Electrical low-frequency stimulation induces homotopic long-term depression of nociception and pain from hand in man.
OBJECTIVE
Electrical low-frequency stimulation (LFS) of cutaneous afferents evokes long-term depression (LTD) of nociception. In vitro studies suggest a sole homosynaptic effect on the conditioned pathway. The present study addresses homotopy of LTD in human nociception and pain.


METHODS
In 30 healthy volunteers, nociceptive Adelta fibers were electrically stimulated by a concentric electrode. Test stimulation (0.125 Hz) was alternately applied unilateral to radial and ulnar side of right hand dorsum (ExpUni) or bilateral to radial side of right and left hand dorsum (ExpBi). Conditioning LFS (1 Hz, 1,200 pulses) was applied to radial side of right hand dorsum. Somatosensory evoked cortical vertex potentials (SEP) were recorded, and volunteers rated stimulus intensity.


RESULTS
After homotopic LFS, SEP amplitude (ExpUni: -34.6%; ExpBi: -33.6%) and pain rating (ExpUni: -44.1%; ExpBi: -29.1%) significantly decreased. Amplitude reduction after heterotopic LFS did not differ from habituation effects in Control experiment without LFS. Heterotopic pain perception was not affected.


CONCLUSIONS
The electrophysiological and psychophysical study on synaptic plasticity in healthy man demonstrates homotopic organization of LTD.


CONCLUSIONS
Homotopy is probably due to a homosynaptic effect at first nociceptive synapse, but descending inhibitory systems may also be involved. These experiments may help to judge the potency of LTD for future therapy in chronic pain.
Rottmann
Silke
S
Interdisciplinary Center for Clinical Research, RWTH Aachen University, Pauwelsstrasse 30, D-52074 Aachen, Germany.
Jung
Kerstin
K
Center for Sensory-Motor Interaction SMI, Department of Health Science and Technology, Medical Faculty, Aalborg University, Fredrik Bajers Vej 7D2, DK-9220 Aalborg, Denmark.
Ellrich
Jens
J
Center for Sensory-Motor Interaction SMI, Department of Health Science and Technology, Medical Faculty, Aalborg University, Fredrik Bajers Vej 7D2, DK-9220 Aalborg, Denmark. Electronic address: jellrich@hst.aau.dk.
D000328:Adult; D000704:Analysis of Variance; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000009:adverse effects*; D005073:Evoked Potentials, Somatosensory / Q000502:physiology / Q000528:radiation effects; D005260:Female; D007839:Functional Laterality; D006225:Hand / Q000294:innervation*; D006801:Humans; D036881:Long-Term Synaptic Depression / Q000528:radiation effects*; D008297:Male; D009619:Nociceptors / Q000503:physiopathology*; D010146:Pain / Q000209:etiology*; D010147:Pain Measurement / Q000379:methods; D017288:Pain Threshold / Q000528:radiation effects*; D011601:Psychophysics