Tumor necrosis factor-α increases brain-derived neurotrophic factor expression in trigeminal ganglion neurons in an activity-dependent manner

Role of TNF-α in the Pathogenesis of Migraine

Background

Neurogenic neuroinflammation has a wide role in migraine pathogenesis including the transition from episodic migraine to chronic one. The seed molecule of neurogenic neuroinflammation, i.e., the TNF-α proinflammatory molecule, has gathered a lot of attention. This pleiotropic cytokine is a classical component of inflammatory soup, secreted by the microglial cell, and promotes a wide range of inflammatory reactions.

Aim

In this review, we aimed to provide a culminating and comprehending glimpse into the TNF-α in association with the migraine.

Method

A systematic literature survey method with a mixture of keywords was utilized to grasp the different elements that represent the association between TNF-α and migraine. Discussion. Highlighted the probable involvement of the TNF-α with migraine, the complexity of the matter such as activation of NF-KB signaling cascade, autoactivation, sensitization, and increased likelihood of transition cannot be neglected. Being TNF-α as a core node, it becomes the factor for linking diseases such as chronic inflammatory disorders, including COVID-19, and also interaction with other genes to develop severe conditions.

Conclusion

To this end, TNF-α plays a critical role in chronification, and inhibiting its signaling would likely be a crucial strategy for migraine therapy.

Astrocytes and brain-derived neurotrophic factor (BDNF)

Astrocytes are emerging in the neuroscience field as crucial modulators of brain functions, from the molecular control of synaptic plasticity to orchestrating brain-wide circuit activity for cognitive processes. The cellular pathways through which astrocytes modulate neuronal activity and plasticity are quite diverse. In this review, we focus on neurotrophic pathways, mostly those mediated by brain-derived neurotrophic factor (BDNF). Neurotrophins are a well-known family of trophic factors with pleiotropic functions in neuronal survival, maturation and activity. Within the brain, BDNF is the most abundantly expressed and most studied of all neurotrophins. While we have detailed knowledge of the effect of BDNF on neurons, much less is known about its physiology on astroglia. However, over the last years new findings emerged demonstrating that astrocytes take an active part into BDNF physiology. In this work, we discuss the state-of-the-art knowledge about astrocytes and BDNF. Indeed, astrocytes sense extracellular BDNF through its specific TrkB receptors and activate intracellular responses that greatly vary depending on the brain area, stage of development and receptors expressed. Astrocytes also uptake and recycle BDNF / proBDNF at synapses contributing to synaptic plasticity. Finally, experimental evidence is now available describing deficits in astrocytic BDNF in several neuropathologies, suggesting that astrocytic BDNF may represent a promising target for clinical translation.

Effect of l-Dopa in acute temozolomide-induced cognitive impairment in male mice: a possible antineuroinflammatory role

Temozolomide is used commonly in the treatment of some types of cancers, but it may also result in cognitive impairments such as memory deficits. l-Dopa, a well known medicine for the central nervous system, has been shown to have positive effects on some cognitive disorders. Here we sought to investigate the effect of l-Dopa on temozolomide-induced cognitive impairments. BALB/c mice were subjected to 3-days temozolomide and 6-days concomitant l-Dopa/benserazide administration in six groups (control, l-Dopa 25 mg/kg, l-Dopa 75 mg/kg, temozolomide, temozolomide + l-Dopa 25 mg/kg, and temozolomide + l-Dopa 75 mg/kg). Open field test, object location recognition, novel object recognition test, and shuttle-box test were carried out to determine the locomotor, anxiety-like behavior, and memory function of subjects. TNF-α and brain-derived neurotrophic factor (BDNF) gene expression in the hippocampus was measured by real-time PCR. Mice treated with temozolomide showed recognition memory impairment, along with hippocampal TNF-α and BDNF mRNA expression level raise, and detection of histological insults in hematoxylin and eosin hippocampal slides. Mice that received temozolomide + l-Dopa showed normal behavioral function and lower TNF-α and BDNF hippocampal mRNA expression levels, and histologically normal hippocampal CA1 region in comparison with mice in the temozolomide group. Our results provide evidence that l-Dopa prevents temozolomide-induced recognition memory deficit in mice at the acute phase probably via l-Dopa antineuroinflammatory effects.

DAPTA, a C-C Chemokine Receptor 5 (CCR5), Leads to the Downregulation of Notch/NF-κB Signaling and Proinflammatory Mediators in CD40+ Cells in Experimental Autoimmune Encephalomyelitis Model in SJL/J Mice

Multiple sclerosis (MS) is an autoimmune inflammatory disease of the central nervous system characterized by motor deficits, cognitive impairment, fatigue, pain, and sensory and visual dysfunction. CD40, highly expressed in B cells, plays a significant role in MS pathogenesis. The experimental autoimmune encephalomyelitis (EAE) mouse model of MS has been well established, as well as its relevance in MS patients. This study aimed to evaluate the therapeutic potential of DAPTA, a selective C-C chemokine receptor 5 (CCR5) antagonist in the murine model of MS, and to expand the knowledge of its mechanism of action. Following the induction of EAE, DAPTA was administrated (0.01 mg/kg, i.p.) daily from day 14 to day 42. We investigated the effects of DAPTA on NF-κB p65, IκBα, Notch-1, Notch-3, GM-CSF, MCP-1, iNOS, and TNF-α in CD40⁺ spleen B cells using flow cytometry. Furthermore, we also analyzed the effect of DAPTA on NF-κB p65, IκBα, Notch-1, Notch-3, GM-CSF, MCP-1, iNOS, and TNF-α mRNA expression levels using qRT-PCR in brain tissue. EAE mice treated with DAPTA showed substantial reductions in NF-κB p65, Notch-1, Notch-3, GM-CSF, MCP-1, iNOS, and TNF-α but an increase in the IκBα of CD40⁺ B lymphocytes. Moreover, EAE mice treated with DAPTA displayed decreased NF-κB p65, Notch-1, Notch-3, GM-CSF, MCP-1, iNOS, and TNF-α and but showed increased IκBα mRNA expression levels. This study showed that DAPTA has significant neuroprotective potential in EAE via the downregulation of inflammatory mediators and NF-κB/Notch signaling. Collectively, DAPTA might have potential therapeutic targets for use in MS treatment.

Role of ATP in migraine mechanisms: focus on P2X3 receptors

Migraine is a major health burden worldwide with complex pathophysiology and multifarious underlying mechanisms. One poorly understood issue concerns the early steps in the generation of migraine pain. To elucidate the basic process of migraine pain further, it seems useful to consider key molecular players that may operate synergistically to evoke headache. While the neuropeptide CGRP is an important contributor, we propose that extracellular ATP (that generally plays a powerful nociceptive role) is also a major component of migraine headache, acting in concert with CGRP to stimulate trigeminal nociceptive neurons. The aim of the present focused review is to highlight the role of ATP activating its P2X3 membrane receptors selectively expressed by sensory neurons including their nerve fiber terminals in the meninges. Specifically, we present data on the homeostasis of ATP and related purines in the trigeminovascular system and in the CNS; the basic properties of ATP signalling at peripheral and central nerve terminals; the characteristics of P2X3 and related receptors in trigeminal neurons; the critical speed and persistence of P2X3 receptor activity; their cohabitation at the so-called meningeal neuro-immune synapse; the identity of certain endogenous agents cooperating with ATP to induce neuronal sensitization in the trigeminal sensory system; the role of P2X3 receptors in familial type migraine; the current state of P2X3 receptor antagonists and their pharmacological perspectives in migraine. It is proposed that the unique kinetic properties of P2X3 receptors activated by ATP offer an interesting translational value to stimulate future studies for innovative treatments of migraine pain.

