Mirogabalin: a novel gabapentinoid or another false dawn?

PURPOSE OF REVIEW: Mirogabalin is a novel gabapentinoid medication for the treatment of neuropathic pain. The purpose of this review is to discuss current evidence for its use. Gabapentinoids are widely prescribed for neuropathic pain. Mirogabalin offers theoretical advantages over traditional gabapentinoids due to its specificity for the α2δ-1 subunit of voltage-gated calcium channels. It is theorised that this specificity may reduce adverse drug reactions by minimising binding to the α2δ-2 subunit which is responsible for many of the gabapentinoid side effects. RECENT FINDINGS: Mirogabalin's slower dissociation from the α2δ-1 compared with α2δ-2, and its higher potency may also impart an efficacy benefit over traditional gabapentinoids. These theoretical advantages of mirogabalin remain inconclusive in clinical practice, with mixed evidence regarding mirogabalin versus traditional gabapentinoids. Some studies suggest a reduced side effect profile yet, others fail to demonstrate significant differences. Regarding efficacy, mirogabalin may be superior to placebo for several neuropathic pain syndromes, but evidence of widespread benefit over traditional gabapentinoids is currently lacking. SUMMARY: Mirogabalin offers theoretical promise, but large, independent studies are required to further assess its performance versus traditional gabapentinoids.

Occurrence of somnolence and respiratory depression induced by pregabalin and mirogabalin use and the influence of opioid treatment using the Japanese adverse drug event report database.

Background: Gabapentinoid anticonvulsants are standard treatment for neuropathic pain and are often combined with opioids for treating cancer. It is assumed that this combination may heighten somnolence and respiratory depression due to the inhibitory effects of opioids on the central nervous system. Although pregabalin, a gabapentinoid, is known to increase somnolence frequency during opioid therapy, whether mirogabalin exerts similar effects on somnolence frequency under opioid therapy remains unknown. This study examined the signals of somnolence and respiratory depression in response to pregabalin and mirogabalin use by utilizing data from the Japanese Adverse Drug Event Report database and assessed their interaction with strong opioid analgesics. Methods: Information was obtained from the JADER database from April 2004 to August 2023 via the Pharmaceuticals and Medical Devices Agency website. The study focused on neuropathic pain medications, specifically "pregabalin" and "mirogabalin besilate." Adverse events were defined using preferred terms (PTs) from the Medical Dictionary for Regulatory Activities version 26.1. The PTs considered were "Somnolence (10041349)" and "Respiratory depression (10038678)." To investigate the effect of the combination of strong opioid analgesics with pregabalin and mirogabalin on the occurrence of somnolence, a multivariable logistic regression analysis was conducted. Results: Signals for somnolence were detected with the use of both drugs (pregabalin: information component (IC) [95% confidence intervals (CIs)]: 2.89 [2.70 to 3.08]; mirogabalin: IC [95% CIs] 2.50 [1.85 to 3.16]). When evaluating respiratory depression, a typical and serious adverse event of opioid analgesic use, a signal was detected with pregabalin use but not with mirogabalin use (pregabalin: (IC [95% CIs] 1.28 [0.83 to 1.73]; mirogabalin: IC [95% CIs] -0.15 [-2.20 to 1.89]). Multivariable analysis indicated that the use of strong opioid analgesics increased the occurrence of somnolence when combined with pregabalin but not when combined with mirogabalin (p = 0.004). Conclusion: While the safety of concomitant administation of mirogabalin with opioids remains controversial, caution should be exercised when using pregabalin, especially in combination with opioids for neuropathic pain, compared to that for mirogabalin.

Exploring Analgesic Use Patterns Among Cancer Survivors With Chronic Chemotherapy-Induced Peripheral Neuropathy.

