Pain
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Comparative Study
Control of inflammatory pain by chemokine-mediated recruitment of opioid-containing polymorphonuclear cells.
Opioid-containing leukocytes can counteract inflammatory hyperalgesia. Under stress or after local injection of corticotropin releasing factor (CRF), opioid peptides are released from leukocytes, bind to opioid receptors on peripheral sensory neurons and mediate antinociception. Since polymorphonuclear cells (PMN) are the predominant opioid-containing leukocyte subpopulation in early inflammation, we hypothesized that PMN and their recruitment by chemokines are important for peripheral opioid-mediated antinociception at this stage. ⋯ We found that at 2 h post CFA (i) intraplantar but not subcutaneous injection of CRF produced dose-dependent and naloxone-reversible antinociception (P<0.05, ANOVA). (ii) Opioid-containing leukocytes in the paw and CRF-induced antinociception were reduced after PMN depletion (P<0.05, t-test). (iii) Opioid-containing leukocytes mostly expressed CXCR2. MIP-2 and KC, but not CINC-2 were detectable in inflamed but not in noninflamed tissue (P<0.05, ANOVA). (iv) Combined but not single blockade of MIP-2 and KC reduced the number of opioid-containing leukocytes and peripheral opioid-mediated antinociception (P<0.05, t-test; P>0.05, ANOVA). In summary, in early inflammation peripheral opioid-mediated antinociception is critically dependent on PMN and their recruitment by CXCR2 chemokines.
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A clearer understanding of how pain intensity relates to disability could have important implications for pain treatment goals and definitions of treatment success. The objectives of this study were to determine the optimal pain intensity rating (0-10 scale) cutpoints for discriminating disability levels among individuals with work-related carpal tunnel syndrome (CTS) and low back (LB) injuries, whether these cutpoints differed for these conditions and for different disability measures, and whether the relationship between pain intensity and disability was linear in each injury group. Approximately 3 weeks after filing work injury claims, 2183 workers (1059 CTS; 1124 LB) who still had pain completed pain and disability measures. ⋯ For all disability measures examined, the relationship between pain intensity and disability level was linear in the CTS group, but nonlinear in the LB group. Among study participants with work-related back injuries, when pain level was 1-4, a decrease in pain of more than 1-point corresponded to clinically meaningful improvement in functioning, but when pain was rated as 5-10, a 2-point decrease was necessary for clinically meaningful improvement in functioning. The findings indicate that classifying numerical pain ratings into categories corresponding to levels of disability may be useful in establishing treatment goals, but that classification schemes must be validated separately for different pain conditions.
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Case Reports Comparative Study
Spinal cord stimulation in a patient with persistent oesophageal pain.
This study describes a man with a long history of oesophageal pain that led to inability to swallow food and drink. Over a period of 8 years, he had multiple oesophageal operations that were unsuccessful. He presented, to the pain management team, with persistent oesophageal pain and required jejunostomy tube feeding to maintain nutrition. ⋯ He feels that SCS has been worthwhile. The authors discuss the rationale for this treatment. The decision was based on the use of SCS for refractory angina, and the idea that the neural mechanisms that generate both these pain states may be similar.
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Comparative Study
Electronic diary assessment of pain-related fear, attention to pain, and pain intensity in chronic low back pain patients.
The present study investigated the relationships between pain-related fear, attention to pain, and pain intensity in daily life in patients with chronic low back pain. An experience sampling methodology was used in which electronic diary data were collected by means of palmtop computers from 40 chronic low back pain patients who were followed for one week. Attention to pain was hypothesized to mediate the relation between pain-related fear and pain intensity. ⋯ Instead, results suggested that pain-related fear and attention to pain independently predicted pain intensity. No evidence for moderation of the relation between attention to pain and pain intensity by pain-related fear as a trait characteristic was found. Implications of the results from this study are discussed and suggestions for future research are provided.
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Comparative Study
In vivo recruitment by painful stimuli of AMPA receptor subunits to the plasma membrane of spinal cord neurons.
The persistent increase in pain sensitivity observed after injury, known as hyperalgesia, depends on synaptic plasticity in the pain pathway, particularly in the spinal cord. Several potential mechanisms have been proposed, including post-synaptic exocytosis of the AMPA subclass of glutamate receptors (AMPA-R), which is known to play a critical role in synaptic plasticity in the hippocampus. AMPA-R trafficking has been described in spinal neurons in culture but it is unknown if it can also occur in spinal neurons in vivo, or if it can be induced by natural painful stimulation. ⋯ Brefeldin-A, an antibiotic that inhibits exocytosis of proteins, not only prevented GluR1 trafficking to the membrane but also inhibited referred hyperalgesia in capsaicin-treated mice. Our results show that delivery of GluR1 AMPA receptor subunits to the cell membrane through a CaMKII activity-dependent exocytotic regulated pathway contributes to the development of hyperalgesia after a painful stimulus. We conclude that AMPA-R trafficking contributes to the synaptic strengthening induced in the pain pathway by natural stimulation.