Pain
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Chemotherapy-induced peripheral neuropathy accompanied by chronic neuropathic pain is the major dose-limiting toxicity of several anticancer agents including the taxane paclitaxel (Taxol). A critical mechanism underlying paclitaxel-induced neuropathic pain is the increased production of peroxynitrite in spinal cord generated in response to activation of the superoxide-generating enzyme, NADPH oxidase. Peroxynitrite in turn contributes to the development of neuropathic pain by modulating several redox-dependent events in spinal cord. ⋯ The first relies on inhibition of the redox-sensitive transcription factor (NFκB) and mitogen activated protein kinases (ERK and p38) resulting in decreased production of neuroexcitatory/proinflammatory cytokines (TNF-α, IL-1β) and increased formation of the neuroprotective/anti-inflammatory IL-10. The second involves inhibition of redox-mediated posttranslational tyrosine nitration and modification (inactivation) of glia-restricted proteins known to play key roles in regulating synaptic glutamate homeostasis: the glutamate transporter GLT-1 and glutamine synthetase. Our results unravel a mechanistic link into biomolecular signaling pathways employed by A3AR activation in neuropathic pain while providing the foundation to consider use of A3AR agonists as therapeutic agents in patients with chemotherapy-induced peripheral neuropathy.
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Activity pacing is a widely used self-management strategy, but we lack a clear understanding of its nature and usefulness. One source of confusion is a lack of clarity about the use of pacing in everyday life (ie, naturalistic pacing) in people not trained on how to pace activities. It is unknown whether people engage in more pacing when pain is high (pain-contingent) or when fatigue is high (fatigue-contingent). ⋯ Contrary to our hypothesis, increased pacing was associated with higher subsequent levels of pain and fatigue. Naturalistic pacing seems symptom-contingent and not reinforced by symptom reduction. Naturalistic pacing may be distinct from trained or programmatic pacing in terms of outcomes, and further research into naturalistic pacing may provide an important foundation for how best to deliver activity pacing interventions.
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Detection of external irritants by head nociceptor neurons has deep evolutionary roots. Irritant-induced aversive behavior is a popular pain model in laboratory animals. It is used widely in the formalin model, where formaldehyde is injected into the rodent paw, eliciting quantifiable nocifensive behavior that has a direct, tissue-injury-evoked phase, and a subsequent tonic phase caused by neural maladaptation. ⋯ Using TRPA1-blocker and Trpa1(-/-) mice, we found that both TRP channels co-contribute to the formalin trigeminal pain response. These results imply TRPV4 as an important signaling molecule in irritation-evoked trigeminal pain. TRPV4-antagonistic therapies can therefore be envisioned as novel analgesics, possibly for specific targeting of trigeminal pain disorders, such as migraine, headaches, temporomandibular joint, facial, and dental pain, and irritation of trigeminally innervated surface epithelia.
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A sound strategy for improving the clinical efficacy of opioids involves exploiting positive interactions with drugs directed at other targets in pain pathways. The current study investigated the role of dopamine receptor D2 (D2R) in modulation of spinal dorsal horn excitability to noxious input, and interactions therein with μ-opioid receptor (MOR) in an animal model of neuropathic pain induced by spinal nerve ligation (SNL). C-fiber-evoked field potentials in the spinal dorsal horn were depressed concentration dependently by spinal superfusion with the D2R agonist quinpirole both in nerve-injured and sham-operated (control) rats. ⋯ Co-administration of 1 μmol/L quinpirole, insufficient per se to alter evoked potentials, dramatically enhanced inhibition of evoked potentials by MOR agonist DAMGO, reducing the IC50 value of DAMGO by 2 orders of magnitude. The present data provide evidence of profound functional and subcellular changes in D2R-mediated modulation of noxious input after nerve injury, including positive interactions with spinal MOR. These results suggest D2R co-stimulation as a potential avenue to improve MOR analgesia in sustained pain states involving peripheral nerve injury.
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Use of chronic opioid therapy (COT) for chronic noncancer pain has dramatically increased in the United States. Patients seek compassionate care and relief while physicians struggle to manage patients' pain effectively without doing harm. This study explores the narratives of chronic noncancer pain patients receiving chronic opioid therapy and those of their physicians to better understand the effects of COT on the doctor-patient relationship. A mixed method study was conducted that included in-depth interviews and qualitative analysis of 21 paired patients with chronic pain and their physicians in the following groups: patients, physicians, and patient-physician pairs. Findings revealed that patients' narratives focus on suffering from chronic pain, with emphasis on the role of opioid therapy for pain relief, and physicians' narratives describe the challenges of treating patients with chronic pain on COT. Results elucidate the perceptions of ideal vs difficult patients and show that divergent patterns surrounding the consequences, utility, and goals of COT can negatively affect the doctor-patient relationship. The use of paired interviews through a narrative lens in this exploratory study offers a novel and informative approach for clinical practice and research. The findings have significant implications for improving doctor-patient communication and health outcomes by encouraging shared decision making and goal-directed health care encounters for physicians and patients with chronic pain on COT. ⋯ This study found patterns of understanding pain, opioid pain medications, and the doctor-patient relationship for patients with chronic pain and their physicians using a narrative lens. Thematic findings in this exploratory study, which include a portrayal of collaborative vs conflictual relationships, suggest areas of future intervention and investigation.