OBJECTIVES: To explore cancer survivors' historical and current use of analgesics for chronic chemotherapy-induced peripheral neuropathy (CIPN). SAMPLE & SETTING: 142 post-treatment cancer survivors who received neurotoxic chemotherapy and were experiencing moderate to severe CIPN. METHODS & VARIABLES: Participants completed the Treatment-Induced Neuropathy Assessment Scale at baseline and reported all analgesics used to manage CIPN. Frequency of historical or current prescription analgesic use for chronic CIPN was described and stratified by CIPN pain severity. RESULTS: At baseline, 31% of participants reported historical use of analgesics for CIPN and 46% of participants were currently using analgesics for CIPN. Gabapentin was the most frequently used analgesic, historically (20%) and currently (34%), and duloxetine was used less frequently (6% historical use, 10% current use). Many participants with severe pain (59%) reported using analgesics for CIPN. IMPLICATIONS FOR NURSING: Duloxetine, the first-line treatment for chronic CIPN pain, was used less frequently than gabapentin, a common prescription analgesic for neuropathic pain. Further research is needed to determine strategies to promote the implementation of evidence-based CIPN treatments in clinical practice.

Sigma-1 Receptors Control Neuropathic Pain and Peripheral Neuroinflammation After Nerve Injury in Female Mice: A Transcriptomic Study.

The mechanisms for neuropathic pain amelioration by sigma-1 receptor inhibition are not fully understood. We studied genome-wide transcriptomic changes (RNAseq) in the dorsal root ganglia (DRG) from wild-type and sigma-1 receptor knockout mice prior to and following Spared Nerve Injury (SNI). In wildtype mice, most of the transcriptomic changes following SNI are related to the immune function or neurotransmission. Immune function transcripts contain cytokines and markers for immune cells, including macrophages/monocytes and CD4 + T cells. Many of these immune transcripts were attenuated by sigma-1 knockout in response to SNI. Consistent with this we found, using flow cytometry, that sigma-1 knockout mice showed a reduction in macrophage/monocyte recruitment as well as an absence of CD4 + T cell recruitment in the DRG after nerve injury. Sigma-1 knockout mice showed a reduction of neuropathic (mechanical and cold) allodynia and spontaneous pain-like responses (licking of the injured paw) which accompany the decreased peripheral neuroinflammatory response after nerve injury. Treatment with maraviroc (a CCR5 antagonist which preferentially inhibits CD4 + T cells in the periphery) of neuropathic wild-type mice only partially replicated the sigma-1 knockout phenotype, as it did not alter cold allodynia but attenuated spontaneous pain-like responses and mechanical hypersensitivity. Therefore, modulation of peripheral CD4 + T cell activity might contribute to the amelioration of spontaneous pain and neuropathic tactile allodynia seen in the sigma-1 receptor knockout mice, but not to the effect on cold allodynia. We conclude that sigma-1 receptor inhibition decreases DRG neuroinflammation which might partially explain its anti-neuropathic effect.

Gabapentin-induced Multifocal Myoclonus.

BACKGROUND: Gabapentin is the most commonly preferred agent for neuropathic pain in general practice as it is usually well tolerated, but occasionally, its toxicity may occur at standard doses, especially in elderly individuals, even without any prior comorbidities. CASE: We present an elderly male with normal renal parameters, who was started on gabapentin for neuropathic pain. He developed multifocal myoclonus all over the body within few days after starting gabapentin and subsided completed after withdrawal of the drug. CONCLUSION: Acute hyperkinetic movement disorders such as multifocal or segmental myoclonus in elderly patients warrant a prompt review of recent drug history, especially gabapentin, even in the background of normal renal function.

AR71, Histamine H3 Receptor Ligand-In Vitro and In Vivo Evaluation (Anti-Inflammatory Activity, Metabolic Stability, Toxicity, and Analgesic Action).

