Pain
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We previously reported that women exhibit greater heat pain adaptation to a prolonged painful stimulus and greater habituation to repeated painful stimuli than men. The neural mechanism underlying this sex difference is unknown. However, Bingel et al. (2007) have shown that pain habituation after 8 days of daily pain testing is associated with an increase in pain-evoked activity of the subgenual anterior cingulate cortex (sgACC), suggesting that pain habituation may be mediated via connectivity between the sgACC and the descending pain antinociceptive system. ⋯ These data indicate that brain circuitry in women may provide for greater engagement of the descending modulation system mediating pain habituation. In contrast, in men, the salience network may be more engaged, which could support greater sustained attention to pain, thereby preventing pain habituation. Furthermore, the hypothalamus findings suggest a more powerful stress and endorphin-based system at play in men than women.
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The different neuropathic pain types (e.g., ongoing burning pain and allodynia) are frequent and disabling complaints in patients with peripheral neuropathies. Although the reference standard technique for diagnosing painful small-fibre neuropathies is nerve fibre density assessment by skin biopsy, the relationship between the epidermal nerve fibre (ENF) density and neuropathic pain is still unclear. In a clinical and skin biopsy study designed to investigate whether changes in ENF density are directly related to pain, we enrolled 139 consecutive patients with distal symmetric peripheral neuropathy. ⋯ The variable association between ENF density and symptoms of neuropathic pain supports the idea that neuropathic pain symptoms arise through distinct underlying mechanisms. The lack of relationship between ongoing burning pain and ENF density suggests that this type of pain reflects factors other than loss of nociceptive afferents. The association between ENF density and provoked pain (including mechanical dynamic allodynia) suggests that this type of pain might be mediated by spared and sensitised nociceptive afferents.
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We investigated the contributions of warm and cool signals in generating the thermal grill illusion (TGI), a phenomenon in which interlaced warm and cool bars generate an experience of burning, and under some conditions painful, heat. Each subject underwent 3 runs, 2 of which tested the effects of preadapting subjects to the grill's warm or cool bars (while the interlaced bars were thermally neutral) on the subsequent intensity of the illusion. In a control run, all bars were neutral during the adaptation phase. ⋯ The inability of warm adaptation to attenuate the TGI is at odds with theories suggesting that the illusion depends upon a simple addition of warm and cool signals. While the grill's cool bars are necessary for the TGI's painfulness, we also observed that the more often a participant reported feeling coolness or coldness, the less pain he or she experienced from the TGI. These results are consistent with research showing that cool temperatures generate activity in both thermoreceptive-specific, pain-inhibitory neurons and nociceptive dorsal horn neurons.
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Chronic low back pain (CLBP) and obesity are interrelated, but the physiological mechanisms linking the 2 conditions remain to be determined. Functional brain imaging data from CLBP patients show functional and structural alterations in areas mediating the attribution of hedonic value to food. Accordingly, we hypothesized that CLBP patients would exhibit alteration in the hedonic perception of highly palatable, calorie-containing foods. ⋯ In contrast, the patients' sensory evaluation of these stimuli was not different from those of healthy controls. In addition, whereas in healthy controls caloric intake from pudding closely matched hedonic ratings and decreased hunger after ad libitum pudding intake, such effect was totally abolished in CLBP patients. Our data thus reveal a decoupling between hedonic perception and fat calorie intake in CLBP patents, suggesting altered hedonic perception of fat as a potential mechanism linking CLBP to overeating and obesity.
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Occupational activities such as lifting loads, working in constrained spaces, and training increase the risk of pain-related musculoskeletal disorders (MSDs) in military veterans. Few studies have investigated MSD and psychological disorder in veterans, and previous studies had limitations. This cross-sectional study compared pain-related MSD and psychological comorbidity and well-being between 1381 male Australian 1990-1991 Gulf War veterans (veterans) and a military comparison group (n=1377, of whom 39.6% were serving and 32.7% had previously deployed). ⋯ Comorbidity of any MSD and psychological disorder was more common in veterans, but MSDs were associated with depression, PTSD, and poorer well-being in both groups. Psychological comorbidity needs consideration in MSD management. Longitudinal studies are needed to assess directionality and causality.