Involvement of TRPV1 and the efficacy of α-spinasterol on experimental fibromyalgia symptoms in mice

Nano-pregabalin effectively mitigates Glut, CGRP and NE neurotransmitters abnormalities in the brain of gamma irradiated rats with reserpine-induced fibromyalgia model: Behavioral and neurochemical studies

AIMS

Fibromyalgia (FM) is an idiopathic syndrome with painful burdensome symptoms. Radiotherapy is one of the main therapeutic modalities for treating various malignancies and there is a probable association between FM exacerbation and exposure to ionizing radiation. Based on that nanomedicines progressively being explored for their promising applications in medicine, the aim of the current study is to assess the possible therapeutic benefits of nanoform of pregabalin (N-PG) in managing FM symptoms during being exposed to ionizing radiation.

MAIN METHODS

Rats were allocated into four groups. First group served as control, the other three groups received gamma radiation (2 Gy/day) after 1 h of reserpine administration (1 ml/kg per day, s.c.) to induce FM for three successive days. On the next day, third and fourth groups received (30 mg/kg, p.o.) of PG and N-PG, respectively once daily for ten consecutive days. Tail flick test was performed and von Frey filaments were used to assess mechanical allodynia/hyperalgesia, and then rats were sacrificed to obtain brains.

KEY FINDINGS

N-PG effectively replenished reserpine effects and treated both allodynia and hyperalgesia, improved thermal allodynia, effectively recovered all neurotransmitters near to normal baseline, inhibited oxidative stress status via decreasing malondialdehyde (MDA), increasing glutathione (GSH) and superoxide dismutase (SOD), it had strong anti-inflammatory effect as verified by reducing both cyclooxygenase-2 (COX-2) and nuclear factor kappa B (NF-kB) in addition to inhibition of intrinsic apoptosis through caspase-3 (casp-3) decrease and B-cell lymphoma-2 (Bcl-2) increase. Histopathological and immunohistochemical results confirmed the biochemical findings.

SIGNIFICANCE

N-PG could be a promising drug for treating FM especially when there is urgent need to expose patient to ionizing radiation.

Electroacupuncture Mitigates TRPV1 Overexpression in the Central Nervous System Associated with Fibromyalgia in Mice

BACKGROUND

Fibromyalgia (FM) is characterized by chronic pain, significantly affecting the quality of life and functional capabilities of patients. In addition to pain, patients may experience insomnia, chronic fatigue, depression, anxiety, and headaches, further complicating their overall well-being. The Transient Receptor Potential Vanilloid 1 (TRPV1) receptor responds to various noxious stimuli and plays a key role in regulating pain sensitivity and inflammation. Thus, targeting TRPV1 may provide analgesic and anti-inflammatory benefits. This study investigates the efficacy of electroacupuncture (EA) in alleviating chronic pain in FM through TRPV1 and its downstream molecules in the central nervous system (CNS).

METHODS

To model FM, we subjected mice to intermittent cold stress (ICS) for three days. The study comprised five rodent groups: Control (CON), ICS, ICS + EA, ICS + Sham EA, and ICS + KO (TRPV1 knockout mice).

RESULTS

Our findings revealed that ICS induced allodynia and hyperalgesia in mice by day four, persisting until day 21. EA at 2 Hz and TRPV1 KO significantly decreased both mechanical and thermal hypersensitivity (Withdrawal-Day 14: 2.43 ± 0.19 g; Day 21: 5.88 ± 0.47 g, n = 6, p < 0.05; Latency-Day 14: 2.77 ± 0.22 s; Day 21: 5.85 ± 0.41 s, n = 6, p < 0.05). In contrast, sham EA did not produce significant effects. Additionally, TRPV1 and several pain-related proteins were significantly elevated in the thalamus, somatosensory cortex (SSC), medial prefrontal cortex (mPFC), hippocampus, hypothalamus, cerebellum regions V (CB V), VI (CB VI) and VII (CB VII) after the ICS model. Both EA at the ST36 acupoint and TRPV1 KO mice showed diminished overexpression of pain-related proteins, with the sham EA group showing no significant changes compared to the ICS group.