The Role of Brain-Derived Neurotrophic Factor in Immune-Related Diseases: A Narrative Review

Brain-derived neurotrophic factor (BDNF) is a neurotrophin regulating synaptic plasticity, neuronal excitability, and nociception. It seems to be one of the key molecules in interactions between the central nervous system and immune-related diseases, i.e., diseases with an inflammatory background of unknown etiology, such as inflammatory bowel diseases or rheumatoid arthritis. Studies show that BDNF levels might change in the tissues and serum of patients during the course of these conditions, e.g., affecting cell survival and modulating pain severity and signaling pathways involving different neurotransmitters. Immune-related conditions often feature psychiatric comorbidities, such as sleep disorders (e.g., insomnia) and symptoms of depression/anxiety; BDNF may be related as well to them as it seems to exert an influence on sleep structure; studies also show that patients with psychiatric disorders have decreased BDNF levels, which increase after treatment. BDNF also has a vital role in nociception, particularly in chronic pain, hyperalgesia, and allodynia, participating in the formation of central hypersensitization. In this review, we summarize the current knowledge on BDNF's function in immune-related diseases, sleep, and pain. We also discuss how BDNF is affected by treatment and what consequences these changes might have beyond the nervous system.

Effect of treadmill exercise and bone marrow stromal cell engraftment on activation of BDNF-ERK-CREB signaling pathway in the crushed sciatic nerve

The effect of combined approach of exercise training and bone marrow stromal cell (BMSC) engraftment on activation of brain-derived neurotrophic factor (BDNF)-extracellular signal-regulated kinase 1 and 2 (ERK1/2)-cyclic adenosine monophosphate response element-binding protein (CREB) signaling pathway after sciatic nerve injury (SNI) was investigated. Sixty male Sprague-Dawley rats divided into the normal control, nonexercise (NEX), exercise training (EX), BMSC transplantation (TP), and exercise training+BMSC transplantation (EX+TP) groups 4 weeks after SCI. Exercise training was carried out on the treadmill device at 5-10 m/min for 20 min for 4 weeks. Single dose of 5×10⁶ harvested BMSC was injected into the injury area of the injured sciatic nerve. In order to evaluate induction levels of BDNF-ERK1/2-CREB signaling molecules in the whole cell and nuclear cell lysates of the injured sciatic nerve, we applied Western blot analysis. BDNF was significantly increased only in EX+TP compared to NEX, EX, and TP groups. Phosphoinositide-dependent kinase-1 was more increased in EX, TP, and EX+TP groups than NEX group, but EX+TP group showed the most upregulation of phosphorylated protein kinase B compared to other groups. In addition, in the whole cell lysate, phosphorylated ERK1/2, but not activating transcription factor-3 (ATF-3) and phosphorylated CREB, was significantly increased in TP and EX+TP groups. In the nuclear cell lysate, ATF-3 and phosphorylated CREB were strongly activated in EX+TP group compared to EX group. Regular exercise training combined with BMSC engraftment would seem to be more effective in controlling activation of regeneration-related signaling pathway after SNI.

Associations of Serum Cytokines, Growth Factors, and High-Sensitivity C-Reactive Protein Levels in Patients with Major Depression with and without Type 2 Diabetes Mellitus: An Explanatory Investigation

PURPOSE

We investigated the serum levels of cytokines, including interleukin 1β (IL-β), IL-6, IL-8, IL-10, tumor necrosis factor-alpha (TNF-α), and growth factors, including brain-derived neurotrophic factor, vascular endothelial growth factor, and insulin-like growth factor 1, and their association with major depression in patients with and without type 2 diabetes mellitus. We also investigated the response to antidepressant treatment in both groups.

PATIENTS AND METHODS

Forty-one patients with major depression were recruited at the University Hospital of Occupational and Environmental Health. All patients were diagnosed with major depression using the Diagnostic and Statistical Manual for Mental Disorders, Fifth Edition. Type 2 diabetes mellitus was diagnosed according to the criteria of the Japan Diabetes Society. Six healthy controls with no history of psychiatric or physical diseases were also enrolled. Serum levels of several cytokines, growth factors, and high-sensitivity C-reactive protein (hs-CRP) were measured. The clinical symptoms of patients with major depression were assessed using the Montgomery-Asberg Depression Rating Scale.

RESULTS

Significant differences in cytokines, growth factors, and hs-CRP were observed between the major depression and healthy control groups. Serum TNF-α levels were significantly higher in patients with major depression and type 2 diabetes mellitus than in those without type 2 diabetes mellitus. In the major depression group, serum IL-6 and hs-CRP levels tended to be higher in patients with type 2 diabetes mellitus than in those without. Several correlations among cytokines, growth factors, and hs-CRP were observed in patients with major depression with and without type 2 diabetes mellitus. Responses to pharmacological interventions for major depression did not differ between patients with and without type 2 diabetes mellitus.

CONCLUSION

Serum levels of TNF-α, hs-CRP, and IL-6 were different between patients with major depression with and without type 2 diabetes mellitus. Also, correlations were found between serum levels of cytokines, growth factors, and hs-CRP in patients with major depression. Inflammatory factors, which may be associated with growth factors, may be involved in the pathophysiology of major depression, particularly among patients with comorbid type 2 diabetes mellitus.

The ratio and interaction between neurotrophin and immune signaling during electroconvulsive therapy in late-life depression

Background

Electroconvulsive therapy (ECT) is the most effective treatment for severe late-life depression (LLD), and several hypotheses on the precise working mechanism have been proposed. Preclinical evidence suggests that ECT induces changes in neurotrophin and inflammatory signaling and that these neurotrophic and inflammatory systems affect each other. We examine the relation, interaction, and ratio between the neurotrophic brain-derived neurotrophic factor (BDNF) and the proinflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor α (TNF-α), and depression severity during ECT.

Methods

In this naturalistic longitudinal study, linear mixed models were used to analyze the relation between BDNF, IL-6, TNF-α, and depression severity (determined by the Montgomery-Åsberg Depression Rating Scale; MADRS) in 99 patients with severe LLD before ECT (T0), three weeks after the first ECT (T1), and one week after the last ECT (T2).

Results

No significant association was found between BDNF, IL-6 and TNF-α, and MADRS scores at any time point. However, a significant interaction between TNF-α and BDNF in relation to MADRS was established (p ​= ​.020) at all time points. With higher levels of TNF-α, the relation between BDNF and MADRS becomes more negative. Furthermore, a higher ratio of TNF-α/BDNF was associated with a higher score on the MADRS (p ​= ​.007).

Conclusion

A possible explanation for the absence of a significant coevolution between the proinflammatory cytokines and BDNF could be that the study design was unable to determine parameters shortly after ECT sessions. However, the TNF-α/BDNF ratio was positively associated with depression severity, and the association of BDNF-level and depression severity depended on the level of TNF-α. This suggests that the interaction and balance between neurotrophin and immune signaling, specifically BDNF and TNF-α, could be relevant in LLD. This could be a focus in future research regarding treatment and the working mechanism of ECT.

