Sleep architecture is altered in the reserpine-induced fibromyalgia model in ovariectomized rats

Sleep deprivation induces late deleterious effects in a pharmacological model of Parkinsonism

Parkinson's disease is a degenerative, chronic and progressive disease, characterized by motor dysfunctions. Patients also exhibit non-motor symptoms, such as affective and sleep disorders. Sleep disorders can potentiate clinical and neuropathological features and lead to worse prognosis. The goal of this study was to evaluate the effects of sleep deprivation (SD) in mice submitted to a progressive pharmacological model of Parkinsonism (chronic administration with a low dose of reserpine). Male Swiss mice received 20 injections of reserpine (0.1 mg/kg) or vehicle, on alternate days. SD was applied before or during reserpine treatment and was performed by gentle handling for 6 h per day for 10 consecutive days. Animals were submitted to motor and non-motor behavioral assessments and neurochemical evaluations. Locomotion was increased by SD and decreased by reserpine treatment. SD during treatment delayed the onset of catalepsy, but SD prior to treatment potentiated reserpine-induced catalepsy. Thus, although SD induced an apparent beneficial effect on motor parameters, a delayed deleterious effect on alterations induced by reserpine was found. In the object recognition test, both SD and reserpine treatment produced cognitive deficits. In addition, the association between SD and reserpine induced anhedonic-like behavior. Finally, an increase in oxidative stress was found in hippocampus of mice subjected to SD, and tyrosine hydroxylase immunoreactivity was reduced in substantia nigra of reserpine-treated animals. Results point to a possible late effect of SD, aggravating the deficits in mice submitted to the reserpine progressive model of PD.

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.

Sleep disorders in chronic pain and its neurochemical mechanisms: a narrative review

Chronic pain (CP) is a prevalent problem, and more than half of patients with CP have sleep disorders. CP comorbidity with sleep disorders imposes immense suffering and seriously affects the patient's quality of life, which is a challenging issue encountered by clinicians. Although the reciprocal interactions between pain and sleep have been studied to some degree, there is still a lack of awareness and comprehensive description of CP comorbidity with sleep disorders. In this narrative review article, we summarize the current knowledge about the present estimates of the prevalence of comorbid sleep disorders in CP patients, sleep detection methods, sleep characterization in CP, and the effect of sleep disorders on CP and current therapies. We also summarize current knowledge of the neurochemical mechanisms of CP comorbidity with sleep disorders. In conclusion, insufficient attention has been paid to the role of sleep disorders in CP patients, and CP patients should be screened for sleep disorders in the clinic. Special attention should be given to a possible risk of drug-drug interaction when using two types of drugs targeting pain and sleep simultaneously. The current insight into the neurobiological mechanisms underlying CP comorbidity with sleep disorders is still rather limited.

Targeting α7-nAChR by galantamine mitigates reserpine-induced fibromyalgia-like symptoms in rats: Involvement of cAMP/PKA, PI3K/AKT, and M1/M2 microglia polarization

Fibromyalgia (FM) is a pain disorder marked by generalized musculoskeletal pain accompanied by depression, fatigue, and sleep disturbances. Galantamine (Gal) is a positive allosteric modulator of neuronal nicotinic acetylcholine receptors (nAChRs) and a reversible inhibitor of cholinesterase. The current study aimed to explore the therapeutic potential of Gal against reserpine (Res)-induced FM-like condition along with investigating the α7-nAChR's role in Gal-mediated effects. Rats were injected with Res (1 mg/kg/day; sc) for 3 successive days then Gal (5 mg/kg/day; ip) was given alone and with the α7-nAChR blocker methyllycaconitine (3 mg/kg/day; ip), for the subsequent 5 days. Galantamine alleviated Res-induced histopathological changes and monoamines depletion in rats' spinal cord. It also exerted analgesic effect along with ameliorating Res-induced depression and motor-incoordination as confirmed by behavioral tests. Moreover, Gal produced anti-inflammatory effect through modulating AKT1/AKT2 and shifting M1/M2 macrophage polarization. The neuroprotective effects of Gal were mediated through activating cAMP/PKA and PI3K/AKT pathways in α7-nAChR-dependent manner. Thus, Gal can ameliorate Res-induced FM-like symptoms and mitigate the associated monoamines depletion, neuroinflammation, oxidative stress, apoptosis, and neurodegeneration through α7-nAChR stimulation, with the involvement of cAMP/PKA, PI3K/AKT, and M1/M2 macrophage polarization.

Stem cells therapeutic effect in a reserpine-induced fibromyalgia rat model: A possible NLRP3 inflammasome modulation with neurogenesis promotion in the cerebral cortex

Fibromyalgia is a chronic pain syndrome with a multifactorial pathophysiology affecting 2-8 % of the population.

AIMS

To investigate the therapeutic effects of bone marrow mesenchymal stem cells (BMSCs) against fibromyalgia-related cerebral cortex damage and the possible underlying mechanisms of action.

MATERIALS AND METHODS

Rats were randomly allocated into three groups; control, fibromyalgia and fibromyalgia treated with BMSCs groups. Physical and behavioural assessments were performed. Cerebral cortices were collected for biochemical and histological assessment.

KEY FINDINGS

Fibromyalgia group showed behavioural changes indicating presence of pain, fatigue, depression, and sleep disturbances. Moreover, biochemical biomarkers alterations were demonstrated by a significant decrease in brain monoamines and GSH levels, but MDA, NO, TNF-alpha, HMGB-1, NLRP3, and caspase-1 levels significantly increased. Furthermore, histological assessment revealed structural and ultrastructural alterations indicating neuronal and neuroglial degeneration with microglia activation, an increase in mast cell number and IL-1β immune-expression. Additionally, a significant decrease in Beclin-1 immune-expression, and blood brain barrier disruption were noticed. Interestingly, BMSCs administration significantly improved behavioural alterations, restored the reduced brain monoamines and oxidative stress markers, and reduced TNF-alpha, HMGB-1, NLRP3, and caspase-1 levels. Profoundly, cerebral cortices demonstrated improved histological structure, significant decrease in mast cell number and IL-1β immune-expression, besides a significant increase in Beclin-1 and DCX immune-expression.

