European journal of pain : EJP
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The purpose of this study was to assess possible segmental (uni- and/or bilateral) and plurisegmental changes in pressure pain thresholds (PPTs) during static muscle contractions. Twenty-four healthy subjects (12 female, 12 male) performed a standardised isometric contraction with the dominant m. quadriceps femoris (MQF) and m. infraspinatus (MI), respectively. PPTs were assessed using pressure algometry at the contracting muscle, at the contralateral (resting) muscle and at a distant resting muscle (MI during contraction of MQF and vice versa). ⋯ Following the contractions PPTs returned to baseline. Submaximal isometric contraction of MQF and MI gave rise to a statistically significant increase in PPTs at the contracting muscle, the resting homologous contralateral muscle and at the distant resting muscle indicating that generalised pain inhibitory mechanisms were activated. Contraction of MI, but not of MQF, gave rise to an additional activation of unilateral segmental antinociceptive effects.
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Although the antinociceptive effect of NMDA antagonists in the formalin test is well recognised, these compounds can induce adverse motor effects. The aim of this study was to identify the systemic doses of NMDA antagonists that induce analgesia without causing side effects. Male Swiss mice (30-40g) received a subcutaneous (sc) injection of 1.25% formalin (50 micro l) in the dorsal surface of the right hind-paw and, 15min before or after formalin, an ip injection of one of the following NMDA receptor antagonists: MK 801 (0.01, 0.025, and 0.05mg/kg), memantine (0.1, 0.5, and 1mg/kg), ketamine (0.125, 0.25, and 0.5mg/kg), dextromethorphan (5, 10, and 20mg/kg), and CGP 37849 (4, 6, and 8mg/kg). ⋯ The rank order potency of antinociceptive activity of NMDA antagonists was: MK801>memantine>ketamine>dextromethorphan>CGP37849. The NMDA antagonists administered after formalin (during the analgesic interval) did not affect the late phase of the formalin test. In conclusion, systemic administration of NMDA receptor antagonists decreases the nociception observed during the late phase of the formalin test.
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We have recently demonstrated dose-related analgesic-induced reductions in the occurrence of 7 behavioural activities following midline laparotomy in rats. For these behaviours to be useful in evaluating pain in laboratory rats they must be shown to occur after different types of surgery, and frequently enough to allow rapid scoring of animals. Here, the relevant behaviours were used to test the analgesic efficacy of meloxicam with a variation of our previous laparotomy model. ⋯ Irrespective of whether analyses included only 5 or all 10 min of the observation period, the relevant behaviours occurred significantly more often in rats given saline or low dose meloxicam than in those given 1 or 2 mg/kg of meloxicam, or any dose of carprofen. We conclude that this technique of quantifying post-surgery behaviour is an effective pain scoring method following abdominal surgery in rats, and that 1 mg/kg meloxicam significantly attenuates laparotomy induced pain. Since only a short observation period is required, this approach represents an important practical advance in assessing abdominal pain severity and clinical drug potency.
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Black and white pain drawings were introduced as a proposed means to identify patients, presenting with low back pain, who demonstrated functional overlay upon neurological testing. The use of color may enhance the usefulness of such pain drawings, but has not been described for adult patients. ⋯ Our findings agree with previous observations using black and white pain drawings, indicating that colored pain drawings are no less useful than the black and white approach. Further research is necessary to examine the psychometric properties and clinical usefulness of colored pain drawings to predict outcomes and/or determine treatment.
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Comparative Study Clinical Trial Controlled Clinical Trial
Hypoalgesia to pressure pain in referred pain areas triggered by spatial summation of experimental muscle pain from unilateral or bilateral trapezius muscles.
Animal and human experimental studies have suggested the importance of spatial summation in the nociception processing and in the activation of descending inhibition. However, the relationship between the areas (size) of muscles stimulated and the recruitment of descending inhibition has not been addressed. Consequently, we tested whether bilateral versus unilateral injection of hypertonic saline into trapezius muscles caused hypoalgesia to pressure pain (pressure pain thresholds, PPTs) in the local pain areas (the trapezius muscles) and the referred pain areas (the posterolateral neck muscles). ⋯ In the referred pain areas, the PPTs 7.5 and 15 min after the second injection were significantly increased compared with the first injection, while no changes in the PPT were observed in local and referred pain areas after unilateral injection. This suggests that the induction of descending inhibition was triggered by spatial summation during the later phase of experimentally induced muscle pain. The present experimental model might be used for further investigation of descending inhibition related to the spatial characteristics of nociceptive stimuli in humans.