Somatosensory & motor research
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Clinical Trial
C- and Adelta-fibre mediated thermal perception: response to rate of temperature change using method of limits.
Studies investigating the effect of rate of temperature change on thermal thresholds have used a variety of different methods and threshold combinations, and many display incomplete reporting of statistical analyses. It has been suggested that C- and Adelta-fibre mediated thresholds differ in their reaction to different rates of temperature change. Ten healthy female volunteers (aged 18-26 years; mean 21 +/- S. ⋯ A traditional explanation of measurement artefact alone is insufficient in rationalizing these results, with additional factors potentially involved. Slow rates of temperature change were shown to reduce mean intra-individual differences in recorded threshold values, and also to abolish ceiling effects with HP threshold determinations. Clinically, therefore, using slow rates of temperature change with method of limits has a range of benefits over and above simply minimizing measurement artefact.
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This study examined the effect of repeated intradermal capsaicin injections on capsaicin pain intensity and areas of allodynia and punctate hyperalgesia. Seventeen healthy volunteers participated in four sessions separated by at least 5 days. Each session included four intradermal injections of 10 microg of capsaicin. ⋯ There were no significant relations between capsaicin pain intensity and areas of allodynia and punctate hyperalgesia after first injections. The findings indicate that the response to intradermal injection of capsaicin is dependent on the time and distance between injections. The lack of significant relation between capsaicin pain intensity and area of allodynia and punctate hyperalgesia suggests that the two phenomena are mediated by different central mechanisms.
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Comparative Study
Contralateral but not systemic administration of bupivacaine reduces acute inflammation in the rat hindpaw.
The effects of contralateral treatment with local anesthetics following acute hindpaw inflammation were investigated in rats. Inflammation was induced by unilateral injection of either 50 or 100 microl of 1% carrageenan into the right paw. Contralateral injection of either bupivacaine or saline was given immediately before the carrageenan. ⋯ Sciatic nerve ligation on the contralateral side or intrathecal administration of saline significantly reduced the effects of bupivacaine when respectively compared with sham-operation and subcutaneous saline injection. Contralateral treatment with bupivacaine into the knee joint induced the same anti-nociceptive effect as administered into the paw. Our findings indicate that contralateral administration of bupivacaine induces long-lasting anti-nociceptive effects and may serve as a new or complementary treatment approach in acute inflammatory pain conditions.
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The present study analyzes the activity of 120 neurons recorded in the two ventro-postero-medial (VPM) nuclei of the thalamus in a rat model of trigeminal neuropathic pain. Twenty-eight rats were tested 2 weeks after a chronic constriction injury (CCI) of the infraorbital nerve (IoN). These animals exhibited violent pain-related reactions to extremely weak mechanical stimuli applied to the lesioned and, to a lesser extent, unlesioned IoN territories. ⋯ In contrast to the VPMn neurons, the RFs of both the VPMc and VPMi neurons included two vibrissae at least, and were occasionally discontinuous and multimodal, including both vibrissae and cutaneous areas for VPMc units. The bilateral changes in VPM responsiveness and in behavior suggest the involvement of central processing of sensory information, which are set off by the CCI-IoN. The putative mechanisms and functional implication of the changes in the VPM neuronal activities are discussed.
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Comparative Study Clinical Trial Controlled Clinical Trial
Enhancement of experimental pruritus and mechanically evoked dysesthesiae with local anesthesia.
Pain reduces itch-a commonly known effect of scratching the skin. Experimentally produced itch from histamine is sometimes accompanied by secondary sensations of pain. The present study investigated the effects of eliminating this pain, by means of a local anesthetic, on the itch and the enhanced mechanically evoked itch and pain that occur after an intradermal injection of histamine. ⋯ It is hypothesized that there exist two classes of histamine-sensitive primary afferent neurons. One class is "pruritic", and mediates itch whereas the other is "antipruritic", and evokes a centrally mediated reduction in histamine-evoked itch and dysesthesiae. It is further suggested that the anesthetic blocked the discharges of the antipruritic afferents, preventing the central inhibition from occurring and thereby unmasking the effects of the pruritic afferents.