Effects of High-Definition Transcranial Direct Current Stimulation Targeting the Anterior Cingulate Cortex on the Pain Thresholds: A Randomized Controlled Trial

IDO1 modulates pain sensitivity and comorbid anxiety in chronic migraine through microglial activation and synaptic pruning

BACKGROUND

Chronic migraine is a prevalent and potentially debilitating neurological disorder that is often comorbid with mental health conditions (such as anxiety and depression), but the underlying mechanisms linking these conditions remain poorly understood. Indoleamine 2,3-dioxygenase 1 (IDO1) has been implicated in inflammatory processes, including neuroinflammation and pain. However, its role as a link between neuroinflammation and pain sensitization in chronic migraine is not well defined.

METHODS

Male mice were used to establish a model of chronic migraine by recurrent intraperitoneal injections of nitroglycerin (NTG, 10 mg/kg). Using pharmacological approaches, transgenic strategies and adeno-associated virus (AAV) intervention, we investigated the role of IDO1 in pain sensitization and migraine-related mood disorders in an NTG-induced chronic migraine mouse model. We employed a combination of immunoblotting, immunohistochemistry, three-dimensional reconstruction, RNA sequencing, electrophysiology, in vivo fiber photometry, and behavioral assays to elucidate the underlying mechanisms involved.

RESULTS

Our findings demonstrated that pharmacological inhibition and genetic knockout of IDO1 significantly alleviated pain sensitivity in a chronic migraine model. Neuronal activity in the anterior cingulate cortex (ACC) was evaluated with in vitro c-Fos immunostaining as well as in vivo fiber photometry, and a shift in the excitation/inhibition (E/I) balance toward excitation was observed through whole-cell patch clamp recording. Notably, IDO1 expression was increased in the ACC, and AAV-mediated IDO1 knockdown in the ACC rescued pain sensitivity, electrophysiological E/I balance changes, and anxiety-like behavior in chronic migraine model mice. Furthermore, IDO1 regulated microglial activation and pruning of neuronal synapses in the ACC. IDO1's microglial pruning function appears to be mediated through the interferon (IFN) signaling pathway, and the behavioral changes induced by IDO1 knockdown in the ACC could be reversed by activating this pathway.

CONCLUSIONS

Our findings revealed that microglial IDO1 in the ACC drives pain sensitization and anxiety in chronic migraine, highlighting IDO1 as a potential therapeutic target for chronic migraine treatment.

Transcranial direct current stimulation in the management of pain in oncology patients. A systematic review and meta-analysis with meta-regression of randomized controlled trials

PURPOSE

To evaluate the efficacy of transcranial direct current stimulation (tDCS) in pain management in subjects with oncologic process.

MATERIAL AND METHODS

Several databases were searched in December 2023. Randomized Controlled Trials that evaluated the application of tDCS on pain in adults with oncologic process were selected. Random-effects meta-analysis with 95%CI were used to quantify the change scores in pain between tDCS and control groups.

RESULTS

Six trials with 482 participants were included. There were significant differences in favor of tDCS in pain intensity in surgical oncology patients compared to sham stimulation (p < 0.001). Non-surgical patients showed no significant effect. Meta-regression analysis in this group of patients showed that the timing of the evaluation moderated the effect of tDCS on pain (p= .042), with longer time after tDCS being associated with greater pain reduction.

CONCLUSIONS

The application of a-tDCS for at least 20 min, with a current density higher than 0.057 mA/cm2, applied over M1, left DLPFC, or the insula area, between 2-5 sessions appears to be an effective and safe treatment of pain in surgical oncology patients compared to sham. The tDCS appears to be more effective for high-intensity pain, and in the long term.