The future of therapy for neurodegenerative diseases (NDs) relies on new strategies targeting multiple pharmacological pathways. Our research led to obtaining the compound AR71 [(E)-3-(3,4,5-trimethoxyphenyl)-1-(4-(3-(piperidin-1-yl)propoxy)phenyl)prop-2-en-1-one], which has high affinity for human H3R (Ki = 24 nM) and selectivity towards histamine H1 and H4 receptors (Ki > 2500 nM), and showed anti-inflammatory activity in a model of lipopolysaccharide-induced inflammation in BV-2 cells. The presented tests confirmed its antagonist/inverse agonist activity profile and good metabolic stability while docking studies showed the binding mode to histamine H1, H3, and H4 receptors. In in vitro tests, cytotoxicity was evaluated at three cell lines (neuroblastoma, astrocytes, and human peripheral blood mononuclear cells), and a neuroprotective effect was observed in rotenone-induced toxicity. In vivo experiments in a mouse neuropathic pain model demonstrated the highest analgesic effects of AR71 at the dose of 20 mg/kg body weight. Additionally, AR71 showed antiproliferative activity in higher concentrations. These findings suggest the need for further evaluation of AR71's therapeutic potential in treating ND and CNS cancer using animal experimental models.

(+)-Catechin attenuates CCI-induced neuropathic pain in male rats by promoting the Nrf2 antioxidant pathway to inhibit ROS/TLR4/NF-κB-mediated activation of the NLRP3 inflammasome.

The objective of this study was to investigate the potential mechanisms by which (+)-catechin alleviates neuropathic pain. Thirty-two male Sprague-Dawley rats were divided into four groups: the sham group, the chronic constriction injury (CCI)group, the CCI+ ibuprofen group, and the CCI+ (+)-catechin group. CCI surgery induces thermal hyperalgesia in rats and (+)-catechin ameliorated CCI-induced thermal hyperalgesia and repaired damaged sciatic nerve in rats. CCI decreased SOD levels in male rat spinal cord dorsal horn and promoted MDA production, induced oxidative stress by increasing NOX4 levels and decreasing antioxidant enzyme HO-1 levels, and also increased protein levels of TLR4, p-NF-κB, NLRP3 inflammasome components, and IL-1ß. In contrast, (+)-catechin reversed the above results. In i vitro experiments, (+)-catechin reduced the generation of reactive oxygen species (ROS) in GMI-R1 cells after LPS stimulation and attenuated the co-expression of IBA-1 and NLRP3. It also showed significant inhibition of the NF-κB and NLRP3 inflammatory pathways and activation of the Nrf2-mediated antioxidant system. Overall, these findings suggest that (+)-catechin inhibits the activation of the NLRP3 inflammasome through the triggering of the Nrf2-induced antioxidant system, the inhibition of the TLR4/NF-κB pathway, and the production of ROS to alleviate CCI-induced neuropathic pain in male rats.

FTY720/Fingolimod mitigates paclitaxel-induced Sparcl1-driven neuropathic pain and breast cancer progression.

Paclitaxel is among the most active chemotherapy drugs for the aggressive triple negative breast cancer (TNBC). Unfortunately, it often induces painful peripheral neuropathy (CIPN), a major debilitating side effect. Here we demonstrate that in naive and breast tumor-bearing immunocompetent mice, a clinically relevant dose of FTY720/Fingolimod that targets sphingosine-1-phosphate receptor 1 (S1PR1), alleviated paclitaxel-induced neuropathic pain. FTY720 also significantly attenuated paclitaxel-stimulated glial fibrillary acidic protein (GFAP), a marker for activated astrocytes, and expression of the astrocyte-secreted synaptogenic protein Sparcl1/Hevin, a key regulator of synapse formation. Notably, the formation of excitatory synapses containing VGluT2 in the spinal cord dorsal horn induced by paclitaxel was also inhibited by FTY720 treatment, supporting the involvement of astrocytes and Sparcl1 in CIPN. Furthermore, in this TNBC mouse model that mimics human breast cancer, FTY720 administration also enhanced the anti-tumor effects of paclitaxel, leading to reduced tumor progression and lung metastasis. Taken together, our findings suggest that targeting the S1P/S1PR1 axis with FTY720 is a multipronged approach that holds promise as a therapeutic strategy for alleviating both CIPN and enhancing the efficacy of chemotherapy in TNBC treatment.

Successful spinal cord stimulation using fast-acting sub-perception therapy for postoperative neuropathic pain of syringomyelia with Chiari malformation type 1: a case report and literature review.

BACKGROUND: Central neuropathic pain after foramen magnum decompression (FMD) for Chiari malformation type 1 (CM-1) with syringomyelia can be residual and refractory. Here we present a case of refractory central neuropathic pain after FMD in a CM-1 patient with syringomyelia who achieved improvements in pain following spinal cord stimulation (SCS) using fast-acting sub-perception therapy (FAST™). CASE PRESENTATION: A 76-year-old woman presented with a history of several years of bilateral upper extremity and chest-back pain. CM-1 and syringomyelia were diagnosed. The pain proved drug resistant, so FMD was performed for pain relief. After FMD, magnetic resonance imaging showed shrinkage of the syrinx. Pain was relieved, but bilateral finger, upper arm and thoracic back pain flared-up 10 months later. Due to pharmacotherapy resistance, SCS was planned for the purpose of improving pain. A percutaneous trial of SCS showed no improvement of pain with conventional SCS alone or in combination with Contour™, but the combination of FAST™ and Contour™ did improve pain. Three years after FMD, percutaneous leads and an implantable pulse generator were implanted. The program was set to FAST™ and Contour™. After implantation, pain as assessed using the McGill Pain Questionnaire and visual analog scale was relieved even after reducing dosages of analgesic. No adverse events were encountered. CONCLUSION: Percutaneously implanted SCS using FAST™ may be effective for refractory pain after FMD for CM-1 with syringomyelia.

Puerarin alleviates oxaliplatin-induced neuropathic pain by promoting Nrf2/GPX4-mediated antioxidative response.

Oxaliplatin (OXA) as the platinum-based agent induces the cumulative neuropathy including functional impairment and neuropathic pain. OXA treatment triggered oxidative stress and inflammatory reaction in the spinal cord. Puerarin as a natural product has the neuroprotective effect on neuropathic pain. Hence, the roles and mechanisms of Pue on OXA induced neuropathic pain were studied. In this study, OXA-induced neuropathic pain mouse model was constructed by oxaliplatin injection for 5 consecutive days and two cycles. Pue (10 mg/kg) was administered intraperitoneally for seven consecutive days. The changes of behavior, morphology and levels of related proteins were detected. As a result, OXA-induced mice exhibited as the increased pain hypersensitivity, the impaired motor coordination, the activated NLRP3 inflammasome mediated inflammation and the suppressed nuclear factor erythroid 2-related factor 2 (Nrf2) mediated antioxidative reaction in the spinal cord (P<0.05 vs Control). After Pue administration, the mechanical pain threshold, thermal pain latency, spontaneous pain number and motor latency were improved (P<0.05 vs OXA). In the spinal cord, Pue administration reduced the levels of inflammatory elements, increased the levels of antioxidative elements and decreased the levels of oxidative factors (P<0.05 vs OXA). Furthermore, Pue also bind with Nrf2 and increased the association of Nrf2 to glutathione peroxidase 4 (GPX4). In summary, Pue alleviates oxaliplatin induced neuropathic pain by enhancing Nrf2/GPX4-mediated antioxidant response and suppressing inflammatory reaction in the spinal cord.

Sciatic nerve stimulation alleviates neuropathic pain and associated neuroinflammation in the dorsal root ganglia in a rodent model.

