Autonomic neuroscience : basic & clinical
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Comparative Study
Chemically and electrically induced sweating and flare reaction.
Both thin afferent (nociceptors) and efferent (sympathetic sudomotor) nerve fibers can be activated electrically and chemically, resulting in neurogenic erythema and sweating. These reactions have been used before to assess the impairment of sympathetic and nociceptor fibers in humans. In this study, electrically induced sweating and erythema were assessed simultaneously in the foot dorsum and thigh, and were compared to chemically induced activation. ⋯ The steepest increase of the sweat response was induced at lower intensities as compared to that of the erythema (18.3 mA vs. 25.7 mA, p<0.01) and reached a plateau for intensities above 25 mA, suggesting lower electrical thresholds for sudomotor fibers. Maximum flare areas induced electrically with 30 mA were smaller than those evoked chemically (flare size: 4.5 cm2 vs. 10.6 cm2). In contrast, the electrically evoked sweating rate was higher than that evoked chemically (acetylcholine, or ACh; sweating rate 0.31 vs. 0.21 microl/cm2/min, p<0.01), which might be attributed to an increased effectiveness of synchronized discharge in sympathetic fibers upon electrical stimulation.
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Comparative Study
Mechanisms of sustained cutaneous vasodilation induced by spinal cord stimulation.
This study was performed to investigate whether spinal cord stimulation (SCS) at intensities below motor threshold prolongs cutaneous vasodilation and whether sustained vasodilation by SCS is mediated through sympathetic inhibition and/or antidromic activation of sensory fibers. SCS was applied to the dorsal surface of the L2-L3 spinal cord of anesthesized rats with stimulus parameters used clinically (i.e., 50 Hz, 0.2 ms duration, and stimulus intensity at 30%, 60%, or 90% of motor threshold). ⋯ SCS-induced vasodilation at 90% of motor threshold persisted for the entire stimulation period up to 30 min, and the vasodilation was not attenuated by hexamethonium. It is concluded that sustained vasodilation, which is induced by SCS at only 90% of motor threshold, in this study was mediated via antidromic activation of sensory fibers.