rTMS induces analgesia and modulates neuroinflammation and neuroplasticity in neuropathic pain model rats

rTMS applied to the PFC relieves neuropathic pain and modulates neuroinflammation in CCI rats

The study aimed to assess the analgesic effect of 10 Hz repetitive transcranial magnetic stimulation (rTMS) targeted to the prefrontal cortex (PFC) region on neuropathic pain (NPP) in rats with chronic constriction injury (CCI) of the sciatic nerve, and to investigate the possible underlying mechanism. Rats were randomly divided into three groups: sham operation, CCI, and rTMS. In the latter group, rTMS was applied to the left PFC. Von Frey fibres were used to measure the paw withdrawal mechanical threshold (PWMT). At the end of the treatment, immunofluorescence and western blotting were applied to detect the expression of M1 and M2 polarisation markers in microglia in the left PFC and sciatic nerve. ELISA was further used to detect the concentrations of inflammation-related cytokines. The results showed that CCI caused NPP in rats, reduced the pain threshold, promoted microglial polarisation to the M1 phenotype, and increased the secretion of pro-inflammatory and anti-inflammatory factors. Moreover, 10 Hz rTMS to the PFC was shown to improve NPP induced by CCI, induce microglial polarisation to M2, reduce the secretion of pro-inflammatory factors, and further increase the secretion of anti-inflammatory factors. Our data suggest that 10 Hz rTMS can alleviate CCI-induced neuropathic pain, while the underlying mechanism may potentially be related to the regulation of microglial M1-to-M2-type polarisation to regulate neuroinflammation.

Treating neuropathic pain and comorbid affective disorders: Preclinical and clinical evidence

INTRODUCTION

Neuropathic pain (NP) significantly impacts quality of life and often coexists with affective disorders such as anxiety and depression. Addressing both NP and its psychiatric manifestations requires a comprehensive understanding of therapeutic options. This study aimed to review the main pharmacological and non-pharmacological treatments for NP and comorbid affective disorders to describe their mechanisms of action and how they are commonly used in clinical practice.

METHODS

A review was conducted across five electronic databases, focusing on pharmacological and non-pharmacological treatments for NP and its associated affective disorders. The following combination of MeSH and title/abstract keywords were used: "neuropathic pain," "affective disorders," "depression," "anxiety," "treatment," and "therapy." Both animal and human studies were included to discuss the underlying therapeutic mechanisms of these interventions.

RESULTS

Pharmacological interventions, including antidepressants, anticonvulsants, and opioids, modulate neural synaptic transmission to alleviate NP. Topical agents, such as capsaicin, lidocaine patches, and botulinum toxin A, offer localized relief by desensitizing pain pathways. Some of these drugs, especially antidepressants, also treat comorbid affective disorders. Non-pharmacological techniques, including repetitive transcranial magnetic stimulation, transcranial direct current stimulation, and photobiomodulation therapy, modulate cortical activity and have shown promise for NP and mood disorders.

CONCLUSIONS

The interconnection between NP and comorbid affective disorders necessitates holistic therapeutic strategies. Some pharmacological treatments can be used for both conditions, and non-pharmacological interventions have emerged as promising complementary approaches. Future research should explore novel molecular pathways to enhance treatment options for these interrelated conditions.

Repetitive transcranial magnetic stimulation regulates neuroinflammation in neuropathic pain

Neuropathic pain (NP) is a frequent condition caused by a lesion in, or disease of, the central or peripheral somatosensory nervous system and is associated with excessive inflammation in the central and peripheral nervous systems. Repetitive transcranial magnetic stimulation (rTMS) is a supplementary treatment for NP. In clinical research, rTMS of 5-10 Hz is widely placed in the primary motor cortex (M1) area, mostly at 80%-90% RMT, and 5-10 treatment sessions could produce an optimal analgesic effect. The degree of pain relief increases greatly when stimulation duration is greater than 10 days. Analgesia induced by rTMS appears to be related to reestablishing the neuroinflammation system. This article discussed the influences of rTMS on the nervous system inflammatory responses, including the brain, spinal cord, dorsal root ganglia (DRG), and peripheral nerve involved in the maintenance and exacerbation of NP. rTMS has shown an anti-inflammation effect by decreasing pro-inflammatory cytokines, including IL-1β, IL-6, and TNF-α, and increasing anti-inflammatory cytokines, including IL-10 and BDNF, in cortical and subcortical tissues. In addition, rTMS reduces the expression of glutamate receptors (mGluR5 and NMDAR2B) and microglia and astrocyte markers (Iba1 and GFAP). Furthermore, rTMS decreases nNOS expression in ipsilateral DRGs and peripheral nerve metabolism and regulates neuroinflammation.

