title: Long-lasting depression of soleus motoneurons excitability following repetitive magnetic stimuli of the spinal cord in multiple sclerosis patients.
abstract: The effect of repetitive magnetic stimulation at the spinal level on the soleus H-reflex amplitude was evaluated in II MS patients with lower limb spasticity and in nine healthy subjects. In MS patients stimulation with a train of 16 stimuli at 25 Hz induced a decrease in amplitude to 61.2 +/- 25.7% of the unconditioned H-reflex amplitude at interstimulus interval (ISI) of 10-1000 ms (P < 0.01). The amount of decrease in H-reflex amplitude was highly dependent on the stimulation intensity and the placement of the coil, and to a lesser extent influenced by the stimulation frequency. No decrease in motor evoked potentials (MEPs) evoked by transcranial magnetic stimulation was seen following trains of 16 stimuli at mid-thoracic in contrast to the post-stimulation depression in H-reflex amplitude which could imply that mechanisms acting at presynaptic level were involved. In response to repetitive magnetic stimuli for 5 min, a long-lasting decrease in H-reflex amplitude to a level of about 70% of the pre-stimulation H-reflex amplitude occurred in MS patients (P < 0.01). A similar although not significant decrease was observed in healthy subjects. We propose that long-lasting depression of the soleus H-reflex amplitude after repetitive magnetic stimuli is due to long-term depression of the synaptic transmission.
authors.affiliation: Department of Neurology, Aarhus University Hospital, Denmark.
authors.forename: J F
authors.initials: JF
authors.lastname: Nielsen
authors.forename: T
authors.initials: T
authors.lastname: Sinkjaer
mesh_terms: D000328:Adult; D019054:Evoked Potentials, Motor; D005260:Female; D006181:H-Reflex; D006801:Humans; D017774:Long-Term Potentiation; D008280:Magnetics; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D009103:Multiple Sclerosis / Q000473:pathology / Q000503:physiopathology*; D010812:Physical Stimulation; D013116:Spinal Cord / Q000473:pathology / Q000503:physiopathology*; D013997:Time Factors