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IL-6 and TNF-α, BDNF, and depression severity were not significantly associated.

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The TNF-α/BDNF ratio is positively associated with depression severity.

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The association of BDNF-levels and depression severity depends on the level of TNF-α.

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Interplay between neurotrophin and immune signaling could be relevant in LLD.

Activation of the trigeminal system as a likely target of SARS-CoV-2 may contribute to anosmia in COVID-19

Clinical publications show consistently that headache is a common symptom in the coronavirus disease of 2019 (COVID-19). Several studies specifically investigated headache symptomatology and associated features in patients with COVID-19. The headache is frequently debilitating with manifold characters including migraine-like characteristics. Studies suggested that COVID-19 patients with headache vs. those without headache are more likely to have anosmia. We present a pathophysiological hypothesis which may explain this phenomenon, discuss current hypotheses about how the coronavirus SARS-CoV-2 enters the central nervous system and suggest that activation of the trigeminal nerve may contribute to both headache and anosmia in COVID-19.

Brain-derived neurotrophic factor is elevated in the blood serum of Crohn's disease patients, but is not influenced by anti-TNF-α treatment-A pilot study

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is associated with depression, pain, or sleep disorders, factors that are thought to be involved in the pathogenesis and clinical course of Crohn's disease (CD). Therefore, the study aimed at assessing the BDNF serum level in patients with CD and evaluates the effect of anti-TNF-α therapy on the BDNF level and its impact on sleep, mood, and pain parameters.

METHODS

Fifty-eight CD patients and 26 healthy controls (HC) were included in the study. The severity of insomnia symptoms was assessed by the Athens Insomnia Scale (AIS). Subjective pain intensity was estimated by the Visual Analogue Scale (VAS) and Laitinen Pain Scale. Mood level was measured using the Beck Depression Inventory (BDI). Seventeen patients were treated with anti-TNF-α therapy for 14 weeks and were re-examined after treatment.

KEY RESULTS

CD patients had a higher serum BDNF level than HC (P = .010). No correlation between clinical severity and BDNF was found. There were positive correlations between the BDNF level and the results of AIS (r = 0.253, P = .020), the severity of pain measured using the VAS (r = 0.251, P = .021) and the Laitinen Pain Scale (r = 0.218, P = .047), but not BDI. No differences were observed in the BDNF level before and after 14 weeks of anti-TNF-α therapy.

CONCLUSIONS AND INFERENCES

Increased BDNF level in CD patients suggests that it may be involved in the pathogenesis and clinical course of the disease. Further research into BDNF might contribute to a better understanding of the effects of sleep and pain on the course of CD.

Effects of the Prenatal Administration of Tetanus Toxoid on the Sociability and Explorative Behaviors of Rat Offspring: A Preliminary Study

Objective

Autism spectrum disorder (ASD) is a severely disabling psychiatric disease characterized by impairments in communication and social skills. Although efforts have been made to explore the etiology of ASD, its pathophysiology remains unclear. This issue is rendered more challenging by confounding data about the effects of vaccination on disease etiology. In this study, therefore, we investigated the neurodevelopmental effects of maternal tetanus toxoid administration on rat offspring. We hypothesized that the vaccine affects the sociability and preference for social novelty of rat offspring as well as the production of immunological and neurotrophic factors, including tumor necrosis factor-alfa (TNF-α), neuregulin-1 (NRG-1), neuron growth factor (NGF), and oxytocin.

Methods

The study involved 12 female and 4 male adult Sprague-Dawley rats (238 ± 10 g), which were assigned to two groups. Group 1 (control group) was given 0.5 ml of normal saline (0.9% NaCl) on the 10th day of pregnancy, whereas Group 2 (experimental group) was administered 0.5 ml of tetanus vaccine (tetanus toxoid, 40 IU).

Results

Maternal tetanus toxoid administration exerted beneficial effects on the sociability and explorative behaviors of the rats. The brain tissue levels of TNF-α, NGF, NRG-1, and oxytocin were higher in the experimental group than those among the controls. All these significant differences were found in both the male and female rats.

Conclusion

This study is the first to demonstrate the advantages of tetanus toxoid administration in relation to the sociability and explorative behaviors of rat offspring. The results showed that the vaccine also influences NRG-1, neuregulin, and oxytocin production.

Exercise in Treatment of Migraine Including Chronic Migraine

PURPOSE OF REVIEW

With this review, we aimed to investigate the effect of exercise on migraine and explored the possibility of exercise as a treatment option for migraine.

RECENT FINDINGS

A close association of physical activity and exercise with migraine has been reported in clinical and population-based studies. Recent randomized controlled trials investigating the effect of aerobic exercise as a migraine-preventive treatment have revealed a notable improvement in migraine symptoms. Data on the effect of anaerobic exercise and exercise for flexibility, coordination, and relaxation on migraine are currently insufficient to make any recommendations. Possible pathways for the attenuation of migraine by exercise include the endogenous opioid and cannabinoid systems, brain-derived neurotrophic factor, inflammation, and behavioral/psychological factors. Regarding efficacy, side effects, and health benefits, aerobic exercise is a potentially beneficial strategy in the preventive treatment of migraine. Further studies are needed to delineate an evidence-based exercise program for migraine treatment.

Mechanistic aspects of photobiomodulation therapy in the nervous system

Photobiomodulation therapy (PBMT) previously known as low-level laser therapy (LLLT) has been used for over 30 years, to treat neurological diseases. Low-powered lasers are commonly used for clinical applications, although recently LEDs have become popular. Due to the growing application of this type of laser in brain and neural-related diseases, this review focuses on the mechanisms of laser action. The most important points to consider include the photon absorption by intracellular structures; the effect on the oxidative state of cells; and the effect on the expression of proteins involved in oxidative stress, inflammation, pain, and neuronal growth.

The Effect of Endurance Training on Brain-Derived Neurotrophic Factor and Inflammatory Markers in Healthy People and Parkinson's Disease. A Narrative Review

Background: One purpose of the training conducted by people is to lose bodyweight and improve their physical condition. It is well-known that endurance training provides many positive changes in the body, not only those associated with current beauty standards. It also promotes biochemical changes such as a decreased inflammatory status, memory improvements through increased brain-derived neurotrophic factor levels, and reduced stress hormone levels. The positive effects of training may provide a novel solution for people with Parkinson's disease, as a way to reduce the inflammatory status and decrease neurodegeneration through stimulation of neuroplasticity and improved motor conditions. Aim: This narrative review aims to focus on the relationship between an acute bout of endurance exercise, endurance training (continuous and interval), brain-derived neurotrophic factor and inflammatory status in the three subject groups (young adults, older adult, and patients with Parkinson's disease), and to review the current state of knowledge about the possible causes of the differences in brain-derived neurotrophic factor and inflammatory status response to a bout of endurance exercise and endurance training. Furthermore, short practical recommendations for PD patients were formulated for improving the efficacy of the training process during rehabilitation. Methods: A narrative review was performed following an electronic search of the database PubMed/Medline and Web of Science for English-language articles between January 2010 and January 2020. Results: Analysis of the available publications with partial results revealed (1) a possible connection between the brain-derived neurotrophic factor level and inflammatory status, and (2) a more beneficial influence of endurance training compared with acute bouts of endurance exercise. Conclusion: Despite the lack of direct evidence, the results from studies show that endurance training may have a positive effect on inflammatory status and brain-derived neurotrophic factor levels. Introducing endurance training as part of the rehabilitation in Parkinson's disease might provide benefits for patients in addition to pharmacological therapy supplementation.