CONCLUSIONS

Chronic widespread pain was reduced by EA and TRPV1 KO, with the effects of EA on the TRPV1 pain pathway clearly evident in the CNS after 21 days.

Schwann cell TRPA1 elicits reserpine-induced fibromyalgia pain in mice

BACKGROUND AND PURPOSE

Fibromyalgia is a complex clinical disorder with an unknown aetiology, characterized by generalized pain and co-morbid symptoms such as anxiety and depression. An imbalance of oxidants and antioxidants is proposed to play a pivotal role in the pathogenesis of fibromyalgia symptoms. However, the precise mechanisms by which oxidative stress contributes to fibromyalgia-induced pain remain unclear. The transient receptor potential ankyrin 1 (TRPA1) channel, known as both a pain sensor and an oxidative stress sensor, has been implicated in various painful conditions.

EXPERIMENTAL APPROACH

The feed-forward mechanism that implicates reactive oxygen species (ROS) driven by TRPA1 was investigated in a reserpine-induced fibromyalgia model in C57BL/6J mice employing pharmacological interventions and genetic approaches.

KEY RESULTS

Reserpine-treated mice developed pain-like behaviours (mechanical/cold hypersensitivity) and early anxiety-depressive-like disorders, accompanied by increased levels of oxidative stress markers in the sciatic nerve tissues. These effects were not observed upon pharmacological blockade or global genetic deletion of the TRPA1 channel and macrophage depletion. Furthermore, we demonstrated that selective silencing of TRPA1 in Schwann cells reduced reserpine-induced neuroinflammation (NADPH oxidase 1-dependent ROS generation and macrophage increase in the sciatic nerve) and attenuated fibromyalgia-like behaviours.

CONCLUSION AND IMPLICATIONS

Activated Schwann cells expressing TRPA1 promote an intracellular pathway culminating in the release of ROS and recruitment of macrophages in the mouse sciatic nerve. These cellular and molecular events sustain mechanical and cold hypersensitivity in the reserpine-evoked fibromyalgia model. Targeting TRPA1 channels on Schwann cells could offer a novel therapeutic approach for managing fibromyalgia-related behaviours.

Electroacupuncture Reduced Fibromyalgia-Pain-like Behavior through Inactivating Transient Receptor Potential V1 and Interleukin-17 in Intermittent Cold Stress Mice Model

Fibromyalgia (FM) is a widespread musculoskeletal pain associated with psychological disturbances, the etiopathogenesis of which is still not clear. One hypothesis implicates inflammatory cytokines in increasing central and peripheral sensitization along with neuroinflammation, leading to an elevation in pro-inflammatory cytokines, e.g., interleukin-17A (IL-17A), enhanced in FM patients and animal models. The intermittent cold stress (ICS)-induced FM-like model in C57BL/6 mice has been developed since 2008 and proved to have features which mimic the clinical pattern in FM patients such as mechanical allodynia, hyperalgesia, and female predominance of pain. Electroacupuncture (EA) is an effective treatment for relieving pain in FM patients, but its mechanism is not totally clear. It was reported as attenuating pain-like behaviors in the ICS mice model through the transient receptor potential vanilloid 1 (TRPV1) pathway. Limited information indicates that TRPV1-positive neurons trigger IL-17A-mediated inflammation. Therefore, we hypothesized that the IL-17A would be inactivated by EA and TRPV1 deletion in the ICS-induced FM-like model in mice. We distributed mice into a control (CON) group, ICS-induced FM model (FM) group, FM model with EA treatment (EA) group, FM model with sham EA treatment (Sham) group, and TRPV1 gene deletion (Trpv1-/-) group. In the result, ICS-induced mechanical and thermal hyperalgesia increased pro-inflammatory cytokines including IL-6, IL-17, TNFα, and IFNγ in the plasma, as well as TRPV1, IL-17RA, pPI3K, pAkt, pERK, pp38, pJNK, and NF-κB in the somatosensory cortex (SSC) and cerebellum (CB) lobes V, VI, and VII. Moreover, EA and Trpv1-/- but not sham EA countered these effects significantly. The molecular mechanism may involve the pro-inflammatory cytokines, including IL-6, IL-17, TNFα, and IFNγ. IL-17A-IL-17RA play a crucial role in peripheral and central sensitization as well as neuroinflammation and cannot be activated without TRPV1 in the ICS mice model. EA alleviated FM-pain-like behaviors, possibly by abolishing the TRPV1- and IL-17A-related pathways. It suggests that EA is an effective and potential therapeutic strategy in FM.