Association of inflammation and cognition in the elderly: A systematic review and meta-analysis

Background

The development of mild cognitive impairment (MCI) and Alzheimer's disease (AD) may be associated with an inflammatory process. Inflammatory cytokines may be a surrogate for systemic inflammation leading to worsening neurological function. We aim to investigate the association between cognitive impairment and inflammation by pooling and analyzing the data from previously published studies.

Methods

We performed a systematic literature search on MEDLINE, PubMed, Embase, Web of Science, and Scopus for prospective longitudinal and cross-sectional studies evaluating the relationship between inflammation and cognitive functions.

Results

A total of 79 articles were included in our systematic review and meta-analysis. Pooled estimates from cross-sectional studies have demonstrated an increased level of C-reactive protein (CRP) [Hedges's g 0.35, 95% CI (0.16, 0.55), p < 0.05], IL-1β [0.94, 95% CI (-0.04, 1.92), p < 0.05], interleukin-6 (IL-6) [0.46, 95% CI (0.05, 0.88), p < 0.005], TNF alpha [0.22, 95% CI (-0.24, 0.68), p < 0.05], sTNFR-1 [0.74, 95% CI (0.46, 1.02), p < 0.05] in AD compared to controls. Similarly, higher levels of IL-1β [0.17, 95% CI (0.05, 0.28), p < 0.05], IL-6 [0.13, 95% CI (0.08, 0.18), p < 0.005], TNF alpha [0.28, 95% CI (0.07, 0.49), p < 0.05], sTNFR-1 [0.21, 95% CI (0.05, 0.48), p < 0.05] was also observed in MCI vs. control samples. The data from longitudinal studies suggested that levels of IL-6 significantly increased the risk of cognitive decline [OR = 1.34, 95% CI (1.13, 1.56)]. However, intermediate levels of IL-6 had no significant effect on the final clinical endpoint [OR = 1.06, 95% CI (0.8, 1.32)].

Conclusion

The data from cross-sectional studies suggest a higher level of inflammatory cytokines in AD and MCI as compared to controls. Moreover, data from longitudinal studies suggest that the risk of cognitive deterioration may increase by high IL-6 levels. According to our analysis, CRP, antichymotrypsin (ACT), Albumin, and tumor necrosis factor (TNF) alpha may not be good surrogates for neurological degeneration over time.

Application of Repetitive Transcranial Magnetic Stimulation in Neuropathic Pain: A Narrative Review

Neuropathic pain, affecting 6.9-10% of the general population, has a negative impact on patients' quality of life and potentially leads to functional impairment and disability. Repetitive transcranial magnetic stimulation (rTMS)-a safe, indirect and non-invasive technique-has been increasingly applied for treating neuropathic pain. The mechanism underlying rTMS is not yet well understood, and the analgesic effects of rTMS have been inconsistent with respect to different settings/parameters, causing insufficient evidence to determine its efficacy in patients with neuropathic pain. This narrative review aimed to provide an up-to-date overview of rTMS for treating neuropathic pain as well as to summarize the treatment protocols and related adverse effects from existing clinical trials. Current evidence supports the use of 10 Hz HF-rTMS of the primary motor cortex to reduce neuropathic pain, especially in patients with spinal cord injury, diabetic neuropathy and post-herpetic neuralgia. However, the lack of standardized protocols impedes the universal use of rTMS for neuropathic pain. rTMS was hypothesized to achieve analgesic effects by upregulating the pain threshold, inhibiting pain impulse, modulating the brain cortex, altering imbalanced functional connectivity, regulating neurotrophin and increasing endogenous opioid and anti-inflammatory cytokines. Further studies are warranted to explore the differences in the parameters/settings of rTMS for treating neuropathic pain due to different disease types.

Design and evaluation of a rodent-specific focal transcranial magnetic stimulation coil with the custom shielding application in rats

Repetitive TMS has been used as an alternative treatment for various neurological disorders. However, most TMS mechanism studies in rodents have been based on the whole brain stimulation, the lack of rodent-specific focal TMS coils restricts the proper translation of human TMS protocols to animal models. In this study, we designed a new shielding device, which was made of high magnetic permeability material, to enhance the spatial focus of animal-use TMS coils. With the finite element method, we analyzed the electromagnetic field of the coil with and without the shielding device. Furthermore, to assess the shielding effect in rodents, we compared the c-fos expression, the ALFF and ReHo values in different groups following a 15 min 5 Hz rTMS paradigm. We found that a smaller focality with an identical core stimulation intensity was achieved in the shielding device. The 1 T magnetic field was reduced from 19.1 mm to 13 mm in diameter, and 7.5 to 5.6 mm in depth. However, the core magnetic field over 1.5 T was almost the same. Meanwhile, the area of electric field was reduced from 4.68 cm² to 4.19 cm², and 3.8 mm to 2.6 mm in depth. Similar to this biomimetic data, the c-fos expression, the ALFF and ReHo values showed more limited cortex activation with the use of the shielding device. However, compared to the rTMS group without the shielding application, more subcortical regions, like the striatum (CPu), the hippocampus, the thalamus, and the hypothalamus were also activated in the shielding group. This indicated that more deep stimulation may be achieved by the shielding device. Generally, compared with the commercial rodents' TMS coil (15 mm in diameter), TMS coils with the shielding device achieved a better focality (~6 mm in diameter) by reducing at least 30% of the magnetic and electric field. This shielding device may provide a useful tool for further TMS studies in rodents, especially for more specific brain area stimulation.

Non-invasive brain neuromodulation techniques for chronic low back pain

Structural and functional changes of the brain occur in many chronic pain conditions, including chronic low back pain (CLBP), and these brain abnormalities can be reversed by effective treatment. Research on the clinical applications of non-invasive brain neuromodulation (NIBS) techniques for chronic pain is increasing. Unfortunately, little is known about the effectiveness of NIBS on CLBP, which limits its application in clinical pain management. Therefore, we summarized the effectiveness and limitations of NIBS techniques on CLBP management and described the effects and mechanisms of NIBS approaches on CLBP in this review. Overall, NIBS may be effective for the treatment of CLBP. And the analgesic mechanisms of NIBS for CLBP may involve the regulation of pain signal pathway, synaptic plasticity, neuroprotective effect, neuroinflammation modulation, and variations in cerebral blood flow and metabolism. Current NIBS studies for CLBP have limitations, such as small sample size, relative low quality of evidence, and lack of mechanistic studies. Further studies on the effect of NIBS are needed, especially randomized controlled trials with high quality and large sample size.

Systematic Review and Meta-Analysis of High-Frequency rTMS over the Dorsolateral Prefrontal Cortex .on Chronic Pain and Chronic-Pain-Accompanied Depression

The effect of high-frequency (HF) repetitive transcranial magnetic stimulation (rTMS) on the dorsolateral prefrontal cortex (DLPFC) can relieve chronic pain and accompanying depressive symptoms. However, in recent years, some high-quality studies have challenged this view. Therefore, it is necessary to update the data and analyze the effects of HF rTMS on the DLPFC on chronic pain and accompanying depression. We performed a systematic review and meta-analysis to evaluate the effect of HF rTMS on the DLPFC on chronic pain and accompanying depression. We searched PubMed, Medline, Web of Science, and Cochrane through September 2021. The search strings searched were : "pain" AND ("TMS" OR "transcranial magnetic stimulation") AND "prefrontal cortex". The inclusion criteria according to PICOS was as follows: P, patient with chronic pain; I, HF (≥5 Hz) rTMS on the DLPFC; C, included a sham treatment condition; O, pain indicators; S, pre-/poststudies, crossover, or parallel-group. We extracted the pain and accompanying depression evaluation indicators. The short-term analgesic effect of HF rTMS over the left DLPFC is not significant (WMD = 0.34, 95% CI: [-1.60, 2.28]) but has a significant mid-term and long-term analgesic effect on chronic pain (WMD = -0.50, 95% CI: [-0.99, -0.01]; WMD = -1.10, 95% CI: [-2.00, -0.19], respectively). HF rTMS over the DLPFC can effectively alleviate the depressive symptoms of patients with chronic pain (WMD = -0.83, 95% CI: [-3.01, 1.36]). Thus, HF rTMS on the left DLPFC can relieve chronic pain and accompanying depressive symptoms.