BACKGROUND: Satellite glial cells (SGCs) in the dorsal root ganglia (DRG) play a pivotal role in the formation of neuropathic pain (NP). Sciatic nerve stimulation (SNS) neuromodulation was reported to alleviate NP and reduce neuroinflammation. However, the mechanisms underlying SNS in the DRG remain unclear. This study aimed to elucidate the mechanism of electric stimulation in reducing NP, focusing on the DRG. METHODS: L5 nerve root ligation (NRL) NP rat model was studied. Ipsilateral SNS performed 1 day after NRL. Behavioral tests were performed to assess pain phenotypes. NanoString Ncounter technology was used to explore the differentially expressed genes and cellular pathways. Activated SGCs were characterized in vivo and in vitro. The histochemical alterations of SGCs, macrophages, and neurons in DRG were examined in vivo on post-injury day 8. RESULTS: NRL induced NP behaviors including decreased pain threshold and latency on von Frey and Hargreaves tests. We found that following nerve injury, SGCs were hyperactivated, neurotoxic and had increased expression of NP-related ion channels including TRPA1, Cx43, and SGC-neuron gap junctions. Mechanistically, nerve injury induced reciprocal activation of SGCs and M1 macrophages via cytokines including IL-6, CCL3, and TNF-α mediated by the HIF-1α-NF-κB pathways. SNS suppressed SGC hyperactivation, reduced the expression of NP-related ion channels, and induced M2 macrophage polarization, thereby alleviating NP and associated neuroinflammation in the DRG. CONCLUSIONS: NRL induced hyperactivation of SGCs, which had increased expression of NP-related ion channels. Reciprocal activation of SGCs and M1 macrophages surrounding the primary sensory neurons was mediated by the HIF-1α and NF-κB pathways. SNS suppressed SGC hyperactivation and skewed M1 macrophage towards M2. Our findings establish SGC activation as a crucial pathomechanism in the gliopathic alterations in NP, which can be modulated by SNS neuromodulation.

Exploring the Analgesic Initiation Mechanism of Tuina in the Dorsal Root Ganglion of Minor CCI Rats via the TRPV1/TRPA1-cGMP Pathway.

Tuina is a treatment method in traditional Chinese medicine which has analgesic effects and effectively alleviates the symptoms of neuropathic pain (NP). Transient receptor potential vanilloid type 1 (TRPV1) and transient receptor potential ankyrin type 1 (TRPA1) play major roles in transmitting nociceptive sensory signals in the nociceptive primary sensory dorsal root ganglion (DRG) nerve. The nitric oxide (NO)/cyclic guanosine 3',5'-monophosphate(cGMP) pathway exerts both nociceptive and antinociceptive effects in various chronic pain models. TRPV1 and TRPA1 mediate the influx of calcium, which stimulates the generation of NO. Subsequently, NO activates the NO/cGMP/protein kinase G (PKG) signaling pathway, thereby improving hyperalgesia. In the present study, oa rat model of NP with minor chronic constriction injury (CCI) of the right sciatic nerve of NP was established. The results of behavioral testing showed that, after a one-time tuina intervention, the mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were prolonged to varying degrees in the tuina group compared with the model group. Similarly, the expression of TRPV1, TRPA1, NO, soluble guanylate cyclase ß (sGCß), cGMP, and PKG1 was significantly decreased in the DRG of the tuina and tuina + TRPV1/TRPA1 antagonist group was significantly decreased. These findings suggest that the tuina intervention can effectively improve the symptoms of thermal and mechanical allodynia caused by peripheral nerve injuries. Tuina exerts immediate analgesic effects through the TRPV1/TRPA1-NO-cGMP-PKG signaling pathway.

Rehabilitation interventions for neuropathic pain: a systematic review and meta-analysis of randomized controlled trials.

OBJECTIVE: Rehabilitation interventions for chronic pain typically include education, cognitive behavioural therapy, and exercise therapy, or a combination of these. A systematic review and meta-analysis of rehabilitation interventions for neuropathic pain was conducted. DESIGN: Randomized controlled trials were identified in PubMed, EMBASE, Cochrane Central Register of Controlled Trials, and PsycINFO databases from inception up to 3 March 2022. SUBJECTS/PATIENTS: Adults with chronic (> 3 months) neuropathic pain. METHODS: Primary outcomes were pain intensity, pain-related disability, and work participation. Secondary outcomes were quality of life, emotional strain, insomnia, and adverse outcomes, according to VAPAIN guidelines. Analyses were made post-intervention, which was defined as the assessment point immediately following the intervention or at the first-time measurement conducted after the intervention period. RESULTS: In total, 15 studies (total population, n = 764) were incorporated. Most common interventions were cognitive behavioural programmes including acceptance and commitment therapy (n = 4), mindfulness-based interventions (n = 5), and yoga (n = 2). Psychological interventions reduced both pain intensity (SMD -0.49, 95% CI -0.88 to -0.10) and pain-related disability (SMD -0.51, 95% CI -0.98 to -0.03), whereas other interventions had an effect on pain intensity but not on pain-related disability. CONCLUSION: Rehabilitation interventions, and psychological interventions in particular, seem to be of value for patients with chronic neuropathic pain.