Electroacupuncture Inhibits Hyperalgesia by Alleviating Inflammatory Factors in a Rat Model of Migraine

Objective

Acupuncture has a therapeutic effect similar to that of prophylactic drugs and can be considered a treatment option for migraineurs. However, the mechanism of acupuncture treatment's effect on migraine is uncertain. An approach based on anti-inflammatory effects is an important treatment strategy for migraine because non-steroidal anti-inflammatory drugs (NSAIDs) are usually used during migraine attacks. Meningeal inflammation is thought to be responsible for the activation of the trigeminovascular system. Our previous study found that electroacupuncture (EA) decreased neurogenic inflammation mediator expression in the trigeminal ganglion (TG) and alleviated hyperalgesia. The present study examined whether EA would inhibit hyperalgesia by alleviating neurogenic inflammatory factors.

Methods

A rat model of migraine was established using dural electrical stimulation (DES). Five groups were analyzed in this study. The Model group received DES three times to mimic migraine attacks, a Control group had sham DES, and three groups received electroacupuncture after DES: a Non-Acu group at a non-acupuncture point, a GB20 group at GB20, and a GB20/34 group at GB20 and GB34 acupuncture points. We evaluated mechanical hyperalgesia using an electronic von Frey esthesiometer in the awake state. After sacrifice, the dura mater was analyzed using immunofluorescence. Serum calcitonin gene-related peptide, cyclooxygenase-2, brain-derived neurotrophic factor, IL-1β, IL-6, and TNF levels were determined using enzyme-linked immunosorbent assays to evaluate the anti-inflammatory effect of acupuncture.

Results

After repeated DES, we observed facial and hind paw mechanical hyperalgesia, which was inhibited by electroacupuncture. Electrical stimulation increased the number of mast cells and macrophages and serum levels of inflammatory factors. GB20 and GB20/34 electroacupuncture significantly decreased the number of mast cells and macrophages and serum levels of inflammatory factors. Moreover, electroacupuncture at GB20/34 was superior to that at GB20 alone in inhibiting hyperalgesia and alleviating inflammatory factors.

Conclusion

Electroacupuncture inhibits DES-induced hyperalgesia by alleviating inflammatory factors. Inhibition of dural mast cells, macrophages, and serum inflammatory factors may be one of the mechanisms involved in acupuncture treatment's effect on migraine.

BDNF promotes activation of astrocytes and microglia contributing to neuroinflammation and mechanical allodynia in cyclophosphamide-induced cystitis

BACKGROUND

Patients with interstitial cystitis/bladder pain syndrome (IC/BPS) often grieve over a low quality of life brought about by chronic pain. In our previous studies, we determined that neuroinflammation of the spinal dorsal horn (SDH) was associated with mechanisms of interstitial cystitis. Moreover, it has been shown that brain-derived neurotrophic factor (BDNF) participates in the regulation of neuroinflammation and pathological pain through BDNF-TrkB signaling; however, whether it plays a role in cyclophosphamide (CYP)-induced cystitis remains unclear. This study aimed to confirm whether BDNF-TrkB signaling modulates neuroinflammation and mechanical allodynia in CYP-induced cystitis and determine how it occurs.

METHODS

Systemic intraperitoneal injection of CYP was performed to establish a rat cystitis model. BDNF-TrkB signaling was modulated by intraperitoneal injection of the TrkB receptor antagonist, ANA-12, or intrathecal injection of exogenous BDNF. Mechanical allodynia in the suprapubic region was assessed using the von Frey filaments test. The expression of BDNF, TrkB, p-TrkB, Iba1, GFAP, p-p38, p-JNK, IL-1β, and TNF-α in the L6-S1 SDH was measured by Western blotting and immunofluorescence analysis.

RESULTS

BDNF-TrkB signaling was upregulated significantly in the SDH after CYP was injected. Similarly, the expressions of Iba1, GFAP, p-p38, p-JNK, IL-1β, and TNF-α in the SDH were all upregulated. Treatment with ANA-12 could attenuate mechanical allodynia, restrain activation of astrocytes and microglia and alleviate neuroinflammation. Besides, the intrathecal injection of exogenous BDNF further decreased the mechanical withdrawal threshold, promoted activation of astrocytes and microglia, and increased the release of TNF-α and IL-1β in the SDH of our CYP-induced cystitis model.

CONCLUSIONS

In our CYP-induced cystitis model, BDNF promoted the activation of astrocytes and microglia to release TNF-α and IL-1β, aggravating neuroinflammation and leading to mechanical allodynia through BDNF-TrkB-p38/JNK signaling.

Tumor necrosis factor alpha mediates orofacial discomfort in an occlusal dental interference model in rats: The role of trigeminal ganglion inflammation

BACKGROUND

Tumor necrosis factor alpha (TNF-α) is a proinflammatory cytokine that plays an important role in the early stages of inflammation. In this study, we investigated its role in orofacial discomfort in rats subjected to occlusal dental interference (ODI).

METHODS

Female Wistar rats (180-200 g) were divided in three groups (n = 30/group): sham group, without ODI, and two experimental groups with ODI pre-treated with 0.1 mL/kg saline (ODI + SAL) or 5 mg/kg infliximab (ODI + INF) and treated every 3 days. The animals were euthanized after 1, 3, and 7 days. The number of bites and scratches and grimace scale scores were determined daily, and the bilateral trigeminal ganglion was histomorphometrically (neuronal body area) analyzed and submitted for immunohistochemistry for TNF-α, nitric oxide synthesis (NOS) neuronal (nNOS) and inducible (iNOS), peroxisome proliferator-activated receptors (PPAR) y (PPARy) and δ/β (PPARδ/β), and glial fibrillary acidic protein (GFAP). One-way/two-way ANOVA/Bonferroni tests were used (P < .05, GraphPad Prism 5.0).

RESULTS

ODI + SAL showed a large number of bites (P = .002), scratches (P = .002), and grimace scores (P < .001) in the firsts days, and ODI + INF partially reduced these parameters. The contralateral and ipsilateral neuronal body area was significantly reduced on day 1 in ODI + SAL, but returned to the basal size on days 3 and 7, by increase in TNF-α, nNOS, PPARy, PPARδ/β, and GFAP immunostaining. The infliximab treatment attenuated these alterations (P < .05). There was no iNOS immunostaining.

CONCLUSION

Occlusal dental interference induced transitory orofacial discomfort by trigeminal inflammatory mediator overexpression, and TNF-α blockage attenuated these processes.

