastrocnemius muscle weight and nerve fiber count were examined as anatomic recovery indices, and autotomy score (ATS) and toe-out angle as functional recovery indices. The results showed that SR-g had a significantly low functional recovery compared with PG-g and GR-g. However, there was no difference found in the anatomic recovery. These findings suggest that the stump rotation in nerve autograft had no effect on neural regeneration and muscle reinnervation; however, it had a negative effect on functional recovery. Because GR-g was similar to PG-g rather than SR-g in functional recovery, the diameter difference between fascicles appears to have had little effect on the functional recovery. The results of this study suggest that a novel approach to ATS interpretation is needed. It is recommended that (1) ATS 2 be considered the onset of autotomy instead of ATS 1; and (2) the frequency of "ATS 2 and above" should be considered for the comparison of the autotomy rather than the mean ATS.

Brain-derived neurotrophic factor redistribution in the dorsal root ganglia correlates with neuropathic pain inhibition after resiniferatoxin treatment

BACKGROUND CONTEXT

Brain-derived neurotrophic factor (BDNF) and its cognate receptor, the tyrosine kinase B (TrkB), are normally expressed in neurons and implicated in multiple pathological conditions. Brain-derived neurotrophic factor is produced in the central nervous system microglia in response to noxious stimuli and appear to potentiate central sensitization. Resiniferatoxin (RTX) is an excitotoxic agonist of the vanilloid receptor 1 (VR1), a cation channel protein considered an integrator for nociception. Resiniferatoxin, administered into the dorsal root ganglia (DRG), selectively eliminates the VR1-positive neurons and improves tactile allodynia in a neuropathic pain rat model.

PURPOSE

The goal of the present study was to evaluate the role of BDNF in RTX-induced neuropathic pain suppression.

STUDY DESIGN

The study design was a sciatic nerve injury animal model with intraganglionic RTX injection.

METHODS

Resiniferatoxin was injected into the DRG of the L3-L6 spinal nerves after the rats displayed tactile allodynia and thermal hyperalgesia produced by a photochemical injury to the sciatic nerve. Behavioral testing and immunohistochemical and mRNA analysis of the DRG were performed to determine BDNF's role in pain modulation.

RESULTS

Brain-derived neurotrophic factor expression in the DRG of neuropathic rats was upregulated in the small- and medium-size neurons, whereas the upregulation was observed in the large-size neurons of non-neuropathic rat DRG. A high-dose RTX injection in the DRG of neuropathic rats led to elimination of both thermal hyperalgesia and tactile allodynia and also upregulated BDNF in the large-size neurons, similar to the nonallodynic rats. Tyrosine kinase B changes mirrored the BDNF ones.

CONCLUSION

Resiniferatoxin injection in the DRG of neuropathic rats upregulates BDNF expression in the same pattern as in the large-size neurons of non-neuropathic rats. Therefore, BDNF upregulation may have pain suppressive effects. These effects are likely mediated by TrkB.

Serial changes in bladder, locomotion, and levels of neurotrophic factors in rats with spinal cord contusion

The aims of this study were to evaluate the evolution of the neurogenic bladder after spinal cord contusion and to correlate changes in bladder function with locomotor function and levels of neurotrophic factors. The MASCIS impactor was used to cause a mild contusion injury of the lower thoracic spinal cord of Sprague-Dawley rats. Rats were divided into four groups according to the length of time from injury to sacrifice, at 4, 14, 28, and 56 days after injury. Gait analysis was performed each week, and urodynamic study was performed just before sacrifice. Basso, Beattie, and Bresnahan (BBB) and coupling scores showed gradual recovery, as did the urinary voiding pattern and bladder volume; some parameters of micturition reached normal ranges. Brain-derived neurotrophic factor (BDNF) levels in the spinal cord, as detected by enzyme-linked immunosorbent assay, decreased with time, whereas neurotrophin-3 (NT-3) levels remained unchanged. The micturition pattern, bladder volume, and locomotor function continued to recover during the time of observation; BDNF levels in the spinal cord and bladder were inversely correlated with BBB scores and the restoration of bladder volume. We conclude that urodynamic changes in the bladder correlate with locomotion recovery but not with the levels of BDNF or NT-3 after modified mild contusion injury in rats.

