European journal of pain : EJP
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The mechanisms through which electro-acupuncture (EA) and tricyclic antidepressants produce analgesia seem to be complementary: EA inhibits the transmission of noxious messages by activating supraspinal serotonergic and noradrenergic neurons that project to the spinal cord, whereas tricyclic antidepressants affect pain transmission by inhibiting the reuptake of norepinephrine and serotonin at the spinal level. This study utilized the tail-flick test and a model of post-incision pain to compare the antihyperalgesic effects of EA at frequencies of 2 or 100 Hz in rats treated with intraperitoneal or intrathecal amitriptyline (a tricyclic antidepressant). A gradual increase in the tail-flick latency (TFL) occurred during a 20-min period of EA. ⋯ In contrast, it did not significantly change the intensity of the antihyperalgesic effect of 2-Hz EA. The EA-induced antihyperalgesic effects lasted longer after intraperitoneal or intrathecal amitriptyline than after saline, with this effect of amitriptyline being more evident after 100- than after 2-Hz EA. The synergetic effect of amitriptyline and EA against post-incision pain shown here may therefore represent an alternative for prolonging the efficacy of EA in the management of post-surgical clinical pain.
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The American Academy of Pediatrics states that ongoing assessment of pain is essential for adequate pain treatment. Pain assessment by means of the COMFORT behaviour scale and the Numeric Rating Scale is therefore an important component of the post-operative pain treatment protocol for neonates and infants in our intensive care unit (ICU). ⋯ The post-operative pain protocol applied in our ICU appears to be effective; however, full compliance to the protocol was marginal, possibly leading to under-treatment of pain.
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There is equivocal evidence regarding pain responding in endurance athletes. When performing, their pain experience appears reduced but it is uncertain whether this persists when not competing or training. This study aimed to clarify how marathon runners perceive pain, and the influence of self-efficacy and coping strategy use on their pain threshold and tolerance when they are not affected by immediate exercise. ⋯ Coping and catastrophizing did not differ between the two groups but higher associative coping when accompanied by lower dissociative coping was related to higher pain tolerance. These results indicate that marathon runners have a reduced experience of pain compared with non-runners. This ability appears to be augmented by a high level of pain specific self-efficacy but is unaffected by the influence of general cognitive coping strategies, although higher associative coping and lower dissociative coping together were related to reduced pain tolerance independent of running involvement.
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Observing other people's pain increases our own reports to painful stimuli, a phenomenon that can be defined as 'compassional hyperalgesia' (CH). This functional magnetic resonance imaging study examined the neural correlates of CH, and whether CH could emerge when exposure to the driving stimulus was subliminal. Subjects received electric somatosensory stimuli while observing images of people undergoing painful or enjoyable somatic sensations, presented during a period allowing or not allowing conscious perception. ⋯ CH appears as a high-order phenomenon needing conscious appraisal of the eliciting visual stimulus, and supported by polymodal areas distinct from the basic Pain Matrix. This suggests that compassion to pain does not result from a mere 'sensory resonance' in pain networks, but rather from an interaction between the output of a first-line processing in the Pain Matrix, and the activity of a high-order network involving multisensory integration (temporo-parietal), encoding of internal states (mid-prefrontal) and short-time memory encoding (dorsolateral prefrontal). The Pain Matrix cannot be considered as an 'objective' correlate of the pain experience in all situations.
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The contribution of supraspinal, spinal or peripheral mu-opioid receptors (MORs) to the overall antinociception of systemic centrally penetrating versus peripherally restricted opioids has not been thoroughly investigated. Therefore, we examined paw pressure thresholds in Wistar rats with complete Freund's adjuvant hindpaw inflammation following different doses of intraplantar (i.pl.) as well as intravenous (i.v.) fentanyl (6.25-50 μg/kg), morphine (1-7.5 mg/kg) or loperamide (1-7.5 mg/kg). Antagonism of the i.v. mu-opioid agonists by intracerebroventricular (i.c.v.), intrathecal (i.t.) or i.pl. naloxone-methiodide (NLXM) revealed the relative contributions of supraspinal, spinal and peripheral MOR to the overall antinociceptive effects. ⋯ In conclusion, in comparison with supraspinal and spinal opioid receptors, peripheral opioid receptors do not significantly contribute to the antinociception of systemic fentanyl and morphine during inflammatory pain. Antinociception of their i.v. administration was superior over both i.v and i.pl. loperamide, acting exclusively via peripheral MOR. These findings may guide the future development of novel peripherally restricted opioids.