抄録
Transcranial magnetic stimulation (TMS) can change the size of the H-reflex. An important feature of pulsed magnetic stimulation is the direction in which the induced eddy current flows within the target tissue. The purpose of the present study was to clarify the relationship between the direction of eddy current and the modulation of H-reflex in rats. Rats were anesthetized with ketamine, and TMS was applied using a figure-eight coil. In motor evoked potentials (MEPs), the direction of the eddy current was defined as 0 degree at midline from caudal to the rostral sides and 90 degrees at the line between both ears. The coil was rotated in clockwise and counterclockwise directions, so that it was oriented right (R) and left (L) at 0-90 degrees. In H-reflex, a silver bipolar electrode was used for sciatic nerve stimulation. Compound muscle action potentials were recorded using copper wire electrodes implanted surgically into the tibialis anterior muscle. The effects of TMS on the H-reflex were studied with a conditioning-test paradigm and various interstimulus intervals (ISIs). The H-reflex was conditioned by TMS at ISIs ranging from 2 to 10 ms. The effects of conditioning TMS on the test H-reflex differed according to the intensity of the magnetic stimuli and the direction of eddy current. The conditioned H-reflex decreased significantly but at ISIs from 5 to 8 ms remained unchange when eddy current was perpendicular to the midline of the brain (L90 and R90). Our finds suggest that the changes in the TMS-conditioned H-reflex reflect modulating excitability in the spinal motoneuronal population. [J Physiol Sci. 2007;57 Suppl:S158]