The Role of the Brain-Derived Neurotrophic Factor in Chronic Pain: Links to Central Sensitization and Neuroinflammation

Chronic pain is sustained, in part, through the intricate process of central sensitization (CS), marked by maladaptive neuroplasticity and neuronal hyperexcitability within central pain pathways. Accumulating evidence suggests that CS is also driven by neuroinflammation in the peripheral and central nervous system. In any chronic disease, the search for perpetuating factors is crucial in identifying therapeutic targets and developing primary preventive strategies. The brain-derived neurotrophic factor (BDNF) emerges as a critical regulator of synaptic plasticity, serving as both a neurotransmitter and neuromodulator. Mounting evidence supports BDNF's pro-nociceptive role, spanning from its pain-sensitizing capacity across multiple levels of nociceptive pathways to its intricate involvement in CS and neuroinflammation. Moreover, consistently elevated BDNF levels are observed in various chronic pain disorders. To comprehensively understand the profound impact of BDNF in chronic pain, we delve into its key characteristics, focusing on its role in underlying molecular mechanisms contributing to chronic pain. Additionally, we also explore the potential utility of BDNF as an objective biomarker for chronic pain. This discussion encompasses emerging therapeutic approaches aimed at modulating BDNF expression, offering insights into addressing the intricate complexities of chronic pain.

Transcranial Direct Current Stimulation (tDCS) Effects on Quantitative Sensory Testing (QST) and Nociceptive Processing in Healthy Subjects: A Systematic Review and Meta-Analysis

BACKGROUND

The aim of this study is to determine the effect that different tDCS protocols have on pain processing in healthy people, assessed using quantitative sensory tests (QST) and evoked pain intensity.

METHODS

We systematically searched in EMBASE, CINAHL, PubMed, PEDro, PsycInfo, and Web of Science. Articles on tDCS on a healthy population and regarding QST, such as pressure pain thresholds (PPT), heat pain thresholds (HPT), cold pain threshold (CPT), or evoked pain intensity were selected. Quality was analyzed using the Cochrane Risk of Bias Tool and PEDro scale.

RESULTS

Twenty-six RCTs were included in the qualitative analysis and sixteen in the meta-analysis. There were no significant differences in PPTs between tDCS and sham, but differences were observed when applying tDCS over S1 in PPTs compared to sham. Significant differences in CPTs were observed between tDCS and sham over DLPFC and differences in pain intensity were observed between tDCS and sham over M1. Non-significant effects were found for the effects of tDCS on HPTs.

CONCLUSION

tDCS anodic over S1 stimulation increases PPTs, while a-tDCS over DLPFC affects CPTs. The HPTs with tDCS are worse. Finally, M1 a-tDCS seems to reduce evoked pain intensity in healthy subjects.

Precision, integrative medicine for pain management in sickle cell disease

Sickle cell disease (SCD) is a prevalent and complex inherited pain disorder that can manifest as acute vaso-occlusive crises (VOC) and/or chronic pain. Despite their known risks, opioids are often prescribed routinely and indiscriminately in managing SCD pain, because it is so often severe and debilitating. Integrative medicine strategies, particularly non-opioid therapies, hold promise in safe and effective management of SCD pain. However, the lack of evidence-based methods for managing SCD pain hinders the widespread implementation of non-opioid therapies. In this review, we acknowledge that implementing personalized pain treatment strategies in SCD, which is a guideline-recommended strategy, is currently fraught with limitations. The full implementation of pharmacological and biobehavioral pain approaches targeting mechanistic pain pathways faces challenges due to limited knowledge and limited financial and personnel support. We recommend personalized medicine, pharmacogenomics, and integrative medicine as aspirational strategies for improving pain care in SCD. As an organizing model that is a comprehensive framework for classifying pain subphenotypes and mechanisms in SCD, and for guiding selection of specific strategies, we present evidence updating pain research pioneer Richard Melzack's neuromatrix theory of pain. We advocate for using the updated neuromatrix model to subphenotype individuals with SCD, to better select personalized multimodal treatment strategies, and to identify research gaps fruitful for exploration. We present a fairly complete list of currently used pharmacologic and non-pharmacologic SCD pain therapies, classified by their mechanism of action and by their hypothesized targets in the updated neuromatrix model.