Excitability of the soleus motoneuron pool revealed by the developmental slope of the H-reflex as reflex gain.
The excitability of a motoneuron (MN) pool was evaluated by the developmental slope of H-reflexes (Hslp) evoked at a range of a stimulus intensity less than the threshold of an M-response. The Hslp has been regarded as the "reflex gain", which is the changing rate in MN excitability as a function of the increase of Ia input to an MN pool. In a comparison of two parameters used in the H-reflex technique, such as the ratio of the maximal H-reflex to the maximal M-response and the ratio of the threshold of an H-reflex to that of an M-response, the Hslp was predicted to be a reasonable parameter to evaluate motoneuronal excitability, because the Hslp is free from the effect of any collision between the H-reflex discharge and the antidromic volley drived from the occurrence of an M-response within the alpha-efferents, and the Hslp can estimate the recruitment properties of a whole MN pool. The Hslp was alleviated during dorsi-flexion and steepened during plantar-flexion, according to the inhibitory or facilitatory synaptic modifications onto soleus MNs. The developmental slope of an M-response (Mslp), which shows the recruitment property of axons of soleus MNs, was alleviated especially in plantar-flexion. In order to exclude the peripheral neuromuscular factors in evaluating substantial MN excitability, the Hslp/Mslp is proposed as a more effective parameter than the Hslp.
Funase
K
K
Department of General Education, School of Allied Medical Sciences Nagasaki University, Japan.
Imanaka
K
K
Nishihira
Y
Y
D000293:Adolescent; D000328:Adult; D001369:Axons / Q000502:physiology; D004558:Electric Stimulation; D004594:Electrophysiology; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D005544:Forecasting; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation*; D009433:Neural Inhibition / Q000502:physiology; D009469:Neuromuscular Junction / Q000502:physiology; D009476:Neurons, Efferent / Q000502:physiology; D011999:Recruitment, Neurophysiological / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D013569:Synapses / Q000502:physiology