Diosmetin attenuates fibromyalgia-like symptoms in a reserpine-induced model in mice

Fibromyalgia is a potentially disabling idiopathic disease characterized by widespread chronic pain associated with comorbidities such as fatigue, anxiety, and depression. Current therapeutic approaches present adverse effects that limit adherence to therapy. Diosmetin, an aglycone of the flavonoid glycoside diosmin found in citrus fruits and the leaves of Olea europaea L., has antinociceptive, anti-inflammatory, and antioxidant properties. Here, we investigated the effect of diosmetin on nociceptive behaviors and comorbidities in an experimental fibromyalgia model induced by reserpine in mice. To induce the experimental fibromyalgia model, a protocol of subcutaneous injections of reserpine (1 mg/kg) was used once a day for three consecutive days in adult male Swiss mice. Mice received oral diosmetin on the fourth day after the first reserpine injection. Nociceptive (mechanical allodynia, muscle strength, and thermal hyperalgesia) and comorbid (depressive-like and anxiety behavior) parameters were evaluated. Potential adverse effects associated with diosmetin plus reserpine (locomotor alteration, cataleptic behavior, and body weight and temperature changes) were also evaluated. Oral diosmetin (0.015-1.5 mg/kg) reduced the mechanical allodynia, thermal hyperalgesia, and loss of muscle strength induced by reserpine. Diosmetin (0.15 mg/kg) also attenuated depressive-like and anxiety behaviors without causing locomotor alteration, cataleptic behavior, and alteration in weight and body temperature of mice. Overall, diosmetin can be an effective and safe therapeutic alternative to treat fibromyalgia symptoms, such as pain, depression and anxiety.

The Fibromyalgia Pain Experience: A Scoping Review of the Preclinical Evidence for Replication and Treatment of the Affective and Cognitive Pain Dimensions

Fibromyalgia is a chronic, widespread pain disorder that is strongly represented across the affective and cognitive dimensions of pain, given that the underlying pathophysiology of the disorder is yet to be identified. These affective and cognitive deficits are crucial to understanding and treating the fibromyalgia pain experience as a whole but replicating this multidimensionality on a preclinical level is challenging. To understand the underlying mechanisms, animal models are used. In this scoping review, we evaluate the current primary animal models of fibromyalgia regarding their translational relevance within the affective and cognitive pain realms, as well as summarize treatments that have been identified preclinically for attenuating these deficits.

