Pain
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Sex-related exacerbation of injury-induced mechanical hypersensitivity in GAD67 haplodeficient mice.
Decreased GABA levels in injury-induced loss of spinal inhibition are still under intense interest and debate. Here, we show that GAD67 haplodeficient mice exhibited a prolonged injury-induced mechanical hypersensitivity in postoperative, inflammatory, and neuropathic pain models. In line with this, we found that loss of 1 copy of the GAD67-encoding gene Gad1 causes a significant decrease in GABA contents in spinal GABAergic neuronal profiles. ⋯ Remarkably, all these phenotypes were more pronounced in GAD67 haplodeficient females. These mice had significantly much lower amount of spinal GABA content, exhibited an exacerbated pain phenotype during the second phase of the formalin test, developed a longer lasting mechanical hypersensitivity in the chronic constriction injury of the sciatic nerve model, and were unresponsive to the pain relief effect of the GABA-transaminase inhibitor phenylethylidenehydrazine. Our study provides strong evidence for a role of GABA levels in the modulation of injury-induced mechanical pain and suggests a potential role of the GABAergic system in the prevalence of some painful diseases among females.
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Although regulation of nociceptive processes in the dorsal horn by deep brain structures has long been established, the role of cortical networks in pain regulation is minimally explored. The medial prefrontal cortex (mPFC) is a key brain area in pain processing that receives ascending nociceptive input and exerts top-down control of pain sensation. We have shown critical changes in mPFC synaptic function during neuropathic pain, controlled by endocannabinoid (eCB) signaling. ⋯ Spared nerve injury reduced the mechanical threshold to induce action potential firing of dorsal horn wide-dynamic-range neurons, but this was reversed in rats by WIN in the chronic phase of SNI and by mPFC injection of AM4113 in the early phase of SNI. Elevated dorsal root ganglion neuronal activity after injury was also diminished in rats by mPFC injection of AM4113, potentially by reducing antidromic activity and subsequent neuronal inflammation. These findings suggest that depending on the phase of the pain condition, both blocking and activating CB1 receptors in the mPFC can regulate descending control of pain and affect both dorsal horn neurons and peripheral sensory neurons, contributing to changes in pain sensitivity.
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The most recent prevalence estimate of post-traumatic headache (PTH) after traumatic brain injury (TBI) in veterans and civilians dates back to 2008. The prevalence was found to be 57.8%, with surprising higher rates (75.3%) in mild TBI when compared with those with moderate/severe TBI (32.1%). However, the revision of mild TBI diagnostic criteria and an historic peak of TBI in the elderly individuals attributed to the ageing population may lead to different results. ⋯ The overall prevalence of PTH after TBI over the past 14 years remains high even if assessed only in civilians. However, the prevalence rates attributed to mild and moderate/severe TBI were similar, differing significantly from previous reports. Efforts are needed to improve TBI outcomes.
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Randomized Controlled Trial
STRategies to Improve Pain and Enjoy life (STRIPE): results of a pragmatic randomized trial of pain coping skills training and opioid medication taper guidance for patients on long-term opioid therapy.
Because long-term opioid therapy (LtOT) for chronic pain has uncertain benefits and dose-dependent harms, safe and effective strategies for opioid tapering are needed. Adapting a promising pilot study intervention, we conducted the STRategies to Improve Pain and Enjoy life (STRIPE) pragmatic clinical trial. Patients in integrated health system on moderate-to-high dose of LtOT for chronic noncancer pain were randomized individually to usual care plus intervention (n = 79) or usual care only (n = 74). ⋯ We did not observe significant differences between intervention and usual care for MME (adjusted mean difference: -2.3 MME; 95% confidence interval: -10.6, 5.9; P = 0.578), the Pain, Enjoyment of Life, General Activity scale (0.0 [95% confidence interval: -0.5, 0.5], P = 0.985), or most secondary outcomes. The intervention did not lower opioid dose or improve pain or functioning. Other strategies are needed to reduce opioid doses while improving pain and function for patients who have been on LtOT for years with high levels of medical, mental health, and substance use comorbidity.