Acta Physiologica 2010; Volume 198, Supplement 677
Joint Meeting of the Scandinavian and German Physiological Societies
HETEROTOPIC LOW-FREQUENCY STIMULATION INDUCES NOCICEPTIVE LTD WITHIN THE SAME CENTRAL RECEPTIVE FIELD IN MAN
Abstract number: P-MON-117
LARSEN1 LE, JUNG1 K, ELLRICH1 J
Electrical low-frequency stimulation (LFS) evokes long-term depression (LTD) of nociception in man. Studies suggest a strictly homotopic organization of LTD. It is hypothesized that even heterotopic LFS evokes LTD within the same central receptive field (RF). In 29 healthy volunteers painful electrical test stimulation and conditioning LFS (1200 pulses, 1 Hz) were applied to the low back by a concentric electrode in experiment ExpBack and to the left forearm by a multiarray electrode in ExpArm. In both experiments nociceptive RFs were determined by two-point discrimination using pinprick dividers and noxious electrical stimulation. Test stimulation was applied in two series each before (pre) and after (post) conditioning LFS. Volunteers rated pain perception during test stimulation according to a verbal rating scale. In ExpBack, test stimuli were administered within the right T12 dermatome. LFS was applied heterotopically within the same RF or remote in dermatome T8 in two sessions. In ExpArm, test stimulation was performed in the center of the RF whereas LFS was applied to the center or the margin of the RF, or outside the RF in three sessions. Average ratings of pre and post series were statistically analyzed. In ExpBack (n=9), pain ratings decreased significantly stronger in T12 (-33%) than in T8 dermatome (-5%; p<0.01). In ExpArm (n=20), LFS effects on pain rating significantly differed in three sessions (p<0.001). LFS in the center ( 27%) induced stronger pain reduction than LFS outside the RF (-9%; p<0.001) and in the margin of RF (-18%; p<0.05). LFS in the margin of RF was more effective than outside the RF (p<0.05). Data indicate that noxious LFS is able to induce LTD not only at exactly the same site but also within the same central RF. Forearm and low-back areas have large central RFs with distinctive convergence of primary neurons onto spinal secondary neurons. Thus, present results demonstrate heterotopic and probably heterosynaptic, nociceptive LTD in man.
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Acta Physiologica 2010; Volume 198, Supplement 677 :P-MON-117