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Chronic pain is prevalent, and approximately half of patients with chronic pain experience sleep disturbance. Exogenous melatonin is licensed to treat primary insomnia and there is some evidence for analgesic effects of melatonin.The aim of this study is to investigate the effects of oral melatonin (as Circadin) 2 mg at night in adults with severe non-malignant pain of at least 3 months' duration.
Learn More >The exact mechanisms underlying the development and maintenance of phantom limb pain are still unclear. This study aimed to identify the factors affecting pain intensity in chronic, lower limb, traumatic phantom limb pain patients.
Learn More >The Pain Assessment for Lower Back-Symptoms (PAL-S) and Impacts (PAL-I) were developed to incorporate patient perspective of treatment benefit in chronic low back pain (cLBP) trials. This study documents psychometric measurement properties of the PAL-S and PAL-I. In this multicenter, observational study, eligible participants clinically diagnosed with cLBP provided sociodemographic information and completed PAL measures and other patient-reported outcome measures of pain and/or disability. Confirmatory factor analyses (CFA), construct validity, and reliability were assessed. The 104 participants were 61% female, 89% white, and mean 55 years old; mean cLBP duration was 11.4 (range 0-47) years. Using painDETECT scores, 36.5% reported small likelihood of neuropathic pain, 30.8% reported unclear likelihood, and 32.7% reported definite likelihood. Persistent pain with pain attacks was reported by 38.5% of participants. CFA confirmed single components with adequate fit indices. Cronbach's alpha was 0.83 (PAL-S) and 0.87 (PAL-I), indicating reliable scales. Intraclass correlation coefficients (test-retest reproducibility, n = 44) were 0.81 (PAL-S) and 0.85 (PAL-I). PAL-S score correlation was 0.49 with Roland-Morris Disability Questionnaire (RMDQ) and 0.77 with Neuropathic Pain Symptom Inventory (NPSI). PAL-I correlated at 0.73 with RMDQ and -0.60 with Medical Outcomes Study (MOS)-36 Bodily Pain. Both measures significantly differentiated between pain intensity levels (based on numeric response scale) and painDETECT groups. The PAL-S and PAL-I generated highly reliable scores with substantial evidence of construct validity. Routine use of these measures in treatment trials will enhance comparability of LBP-related symptom and impact results, including patient perspective of treatment benefit.
Learn More >Chronic pain affects over 100 million American adults. The prevalence of chronic pain is even higher among U.S. military personnel. Approximately 44% of active duty military experience pain upon returning from deployment compared with 26% of the general public who experience chronic pain. The high prevalence of chronic pain within the Military Health System is compounded by limited access to chronic pain specialists, specifically with regard to patients at remote military treatment facilities (MTFs). Thus, when compared to personnel at tertiary care MTFs, they often have decreased access to care and experience increased time away from their mission to receive care. Since 2009, Walter Reed National Military Medical Center (WRNMMC) has been using telemedicine to extend chronic pain consults to remote MTFs within the National Capital Region (NCR). The goal of this study was to determine if patients referred to the WRNMMC Telepain Program reported improvements in subjective measures associated with accessing care. To accomplish this, we surveyed a convenience sample of patients using the service to determine if participation: (1) improved pain, (2) improved quality of life, (3) decreased travel time, (4) improved access to care, and (5) decreased time away from work.
Learn More >Glycine receptors (GlyRs) are anion-permeable pentameric ligand-gated ion channels (pLGICs). The GlyR activation is critical for the control of key neurophysiological functions, such as motor coordination, respiratory control, muscle tone and pain processing. The relevance of the GlyR function is further highlighted by the presence of abnormal glycinergic inhibition in many pathophysiological states, such as hyperekplexia, epilepsy, autism and chronic pain. In this context, previous studies have shown that the functional inhibition of GlyRs containing the α3 subunit is a pivotal mechanism of pain hypersensitivity. This pathway involves the activation of EP2 receptors and the subsequent PKA-dependent phosphorylation of α3GlyRs within the intracellular domain (ICD), which decrease the GlyR-associated currents and enhance neuronal excitability. Despite the importance of this mechanism of glycinergic dis-inhibition associated with dysfunctional α3GlyRs, our current understanding of the molecular events involved is limited. Here, we report that the activation of PKA signaling pathway decreases the unitary conductance of α3GlyRs. We show in addition that the substitution of the PKA-targeted serine with a negatively charged residue within the ICD of α3GlyRs and of chimeric receptors combining bacterial GLIC and α3GlyR was sufficient to generate receptors with reduced conductance. Thus, our findings reveal a potential biophysical mechanism of glycinergic dis-inhibition and suggest that post-translational modifications of the ICD, such as phosphorylation, may shape the conductance of other pLGICs.
