Pain
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One of the most commonly used experimental animal models for neuropathic pain is the chronic constriction injury (CCI) where four loose ligatures are tied around the sciatic nerve. One disadvantage of this model is the introduction of foreign material into the wound, which causes a local inflammatory reaction. Thus the distinction between the neuropathic and the inflammatory component of pain is difficult in this model. ⋯ In the epineurium the number of macrophages was strikingly increased after CCI compared with PST, indicating that the response of the immune system is different in a structural lesion with and without foreign material. In conclusion, PST is a pure nerve injury model without an epineurial inflammatory component due to foreign material and is therefore well suited for studying the role of local endoneurial processes in the development and maintenance of neuropathic pain. Also, the importance of regeneration in the termination of hyperalgesia can convincingly be shown in this model.
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Evidence from animal models and studies of human sensory nerves demonstrate that tetrodotoxin (TTX)-resistant Na(+) channels are present in sensory neurons and might play an important role in pain conduction and chronic pain. Recent investigations suggest that TTX-resistant Na(+) channels in the peripheral nervous system are less sensitive to local anesthetics than TTX-sensitive Na(+) channels. To test the effects of the clinically used local anesthetics lidocaine and bupivacaine on TTX-resistant action potentials (APs) in sensory neurons, we performed electrophysiological experiments on small dorsal root ganglion (DRG) neurons from young rats. ⋯ Time to peak and duration of TTX-resistant APs were prolonged by local anesthetics. Trains of APs could be elicited in some neurons by long-lasting current injections, and the half-maximal concentrations needed to suppress these trains were 30 microM lidocaine or 10 microM bupivacaine. We suggest that the reduction in firing frequency at low concentrations of local anesthetic may explain the phenomenon of paresthesia when sensory information is gradually suppressed during spinal anesthesia.
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Randomized Controlled Trial Clinical Trial
Expectations of analgesia do not affect spinal nociceptive R-III reflex activity: an experimental study into the mechanism of placebo-induced analgesia.
The purpose of this study was to investigate whether placebo analgesia is mediated by the release of beta-endorphin. In addition to subjective pain reports, we included an objective physiological parameter of nociception reflected by the opioid sensitive nociceptive R-III reflex. Placebo consisted of strong suggestions of pain relief and an intravenous injection of saline. ⋯ Consistently, the antagonizing effects of naloxone were negligible. A subgroup analysis of those who did show a placebo response as indicated on the VAS did not support the supposition that beta-endorphin is released due to placebo suggestion. It is suggested that intensified stimuli and a more effective procedure to induce placebo analgesia (e.g. conditioning) may produce a proper placebo effect.
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Both physicians and nurses are responsible for adequate pain management. The aim of this study was to assess pain management behavior of physicians and nurses, and to evaluate the effects of a Pain Monitoring Program for nurses on the extent to which nurses administer analgesics. The Pain Monitoring Program consisted of two components: educating nurses about pain, pain assessment and pain management; and implementing daily pain assessment by means of a numeric rating scale. ⋯ Based on this study it can be concluded that the use of a simple method such as a numeric rating scale together with pain education for nurses is effective in improving the administration of analgesics by nurses. These are important results because nurses play an essential role in helping patients to cope with their pain. Because the Pain Monitoring Program (PMP) was effective in a heterogeneous population in multiple care settings, the possibility of implementing the PMP in routine nursing practice should be considered.
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We investigated the scoring properties of the mouse formalin test using the time-sampling method recently developed for infant and adult rats. Formalin was injected under the plantar surface of one rear paw (10 microl, 1-8%), and pain behaviours (paw favouring, lifting and licking) and behavioural state were recorded. Correlational and regression analyses indicated that scores composed of combinations of all three pain behaviours, either summed or weighted, provided less variable indices of pain than licking alone. ⋯ Formalin dose-dependently reduced locomotion, rearing and sniffing in both the first phase and the early part of the second phase. The combination measures were sensitive to morphine (2-8 mg/kg), amphetamine (1-4 mg/kg), dipyrone (50-200 mg/kg), xylazine (0.25-1 mg/kg), and acepromazine (0.25-1 mg/kg), and resistant to diazepam (0.5-2 mg/kg), pimozide (0.05-0.25 mg/kg), pentobarbital (10 and 15 mg/kg) and indomethacin (2-8 mg/kg). Decreased pain was correlated with increased motor activity for morphine and amphetamine, and with decreased activity for xylazine and acepromazine; dipyrone and indomethacin did not alter activity levels.