Pain
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Comparative Study
Mechanical allodynia and thermal hyperalgesia upon acute opioid withdrawal in the neonatal rat.
Upon withdrawal from opioids many patients experience a heightened sensitivity to stimuli and an exaggerated pain response. We present evidence that neonatal rats exhibit allodynia and hyperalgesia on acute opiate withdrawal. Postnatal 7 and 21 day rats were used to approximately model a full term human infant and a human child, respectively. ⋯ Spontaneous and precipitated withdrawal from a single acute administration of morphine produced mechanical allodynia and thermal hyperalgesia in postnatal day 7 rats and mechanical allodynia in postnatal day 21 rats. A higher dose of morphine was required to produce mechanical allodynia in postnatal day 21 versus 7 rats but this increase was independent of the analgesic efficacy of morphine at these two ages. The present work illustrates the need to examine the phenomenon of hypersensitivity upon opioid withdrawal in the human pediatric population.
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Comparative Study
P300-amplitudes in upper limb amputees with and without phantom limb pain in a visual oddball paradigm.
The aim of the study was to investigate to what extent cortical hyper-reactivity to visual stimuli is present in upper limb amputees. Five amputees with phantom limb pain (PLP), five amputees without PLP (Non-PLP) and 10 healthy controls (HC) were investigated using a visual oddball paradigm. Two hundred visual stimuli were presented with target stimuli occurring at a probability of 25% and standard stimuli at a probability of 75%. ⋯ The size of the P300-amplitude was positively correlated with the intensity of PLP. These findings suggest a higher magnitude of non-specific cortical excitability in amputees with PLP and a reduced excitability in amputees without PLP. This extends previous findings of differences in cortical excitability in PLP and non-PLP patients in the sensorimotor domain.
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Comparative Study
Block of NMDA and non-NMDA receptor activation results in reduced background and evoked activity of central amygdala neurons in a model of arthritic pain.
The latero-capsular division of the central nucleus of the amygdala (CeA) is now defined as the 'nociceptive amygdala' because of its high content of neurons activated exclusively or preferentially by noxious stimuli. Multireceptive (MR) neurons that respond to innocuous and, more strongly, to noxious stimuli become sensitized in arthritis pain. This form of nociceptive plasticity involves presynaptic group I metabotropic glutamate receptors, which increase glutamate release. ⋯ All neurons examined received excitatory input from the knee(s) and were MR neurons. A selective NMDA receptor antagonist (AP5) inhibited responses to noxious stimuli more potently in the arthritic pain state (n = 6) than under control conditions before arthritis (n = 8) AP5 also inhibited the enhanced background activity and increased responses to normally innocuous stimuli in arthritis, but had no significant effects on these parameters under control conditions. A selective non-NMDA receptor antagonist (NBQX) inhibited background activity and evoked responses under normal control conditions (n = 6) and in arthritis (n = 8) These data suggest that activation of both NMDA and non-NMDA receptors contributes to pain-related sensitization of amygdala neurons.
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Comparative Study
Distraction from chronic pain during a pain-inducing activity is associated with greater post-activity pain.
The aim of this study was to investigate the effects of distraction from pain during and after a pain-inducing lifting task in a sample of chronic low back pain (CLBP) patients. Fifty-two CLBP patients (25 males, 27 females; mean age=46.30 years) performed a pain-inducing lifting task twice, once alone and once with a simultaneous cognitive distraction task. ⋯ Further investigation of the catastrophizing data showed that the effect of catastrophizing about pain during the lifting task on the cognitive distraction task was mediated by the amount of attention paid to pain. Clinical implications of these findings are discussed.
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Comparative Study
Comparison of two psychometric scaling methods for ratings of acute musculoskeletal pain.
Psychometric theory allows interindividual comparisons by scaling differences among subjects with respect to some psychological attribute. The most widely used psychometric scaling method is classical test theory. The properties of classical test theory pain scores are limited to the observed range of pain scores in a given sample, to the specific conditions in a given sample that are the source of pain (e.g. surgery vs. cancer), and to a particular pain survey. ⋯ The psychometric scaling methods were compared using standardized residuals (data fit), standard errors of measurement (score precision), and a graphical plot of predicted scores against scale scores (bias). The item response theory scores demonstrated better data fit and less bias than did the classical test theory scores. In addition to superior psychometric properties, item response theory scores have several other important theoretical and practical advantages.