Articles: pain-threshold.
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The basal ganglia modulate somatosensory pain pathways, but it is unclear whether a common circuit exists to mitigate hyperalgesia in pain states induced by peripheral nociceptive stimuli. As a key output nucleus of the basal ganglia, the substantia nigra pars reticulata (SNr) may be a candidate for this role. To test this possibility, we optogenetically modulated SNr GABAergic neurons and examined pain thresholds in freely behaving male mice in inflammatory and neuropathic pain states as well as comorbid depression in chronic pain. ⋯ However, SNr modulation did not affect baseline pain thresholds. We also found that SNr-STN GABAergic projection was attenuated in pain states, resulting in disinhibition of STN neurons. Thus, impairment of the SNr-STN GABAergic circuit may be a common pathophysiology for the maintenance of hyperalgesia in both inflammatory and neuropathic pain states and the comorbid depression in chronic pain; compensating this circuit has potential to effectively treat pain related conditions.
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Randomized Controlled Trial
Non-invasive vagus nerve stimulation modulates trigeminal but not somatosensory perception: functional evidence for a trigemino-vagal system in humans.
Noninvasive vagus nerve stimulation (nVNS) is effective in several types of headache disorders. We sought to unravel the mechanism of how nVNS exhibits this efficacy. This study used a randomized, single-blind, sham-controlled, crossover design and comprised 3 projects with 3 independent cohorts of healthy participants. ⋯ Heart rate variability parameters did not change after nVNS. Our results provide functional evidence of a long hypothesized functional trigemino-vagal system in humans and may explain why nVNS is effective in some headache disorders but not in somatic pain disorders. Because unilateral nVNS modulated the trigeminal thresholds bilaterally, this effect is probably indirect through a central top-down mechanism.
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Conditioned pain modulation (CPM) and offset analgesia quantify impairment of endogenous pain modulation, but magnitude and reliability vary broadly between studies, indicating influencing factors that are not currently controlled for. The aim of this study was to quantify magnitude and retest reliability of CPM and offset analgesia in healthy participants, while investigating the influence of sex and sex hormone levels. ⋯ This study investigated CPM and offset analgesia in parallel, across sexes and during two menstrual cycles while assessing the impact of sex hormones. Reliability seems to depend on experimental parameters rather than participant characteristics, while the magnitude of effect could be weakly linked to sex hormones and sex.
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Observational Study
Effects of Hypovitaminosis D on Preoperative Pain Threshold and Perioperative Opioid Use in Colorectal Cancer Surgery: A Cohort Study.
Postoperative pain after colorectal cancer surgery has a significant impact on postoperative physical and mental health. Vitamin D deficiency has been correlated with both acute pain states, including postoperative and post-traumatic pain, and several chronic pain diseases. The effects of hypovitaminosis D on preoperative pain threshold and perioperative opioid use in colorectal cancer surgery still need to be studied. ⋯ On the basis of the study results, hypovitaminosis D is associated with increased perioperative opioid consumption in colorectal cancer surgery. Sensory perception and pain threshold of patients with insufficient 25 (OH) D3 concentration were more sensitive, and PET was lower. History of DM, vitamin D, and vitamin C may be factors related with SSI. Future studies are needed to investigate their relationship further and discover if postoperative pain and pain threshold can benefit from vitamin D supplementation in these patients.
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Few studies have investigated the underlying mechanisms for unilateral subacromial pain syndrome (SAPS). Therefore, this study examined (1) if 8-weeks of exercise could modulate clinical pain or temporal summation of pain (TSP), conditioned pain modulation (CPM), and exercise-induced hypoalgesia (EIH) and (2) if any of these parameters could predict the effect of 8-weeks of exercise in patients with unilateral SAPS. ⋯ This explorative study suggested reduction in pain, improved sleep quality and increased CPM after 8-weeks of exercise. Furthermore, the results suggests that low pain intensity and high TSP scores (indicative for pain sensitisation) may predict a lack of pain improvement after exercise.