Dual modulating effects of amphetamine on neuronal excitability and stimulation-induced plasticity in human motor cortex.
OBJECTIVE
The objective of the present study is to test the modulating effects of dextro-amphetamine (d-AMP) on excitability and stimulation-induced plasticity in human motor cortex.


METHODS
Transcranial magnetic stimulation (TMS) was used to measure motor threshold, motor evoked potential (MEP) size and paired-pulse intracortical facilitation (ICF) in the biceps muscle of 7 healthy subjects before and after two different experimental manipulations: temporary forearm ischemic nerve block (INB) alone, or INB plus 0.1 Hz repetitive TMS (INB+rTMS) of the motor cortex contralateral to INB. Both manipulations were run after treatment with 10mg of d-AMP or placebo (PBO).


RESULTS
In the PBO experiments, INB alone had no significant effect on MEP size or ICF, while INB+rTMS produced long-lasting (>60 min) increases. Compared with PBO, d-AMP led to a short-lasting ( approximately 10 min) increase in MEP size in the INB alone experiment, but suppressed the long-lasting increases of MEP size and ICF in the INB+rTMS experiment.


CONCLUSIONS
The present findings suggest that d-AMP increases neuronal excitability but suppresses long-lasting stimulation-induced plasticity in human motor cortex. These dual effects may be relevant when using d-AMP to modulate human cortex function.
Human Cortical Physiology Section, NINDS, National Institutes of Health, Building 10, Bethesda, MD 20892, USA. u.ziemann@em.uni-frankfurt.de
Ulf
U
Ziemann
Alda
A
Tam
Cathrin
C
Bütefisch
Leonardo G
LG
Cohen
D000328:Adult; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D003913:Dextroamphetamine / Q000494:pharmacology*; D004558:Electric Stimulation; D004574:Electromagnetic Fields; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005260:Female; D007839:Functional Laterality; D006225:Hand; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000187:drug effects* / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D009407:Nerve Block; D009473:Neuronal Plasticity / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects* / Q000502:physiology*; D010919:Placebos
D000697:Central Nervous System Stimulants; D010919:Placebos; D003913:Dextroamphetamine