Browse by Audience
Latent sensitization is a long-term model of chronic pain in which hyperalgesia is continuously suppressed by opioid receptors, as demonstrated by the induction of mechanical allodynia by opioid antagonists. Different intracellular signals may mediate the initiation, maintenance and expression of latent sensitization. Our criterion for the involvement of a signal in the maintenance of latent sensitization is that inhibitors should permanently eliminate the allodynia produced by an opioid antagonist. We hypothesized that Src family kinases (SFKs) maintain latent sensitization and tested this hypothesis by inducing latent sensitization in rats with complete Freund's adjuvant (CFA) or spared nerve injury. After measures of mechanical allodynia returned to baseline, vehicle or the SFK inhibitor PP2 were injected intrathecally. The opioid antagonist naltrexone injected intrathecally 15 min later produced allodynia in control rats but not in rats injected with PP2. Vehicle or PP2 were injected daily for two more days and naltrexone was injected five days later. Again, naltrexone induced allodynia in the control rats but not in the rats injected with PP2. Results were similar when latent sensitization was induced with CFA or spared nerve injury. We concluded that an SFK, likely Fyn, maintains latent sensitization induced by inflammation or nerve injury.
The pharmacological activation of A receptors has shown potential usefulness in the management of bowel inflammation. However, the role of these receptors in the control of visceral hypersensitivity in the presence of intestinal inflammation has not been investigated. The effects of AR170, a potent and selective A receptor agonist, and dexamethasone (DEX) were tested in rats with 2,4-dinitrobenzene sulfonic acid (DNBS)-induced colitis to assess their tissue inflammatory parameters. The animals received AR170, DEX, or a vehicle intraperitoneally for 6 days, starting 1 day before the induction of colitis. Visceral pain was assessed by recording the abdominal responses to colorectal distension in animals with colitis. Colitis was associated with a decrease in body weight and an increase in spleen weight. The macroscopic damage score and tissue tumor necrosis factor (TNF), interleukin 1β (IL-1β), and myeloperoxidase (MPO) levels were also enhanced. AR170, but not DEX, improved body weight. Both drugs counteracted the increase in spleen weight, ameliorated macroscopic colonic damage, and decreased TNF, IL-1β, and MPO tissue levels. The enhanced visceromotor response (VMR) in rats with colitis was decreased via AR170 administration. In rats with colitis, AR170 counteracted colonic inflammatory cell infiltration and decreased pro-inflammatory cytokine levels, thereby relieving visceral hypersensitivity.
This systematic review and meta-analysis examined the evidence for altered central pain processing in people with non-traumatic neck pain and the relationship between central pain processing, demographics and pain-related characteristics. Case-control studies reporting measures of altered central pain processing using quantitative sensory testing were reviewed. Standardized mean differences (SMDs) and 95% confidence intervals (CIs) between people with non-traumatic neck pain and controls were calculated. Meta-analysis was performed using random-effects models when appropriate. Associations between SMDs with demographics and pain-related characteristics were explored on a study level using meta-regression. Twenty-six studies were eligible with 25 included for meta-analysis. Meta-analysis demonstrated mechanical hyperalgesia at remote non-painful sites in the full sample [sample size (n)=1305, SMD=-0.68] and in the subgroup with moderate/severe disability [n=165, SMD=-0.86] (moderate-quality evidence). Meta-regression indicated that remote mechanical hyperalgesia was negatively associated with age (R=25.4%, P=0.031). Very-low- to low-quality evidence of remote cold and heat hyperalgesia and dysfunctional conditioned pain modulation were identified. This review suggests that altered central pain processing is present in people with non-traumatic neck pain and may be associated with disability levels and age. Perspective: This review found moderate-quality evidence of mechanical hyperalgesia at remote non-painful sites in patients with non-traumatic neck pain compared to controls, indicating altered central pain processing. However, more studies are needed to confirm findings from dynamic quantitative sensory testing.
N-methyl-D-aspartate (NMDA) receptor activation is known to be critical in remifentanil-induced hyperalgesia. Evidence indicates that iron accumulation participates in NMDA neurotoxicity. This study aims to investigate the role of iron accumulation in remifentanil-induced hyperalgesia. Remifentanil was delivered intravenously in rats to induce hyperalgesia. The NMDA receptor antagonist MK-801 was intrathecally administrated. The levels of divalent metal transporter 1 without iron-responsive element [DMT1(-)IRE] and iron were detected. Behavior testing was performed in DMT1(-)IRE knockdown rats and rats treated with iron chelator DFO. Meanwhile, the spinal dorsal horn neurons were cultured and transfected with DMT1(-)IRE siRNA, and then respectively incubated with remifentanil and MK-801. The levels of intracellular Ca and iron were assessed by fluorescence imaging. Our data revealed that spinal DMT1(-)IRE and iron content significantly increased in remifentanil-treated rats, and MK-801 inhibited the enhancements. DMT1(-)IRE knockdown and DFO prevented against remifentanil-induced hyperalgesia. Notably, the levels of Ca and iron increased in remifentanil-incubated neurons, and these growths can be blocked by MK-801. DMT1(-)IRE knockdown attenuated iron accumulation but did not influence Ca influx. This study suggests that DMT1(-)IRE-mediated iron accumulation is likely to be the downstream event following NMDA receptor activation and Ca influx, contributing to remifentanil-induced hyperalgesia. PERSPECTIVE: Remifentanil-induced hyperalgesia is common even when used within clinical accepted doses. This study presents that aberrant iron accumulation is involved in the development of remifentanil-induced hyperalgesia in vivo and in vitro. Iron chelation may be a potential therapeutic strategy for the prevention of hyperalgesia in populations at high risk.
Pain is a major health problem among US adults. Surprisingly little, however, is known about educational disparities in pain, especially among the nonelderly. In this study, we analyze disparities in pain across levels of educational attainment. Using data from the 2010-2017 National Health Interview Survey among adults aged 30-49 (N=74,051), we estimate logistic regression models of pain prevalence using a dichotomous summary pain index and its five constituent pain sites (low back, joint, neck, headache/migraine, and facial/jaw). We find a significant and steep pain gradient: greater levels of educational attainment are associated with less pain, with two important exceptions. First, adults with a high-school equivalency diploma (GED) and those with 'some college' have significantly higher pain levels than high school graduates despite having an equivalent or higher attainment, respectively. Second, the education-pain gradient is absent for Hispanic adults. After taking into account important covariates including employment, economic resources, health behaviors, physical health conditions, and psychological wellbeing, educational disparities in pain are no longer statistically significant except for the GED and 'some college' categories, which still show significantly higher pain levels than high school graduates. We thus document the overall education-pain gradient in most younger US adult populations, and identify groups where pain is higher than expected (certain educational categories) or lower than expected (e.g., less-educated Hispanics). Understanding the causes of these anomalous findings could clarify factors shaping pain prevalence and disparities therein. PERSPECTIVE Over 50% of US adults age 30-49 report pain. Overall, more educated Americans report substantially less pain than the less educated. However, adults with a GED and 'some college' report more pain than other groups. Understanding the causes could help illuminate the mechanisms through which social factors influence pain.
Post-traumatic headache (PTH) is a condition that frequently affects individuals after traumatic brain injury (TBI). Inflammation is one of the major causes of this disability. However, little is known about the trigger for, and endurance of, this painful process. Thus, the involvement of fibers containing the transient receptor potential vanilloid 1 (TRPV1) channels on the PTH and inflammation after TBI through neonatal treatment with capsaicin are investigated. Fluid percussion injury (FPI) in adult male Wistar rats caused periorbital allodynia in one, three and seven days after injury, and the neonatal treatment reversed the painful sensation in seven days. The lack of TRPV1 channels reduced the activation of macrophages and glial cells induced by TBI in the trigeminal system, which were characterized by glial fibrillary acidic protein (GFAP) and ionized calcium binding adapter molecule-1 (IBA-1) immune content in the ipsilateral trigeminal ganglion, brainstem, and perilesional cortex. Immunofluorescence analyses of the ipsilateral Sp5C nucleus demonstrated a hypertrophic astrocytes profile after TBI which was reduced with treatment. Moreover, effects of succinate sumatriptan (SUMA – 1 mg/kg), TRPV1 selective antagonist capsazepine (CPZ – 2 mg/kg), and TRP non-selective antagonist ruthenium red (RR – 3 mg/kg) were evaluated. Although all mentioned drugs reduced the painful sensation, SUMA and CPZ demonstrated a stronger effect compared to the RR treatment, reinforcing the involvement of TRPV1 channels in periorbital allodynia after TBI. Hence, this report suggests that TRPV1-containing fibers and TRPV1 channels are able to induce inflammation of the trigeminal system and maintain the painful sensation after TBI.
