Pain
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Comparative Study
Differential susceptibility of the PAG and RVM to tolerance to the antinociceptive effect of morphine in the rat.
The periaqueductal gray (PAG) and rostral ventromedial medulla (RVM) are part of a nociceptive modulatory system. Microinjection of morphine into either structure produces antinociception. Tolerance develops to ventrolateral PAG mediated antinociception with repeated microinjection of morphine. ⋯ There was a 64% drop in hot plate latency from the first to the fifth injection of morphine into the PAG, but only a 36% drop in latency following RVM microinjections. Reducing the interdose interval to two injections a day or increasing the total number of injections from 4 to 8 did not enhance the development of tolerance to RVM morphine administration. These data demonstrate that opioid-sensitive neurons in the RVM are relatively resistant to the development of tolerance compared to PAG neurons.
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Comparative Study
Acute and persistent pain modulation of attention-related anterior cingulate fMRI activations.
The anterior cingulate cortex (ACC) has been implicated in both sustained attention (SA) and pain perception. Nonetheless, only a small body of literature has examined the relationship between SA and pain perception. This study utilized fMRI to examine activation patterns that emerged in the ACC in healthy participants and participants with chronic pain (due to osteoarthritis (OA) of the knee) while completing a sustained attention task with and without exposure to an acute painful stimulus. ⋯ In the healthy group, there were broadly distributed clusters of voxels within the ACC that were modulated by painful stimulation. But in the chronic pain group, a discrete focal region of the ACC was modulated by pain. These results demonstrate that ACC activity is modulated differently during tasks of SA and pain, and that acute pain in healthy participants and participants with chronic pain result in significantly different ACC activation patterns.
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Comparative Study
Parent-child interactions among children with juvenile fibromyalgia, arthritis, and healthy controls.
Parent-child interactions during pain-inducing exercise tasks among children (11-17 years old) with fibromyalgia, juvenile rheumatoid arthritis, and pain-free controls were examined and the contribution of parent-child interactions to disability was tested. Fifteen children in each of the three diagnostic groups and their parents completed 5-min exercise tasks and completed questionnaire measures of disability (Functional Disability Inventory) and coping (Pain Coping Questionnaire). There were few group differences in parent-child interactions. ⋯ Across the groups, more pain and less time on task during the exercises were related to Functional Disability Inventory scores and more school absences. Parent-child interaction patterns influence children's adaptation to pain during experimental tasks. Parents' discouragement of coping in response to their children's negative statements related to the pain or the pain-evoking task are counter productive to children's ability to maintain activity in a mildly painful situation.
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Comparative Study
Enhanced excitability of dissociated primary sensory neurons after chronic compression of the dorsal root ganglion in the rat.
A chronic compression of the dorsal root ganglion (CCD) produces ipsilateral cutaneous hyperalgesia and allodynia in rats. Intracellular electrophysiological recordings from formerly compressed neurons in the intact dorsal root ganglion (DRG) reveal lower than normal current thresholds (CTs) and abnormal spontaneous activity (SA) (Zhang JM, Song XJ, LaMotte RH. Enhanced excitability of sensory neurons in rats with cutaneous hyperalgesia produced by chronic compression of the dorsal root ganglion. ⋯ The overall incidence of SA was higher for CCD than for control neurons after 1d culture (10.3 vs. 1.8%) and similar to that obtained in the intact DRG. We conclude that the CCD-induced hyperexcitability of medium- and large-sized neurons remains after dissociation and is intrinsic to the soma. For small-sized neurons, the effects of CCD observed in the intact DRG are less apparent after dissociation possibly due to the hyperexcitability produced by the dissociation process itself.
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Comparative Study Clinical Trial
Evidence for cortical hyperexcitability of the affected limb representation area in CRPS: a psychophysical and transcranial magnetic stimulation study.
Functional alterations in noxious, sensory and motor circuits within the central nervous system may play an important role in the pathophysiology of complex regional pain syndrome (CRPS). The aim of the present study was to search for further evidence of hyperexcitability in the hemisphere contralateral to the affected limb in patients with CRPS by employing both psychophysical and transcranial magnetic stimulation (TMS) methods. Twelve patients with CRPS type I, confined to the distal part of a limb (six in an upper-limb and six in a lower-limb), were enrolled in the study. ⋯ A significant reduction in the short intracortical inhibition associated with a significant increase of the I-wave facilitation was found in the hemisphere contralateral to the affected side in the upper-limb CRPS group. No significant inter-hemispheric asymmetry between the affected and the non-affected sides was revealed in the lower-limb CRPS group. Taken together, these results suggest that in patients with well-localized CRPS, there is evidence for sensory and motor CNS hyperexcitability, though it seems to involve only corresponding regions within the CNS rather than the entire hemisphere.