Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Comparative Study
Vasomotor response to cold stimulation in human capsaicin-induced hyperalgesic area.
Cooling the skin induces sympathetically driven vasoconstriction, with some vasoparalytic dilatation at the lowest temperatures. Neurogenic inflammation, on the other hand, entails vasodilatation. In this study we investigated the balance between vasoconstriction and vasodilatation in an area of experimentally induced secondary hyperalgesia (2 degrees HA), in response to low-temperature stimulations. ⋯ In addition, vasodilatory effect (elevated BF) was found following the capsaicin injection compared with baseline for all regions (P<0.001): the non-cooled area was dilated by 450+/-5.1%; The vasoconstrictive effect for the 10 and 20 degrees C did not overcome the capsaicin vasodilatation, but did reduce it, with dilatation of 364+/-7.0% and 329+/-7.3%, respectively. For 0 degrees C, a dilatation of 407+/-6.5% was seen. It is concluded that in this experimental model, and potentially in the equivalent clinical syndromes, vasodilatation induced by the inflammation is only slightly reduced by cold stimulation such that it is still dominant, despite some cold-induced vasoconstriction.
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In the present report, we extend our previous observations on the effect of age on postural stabilization from fingertip contact (Exp Brain Res 157 (2004) 275) to examine the possible influence of sensory thresholds measured at the fingertip on the magnitude of contact forces. Participants (young, n=25, 19-32 years; old, n=35, 60-86 years) underwent psychophysical testing of the right index finger to determine thresholds for spatial acuity, pressure sensitivity and kinesthetic acuity. Spatial acuity was determined from the ability to detect gaps of different widths, while Semmes-Weinstein monofilaments were used for pressure sensitivity. ⋯ The same analyses further revealed that much of the variance explained by the models arose from inter-individual differences in tactile spatial acuity and not from differences in pressure sensitivity or in kinesthetic acuity. Thus, of all three tests, the spatial acuity task was the most sensitive at detecting differences in hand sensibility both within and between age groups and, accordingly, was also better at predicting the magnitude of fingertip forces deployed for postural stabilization. Since spatial acuity is critically dependent upon innervation density, we conclude that the degree of functional innervation at the fingertip was likely an important factor in determining the capacity of older participants to use contact cues for stability purposes, forcing the most affected individuals to exert unusually high pressures in order to achieve stabilization in the presence of reduced tactile inputs arising from contact with the touched surface.