The role of galectin-3 in modulation of anxiety state level in mice

Galectin-3 (Gal-3), a member of lectin family that binds to oligosaccharides, is involved in several biological processes, including maturation and function of nervous system. It had been reported that Gal-3 regulates oligodendrocytes differentiation and that Gal-3/Toll-like receptor-4 (TLR4) axis is involved in neuroinflammation. As both, central nervous system (CNS) maturation and neuroinflammation may affect behavior, the principle aim of this study was to examine the effects of Gal-3 gene deletion on behavior. Here we provide the evidence that Gal-3 deficiency shows clear anxiogenic effect in mature untreated animals (basal conditions). This was accompanied with lower interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) relative gene expression and hippocampal content, with no effect on TLR4 expression. Gal-3 deficiency was also accompanied with lower brain-derived neurotrophic factor (BDNF) relative gene expression and immunoreactivity in hippocampus (predominantly in CA1 region). Besides, the Gal-3 gene deletion resulted in attenuation of the hippocampal relative gene expression of GABA-A receptor subunits 2 and 5 (GABA-AR2S and GABA-AR5S), On the other hand, Gal-3 deficiency attenuates LPS-induced neuroinflammation. The anxiogenic effect of acute neuroinflammation was accompanied with increased hippocampal IL-6, TNF-α and TLR4 gene expression, as well as decreased gene and immunohistochemical BDNF expression in hippocampus, with significant decline in GABA-AR2S in wild type (WT) mice in comparison to basal conditions. Gal-3 gene deletion prevented the increase in IL-6, the decline in BDNF gene expression and immunoreactivity, and reduction in hippocampal GABA-AR2S, and therefore attenuated the anxiogenic effect of neuroinflammation. In summary, our data demonstrate that apparently opposite effects of Gal-3 deficiency on anxiety levels (anxiogenic effect under basal conditions and anxiolytic action during neuroinflammation) seem to be related to the shift in IL-6, TNF-α and hippocampal BDNF.

The Impact of High-Intensity Interval Training on Brain Derived Neurotrophic Factor in Brain: A Mini-Review

The brain-derived neurotrophic factor (BDNF) is a protein mainly synthetized in the neurons. Early evidence showed that BDNF participates in cognitive processes as measured at the hippocampus. This neurotrophin is as a reliable marker of brain function; moreover, recent studies have demonstrated that BDNF participates in physiological processes such as glucose homeostasis and lipid metabolism. The BDNF has been also studied using the exercise paradigm to determine its response to different exercise modalities; therefore, BDNF is considered a new member of the exercise-related molecules. The high-intensity interval training (HIIT) is an exercise protocol characterized by low work volume performed at a high intensity [i.e., ≥80% of maximal heart rate (HRmax)]. Recent evidence supports the contention that HIIT elicits higher fat oxidation in skeletal muscle than other forms of exercise. Similarly, HIIT is a good stimulus to increase maximal oxygen uptake (VO₂max). Few studies have investigated the impact of HIIT on the BDNF response. The present work summarizes the effects of acute and long-term HIIT on BDNF.

The association between migraine and physical exercise

BACKGROUND

There is an unmet need of pharmacological and non-pharmacological treatment options for migraine patients. Exercise can be used in the treatment of several pain conditions, including. However, what exact role exercise plays in migraine prevention is unclear. Here, we review the associations between physical exercise and migraine from an epidemiological, therapeutical and pathophysiological perspective.

METHODS

The review was based on a primary literature search on the PubMed using the search terms "migraine and exercise".

RESULTS

Low levels of physical exercise and high frequency of migraine has been reported in several large population-based studies. In experimental studies exercise has been reported as a trigger factor for migraine as well as migraine prophylaxis. Possible mechanisms for how exercise may trigger migraine attacks, include acute release of neuropeptides such as calcitonin gene-related peptide or alternation of hypocretin or lactate metabolism. Mechanisms for migraine prevention by exercise may include increased beta-endorphin, endocannabinoid and brain-derived neurotrophic factor levers in plasma after exercise.

CONCLUSION

In conclusion, it seems that although exercise can trigger migraine attacks, regular exercise may have prophylactic effect on migraine frequency. This is most likely due to an altered migraine triggering threshold in persons who exercise regularly. However, the frequency and intensity of exercise that is required is still an open question, which should be addressed in future studies to delineate an evidence-based exercise program to prevent migraine in sufferers.

The Cerebral Brain-Derived Neurotrophic Factor Pathway, Either Neuronal or Endothelial, Is Impaired in Rats with Adjuvant-Induced Arthritis. Connection with Endothelial Dysfunction

Cognitive abilities are largely dependent on activation of cerebral tropomyosin-related kinase B receptors (TrkB) by brain-derived neurotrophic factor (BDNF) that is secreted under a bioactive form by both neurons and endothelial cells. In addition, there is mounting evidence for a link between endothelial function and cognition even though the underlying mechanisms are not well known. Therefore, we investigated the cerebral BDNF pathway, either neuronal or endothelial, in rheumatoid arthritis (RA) that combines both endothelial dysfunction (ED) and impaired cognition. Adjuvant-induced arthritis (AIA) in rats was used as a model of RA. Clinical inflammatory symptoms were evaluated from an arthritis score and brains were collected at day 31 ± 2 post-immunization. Neuronal expression of BDNF and TrkB phosphorylated at tyrosine 816 (p-TrkB) was examined in brain slices. Endothelial BDNF and p-TrkB expression was examined on both brain slices (hippocampal arterioles) and isolated cerebral microvessels-enriched fractions (vessels downstream to arterioles). The connection between endothelial nitric oxide (NO) and BDNF production was explored on the cerebrovascular fractions using endothelial NO synthase (eNOS) levels as a marker of NO production, N^ω-Nitro-L-arginine methyl ester hydrochloride (L-NAME) as a NOS inhibitor and glyceryl-trinitrate as a slow releasing NO donor. Brain slices displayed lower BDNF and p-TrkB staining in both neurons and arteriolar endothelial cells in AIA than in control rats. For endothelial cells but not neurons, a strong correlation was observed between BDNF and p-TrkB staining. Of note, a strong correlation was also observed between neuronal p-TrkB and endothelial BDNF staining. In cerebral microvessels-enriched fractions, AIA led to decreased BDNF and eNOS levels with a positive association between the 2 parameters. These effects coincided with decreased BDNF and p-TrkB staining in endothelial cells. The exposure of AIA cerebrovascular fractions to GTN increased BDNF levels while the exposure of control fractions to L-NAME decreased BDNF levels. Changes in the cerebral BDNF pathway were not associated with arthritis score. The present study reveals that AIA impairs the endothelial and neuronal BDNF/TrkB pathway, irrespective of the severity of inflammatory symptoms but dependent on endothelial NO production. These results open new perspectives for the understanding of the link between ED and impaired cognition.

Fascin-1 Contributes to Neuropathic Pain by Promoting Inflammation in Rat Spinal Cord

Neuropathic pain is a complicated clinical syndrome caused by heterogeneous etiology. Despite the fact that the underlying mechanisms remain elusive, it is well accepted that neuroinflammation plays a critical role in the development of neuropathic pain. Fascin-1, an actin-bundling protein, has been proved to be involved in the processing of diverse biological events including cellular development, immunity, and tumor invasion etc. Recent studies have shown that Fascin-1 participates in antigen presentation and the regulation of pro-inflammatory agents. However, whether Fascin-1 is involved in neuropathic pain has not been reported. In the present study we examined the potential role of Fascin-1 by using a rodent model of chronic constriction injury (CCI). Our results showed that Fascin-1 increased rapidly in dorsal root ganglions (DRG) and spinal cord (SC) after CCI. The increased Fascin-1 widely expressed in DRG, however, it localized predominantly in microglia, seldom in neuron, and hardly in astrocyte in the SC. Intrathecal injection of Fascin-1 siRNA not only suppressed the activation of microglia and the release of pro-inflammatory mediators, but also attenuated the mechanical allodynia and thermal hyperalgesia induced by CCI.