The role of brain-derived neurotrophic factor in different animal models of neuropathic pain

Even in present day pain therapy, neuropathic pain remains a challenge for clinicians to treat and a challenge for researchers to investigate. Different animal models have been developed to mimic neuropathic pain. Neurotrophins such as nerve growth factor, brain-derived neurotrophic factor and neurotrophin 3 have been studied extensively in these models, yet few review articles concerning brain-derived neurotrophic factor have been published. This article reassesses the literature concerning brain-derived neurotrophic factor expression in the sciatic nerve chronic constriction injury model, the sciatic nerve transection model, the spinal nerve ligation model and the spinal nerve transection model and discusses differences in regulation of brain-derived neurotrophic factor between these models and their causality with neuropathic pain.

TrkB signaling is required for both the induction and maintenance of tissue and nerve injury-induced persistent pain

Activation of primary afferent nociceptors produces acute, short-lived pain, and tissue or nerve injury induces long-term enhancement of nociceptive processing, manifested as hypersensitivity to thermal and mechanical stimulation. Here we used a chemical-genetic and pharmacological approach to study the contribution of the receptor tyrosine kinase, type 2 (TrkB) to the generation and maintenance of injury-induced persistent pain. We performed the studies in wild-type mice and transgenic (TrkB(F616A)) mice that express mutant but fully functional TrkB receptors. By injecting a small molecule derivative of the protein kinase inhibitor protein phosphatase 1 (1NM-PP1), it is possible to produce highly selective inhibition of TrkB autophosphorylation in adult mice, without interfering with the activity of other protein kinases. We report that oral administration of 1NM-PP1, at doses that blocked phosphorylation of TrkB in the spinal cord, had no effect in behavioral tests of acute heat, mechanical, or chemical pain sensitivity. However, the same pretreatment with 1NM-PP1 prevented the development of tissue- or nerve injury-induced heat and mechanical hypersensitivity. Established hypersensitivity was transiently reversed by intraperitoneal injection of 1NM-PP1. Although interfering with TrkB signaling altered neither acute capsaicin nor formalin-induced pain behavior, the prolonged mechanical hypersensitivity produced by these chemical injuries was prevented by 1NM-PP1 inhibition of TrkB signaling. We conclude that TrkB signaling is not only an important contributor to the induction of heat and mechanical hypersensitivity produced by tissue or nerve injury but also to the persistence of the pain.

Pain after avulsion injuries and complete palsy of the brachial plexus: the possible role of nonavulsed roots in pain generation

OBJECTIVE

Pain after complete brachial palsy has been attributed to the deafferentation of the spinal cord subjected to root avulsion. However, the large majority of patients have at least one nonavulsed root. We postulated that pain, be it subacute or chronic, originates in the stump of the nonavulsed roots.

METHODS

Thirty-six patients underwent brachial plexus grafting within 8 months of their initial injury. Ten other patients with palsy that had lasted for more than 2 years underwent selective, computed tomography-guided anesthetic blocks of the nonavulsed root. Pain was evaluated at different intervals, using a numerical scale ranging from 0 (no pain) to 10 (severe pain).

RESULTS

In all groups, pain decreased substantially or disappeared after a local anesthetic block or grafting. In the patients who underwent grafting, pain reduction was noted the first day after surgery in 56% of the 36 patients. Three weeks after surgery, pain decreased dramatically, by 80% (P < 0.001). By 12 months after surgery, pain had decreased by 90%, and within 24 months, by 95%. Only the difference between 3 weeks and 24 months after surgery was significant (P < 0.001). At final evaluation, 80% of the patients receiving grafts reported either no or minimal pain.

CONCLUSION

Our data suggest that nonavulsed roots mediate pain in subacute and chronic complete brachial plexus palsy.