Effects of Repetitive Transcranial Magnetic Stimulation on Gait and Postural Control Ability of Patients with Executive Dysfunction after Stroke

Objective: To assess the effects of repetitive transcranial magnetic stimulation (rTMS) on the gait and postural control ability of patients with executive dysfunction (ED) after stroke. Methods: A total of 18 patients with ED after stroke were randomly assigned into two groups, including an experimental group and a sham group. Patients in both groups received routine rehabilitation therapy, and patients in the experimental group underwent rTMS on the left dorsolateral prefrontal cortex (DLPFC) for 2 weeks (5 HZ, 80%MT, 1200 pulses). In the sham group, patients experienced sham stimulation treatment, in which the coil was placed vertically with the head. Before and after treatment, patients in both groups were subjected to Montreal cognitive assessment (MoCA) scoring, Fugl−Meyer assessment of lower extremity (L-FMA), Stroop color-word test (SCWT), gait analysis, foot plantar pressure test, 10-m walking test (10MWT), Berg balance scale (BBS), and timed up and go test (TUGT). In the SCWT, it was attempted to record the time of each card (SCWT-T), the correct number (SCWT-C), Stroop interference effect-time (SIE-T), and SIE correct count (SIE-C). The TUGT was categorized into four stages: getting up (GT), walking straight (WT), turning around (TT), and sitting down (ST), in which the total time of TUGT was calculated. Results: After two weeks of treatment, the evaluation indexes were improved in the two groups, some of which were statistically significant. In the experimental group, SCWT-T, SIE-T, SIE-C, GT, WT, TT, ST, and TUGT were significantly improved after treatment (p < 0.05). SCWT-C, L-FMA score, 10MWT, GT, WT, stride length, step width, foot plantar pressure, pressure center curve, and activities of daily living were not statistically different from those before treatment (p > 0.05). After treatment, SCWT-T, SIE-C, SIE-T, BBS score, TT, and ST in the experimental group were significantly shorter than those before treatment, with statistical differences (p < 0.05). Compared with the sham group, SCWT-C, L-FMA score, 10MWT, GT, WT, TUGT, stride length, step width, foot plantar pressure, pressure center curve, and motor skills were not significantly improved (p > 0.05). Conclusion: It was revealed that post-stroke rTMS treatment of patients with ED could improve executive function, improve postural control function, and reduce the risk of falling. In addition, rTMS of DLPFC could be a therapeutic target for improving postural control ability and reducing the risk of falling.

rTMS/iTBS and Cognitive Rehabilitation for Deficits Associated With TBI and PTSD: A Theoretical Framework and Review

Rehabilitation of cognitive and psychosocial deficits resulting from traumatic brain injury (TBI) continues to be an area of concern in health care. Commonly co-occurring psychiatric disorders, such as major depressive disorder and posttraumatic stress disorder, create additional hurdles when attempting to remediate cognitive sequelae. There is increased need for procedures that will yield consistent gains indicative of recovery of function. Intermittent theta-burst stimulation (iTBS), a form of repetitive transcranial magnetic stimulation, has potential as an instrument that can be tailored to aid cognitive processes and support functional gains. The use of iTBS enables direct stimulation of desired neural systems. iTBS, performed in conjunction with behavioral interventions (e.g., cognitive rehabilitation, psychotherapy), may result in additive success in facilitating cognitive restoration and adaptation. The purpose of this theoretical review is to illustrate how the technical and physiological aspects of iTBS may enhance other forms of neurorehabilitation for individuals with TBI. Future research on combinatorial iTBS interventions has the potential to translate to other complex neuropsychiatric conditions.

Spontaneous pain as a challenge of research and management in chronic pain

Spontaneous pain occurring without apparent external stimuli, is a significant complaint of individuals with chronic pain whose mechanisms, somewhat surprisingly, remain poorly understood. Over the past decades, neuroimaging studies start to reveal brain activities accompanying spontaneous pain. Meanwhile, a variety of animal models and behavioral tests have been established, including non-reflexive tests and free-choice tests, which have been shown to be effective in assessing spontaneous pain. For the spontaneous pain mechanisms, multiple lines of research mainly focus on three aspects: (1) sensitization of peripheral nociceptor receptors and ion channels, (2) spontaneous neuronal firing and abnormal activity patterns at the dorsal root ganglion and spinal cord level, (3) functional and structural alterations in the brain, particularly the limbic system and the medial pain pathway. Despite accumulating evidence revealing distinct neuronal mechanisms from evoked pain, we are still far from full understanding of spontaneous pain, leaving a big gap between bench and bedside for chronic pain treatment. A better understanding of the neural processes in chronic pain, with specific linkage as to which anatomical structures and molecules related to spontaneous pain perception and comorbidities, will greatly improve our ability to develop novel therapeutics.