Inhibition of TNF reduces mechanical orofacial hyperalgesia induced by Complete Freund's Adjuvant by a TRPV1-dependent mechanism in mice

BACKGROUND

Inflammation in the orofacial region results in pain and is associated with many pathological states, including migraine, neuralgias and temporomandibular disorder. Although extensively studied, the mechanisms responsible for these conditions are not known and effective treatments are lacking. We reported earlier that the proinflammatory cytokine tumor necrosis factor (TNF) plays an important role in regulation of trigeminal ganglion (TG) neuron function in vitro. In the present study we investigated the role of TNF in mechanical hypersensitivity in mice.

METHODS

We employed the Complete Freund's Adjuvant (CFA)-induced model of orofacial pain and evaluated the effect of blocking of soluble TNF activity by peripheral administration of the novel dominant negative TNF biologic, XPro1595.

RESULTS

We show that CFA administration into the lower lip causes hyperalgesia and an increase in both expression of transient receptor potential vanilloid subfamily member 1 (TRPV1) mRNA and in the average intensity of TRPV1 protein immunoreactivity in TG neurons. We also show that intraperitoneal administration of XPro1595 prevents both CFA-induced mechanical hypersensitivity and, as shown in immunohistochemical staining - upregulation of TRPV1 protein expression in TG neurons.

CONCLUSIONS

We conclude that one of the possible regulatory mechanisms of TNF in pain involves upregulation of the nociceptor TRPV1, and that peripheral treatment with a selective anti-soluble TNF biologic can prevent hyperalgesia caused by inflammation in the orofacial region. Therefore, these new findings suggest that XPro1595 may serve as a novel treatment for orofacial pain disorders.

Involvement of BDNF/TrkB and ERK/CREB axes in nitroglycerin-induced rat migraine and effects of estrogen on these signals in the migraine

Migraine is a highly prevalent headache disorder, especially in women. Brain-derived neurotrophic factor (BDNF) and its receptor tropomyosin receptor kinases (TrkB), as well as extracellular signal-regulated kinase (ERK) and its downstream target c-AMP-responsive element binding protein (CREB) are strongly associated with the transmission of nociceptive information. However, the involvement of these substances in migraine has rarely been examined. In the present study, intraperitoneal injection of nitroglycerin (NTC) successfully induced rat migraine attack, as evidenced by behavioral testing. The location and abundance of these substances in the migraine model were determined by immunohistochemistry, real-time polymerase chain reaction (RT-PCR), western blot and enzyme-linked immunosorbant assays (ELISA). Results showed that BDNF, TrkB, phosphor(p)-ERK and p-CREB were up-regulated in the brain neurons of both male and female rats with NTG-induced migraine compared to non-migraine control, whereas their expression levels were decreased in headache-free intervals of the migraine compared to migraine attacks. Estrogen is an important contributor to migraine. Female ovariectomized rats showed significant reduction in the expression of BDNF, TrkB, p-CREB and p-ERK in both attacks and intervals of NTG-induced migraine, relative to rats that have their ovaries. But, intraperitoneal administration of exogenous estrogen recovered their expression in ovariectomized rats. Collectively, this study unveiled a positive correlation of BDNF/TrkB and ERK/CREB axes in NTG-induced migraine and promoting effects of estrogen on their signals in the migraine. These findings contribute to further understanding the pathogenesis of migraine in the molecular basis.

Summary: This study unveiled a positive correlation of BDNF/TrkB and CREB/ERK axes in NTG-induced migraine and the promoting effects of estrogen on their signals in the migraine.

Neurotrophins and Migraine

Neurotrophins (NTs) have been implicated in generation and modulation of nociceptive pathways. Change in NTs levels is associated with painful conditions and neurological diseases such as migraine. Currently, it is generally recognized that migraine headaches result from the activation and sensitization of trigeminal sensory afferent fibers leading to neuropeptides release such as calcitonin gene-related peptide (CGRP) and substance P (SP). This triggers an inflammatory cascade causing a neurogenic inflammation. The agents responsible for trigeminal activation and release of neuropeptides are still unclear. It is known that the transient receptor potential vanilloid receptor-1 (TRPV1) is an important mediator of CGRP and SP release. TRPV1 is closely associated with tyrosine receptors kinases (Trk), which are NTs receptors. NTs can act on TRPV1 increasing its sensitivity to painful stimuli, therefore predisposing to hyperalgesia. Upregulation of ion channels and pain receptors in dorsal root ganglion neurons may be alternative mechanisms by which NTs contribute to pain development. Only a few studies have been performed to investigate the role of NTs in migraine. These studies have reported changes in NTs levels in migraine patients either during the migraine attack or in free-headache periods.

Traumatic neuroma of the superficial peroneal nerve in a patient: a case report and review of the literature

BACKGROUND

Traumatic neuromas are rare benign tumors, which are common in trauma or post-operation and accompanied with obvious symptoms of pain. This study will show the superficial peroneal nerve neuroma occurring after resection of hemangioma.

CASE PRESENTATION

A 44-year-old male had an operation of the right leg cavernous hemangioma resection in 1995. Half a year after the operation, pain around the wound appeared and gradually aggravated. The patient had the lesion exploration resection in 2013, and the pathological result showed traumatic neuroma. Within half a year of the second operation, severe pain showed up again, so neuroma resection proceeded in May 2015. The postoperative pathological and immunohistochemical results showed traumatic neuroma. According to the postoperative follow-up, there were no symptoms of pain appearing again.

LITERATURE REVIEW

The pain is obvious, and B ultrasonography is the most efficient way to find neuromas. Both conservative and operative therapy have their advantages and disadvantages.

CONCLUSIONS

There remain many unanswered questions in relation to the treatment of traumatic neuromas, and further research is required, although we have already had adequate understanding of traumatic neuromas.

Plasticity in respiratory motor neurons in response to reduced synaptic inputs: A form of homeostatic plasticity in respiratory control?

For most individuals, the respiratory control system produces a remarkably stable and coordinated motor output-recognizable as a breath-from birth until death. Very little is understood regarding the processes by which the respiratory control system maintains network stability in the presence of changing physiological demands and network properties that occur throughout life. An emerging principle of neuroscience is that neural activity is sensed and adjusted locally to assure that neurons continue to operate in an optimal range, yet to date, it is unknown whether such homeostatic plasticity is a feature of the neurons controlling breathing. Here, we review the evidence that local mechanisms sense and respond to perturbations in respiratory neural activity, with a focus on plasticity in respiratory motor neurons. We discuss whether these forms of plasticity represent homeostatic plasticity in respiratory control. We present new analyses demonstrating that reductions in synaptic inputs to phrenic motor neurons elicit a compensatory enhancement of phrenic inspiratory motor output, a form of plasticity termed inactivity-induced phrenic motor facilitation (iPMF), that is proportional to the magnitude of activity deprivation. Although the physiological role of iPMF is not understood, we hypothesize that it has an important role in protecting the drive to breathe during conditions of prolonged or intermittent reductions in respiratory neural activity, such as following spinal cord injury or during central sleep apnea.