SIGNIFICANCE

For the best of our knowledge, this is the first study showing ameliorative effects for BMSCs treatment in fibromyalgia-related cerebral cortical damage. The neurotherapeutic effects of BMSCs could be attributed to NLRP3 inflammasome signaling pathway inhibition, mast cell deactivation, and stimulation of neurogenesis and autophagy.

Spinal dopaminergic D1 and D5 receptors contribute to reserpine-induced fibromyalgia-like pain in rats

Fibromyalgia is a complex pain syndrome without a precise etiology. Reduced monoamines levels in serum and cerebrospinal fluid in fibromyalgia patients has been reported and could lead to a dysfunction of descending pain modulatory system producing the painful syndrome. This study evaluated the role of D₁-like dopamine receptors in the reserpine-induced fibromyalgia-like pain model in female Wistar rats. Reserpine-treated animals were intrathecally injected with different dopamine receptors agonists and antagonists, and small interfering RNAs (siRNAs) against D₁ and D₅ receptor subtypes. Withdrawal and muscle pressure thresholds were assessed with von Frey filaments and the Randall-Selitto test, respectively. Expression of D₁-like receptors in lumbar spinal cord and dorsal root ganglion was determined using real time polymerase chain reaction (qPCR). Reserpine induced tactile allodynia and muscle hyperalgesia. Intrathecal dopamine and D₁-like receptor agonist SKF-38393 induced nociceptive hypersensitivity in naïve rats, whilst this effect was prevented by the D₁-like receptor antagonist SCH-23390. Moreover, SCH-23390 induced a sex-dependent antiallodynic effect in reserpine-treated rats. Furthermore, transient silencing of D₁ and D₅ receptors significantly reduced reserpine-induced hypersensitivity in female rats. Reserpine slightly increased mRNA D₅ receptor expression in dorsal spinal cord, but not in DRG. This work provides new insights about the involvement of the spinal dopaminergic D₁/D₅ receptors in reserpine-induced hypersensitivity in rats.

Pharmacological Interaction of Quercetin Derivatives of Tilia americana and Clinical Drugs in Experimental Fibromyalgia

Fibromyalgia (FM) is a pain syndrome characterized by chronic widespread pain and CNS comorbidities. Tilia americana var. mexicana is a medicinal species used to treat anxiety, insomnia, and acute or chronic pain. However, its spectrum of analgesic efficacy for dysfunctional pain is unknown. To investigate a possible therapeutic alternative for FM-type pain, an aqueous Tilia extract (TE) and its flavonoid fraction (FF) containing rutin and isoquercitrin were evaluated alone and/or combined with clinical drugs (tramadol—TRA and pramipexol—PRA) using the reserpine-induced FM model in rats. Chromatographic analysis allowed the characterization of flavonoids, while a histological analysis confirmed their presence in the brain. TE (10–100 mg/kg, i.p.) and FF (10–300 mg/kg, i.p.) produced significant and dose-dependent antihyperalgesic and antiallodynic effects equivalent to TRA (3–10 mg/kg, i.p.) or PRA (0.01–1 mg/kg, s.c.). Nevertheless, the combination of FF + TRA or FF + PRA resulted in an antagonistic interaction by possible competitive action on the serotonin transporter or µ-opioid and D₂ receptors, respectively, according to the in silico analysis. Flavonoids were identified in cerebral regions because of their self-epifluorescence. In conclusion, Tilia possesses potential properties to relieve FM-type pain. However, the consumption of this plant or flavonoids such as quercetin derivatives in combination with analgesic drugs might reduce their individual benefits.

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.

Coexistence of Alterations of Gastrointestinal Function and Mechanical Allodynia in the Reserpine-Induced Animal Model of Fibromyalgia

BACKGROUND

Fibromyalgia (FM) is a disorder characterized by widespread chronic pain as core symptom and a broad range of comorbidities. Despite the prevalence of gastrointestinal (GI) comorbidities in patients with FM, GI functions have rarely been investigated in animal models of FM.

AIMS

The purpose of the present study is to investigate the coexistence of alterations of GI function in the reserpine-induced myalgia (RIM) rat, a validated FM model associated with disruption of monoamine system.

METHODS

Paw withdrawal threshold (von Frey hair test) was assessed as pain-associated indicator. Gastric emptying (¹³C breath test), small intestinal transit (charcoal meal test), and fecal water content were investigated as GI functions.

RESULTS

The specific regimen of reserpine for the RIM rat, i.e., 1 mg/kg s.c., once daily for three consecutive days, caused a reduction of paw withdrawal threshold (i.e., mechanical allodynia) on days 3, 5, and 7 after the first injection. The ¹³CO₂ excreted from the RIM rat was significantly increased on day 7. The RIM rat exhibited an acceleration of small intestinal transit on day 5. Fecal water content collected from the RIM rat was significantly increased on days 3 and 5. The amount of noradrenaline was significantly decreased in GI tissues on days 3, 5, and 7 in the RIM rat. Conclusions This study revealed that accelerated gastric emptying, accelerated small intestinal transit, and increase in fecal water content coexist with mechanical allodynia in the RIM rat, simulating the coexistence of chronic pain and alterations of GI function in patients with FM.