Somatosensory & motor research
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Clinical Trial
The effects of stimulus location on the gating of touch by heat- and cold-induced pain.
The influence of heat- and cold-induced pain on tactile sensitivity, a "touch gate", was measured under conditions in which the location of the noxious stimuli was varied with respect to the tactile stimulus applied to the thenar eminence of humans. Vibrotactile thresholds were measured in the absence of pain and during administration of a painful stimulus, with the stimulus frequencies selected to activate independently the four psychophysical channels hypothesized to exist in human glabrous skin. Heat-induced pain produced by spatially co-localizing the noxious stimuli with the tactile stimuli was found, on average, to elevate threshold amplitude by 2.2 times (6.7 dB). ⋯ Ipsilateral heat-induced pain caused an elevation in tactile thresholds even when the noxious and non-noxious stimuli were not co-localized, and the effect may seem to require that the painful stimulus be within the somatosensory region defined possibly in terms of dermatomal organization. Thus the effect is probably related to somatotopic organization and is not peripherally mediated. A brief discussion as to the possible locus of the touch gate within the nervous system is also given.
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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 human primary somatosensory cortex consists of four cytoarchitectonic subdivisions (3a, 3b, 1 and 2) that are likely to contain distinct somatosensory representations. The intraareal organization of these areas as well as that of the primary motor cortex (area 4) has been analyzed using histochemical stains of cytochrome oxidase, acetylcholinesterase and NADPH-diaphorase activity in normal human brains. Cytochrome oxidase activity was revealed in individual cortical neurons and neuropil. ⋯ NADPH-diaphorase positive elements included Golgi-like stained non-pyramidal neurons and Nissl-like stained pyramidal neurons; the former were found, in small numbers, in layer II of areas 4, 3a, 3b and 1, and the latter in layers III and V of areas 4 and 3a and in layer V of areas 1 and 2. The dark cytochrome oxidase staining of layer IV and the paucity of acetylcholinesterase positive pyramids in areas 3a and 3b resemble the pattern found in primary visual and auditory areas, whereas the dark cytochrome oxidase staining in layer III and abundance of acetylcholinesterase positive pyramids in areas 1 and 2 that of association areas. These results suggest that the four areas included in human SI constitute hierarchical stages of cortical processing, with 3a and 3b corresponding to primary and 1 and 2 to secondary areas.