Somatosensory & motor research
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This study evaluated the effects of two different types of segmental/extra-segmental conditioning stimuli (tonic muscle pain and non-painful vibration) on the subjective experience (perceived pain intensity) and on the cortical evoked potentials to standardized test stimuli (cutaneous electrical stimuli). Twelve subjects participated in two separate sessions to investigate the effects of tonic muscle pain or cutaneous vibration on experimental test stimuli. The experimental protocol contained a baseline registration (test stimuli only), a registration with the test stimuli in combination with the conditioning stimuli, followed by a registration with the test stimuli only. ⋯ The evoked potentials were generally decreased during hypertonic saline infusion at the extra-segmental sites, but the distribution of the topographic maps did not appear to change. Vibration has previously been shown to inhibit pain, but in the present study the perceived intensity of phasic painful electrical stimuli was unchanged. The reduced perceived pain intensity and the smaller peak-to-peak amplitude of the evoked potential in the presence of extra-segmental conditioning pain are in accordance with the concept of diffuse noxious inhibitory control.
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Clinical Trial Controlled Clinical Trial
Attenuation of experimental pruritus and mechanically evoked dysesthesiae in an area of cutaneous allodynia.
We investigated the effects of tactile allodynia on the itch and mechanically evoked dysesthesiae produced by an intradermal injection of histamine in human volunteers. After an intradermal injection of capsaicin into the volar surface of one forearm, there developed an area of tactile allodynia to stroking and hyperalgesia to pricking the skin. Histamine was then injected simultaneously into the area of allodynia (experimental arm) and into the opposite forearm (control arm). ⋯ The magnitude of itch and the areas of hyperknesis and alloknesis developed normally on the control arm but were absent or greatly reduced on the experimental arm. Thus, both the itch and the alloknesis and hyperknesis normally induced by histamine were absent or greatly reduced when histamine was injected in an area of capsaicin-induced allodynia. These results are compatible with the hypothesis that activity in capsaicin-sensitive, nociceptive primary afferent neurons evokes a central neuronal inhibitory process that prevents or reduces the itch and mechanically evoked dysesthesiae normally produced by an intradermal injection of histamine.
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Chelatable zinc is co-localized with glutamate in the synaptic vesicles of a distinct population of telencephalic neurons. The present study used a histochemical technique to localize zinc-containing terminals within the somatosensory barrel cortex (S1) of normal adult rats and rats that had been subjected to 4-6 weeks of tactile deprivation produced by simple whisker trimming beginning either at birth or during adulthood. In normal adult rats intense staining for synaptic zinc was observed in laminae I, II/III and V. ⋯ This redistribution of synaptic zinc appears to be permanent since altered staining of deprived barrels persists after extended periods of tactile experience with regrown whiskers. The results in normal rats indicate that zinc-containing circuits are distributed heterogeneously within S1 where they most likely subserve intracortical vs thalamocortical processing. The altered distribution of zinc-ergic circuits following neonatal whisker trimming suggests that zinc-sequestering neurons in developing S1 are particularly sensitive to early tactile experience.
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Clinical Trial Controlled Clinical Trial
Quantification of deep and superficial sensibility in saline-induced muscle pain--a psychophysical study.
The aim of the present study was to study the sensibility in the area of saline-induced muscle pain. In three experiments, ten subjects were exposed to computer-controlled infusion of 0.5 ml isotonic (0.9%) or hypertonic (9%) saline into the anterior tibial muscle. The pain intensity was assessed on a visual analogue scale (VAS). ⋯ Moreover, the hypertonic saline infusion given on the second day produced significantly higher (130 +/- 50%) VAS scores than the infusion given on the first day. In experiment 3, the PT was determined in the subcutaneous tissue, but no significant effects of saline infusion were found. The present placebo-controlled experiments failed to show muscular or subcutaneous hyperalgesia after saline-induced muscle pain per se.
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Clinical Trial
"Warmth-insensitive fields": evidence of sparse and irregular innervation of human skin by the warmth sense.
Although more acute in some areas of the body than in others, temperature sensitivity is assumed to be present throughout the skin. Only when very small stimuli have been used (e.g., approximately 1 mm2) has sensitivity to warming or cooling appeared discontinuous. ⋯ The existence of such sites corroborates reports that warm fibers are rare in human cutaneous nerves and confirms the classical theory that cutaneous innervation by the warmth sense is punctate and sparse. The insensitive areas also provide unique opportunities for assessing the contribution of the low-threshold warmth system to perception of heat and heat pain, and their existence in healthy young adults contraindicates use of warmth sensitivity in neurological assessments of C-fiber function.