Involvement of peripheral mast cells in a fibromyalgia model in mice

Fibromyalgia is a painful disorder of unknown aetiology that presents activation and recruitment of innate immune cells, including mast cells. Efforts have been made to understand its pathogenesis to manage it better. Thus, we explored the involvement of peripheral mast cells in an experimental model of fibromyalgia induced by reserpine. Reserpine (1 mg/kg) was subcutaneously (s.c.) injected once daily in the back of male Swiss mice for three consecutive days. We analysed mechanical and cold allodynia, muscle fatigue and number of mast cell in plantar tissue. The fibromyalgia induction produced mast cell infiltration (i.e., mastocytosis) in the mice's plantar tissue. The depletion of mast cell mediators with the compound 48/80 (0.5-4 mg/kg, intraperitoneal (i.p.)) or the mast cell membrane stabilizer ketotifen fumarate (10 mg/kg, oral route (p.o.) widely (80-90 %) and extensively (from 1 up to 10 days) prevented reserpine-induced mechanical and cold allodynia and muscle fatigue. Compound 48/80 also prevented the reserpine-induced mastocytosis. Finally, we demonstrated that PAR-2, 5-HT2A, 5-HT3, H1, NK1 and MrgprB2 receptors, expressed in neuronal or mast cells, seem crucial to mediate fibromyalgia-related cardinal symptoms since antagonists or inhibitors of these receptors (gabexate (10 mg/kg, s.c.), ENMD-1068 (10 mg/kg, i.p.), ketanserin (1 mg/kg, i.p.), ondansetron (1 mg/kg, p.o.), promethazine (1 mg/kg, i.p.), and L733,060 (5 mg/kg, s.c.), respectively) transiently reversed the reserpine-induced allodynia and fatigue. The results indicate that mast cells mediate painful and fatigue behaviours in this fibromyalgia model, representing potential therapy targets to treat fibromyalgia syndrome.

TRPV4 Activation and its Intracellular Modulation Mediated by Kinin Receptors Contribute to Painful Symptoms Induced by Anastrozole

Anastrozole, an aromatase inhibitor, induces painful musculoskeletal symptoms, which affect patients' quality of life and lead to therapy discontinuation. Efforts have been made to understand the mechanisms involved in these painful symptoms to manage them better. In this context, we explored the role of the Transient Receptor Potential Vanilloid 4 (TRPV4), a potential transducer of several nociceptive mechanisms, in anastrozole-induced musculoskeletal pain in mice. Besides, we evaluated the possible sensibilization of TRPV4 by signalling pathways downstream, PLC, PKC and PKCε from kinin B2 (B2R) and B1 (B1R) receptors activation in anastrozole-induced pain. Anastrozole caused mechanical allodynia and muscle strength loss in mice. HC067047, TRPV4 antagonist, reduced the anastrozole-induced mechanical allodynia and muscle strength loss. In animals previously treated with anastrozole, the local administration of sub-nociceptive doses of the TRPV4 (4α-PDD or hypotonic solution), B2R (Bradykinin) or B1R (DABk) agonists enhanced the anastrozole-induced pain behaviours. The sensitizing effects induced by local injection of the TRPV4, B2R and B1R agonists in animals previously treated with anastrozole were reduced by pre-treatment with TRPV4 antagonist. Furthermore, inhibition of PLC, PKC or PKCε attenuated the mechanical allodynia and muscle strength loss induced by TRPV4, B2R and B1R agonists. The generation of painful conditions caused by anastrozole depends on direct TRPV4 activation or indirect, e.g., PLC, PKC and PKCε pathways downstream from B2R and B1R activation. Thus, the TRPV4 channels act as sensors of extracellular and intracellular changes, making them potential therapeutic targets for alleviating pain related to aromatase inhibitors use, such as anastrozole.

Kinin B1 and B2 Receptors Contribute to Cisplatin-Induced Painful Peripheral Neuropathy in Male Mice

Cisplatin is the preferential chemotherapeutic drug for highly prevalent solid tumours. However, its clinical efficacy is frequently limited due to neurotoxic effects such as peripheral neuropathy. Chemotherapy-induced peripheral neuropathy is a dose-dependent adverse condition that negatively impacts quality of life, and it may determine dosage limitations or even cancer treatment cessation. Thus, it is urgently necessary to identify pathophysiological mechanisms underlying these painful symptoms. As kinins and their B1 and B2 receptors contribute to the development of chronic painful conditions, including those induced by chemotherapy, the contribution of these receptors to cisplatin-induced peripheral neuropathy was evaluated via pharmacological antagonism and genetic manipulation in male Swiss mice. Cisplatin causes painful symptoms and impaired working and spatial memory. Kinin B1 (DALBK) and B2 (Icatibant) receptor antagonists attenuated some painful parameters. Local administration of kinin B1 and B2 receptor agonists (in sub-nociceptive doses) intensified the cisplatin-induced mechanical nociception attenuated by DALBK and Icatibant, respectively. In addition, antisense oligonucleotides to kinin B1 and B2 receptors reduced cisplatin-induced mechanical allodynia. Thus, kinin B1 and B2 receptors appear to be potential targets for the treatment of cisplatin-induced painful symptoms and may improve patients’ adherence to treatment and their quality of life.

