Spinal use-dependent plasticity of synaptic transmission in humans after a single cycling session.
The spinal cord is able to express use-dependent plasticity, as demonstrated in spinalized cats following treadmill training. In humans, spinal use-dependent plasticity is inferred from modifications in the size of H reflex, which are often more prominent after skilled motor training. Plasticity can develop at synaptic connections between afferent fibres and/or descending tracts and motoneurones or interneurones interposed in the spinal pathways. Here we explore whether skilled training induces a change in synaptic efficacy at the synapse between Ia afferents and soleus (Sol) motoneurones. Synaptic efficacy can be modulated presynaptically through changes of the probability of transmitter release (homosynaptic depression, HD). The frequency-related depression of the Sol H reflex, thought to reflect HD, was tested at rest, before and after one single skilled (14 subjects) or non-skilled (9 subjects) cycling training session. Performance improved in both groups but to a larger extent with skilled training, while HD increased immediately after and the day following skilled training in the absence of changes with non-skilled training. These results support the view that spinal cord function is able to encode a local motor memory.
Meunier
Sabine
S
Human Cortical Physiology Section, National Institutes of Health, National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892, USA. meunier.sabine@free.fr
Kwon
Jeongyi
J
Russmann
Heike
H
Ravindran
Shashi
S
Mazzocchio
Riccardo
R
Cohen
Leonardo
L
D000328:Adult; D005080:Exercise Test; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D036881:Long-Term Synaptic Depression / Q000502:physiology; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D009473:Neuronal Plasticity / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology; D011597:Psychomotor Performance / Q000502:physiology; D013116:Spinal Cord / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*