Non-invasive Brain Stimulation for Central Neuropathic Pain

The research and clinical application of the noninvasive brain stimulation (NIBS) technique in the treatment of neuropathic pain (NP) are increasing. In this review article, we outline the effectiveness and limitations of the NIBS approach in treating common central neuropathic pain (CNP). This article summarizes the research progress of NIBS in the treatment of different CNPs and describes the effects and mechanisms of these methods on different CNPs. Repetitive transcranial magnetic stimulation (rTMS) analgesic research has been relatively mature and applied to a variety of CNP treatments. But the optimal stimulation targets, stimulation intensity, and stimulation time of transcranial direct current stimulation (tDCS) for each type of CNP are still difficult to identify. The analgesic mechanism of rTMS is similar to that of tDCS, both of which change cortical excitability and synaptic plasticity, regulate the release of related neurotransmitters and affect the structural and functional connections of brain regions associated with pain processing and regulation. Some deficiencies are found in current NIBS relevant studies, such as small sample size, difficulty to avoid placebo effect, and insufficient research on analgesia mechanism. Future research should gradually carry out large-scale, multicenter studies to test the stability and reliability of the analgesic effects of NIBS.

Repetitive Transcranial Magnetic Stimulation (rTMS) Reverses the Long-term Memory Impairment and the Decrease of Hippocampal Interleukin-10 Levels, both Induced by Neuropathic Pain in Rats

Neuropathic pain (NP) is characterized by the presence of spontaneous pain, allodynia and hyperalgesia. Repetitive transcranial magnetic stimulation (rTMS) is one of neuromodulatory techniques that induces satisfactory NP relief, including that from refractory pain patients. The objective of this study was to evaluate rTMS treatment over long term memory (LTM) and hippocampal BDNF and IL-10 levels in rats submitted to a NP model. A total of 81 adult (60-days old) male Wistar rats were randomly allocated to one of the following 9 experimental groups: control, control + sham rTMS, control + rTMS, sham neuropathic pain, sham neuropathic pain + sham rTMS, sham neuropathic pain + rTMS, neuropathic pain (NP), neuropathic pain + sham rTMS and neuropathic pain + rTMS. Fourteen days after the surgery for chronic constriction injury (CCI) of the sciatic nerve, NP establishment was accomplished. Then, rats were treated with daily 5-minute sessions of rTMS for eight consecutive days. LTM was assessed by the object recognition test (ORT) twenty-four hours after the end of rTMS treatment. Biochemical assays (BDNF and IL-10 levels) were performed in hippocampus tissue homogenates. rTMS treatment reversed the reduction of the discrimination index in the ORT and the hippocampal IL-10 levels in NP rats. This result shows that rTMS reverses the impairment LTM and the increase in the hippocampal IL-10 levels, both induced by NP. Moreover, it appears to be a safe non-pharmacological therapeutic tool since it did not alter LTM and neurochemical parameters in naive animals.

Hyperoside Attenuate Inflammation in HT22 Cells via Upregulating SIRT1 to Activities Wnt/β-Catenin and Sonic Hedgehog Pathways

Neuroinflammation plays important roles in the pathogenesis and progression of altered neurodevelopment, sensorineural hearing loss, and certain neurodegenerative diseases. Hyperoside (quercetin-3-O-β-D-galactoside) is an active compound isolated from Hypericum plants. In this study, we investigate the protective effect of hyperoside on neuroinflammation and its possible molecular mechanism. Lipopolysaccharide (LPS) and hyperoside were used to treat HT22 cells. The cell viability was measured by MTT assay. The cell apoptosis rate was measured by flow cytometry assay. The mRNA expression levels of interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-8 (IL-8), and tumor necrosis factor-α (TNF-α) were determined by quantitative reverse transcription polymerase chain reaction. The levels of oxidative stress indices superoxide dismutase (SOD), reactive oxygen species (ROS), catalase (CAT), glutathione (GSH), and malondialdehyde (MDA) were measured by the kits. The expression of neurotrophic factor and the relationship among hyperoside, silent mating type information regulation 2 homolog-1 (SIRT1) and Wnt/β-catenin, and sonic hedgehog was examined by western blotting. In the LPS-induced HT22 cells, hyperoside promotes cell survival; alleviates the level of IL-1β, IL-6, IL-8, TNF-α, ROS, MDA, Bax, and caspase-3; and increases the expression of CAT, SOD, GSH, Bcl-2, BDNF, TrkB, and NGF. In addition, hyperoside upregulated the expression of SIRT1. Further mechanistic investigation showed that hyperoside alleviated LPS-induced inflammation, oxidative stress, and apoptosis by upregulating SIRT1 to activate Wnt/β-catenin and sonic hedgehog pathways. Taken together, our data suggested that hyperoside acts as a protector in neuroinflammation.