[Guasha-fangsha therapy combined with electroacupuncture in treatment of greater occipital neuralgia: a randomized controlled trial].

OBJECTIVE: To observe the clinical effect of guasha-fangsha (scrapping and bleeding) therapy combined with electroacupuncture (EA) on greater occipital neuralgia. METHODS: Ninety patients with greater occipital neuralgia were randomly divided into an observation group (45 cases) and a control group (45 cases, 2 cases dropped out). In the control group, EA was delivered at Fengfu (GV 16) and bilateral Tianzhu (BL 10), Fengchi (GB 20), Wangu (GB 12), Yuzhen (BL 9) and Houxi (SI 3), with disperse-dense wave, at 2 Hz/100 Hz in frequency and 2 mA to 6 mA in intensity, for 30 min in each intervention, once every other days, 3 times a week. In the observation group, on the basis of the intervention as the control group, guasha-fangsha therapy was used along the distribution of the bladder meridian of foot-taiyang on the occipital region and that of the gallbladder meridian of foot-shaoyang on the lateral side of the head, once weekly. The duration of treatment was 3 weeks in the two groups. In the two groups, before treatment, after 1, 2 and 3 weeks of treatment and in follow-up visit after 3 weeks of treatment completion, the score of visual analogue scale (VAS) was observed; before and after treatment, as well as in follow-up visit after 3 weeks of treatment completion, the scores of self-rating anxiety scale (SAS), self-rating depression scale (SDS) and 36-item short-form health survey (SF-36) were observed; after treatment and in follow-up visit after 3 weeks of treatment completion, the clinical efficacy was evaluated. RESULTS: After one week of treatment, the VAS score in the observation group decreased when compared with that before treatment (P<0.05), while the scores in 2 and 3 weeks of treatment and in follow-up visit after 3 weeks of treatment completion were lower than those before treatment in the two groups (P<0.05) separately. At each time point after treatment, the VAS scores in the observation group were lower than those in the control group (P<0.05). After treatment and during the follow-up visit, the scores of SAS and SDS decreased when compared with those before treatment in the two groups (P<0.05), and the scores in the observation group were lower than those in the control group (P<0.05); the scores of each item in SF-36 were elevated in comparison with those before treatment in the two groups (P<0.05), and the scores in the observation group were higher than those in the control group (P<0.05). After treatment, the total effective rate of the observation group was 91.1% (41/45), higher than that (76.7%, 33/43) of the control group (P<0.05). In follow-up visit, the total effective rate of the observation group was 91.1% (41/45), which was higher than 72.1% (31/43) of the control group (P<0.05). CONCLUSION: Guasha-fangsha therapy combined with electroacupuncture can effectively relieve greater occipital neuralgia, alleviate pain severity, ameliorate anxiety and depression and improve the quality of life in the patients.

Neuropathic pain has sex-specific effects on oxycodone-seeking and non-drug-seeking ensemble neurons in the dorsomedial prefrontal cortex of mice.

Approximately 50 million Americans suffer from chronic pain, and nearly a quarter of chronic pain patients have reported misusing opioid prescriptions. Repeated drug seeking is associated with reactivation of an ensemble of neurons sparsely scattered throughout the dorsomedial prefrontal cortex (dmPFC). Prior research has demonstrated that chronic pain increases intrinsic excitability of dmPFC neurons, which may increase the likelihood of reactivation during drug seeking. We tested the hypothesis that chronic pain would increase oxycodone-seeking behaviour and that the pain state would differentially increase intrinsic excitability in dmPFC drug-seeking ensemble neurons. TetTag mice self-administered intravenous oxycodone. After 7 days of forced abstinence, a drug-seeking session was performed, and the ensemble was tagged. Mice received spared nerve injury (SNI) to induce chronic pain during the period between the first and second seeking session. Following the second seeking session, we performed electrophysiology on individual neurons within the dmPFC to assess intrinsic excitability of the drug-seeking ensemble and non-ensemble neurons. SNI had no impact on sucrose seeking or intrinsic excitability of dmPFC neurons from these mice. In females, SNI increased oxycodone seeking and intrinsic excitability of non-ensemble neurons. In males, SNI had no impact on oxycodone seeking or neuron excitability. Data from females are consistent with clinical reports that chronic pain can promote drug craving and relapse and support the hypothesis that chronic pain itself may lead to neuroadaptations which promote opioid seeking.

A 'double-edged' role for type-5 metabotropic glutamate receptors in pain disclosed by light-sensitive drugs.

We used light-sensitive drugs to identify the brain region-specific role of mGlu5 metabotropic glutamate receptors in the control of pain. Optical activation of systemic JF-NP-26, a caged, normally inactive, negative allosteric modulator (NAM) of mGlu5 receptors, in cingulate, prelimbic, and infralimbic cortices and thalamus inhibited neuropathic pain hypersensitivity. Systemic treatment of alloswitch-1, an intrinsically active mGlu5 receptor NAM, caused analgesia, and the effect was reversed by light-induced drug inactivation in the prelimbic and infralimbic cortices, and thalamus. This demonstrates that mGlu5 receptor blockade in the medial prefrontal cortex and thalamus is both sufficient and necessary for the analgesic activity of mGlu5 receptor antagonists. Surprisingly, when the light was delivered in the basolateral amygdala, local activation of systemic JF-NP-26 reduced pain thresholds, whereas inactivation of alloswitch-1 enhanced analgesia. Electrophysiological analysis showed that alloswitch-1 increased excitatory synaptic responses in prelimbic pyramidal neurons evoked by stimulation of presumed BLA input, and decreased BLA-driven feedforward inhibition of amygdala output neurons. Both effects were reversed by optical silencing and reinstated by optical reactivation of alloswitch-1. These findings demonstrate for the first time that the action of mGlu5 receptors in the pain neuraxis is not homogenous, and suggest that blockade of mGlu5 receptors in the BLA may limit the overall analgesic activity of mGlu5 receptor antagonists. This could explain the suboptimal effect of mGlu5 NAMs on pain in human studies and validate photopharmacology as an important tool to determine ideal target sites for systemic drugs.

Exploring viral neuropathic pain: Molecular mechanisms and therapeutic implications.

As the Coronavirus Disease 2019 (COVID-19) pandemic continues, there is a growing concern regarding the relationship between viral infections and neuropathic pain. Chronic neuropathic pain resulting from virus-induced neural dysfunction has emerged as a significant issue currently faced. However, the molecular mechanisms underlying this phenomenon remain unclear, and clinical treatment outcomes are often suboptimal. Therefore, delving into the relationship between viral infections and neuropathic pain, exploring the pathophysiological characteristics and molecular mechanisms of different viral pain models, can contribute to the discovery of potential therapeutic targets and methods, thereby enhancing pain relief and improving the quality of life for patients. This review focuses on HIV-related neuropathic pain (HNP), postherpetic neuralgia (PHN), and neuropathic pain caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infections, examining rodent models and relevant cellular molecular pathways. Through elucidating the connection between viral infections and neuropathic pain, it aims to delineate the current limitations and challenges faced by treatments, thereby providing insights and directions for future clinical practice and research.

Mechanism of gabapentinoid potentiation of opioid effects on cyclic AMP signaling in neuropathic pain.

Over half of spinal cord injury (SCI) patients develop opioid-resistant chronic neuropathic pain. Safer alternatives to opioids for treatment of neuropathic pain are gabapentinoids (e.g., pregabalin and gabapentin). Clinically, gabapentinoids appear to amplify opioid effects, increasing analgesia and overdose-related adverse outcomes, but in vitro proof of this amplification and its mechanism are lacking. We previously showed that after SCI, sensitivity to opioids is reduced by fourfold to sixfold in rat sensory neurons. Here, we demonstrate that after injury, gabapentinoids restore normal sensitivity of opioid inhibition of cyclic AMP (cAMP) generation, while reducing nociceptor hyperexcitability by inhibiting voltage-gated calcium channels (VGCCs). Increasing intracellular Ca2+ or activation of L-type VGCCs (L-VGCCs) suffices to mimic SCI effects on opioid sensitivity, in a manner dependent on the activity of the Raf1 proto-oncogene, serine/threonine-protein kinase C-Raf, but independent of neuronal depolarization. Together, our results provide a mechanism for potentiation of opioid effects by gabapentinoids after injury, via reduction of calcium influx through L-VGCCs, and suggest that other inhibitors targeting these channels may similarly enhance opioid treatment of neuropathic pain.

Human pain channelopathies.

There has been significant progress in our understanding of the molecular basis by which nociceptors transduce and transmit noxious (tissue damaging) stimuli. This is dependent on ion channels, many of which are selectively expressed in nociceptors. Mutations in such proteins have recently been linked to inherited pain disorders in humans. An exemplar is the voltage-gated sodium channel (VGSC) NaV1.7. Loss of function mutations in NaV1.7 result in congenital inability to experience pain while gain-of-function mutations can cause a number of distinct neuropathic pain disorders, including erythromelalgia, paroxysmal extreme pain disorder, and small-fiber neuropathy. Furthermore, variants in the VGSCs 1.8 and 1.9 have also been linked to human pain disorders. There is a correlation between the impact of mutations on the biophysical properties of the ion channel and the severity of the clinical phenotype. Pain channelopathies are not restricted to VGSCs: a mutation in the ligand-gated ion channel TRPA1, (which responds to environmental irritants) causes a familial episodic pain disorder. Ion channel variants have also been linked to more common neuropathic pain disorders such as painful diabetic neuropathy. Not only do these ion channels present targets for novel analgesics, but stratification based on genotype may improve treatment selection of existing analgesics.

Effectiveness of virtual-walking intervention combined with exercise on improving pain and function in incomplete spinal cord injury: a feasibility study.

STUDY DESIGN: A feasibility pilot study. OBJECTIVE: To assess the feasibility a full-scale Randomized Controlled Trial aimed at assessing the beneficial effect of a Virtual Walking (VW)-based (Experimental intervention (EI)) on neuropathic pain and functionality in people with incomplete spinal cord injury (SCI). SETTING: A hospital service (Hospital Universitario y Politécnico La Fe) and disability associations (TetraSport, CODIFIVA and ASPAYM). METHODS: Twelve people with chronic incomplete SCI were randomized to EI (VW plus therapeutic exercise program (TE)) -or Control Intervention (CI (placebo VW and TE)) groups. A six-week intervention (3 sessions/week) was carried out. To assess feasibility, the following outcomes were used: level of restriction and validity of inclusion and exclusion criteria, participants' compliance, accessibility and acceptability of the intervention for participants, adequate pre-training time of physiotherapists. To explore therapy effectiveness, pain severity, and interference, mean and maximum isometric strength, walking speed, and walking ability were assessed before (Time 1, T1) and after (Time 2, T2) the intervention. RESULTS: 20% of the participants initially recruited did not meet inclusion criteria. In addition, all participants completed at least 80% of the intervention sessions and none of the participants dropped out before T2. No serious adverse event was found. Moreover, 91.67% of participants were willing to perform the intervention again and all therapists involved were adequately pre-trained. Finally, our preliminary results suggest that the proposed EI is effective. CONCLUSION: A full-scale RCT is feasible and preliminary results suggest that VW with TE could have a beneficial impact on pain and functionality in this population.