Selected Seeds as Sources of Bioactive Compounds with Diverse Biological Activities

Seeds contain a variety of phytochemicals that exhibit a wide range of biological activities. Plant-derived compounds are often investigated for their antioxidant, anti-inflammatory, immunomodulatory, hypoglycemic, anti-hypercholesterolemic, anti-hypertensive, anti-platelet, anti-apoptotic, anti-nociceptive, antibacterial, antiviral, anticancer, hepatoprotective, or neuroprotective properties. In this review, we have described the chemical content and biological activity of seeds from eight selected plant species-blackberry (Rubus fruticosus L.), black raspberry (Rubus coreanus Miq.), grape (Vitis vinifera L.), Moringa oleifera Lam., sea buckthorn (Hippophae rhamnoides L.), Gac (Momordica cochinchinensis Sprenger), hemp (Cannabis sativa L.), and sacha inchi (Plukenetia volubilis L). This review is based on studies identified in electronic databases, including PubMed, ScienceDirect, and SCOPUS. Numerous preclinical, and some clinical studies have found that extracts, fractions, oil, flour, proteins, polysaccharides, or purified chemical compounds isolated from the seeds of these plants display promising, health-promoting effects, and could be utilized in drug development, or to make nutraceuticals and functional foods. Despite that, many of these properties have been studied only in vitro, and it's unsure if their effects would be relevant in vivo as well, so there is a need for more animal studies and clinical trials that would help determine if they could be applied in disease prevention or treatment.

Pharmacology of α-spinasterol, a phytosterol with nutraceutical values: A review

α-Spinasterol is a phytosterol found in various edible and non-edible plant sources. The edible plant materials containing α-spinasterol include spinach leaves, cucumber fruits, seeds of pumpkin and watermelon, argan seed oil, cactus pear seed oil and Amaranthus sp. It is a bioavailable nutraceutical, and it can cross the blood-brain barrier. It possesses several important pharmacological properties such as anti-diabetes mellitus, antiinflammation, hypolipidemic, antiulcer, neuroprotection, anti-pain and antitumour activities. For this review, literature search was made focusing on the pharmacological properties of α-spinasterol using PubMed and Google Scholar data bases. Recent studies show the promising antidiabetic properties of α-spinasterol. Its anti-diabetic mechanisms include enhancement of insulin secretion, reduction in insulin resistance, anti-diabetic nephropathy, increase in glucose uptake in muscle cells and inhibition of glucose absorption from intestine. Besides, it is a safe antiinflammatory agent, and its antiinflammatory mechanisms include inhibition of cyclooxygenases, antagonism of TRPV1 receptor and attenuation of proinflammatory cytokines and mediators. It is a promising and safe nutraceutical molecule for human health care. Food supplements, value-added products and nutraceutical formulations can be developed with α-spinasterol for the management of diabetes, chronic inflammatory diseases and improving general health. This review provides all scattered pharmacological studies on α-spinasterol in one place and highlights its immense value for human health care.