Adrenomedullin mediates tumor necrosis factor-α-induced responses in dorsal root ganglia in rats

Adrenomedullin (AM), a member of the calcitonin gene-related peptide (CGRP) family, has been demonstrated to be a pain peptide. This study investigated the possible involvement of AM in tumor necrosis factor-alpha (TNF-α)-induced responses contributing to neuronal plasticity in the dorsal root ganglia (DRG). Exposure of the DRG explant cultures to TNF-α (5nM) for 48h upregulated the expression of AM mRNA. The treatment with TNF-α also increased the level of CGRP, CCL-2 and MMP-9 mRNA in the cultured DRG. This increase was attenuated by the co-treatment with the selective AM receptor antagonist AM22-52 (2μM). The blockade of AM receptors inhibited TNF-α-induced increase of the glial fibrillary acidic protein (GFAP), interleukin-1β (IL-1β), phosphorylated cAMP response element binding protein (pCREB) and nuclear factor kappa B (pNF-κB) proteins. On the other hand, the treatment with the AM receptor agonist AM1-50 (10nM) for 96h induced an increase in the level of GFAP, IL-1β, pCREB and pNF-κB proteins. The inhibition of AM activity did not change TNF-α-induced phosphorylation of extracellular signal-related kinase (pERK) while the treatment with AM1-50 still increased the level of pERK in the cultured DRG. Immunofluorescence assay showed the colocalization of AM-like immunoreactivity (IR) with TNF-α-IR in DRG neurons. The present study suggests that the increased AM receptor signaling mediated the many, but not all, TNF-α-induced activities, contributing to peripheral sensitization in neuropathic pain.

Cellular mechanisms of activity-dependent BDNF expression in primary sensory neurons

Brain-derived neurotrophic factor (BDNF) is abundantly expressed by both developing and adult rat visceral sensory neurons from the nodose ganglion (NG) in vivo and in vitro. We have previously shown that BDNF is released from neonatal NG neurons by activity and regulates dendritic development in their postsynaptic targets in the brainstem. The current study was carried out to examine the cellular and molecular mechanisms of activity-dependent BDNF expression in neonatal rat NG neurons, using our established in vitro model of neuronal activation by electrical field stimulation with patterns that mimic neuronal activity in vivo. We show that BDNF mRNA (transcript 4) increases over threefold in response to a 4-h tonic or bursting pattern delivered at the frequency of 6 Hz, which corresponds to the normal heart rate of a newborn rat. No significant increase in BDNF expression was observed following stimulation at 1 Hz. The latter effect suggests a frequency-dependent mechanism of regulated BDNF expression. In addition to BDNF transcript 4, which is known to be regulated by activity, transcript 1 also showed significant upregulation. The increases in BDNF mRNA were followed by BDNF protein upregulation of a similar magnitude after 24h of stimulation at 6 Hz. Electrical stimulation-evoked BDNF expression was inhibited by pretreating neurons with the blocker of voltage-gated sodium channels tetrodotoxin and by removing extracellular calcium. Moreover, our data show that repetitive stimulation-evoked BDNF expression requires calcium influx through N-, but not L-type, channels. Together, our study reveals novel mechanisms through which electrical activity stimulates de novo synthesis of BDNF in sensory neurons, and points to the role of N-type calcium channels in regulating BDNF expression in sensory neurons in response to repetitive stimulation.

Induction of Interleukin-1β by Human Immunodeficiency Virus-1 Viral Proteins Leads to Increased Levels of Neuronal Ferritin Heavy Chain, Synaptic Injury, and Deficits in Flexible Attention

Synaptodendritic pruning and alterations in neurotransmission are the main underlying causes of HIV-associated neurocognitive disorders (HAND). Our studies in humans and nonhuman primates indicated that the protein ferritin heavy chain (FHC) is a critical player in neuronal changes and ensuing cognitive deficit observed in these patients. Here we focus on the effect of HIV proteins and inflammatory cytokines implicated in HAND on neuronal FHC levels, dendritic changes, and neurocognitive behavior. In two well characterized models of HAND (HIV transgenic and gp120-treated rats), we report reductions in spine density and dendritic branches in prefrontal cortex pyramidal neurons compared with age-matched controls. FHC brain levels are elevated in these animals, which also show deficits in reversal learning. Moreover, IL-1β, TNF-α, and HIV gp120 upregulate FHC in rat cortical neurons. However, although the inflammatory cytokines directly altered neuronal FHC, gp120 only caused significant FHC upregulation in neuronal/glial cocultures, suggesting that glia are necessary for sustained elevation of neuronal FHC by the viral protein. Although the envelope protein induced secretion of IL-1β and TNF-α in cocultures, TNF-α blockade did not affect gp120-mediated induction of FHC. Conversely, studies with an IL-1β neutralizing antibody or specific IL-1 receptor antagonist revealed the primary involvement of IL-1β in gp120-induced FHC changes. Furthermore, silencing of neuronal FHC abrogates the effect of gp120 on spines, and spine density correlates negatively with FHC levels or cognitive deficit. These results demonstrate that viral and host components of HIV infection increase brain expression of FHC, leading to cellular and functional changes, and point to IL-1β-targeted strategies for prevention of these alterations. Significance statement: This work demonstrates the key role of the cytokine IL-1β in the regulation of a novel intracellular mediator [i.e., the protein ferritin heavy chain (FHC)] of HIV-induced dendritic damage and the resulting neurocognitive impairment. This is also the first study that systematically investigates dendritic damage in layer II/III prefrontal cortex neurons of two different non-infectious models of HIV-associated neurocognitive disorders (HAND) and reveals a precise correlation of these structural changes with specific biochemical and functional alterations also reported in HIV patients. Overall, these data suggest that targeting the IL-1β-dependent FHC increase may represent a valid strategy for neuroprotective adjuvant therapies in HAND.

Toll-like receptor 4 signaling in neurons of trigeminal ganglion contributes to nociception induced by acute pulpitis in rats

Pain caused by acute pulpitis (AP) is a common symptom in clinical settings. However, its underlying mechanisms have largely remained unknown. Using AP model, we demonstrated that dental injury caused severe pulp inflammation with up-regulated serum IL-1β. Assessment from head-withdrawal reflex thresholds (HWTs) and open-field test demonstrated nociceptive response at 1 day post injury. A consistent up-regulation of Toll-like receptor 4 (TLR4) in the trigeminal ganglion (TG) ipsilateral to the injured pulp was found; and downstream signaling components of TLR4, including MyD88, TRIF and NF-κB, and cytokines such as TNF-α and IL-1β, were also increased. Retrograde labeling indicated that most TLR4 positve neuron in the TG innnervated the pulp and TLR4 immunoreactivity was mainly in the medium and small neurons. Double labeling showed that the TLR4 expressing neurons in the ipsilateral TG were TRPV1 and CGRP positive, but IB4 negative. Furthermore, blocking TLR4 by eritoran (TLR4 antagonist) in TGs of the AP model significantly down-regulated MyD88, TRIF, NF-κB, TNF-α and IL-1β production and behavior of nociceptive response. Our findings suggest that TLR4 signaling in TG cells, particularly the peptidergic TRPV1 neurons, plays a key role in AP-induced nociception, and indicate that TLR4 signaling could be a potential therapeutic target for orofacial pain.

