Effects of trains of high-frequency stimulation of the premotor/supplementary motor area on conditioned corticomotor responses in hemicerebellectomized rats.
We studied the effects of low- and high-frequency premotor electrical stimulations on conditioned corticomotor responses, intra-cortical facilitation (ICF) and spinal excitability in hemicerebellectomized rats (left side). Trains of stimulation were applied in prefrontal region rFr2 (the equivalent of the premotor/supplementary motor area in primates) at a rate of 1 Hz (low-frequency stimulation LFS) or 20 Hz (high-frequency stimulation HFS). Test stimuli on the motor cortex were preceded by a conditioning stimulus in contralateral sciatic nerve (two inter-stimulus intervals ISIs were studied: 5 ms or 45 ms). (A) At ISI-5, conditioning increased amplitudes of MEPs (motor evoked potentials) in the left motor cortex. This afferent facilitation was enhanced if preceded by trains of stimuli administered over the ipsilateral rFr2 area, and HFS had higher effects than LFS. The facilitation was lower for the right motor cortex, for both LFS and HFS. (B) At ISI-45, conditioned motor evoked responses were depressed as compared to unconditioned responses in the left motor cortex (afferent inhibition). Following LFS, the degree of inhibition was unchanged while it increased with HFS. At baseline, inhibition was enhanced in the right motor cortex. Interestingly, the afferent inhibition decreased significantly following HFS. (C) ICF was depressed in the right motor cortex, but increased similarly on both sides following LFS/HFS. These results (1) confirm the increased inhibition in the motor cortex contralaterally to the hemicerebellar ablation, (2) demonstrate for the first time that the cerebellum is necessary for tuning amplitudes of corticomotor responses following a peripheral nerve stimulation, (3) show that the application of LFS or HFS does not cancel the defect of excitability in the motor cortex for short ISIs, and (4) suggest that for longer ISIs, HFS could have interesting properties for the modulation of afferent inhibition in case of extensive cerebellar lesion. Our study underlines that cerebellar ablation impacts on the efficacy of combined peripheral-motor cortex stimulation in an ISI-dependent manner.
Oulad Ben Taib
Nordeyn
N
Service de Neurochirurgie, Hôpital Erasme-ULB, Bruxelles, Belgium.
Manto
Mario
M
D000222:Adaptation, Physiological / Q000502:physiology; D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D002526:Cerebellar Diseases / Q000503:physiopathology; D002531:Cerebellum / Q000293:injuries / Q000502:physiology* / Q000601:surgery; D003213:Conditioning, Psychological / Q000502:physiology*; D003714:Denervation; D004558:Electric Stimulation / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005121:Extremities / Q000294:innervation / Q000502:physiology; D005625:Frontal Lobe / Q000502:physiology*; D007839:Functional Laterality / Q000502:physiology; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009068:Movement / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology; D009434:Neural Pathways / Q000502:physiology; D010525:Peripheral Nerves / Q000502:physiology; D011712:Pyramidal Tracts / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar