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C-nociceptors are generally assumed to have a low maximum discharge frequency of 10 – 30 Hz. However, only mechano-insensitive "silent" C-nociceptors cannot follow electrical stimulation at 5 Hz (75 pulses) whereas polymodal C-nociceptors in the pig follow even 100 Hz without conduction failure. Sensitization by nerve growth factor increases the maximum following frequency of "silent" nociceptors in pig skin and might thereby contribute in particular to intense pain sensations in chronic inflammation. A distinct class of C-nociceptors with mechanical thresholds >150 mN resembles "silent" nociceptors at low stimulation frequencies in pig and human, but is capable of 100 Hz discharge and thus, is suited to encode painfulness of noxious mechanical stimuli.
Learn More >To evaluate the effects of neck-specific sensorimotor training using a virtual reality device compared with 2 standard rehabilitation programmes: with, and without general sensorimotor training, in patients with non-traumatic chronic neck pain.
Learn More >Chronic low back pain (LBP) is the most prevalent chronic pain in adults, and there is no optimal nonpharmacologic management. Exercise is recommended, but no specific exercise-based treatment has been found to be most effective.
Learn More >Pregabalin has become widely used as an alternative to opioids in treating certain types of chronic non-cancer pain, but few studies have examined its clinical efficacy outside trials. We address this gap by examining the utilization, correlates and clinical outcomes of pregabalin use among an Australian community-based cohort of people prescribed opioids for chronic non-cancer pain.
Learn More >This article presents findings from a large prospective examination of Canadian medical cannabis patients, with a focus on the impacts of cannabis on prescription opioid use and quality of life over a 6-month period.
Learn More >Opioids such as morphine are mainstay treatments for clinical pain conditions. Itch is a common side effect of opioids, particularly as a result of epidural or intrathecal administration. Recent progress has advanced our understanding of itch circuits in the spinal cord. However, the mechanisms underlying opioid-induced itch are not fully understood, although an interaction between µ-opioid receptor (MOR) and gastrin-releasing peptide receptor (GRPR) in spinal GRPR-expressing neurons has been implicated. In this study we investigated the cellular mechanisms of intrathecal opioid-induced itch by conditional deletion of MOR-encoding Oprm1 in distinct populations of interneurons and sensory neurons. We found that intrathecal injection of the MOR agonists morphine or DAMGO elicited dose-dependent scratching as well as licking and biting, but this pruritus was totally abolished in mice with a specific Oprm1 deletion in Vgat+ neurons [Oprm1-Vgat (Slc32a1)]. Loss of MOR in somatostatin+ interneurons and TRPV1+ sensory neurons did not affect morphine-induced itch but impaired morphine-induced antinociception. In situ hybridization revealed Oprm1 expression in 30% of inhibitory and 20% of excitatory interneurons in the spinal dorsal horn. Whole-cell recordings from spinal cord slices showed that DAMGO induced outward currents in 9 of 19 Vgat+ interneurons examined. Morphine also inhibited action potentials in Vgat+ interneurons. Furthermore, morphine suppressed evoked inhibitory postsynaptic currents in postsynaptic Vgat- excitatory neurons, suggesting a mechanism of disinhibition by MOR agonists. Notably, morphine-elicited itch was suppressed by intrathecal administration of NPY and abolished by spinal ablation of GRPR+ neurons with intrathecal injection of bombesin-saporin, whereas intrathecal GRP-induced itch response remained intact in mice lacking Oprm1-Vgat. Intrathecal bombesin-saporin treatment reduced the number of GRPR+ neurons by 97% in the lumber spinal cord and 91% in the cervical spinal cord, without changing the number of Oprm1+ neurons. Additionally, chronic itch from DNFB-induced allergic contact dermatitis was decreased by Oprm1-Vgat deletion. Finally, naloxone, but not peripherally restricted naloxone methiodide, inhibited chronic itch in the DNFB model and the CTCL model, indicating a contribution of central MOR signalling to chronic itch. Our findings demonstrate that intrathecal morphine elicits itch via acting on MOR on spinal inhibitory interneurons, leading to disinhibition of the spinal itch circuit. Our data have also provided mechanistic insights into the current treatment of chronic itch with opioid receptor antagonist such as naloxone.
Learn More >To determine the prevalence and breakdown of pain symptoms among patients with coronavirus disease 2019 (COVID-19) infection admitted for nonpain symptoms and the association between the presence of pain and intensive care unit (ICU) admission and death.
Learn More >Most patient-reported outcome (PRO) instruments that measure atopic dermatitis (AD) symptoms do not have sufficient documented evidence of content validity to satisfy regulatory agency guidance for inclusion in product-labelling claims in the USA or Europe. The objective of this study was to develop a PRO instrument in accordance with regulatory agency guidance to assess daily AD symptoms during the course of therapy and to establish its content validity and psychometric properties.
Learn More >To evaluate the role of neutrophil extracellular traps (NETs) in the genesis of joint hyperalgesia using an experimental model of arthritis and transpose the findings to clinical investigation.
Learn More >The analgesic effect of alpha-2 adrenergic receptor (αAR) agonists, which relieve chronic neuropathic pain, is highly variable among individuals. Here, we used a mouse model of spared nerve injury (SNI) to show that treatment time after the establishment of neuropathic pain was important for the variability in the analgesic efficacy of αAR agonists, which was related to the activity of regulator of G-protein signaling protein 4 (RGS4). Intrathecal treatment with αAR agonists, clonidine (0.1-1 nmol) or dexmedetomidine (0.3-1 nmol), relieved mechanical allodynia and thermal hyperalgesia on postoperative day (POD) 14, but their efficacy was weaker on POD28 and absent on POD56. The RGS4 level of plasma membrane was increased on POD56 compared to that on POD14. Moreover, in RGS4-deficient or RGS4 inhibitor (CCG50014)-treated mice, the analgesic effect of the αAR agonists was conserved even on POD56. The increased plasma membrane RGS4 expression and the reduced level of active G after clonidine injection on POD56 were completely restored by CCG50014. Higher doses of clonidine (10 nmol) and dexmedetomidine (3 nmol) relieved neuropathic pain on POD56 but were accompanied with serious side effects. Whereas, the coadministration of CCG50014 with clonidine (1 nmol) or dexmedetomidine (1 nmol) did not cause side effects. These findings demonstrated that SNI-induced increase in plasma membrane RGS4 expression was associated with low efficacy of αAR agonists in a model of persistent, chronic neuropathic pain. Furthermore, αAR agonist administration together with RGS4-targeted intervention represents a novel strategy for the treatment of neuropathic pain to overcome dose-limiting side effects.
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