Learn More >Chronic pain is the most common reason reported for using medical cannabis. The goal of this research was to determine if the two primary phytocannabinoids, THC and CBD, are effective treatments for persistent inflammatory pain. In Experiment 1, inflammation was induced in male and female rats by intraplantar injection of complete Freund's adjuvant (CFA). Then THC (0.0-4.0 mg/kg i.p.) or CBD (0.0-10 mg/kg i.p.) was administered twice-daily for 3 days. On day 4, vehicle, THC, or CBD was administered and allodynia, hyperalgesia, weight-bearing, locomotor activity, and hindpaw edema were assessed 0.5-4 h post-injection. In Experiment 2, CFA- or mineral oil (control)-treated rats were given vehicle, THC (2.0 mg/kg), or CBD (10 mg/kg) in the same manner as in Experiment 1. Four h post-injection on day 4, serum samples were taken for analysis of cytokines known to influence inflammatory pain: interleukin (IL)-1β, IL-6, IL-10, interferon (IFN)-γ, and tumor necrosis factor (TNF)-α. THC dose-dependently reduced pain-related behaviors but did not reduce hindpaw edema, and little tolerance developed to THC's effects. In contrast, CBD effects on inflammatory pain were minimal. THC produced little-to-no change in serum cytokines, whereas CBD decreased IL-1β, IL-10, and IFN-γ, and increased IL-6. Few sex differences in antinociception or immune modulation were observed with either drug, but adjuvant-induced immune activation was greater in males than females. These results suggest that THC may be more beneficial than CBD for reducing inflammatory pain, in that THC maintains its efficacy with short-term treatment in both sexes, and does not induce immune activation. SIGNIFICANCE STATEMENT: CBDs and THCs pain-relieving effects are examined in male and female rats with persistent inflammatory pain to determine if individual phytocannabinoids could be a viable treatment for men and women with chronic inflammatory pain. Additionally, sex differences in the immune response to an adjuvant and to THC and CBD are characterized to provided preliminary insight into immune-related effects of cannabinoid-based therapy for pain.
Learn More >Neuropeptides play important modulatory roles throughout the nervous system, functioning as direct effectors or as interacting partners with other neuropeptide and neurotransmitter systems. Limbic brain areas involved in learning, memory and emotions are particularly rich in neuropeptides. This review will focus on the amygdala, a limbic region that plays a key role in emotional-affective behaviors and pain modulation. The amygdala is comprised of different nuclei; the basolateral (BLA) and central (CeA) nuclei and in between, the intercalated cells (ITC), have been linked to pain-related functions. A wide range of neuropeptides are found in the amygdala, particularly in the CeA, but this review will discuss those neuropeptides that have been explored for their role in pain modulation. Calcitonin gene-related peptide (CGRP) is a key peptide in the afferent nociceptive pathway from the parabrachial area and mediates excitatory drive of CeA neurons. CeA neurons containing corticotropin releasing factor (CRF) and/or somatostatin (SOM) are a source of long-range projections and serve major output functions, but CRF also acts locally to excite neurons in the CeA and BLA. Neuropeptide S (NPS) is associated with inhibitory ITC neurons that gate amygdala output. Oxytocin and vasopressin exert opposite (inhibitory and excitatory, respectively) effects on amygdala output. The opioid system of mu, delta and kappa receptors (MOR, DOR, KOR) and their peptide ligands (β-endorphin, enkephalin, dynorphin) have complex and partially opposing effects on amygdala function. Neuropeptides therefore serve as valuable targets to regulate amygdala function in pain conditions.
Learn More >Fibromyalgia syndrome (FMS) is a chronic pain condition associated with a substantial decrease in health-related quality of life (HRQoL). This study investigated the relationships of HRQoL with clinical parameters of FMS (pain, insomnia and fatigue) and affective variables (depression and anxiety).
Learn More >Haloperidol is a neuroleptic drug with high affinity towards the σ receptor (σR), acting as antagonist that decreases neuropathic pain, but has CNS side effects. This work describes the design and synthesis of a novel analog N‑(1‑benzylpiperidin‑4-yl)‑4‑fluorobenzamide (LMH-2), which produced antihyperalgesic and antiallodynic effects in rats with neuropathy induced by chronic constriction injury of the sciatic nerve (CCI), being more active than gabapentin (The most widely used drug for the treatment of neuropathic pain).
Learn More >Mu opioid receptor (MOPr) agonists are thought to produce analgesia via modulation of G-protein-coupled intracellular signalling pathways whereas the β-arrestin2 pathway is proposed to mediate opioid-related adverse effects. Here, we report the antinociception, constipation and respiratory depressant profile of CYX-6, a potent MOPr agonist that is also a delta and a kappa opioid receptor (DOPr/KOPr) antagonist and that lacks β-arrestin2 recruitment at each of the MOPr, DOPr and the KOPr. In anaesthetised male Sprague Dawley rats, an intracerebroventricular (i.c.v.) guide cannula was stereotaxically implanted. After 5-7 days post-surgical recovery, rats received a single i.c.v. bolus dose of CYX-6 (3-30 nmol), morphine (100 nmol) or vehicle. Antinociception was assessed using the warm water tail flick test (52.5 ± 0.5 °C). Constipation was assessed using the charcoal meal gut motility test and the castor oil-induced diarrhoea test. Respiratory depression was measured by whole-body plethysmography in awake, freely moving animals, upon exposure to a hypercapnic gas mixture (8% CO, 21% O and 71% N). The intrinsic pharmacology of CYX-6 given by the i.c.v. route in rats showed that it produced dose-dependent antinociception. It also produced respiratory stimulation rather than depression and it had a minimal effect on intestinal motility in contrast to the positive control, morphine. CYX-6 is an endomorphin-2 analogue that dissociates antinociception from constipation and respiratory depression in rats. Our findings provide useful insight to inform the discovery and development of novel opioid analgesics with a superior tolerability profile compared with morphine.
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