Therapeutic Approaches to Nociplastic Pain Based on Findings in the Reserpine-Induced Fibromyalgia-Like Animal Model

Nociplastic pain, the third category of chronic pain, has emerged as a serious medical issue. Due to its significant negative influences on patients and society, high prevalence, and lack of sufficiently effective treatments, more efficacious therapies are required. This review highlights the potential therapeutic approaches identified in studies that used reserpine-induced myalgia (RIM) animal model that exhibits nociplastic pain-associated phenotypes. These studies have revealed that biological processes including the chronic reduction of monoamines, increase of oxidative/nitrosative stresses and inflammatory mediators, upregulation of pronociceptive neurotransmitters and their receptors, increase of trophic factors, enhancement of the apoptotic pathway, sensory nerve sensitization, and activation of immune cells in central and/or peripheral regions, underly the nociplastic pain-associated phenotypes in RIM animal model. Potential therapeutic approaches to nociplastic pain, i.e., 1) functional modification of specific molecules which expression is distinctly altered following monoamine reduction, 2) targeting the molecules which are responsible for other major categories of chronic pain (i.e., chronic inflammatory pain and neuropathic pain), 3) supplementation of nutrition to correct the disrupted nutritional balance, 4) improvement of physical constitution by natural substances, and 5) nonpharmacological interventions, have been identified. Significance Statement Studies in RIM animal model have revealed the pathologies that occur after the chronic reduction of monoamines and identified potential therapeutic approaches to nociplastic pain. Translation of their analgesic efficacy from RIM animal model to patients remains an issue to be addressed. Successful translation would lead to better therapies for nociplastic pain.

Pramipexole, a dopamine D3/D2 receptor-preferring agonist, attenuates reserpine-induced fibromyalgia-like model in mice

Fibromyalgia (FM) is a complex pathology described as persistent hyperalgesia including somatic and mood dysfunctions, depression and anxiety. Although the etiology of FM is still unknown, a significant decrease in biogenic amines is a common characteristic in its pathogenesis. Here, our main objective was to investigate the role of dopamine D3/D2 receptor during the reserpine-induced pain in mice. Our results showed that pramipexole (PPX) - a dopaminergic D3/D2 receptor agonist - inhibited mechanical allodynia and thermal sensitivity induced by reserpine. Relevantly, PPX treatment decreased immobility time and increased the number of grooming in the forced swimming test and splash test, respectively. Animals that received PPX remained longer in the open arms than the reserpine group using elevated plus-maze apparatus. The repeated PPX administration, given daily for 4 days, significantly blocked the mechanical and thermal allodynia during FM model, similarly to pregabalin, although it failed to affect the reserpine-induced thermal nociception. Reserpine administration induced significant downregulation of dopamine concentration in the central nervous system, and repeated treatment with PPX restored dopamine levels in the frontal cortex and spinal cord tissues. Moreover, PPX treatment inhibited oxidants production such as DCFH (2',7'-dichlorodihydrofluorescein) and nitrite, also decreased oxidative damage (carbonyl), and upregulated the activity of superoxide dismutase in the spinal cord. Together, our findings demonstrated the ability of dopamine D3/D2 receptor-preferring agonist in reducing pain and mood dysfunction allied to FM in mice. All experimental protocols were approved by the Universidade Federal de Santa Catarina (UFSC) Ethics Committee (approval No. 2572210218) on May 10, 2018.

Animal models of fibromyalgia: What is the best choice?

Fibromyalgia (FM) is a complex syndrome, with an indefinite aetiology and intricate pathophysiology that affects 2 - 3% of the world population. From the beginning of the 2000s, experimental animal models have been developed to mimic clinical FM and help obtain a better understanding of the relevant neurobiology. These animal models have enabled a broad study of FM symptoms and mechanisms, as well as new treatment strategies. Current experimental FM models include the reserpine-induced systemic depletion of biogenic amines, muscle application of acid saline, and stress-based (cold, sound, or swim) approaches, among other emerging models. FM models should: (i) mimic the cardinal symptoms and complaints reported by FM patients (e.g., spontaneous nociception, muscle pain, hypersensitivity); (ii) mimic primary comorbidities that can aggravate quality of life and lead to worse outcomes (e.g., fatigue, sleep disturbance, depression, anxiety); (iii) mimic the prevalent pathological mechanisms (e.g., peripheral and central sensitization, inflammation/neuroinflammation, change in the levels of the excitatory and inhibitory neurotransmitters); and (iv) demonstrate a pharmacological profile similar to the clinical treatment of FM. However, it is difficult for any one of these models to include the entire spectrum of clinical FM features once even FM patients are highly heterogeneous. In the past six years (2015 - 2020), a wide range of experimental FM studies has amounted to the literature reinforcing the need for an updated review. Here we have described, in detail, several approaches used to experimentally study FM, with a focus on recent studies in the field and in previously less discussed mechanisms. We highlight each model's challenges, limitations, and future directions, intending to help preclinical researchers establish the correct experimental FM model to use depending on their goals.