The hippocampus and TNF: Common links between chronic pain and depression

Major depression and chronic pain are significant health problems that seriously impact the quality of life of affected individuals. These diseases that individually are difficult to treat often co-exist, thereby compounding the patient's disability and impairment as well as the challenge of successful treatment. The development of efficacious treatments for these comorbid disorders requires a more comprehensive understanding of their linked associations through common neuromodulators, such as tumor necrosis factor-α (TNFα), and various neurotransmitters, as well as common neuroanatomical pathways and structures, including the hippocampal brain region. This review discusses the interaction between depression and chronic pain, emphasizing the fundamental role of the hippocampus in the development and maintenance of both disorders. The focus of this review addresses the hypothesis that hippocampal expressed TNFα serves as a therapeutic target for management of chronic pain and major depressive disorder (MDD).

Tumor necrosis factor inhibitors - state of knowledge

Tumor necrosis factor (TNF) is considered a major proinflammatory cytokine, affecting various aspects of the immune reaction. All five TNF inhibitors currently available on the market (i.e., etanercept, infliximab, adalimumab, certolizumab and golimumab) are top sellers, although indicated only in autoimmune diseases, including rheumatoid arthritis, Crohn's disease and psoriasis. This article briefly discusses the background and place for TNF inhibitors in modern therapy. The main safety aspects of TNF inhibitor administration are described in particular, with special consideration of the available meta-analyses. Finally, perspectives on the next-generation TNF inhibitors and their use in the clinic are given.

Morphological and functional changes in regenerated primary afferent fibres following mental and inferior alveolar nerve transection

BACKGROUND

It is important to know the mechanisms underlying pain abnormalities associated with inferior alveolar nerve (IAN) regeneration in order to develop the appropriate treatment for orofacial neuropathic pain patients. However, peripheral mechanisms underlying orofacial pain abnormalities following IAN regeneration are not fully understood.

METHODS

Head withdrawal threshold (HWT), jaw opening reflex (JOR) thresholds, single-fibre recordings of the regenerated mental nerve (MN) fibres, calcitonin gene-related peptide (CGRP), isolectin B4 (IB4), peripherin, neurofilament-200 (NF-200) and transient receptor potential vanilloid 1 (TRPV1) expression in trigeminal ganglion (TG) cells, and electron microscopic (EM) observations of the regenerated MN fibres were studied in MN- and IAN-transected (M-IANX) rats.

RESULTS

HWT to mechanical or heat stimulation of the mental skin was significantly lower in M-IANX rats compared with sham rats. Mean conduction velocity of action potentials recorded from MN fibres (n = 124) was significantly slower in M-IANX rats compared with sham rats. The percentage of Fluoro-Gold (FG)-labelled CGRP-, peripherin- or TRPV1-immunoreactive (IR) cells was significantly larger in M-IANX rats compared with that of sham rats, whereas that of FG-labelled IB4- and NF-200-IR cells was significantly smaller in M-IANX rats compared with sham rats. Large-sized myelinated nerve fibres were rarely observed in M-IANX rats, whereas large-sized unmyelinated nerve fibres were frequently observed and were aggregated in the bundles at the distal portion of regenerated axons.

CONCLUSIONS

These findings suggest that the demyelination of MN fibres following regeneration may be involved in peripheral sensitization, resulting in the orofacial neuropathic pain associated with trigeminal nerve injury.

Brain-derived neurotrophic factor enhances the excitability of small-diameter trigeminal ganglion neurons projecting to the trigeminal nucleus interpolaris/caudalis transition zone following masseter muscle inflammation

Background

The trigeminal subnuclei interpolaris/caudalis transition zones (Vi/Vc) play an important role in orofacial deep pain, however, the role of primary afferent projections to the Vi/Vc remains to be determined. This study investigated the functional significance of hyperalgesia to the brain-derived neurotrophic factor (BDNF)-tyrosine kinase B (trkB) signaling system in trigeminal ganglion (TRG) neurons projecting to the Vi/Vc transition zone following masseter muscle (MM) inflammation.

Results

The escape threshold from mechanical stimulation applied to skin above the inflamed MM was significantly lower than in naïve rats. Fluorogold (FG) labeling was used to identify the TRG neurons innervating the MM, while microbeads (MB) were used to label neurons projecting to the Vi/Vc region. FG/MB-labeled TRG neurons were immunoreactive (IR) for BDNF and trkB. The mean number of BDNF/trkB-IR small/medium-diameter TRG neurons was significantly higher in inflamed rats than in naïve rats. In whole-cell current-clamp experiments, the majority of dissociated small-diameter TRG neurons showed a depolarization response to BDNF that was associated with spike discharge, and the concentration of BDNF that evoked a depolarizing response was significantly lower in the inflamed rats. In addition, the relative number of BDNF-induced spikes during current injection was significantly higher in inflamed rats. The BDNF-induced changes in TRG neuron excitability was abolished by tyrosine kinase inhibitor, K252a.

Conclusion

The present study provided evidence that BDNF enhances the excitability of the small-diameter TRG neurons projecting onto the Vi/Vc following MM inflammation. These findings suggest that ganglionic BDNF-trkB signaling is a therapeutic target for the treatment of trigeminal inflammatory hyperalgesia.

The mechanism of functional up-regulation of P2X3 receptors of trigeminal sensory neurons in a genetic mouse model of familial hemiplegic migraine type 1 (FHM-1)

A knock-in (KI) mouse model of FHM-1 expressing the R192Q missense mutation of the Cacna1a gene coding for the α1 subunit of Ca_V2.1 channels shows, at the level of the trigeminal ganglion, selective functional up-regulation of ATP -gated P2X3 receptors of sensory neurons that convey nociceptive signals to the brainstem. Why P2X3 receptors are constitutively more responsive, however, remains unclear as their membrane expression and TRPV1 nociceptor activity are the same as in wildtype (WT) neurons. Using primary cultures of WT or KI trigeminal ganglia, we investigated whether soluble compounds that may contribute to initiating (or maintaining) migraine attacks, such as TNFα, CGRP, and BDNF, might be responsible for increasing P2X3 receptor responses. Exogenous application of TNFα potentiated P2X3 receptor-mediated currents of WT but not of KI neurons, most of which expressed both the P2X3 receptor and the TNFα receptor TNFR2. However, sustained TNFα neutralization failed to change WT or KI P2X3 receptor currents. This suggests that endogenous TNFα does not regulate P2X3 receptor responses. Nonetheless, on cultures made from both genotypes, exogenous TNFα enhanced TRPV1 receptor-mediated currents expressed by a few neurons, suggesting transient amplification of TRPV1 nociceptor responses. CGRP increased P2X3 receptor currents only in WT cultures, although prolonged CGRP receptor antagonism or BDNF neutralization reduced KI currents to WT levels. Our data suggest that, in KI trigeminal ganglion cultures, constitutive up-regulation of P2X3 receptors probably is already maximal and is apparently contributed by basal CGRP and BDNF levels, thereby rendering these neurons more responsive to extracellular ATP.