Somatosensory & motor research
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Knee flexion is a movement that initiates rising from a sitting position, which is a common therapeutic exercise for patients unable to ambulate. We investigated how voluntary isometric biceps femoris contraction affects motor evoked potential (MEP) amplitude following transcranial magnetic stimulation, background electromyographic (EMG) amplitude, and H-reflex amplitude in ipsilateral leg muscles. Subjects were seated on the edge of a bed with their hips and knees flexed at 90 degrees, and the soles of their feet on the floor. ⋯ MEP recorded from TA and SOL with subthreshold stimuli using needle electrodes were more frequent with biceps femoris contraction (p < 0.04). H-reflex amplitude of SOL decreased during biceps femoris contraction (p < 0.001). We concluded that biceps femoris contraction affects leg muscle MEP, background EMG, and H reflexes differently.
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Comparative Study Clinical Trial Controlled Clinical Trial
The effect of heat conditioning of the primary area before and after induction of hyperalgesia by topical/intradermal capsaicin or by controlled heat injury.
The aim of the present study was to test the effect of heat conditioning before and after the induction of hyperalgesia. Three different methods were used for induction of hyperalgesia, topical capsaicin, intradermal capsaicin injection, and a controlled heat injury. The vascular (blood flow and skin temperature) and sensory changes (area of secondary hyperalgesia and ongoing pain) associated with the cutaneous hyperalgesia were compared. ⋯ Post-conditioning caused increased blood flow in the secondary hyperalgesic area for the topical capsaicin method and increased blood flow in the primary hyperalgesic area for the controlled heat injury method. However, conditioning with heat in an attempt to increase the C-fiber input did not have any effect on the ongoing pain ratings and sensory test results in any of the methods. The results of the present study suggest that there is still a need for a better experimental model with more stable allodynia both between sessions and between subjects while at the same time minimizing discomfort to the volunteer.
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Comparative Study
Neurotrophin receptor expression in retrogradely labeled trigeminal nociceptors--comparisons with spinal nociceptors.
In situ hybridization for trkA mRNA in trigeminal ganglion neurons retrogradely labeled with FluoroGold from the mandibular incisor demonstrated limited expression of the high-affinity nerve growth factor (NGF) receptor in this presumptive nociceptor population. Immunocytochemistry using polyclonal anti-trkA antibodies confirmed this result and extended it to show low levels of trkA protein expression in afferents labeled from the cornea. Less than 10% of the cells innervating the incisor, and approximately 15% of those innervating the cornea, were trkA-positive in adult and neonatal mice. ⋯ Approximately 15% of the corneal or pulpal afferent neurons expressed ret-immunoreactivity. These results suggest that trigeminal nociceptors differ from spinal nociceptors in several significant ways. Differences in neurotrophic requirements may be related to differences in target tissues, in embryonic origin of some trigeminal ganglion cells, or in the timing of down-regulation of trkA expression in trigeminal ganglion cells.
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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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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.