Serotonergic Neurotransmission System Modulator, Vortioxetine, and Dopaminergic D2/D3 Receptor Agonist, Ropinirole, Attenuate Fibromyalgia-Like Symptoms in Mice

Fibromyalgia is a disease characterized by lowered pain threshold, mood disorders, and decreased muscular strength. It results from a complex dysfunction of the nervous system and due to unknown etiology, its diagnosis, treatment, and prevention are a serious challenge for contemporary medicine. Impaired serotonergic and dopaminergic neurotransmission are regarded as key factors contributing to fibromyalgia. The present research assessed the effect of serotonergic and dopaminergic system modulators (vortioxetine and ropinirole, respectively) on the pain threshold, depressive-like behavior, anxiety, and motor functions of mice with fibromyalgia-like symptoms induced by subcutaneous reserpine (0.25 mg/kg). By depleting serotonin and dopamine in the mouse brain, reserpine induced symptoms of human fibromyalgia. Intraperitoneal administration of vortioxetine and ropinirole at the dose of 10 mg/kg alleviated tactile allodynia. At 5 and 10 mg/kg ropinirole showed antidepressant-like properties, while vortioxetine had anxiolytic-like properties. None of these drugs influenced muscle strength but reserpine reduced locomotor activity of mice. Concluding, in the mouse model of fibromyalgia vortioxetine and ropinirole markedly reduced pain. These drugs affected emotional processes of mice in a distinct manner. Hence, these two repurposed drugs should be considered as potential drug candidates for fibromyalgia. The selection of a specific drug should depend on patient’s key symptoms.

Relevance of Mitochondrial Dysfunction in the Reserpine-Induced Experimental Fibromyalgia Model

Fibromyalgia (FM) is one of the most common musculoskeletal pain conditions. Although the aetiology of FM is still unknown, mitochondrial dysfunction and the overproduction of reactive oxygen intermediates (ROI) are common characteristics in its pathogenesis. The reserpine experimental model can induce FM-related symptoms in rodents by depleting biogenic amines. However, it is unclear whether reserpine causes other pathophysiologic characteristics of FM. So far, no one has investigated the relevance of mitochondrial dysfunction in the reserpine-induced experimental FM model using protection- and insult-based mitochondrial modulators. Reserpine (1 mg/kg) was subcutaneously injected once daily for three consecutive days in male Swiss mice. We carried out analyses of reserpine-induced FM-related symptoms, and their modulation by using mitochondrial insult on ATP synthesis (oligomycin; 1 mg/kg, intraperitoneally) or mitochondrial protection (coenzyme Q10; 150 mg/kg/5 days, orally). We also evaluated the effect of reserpine on mitochondrial function using high-resolution respirometry and oxidative status. Reserpine caused nociception, loss in muscle strength, and anxiety- and depressive-like behaviours in mice that were consistent with clinical symptoms of FM, without inducing body weight and temperature alterations or motor impairment. Reserpine-induced FM-related symptoms were increased by oligomycin and reduced by coenzyme Q10 treatment. Reserpine caused mitochondrial dysfunction by negatively modulating the electron transport system and mitochondrial respiration (ATP synthesis) mainly in oxidative muscles and the spinal cord. These results support the role of mitochondria in mediating oxidative stress and FM symptoms in this model. In this way, reserpine-inducing mitochondrial dysfunction and increased production of ROI contribute to the development and maintenance of nociceptive, fatigue, and depressive-like behaviours.