Methadone is increasingly being used for its analgesic properties. Despite the increasing popularity, many healthcare providers are not familiar with methadone's complex pharmacology and best practices surrounding its use. The purpose of this narrative review article is to discuss the pharmacology of methadone, the evidence surrounding methadone's use in acute pain management and both chronic cancer and non-cancer pain settings, as well as highlight pertinent safety, monitoring, and opioid rotation considerations. Methadone has a unique mechanism of action when compared with all other opioids and for this reason methadone has come to hold a niche role in the management of opioid-induced hyperalgesia and central sensitization. Understanding of the mechanisms of variability in methadone disposition and drug interactions has evolved over the years, with the latest evidence revealing that CYP 2B6 is the major determinant of methadone elimination and plays a key role in methadone-related drug interactions. From an acute pain perspective, most studies evaluating the use of intraoperative intravenous methadone have reported lower pain scores and post-operative opioid requirements. Oral methadone is predominantly used as a second-line opioid treatment for select chronic pain conditions. As a result, several oral morphine to oral methadone conversion ratios have been proposed, as have methods in which to rotate to methadone. From an efficacy standpoint, limited literature exists regarding the effectiveness of methadone in the chronic pain setting with most of the available efficacy data pertaining to methadone's use in the treatment of cancer pain. Many of the prospective studies that exist feature low participant numbers. Few clinical trials investigating the role of methadone as an analgesic treatment are currently underway. The complicated pharmacokinetic properties of methadone and risks of harm associated with this drug highlight how critically important it is that healthcare providers understand these features before prescribing/dispensing methadone. Particular caution is required when converting patients from other opioids to methadone and for this reason only experienced healthcare providers should undertake such a task. Further randomized trials with larger sample sizes are needed to better define the effective and safe use of methadone for pain management.
Epigenetics of neurotrophic factors holds the potential to unravel the mechanisms underlying the pathophysiology of complex conditions such as chronic fatigue syndrome (CFS). This study explored the role of brain-derived neurotrophic factor (BDNF) genetics, epigenetics, and protein expression in patients with both CFS and comorbid fibromyalgia (CFS/FM).
Tremendous progress has been made in the past decades for the treatment of headache disorders. Chronic migraine is the most disabling type of headache and requires the use of acute and preventive medications, many of which are associated with adverse events that limit patient adherence. Botulinum toxin (BoNT) serotype A, a neurotoxin derived from certain strains of Clostridium, disrupts neuropeptide secretion and receptor translocation related to trigeminal nociception, thereby preventing pain sensitization through peripheral and possibly central mechanisms. Ever since the first randomized controlled trial on onabotulinumtoxinA (onabotA) for migraine was published two decades ago, onabotA has been the only BoNT formulation approved for use in the prevention of chronic migraine. Superior tolerability and efficacy have been demonstrated on multiple migraine endpoints in many controlled trials and real-life studies. OnabotA is a safe and efficacious treatment for chronic migraine and possibly high-frequency episodic migraine. Further research is still needed to understand its mechanism of action to fully develop its therapeutic potential.
The development of antinociceptive morphine tolerance is a clinically intractable problem. Previous studies clarified the pivotal roles of platelet-derived growth factor (PDGF) and its receptor PDGFRβ in morphine tolerance. Herein, we investigated the role of spinal heat shock protein 27 (HSP27) in morphine tolerance and its relationship with PDGFRβ activation.