Analysis of activity of motor units in the biceps brachii muscle after intercostal-musculocutaneous nerve transfer.
We examined respiratory activity of motor units (MUs) in the internal intercostal nerves (IICNs)-transferred biceps brachii muscle (IC-biceps) in cats. MUs of IC-biceps showed respiratory discharges in inspiratory and expiratory phases, and these were enhanced by CO2 inhalation. Narrowing the airway also enhanced inspiratory and expiratory MUs activity. A mechanical load to the thorax immediately enhanced inspiratory MUs activity and weakened expiratory MUs activity. We analyzed the cross-correlation of MUs activity in interchondral muscle and IC-biceps to characterize the respiratory spinal descending inputs to motoneurons. We confirmed the short-term synchronization from interchondral muscles indicating divergence of a single respiratory presynaptic axon to thoracic motoneurons, but could not find synchronization from IC-biceps. The motor axonal conduction velocity (axonal CV) of IC-biceps MUs was lower than that of interchondral muscles. There was no correlation between the respiratory recruitment order of IC-biceps MUs and their axonal CV. These results indicate that IC-biceps shows the respiratory activities and afferent inputs from intercostal muscle spindles in the neighboring segments remain influential on activity of IC-biceps. In addition, the short-term synchronization from IC-biceps could not be found, suggesting that the intercostal nerve transfer alters the respiratory spinal descending inputs to thoracic motoneurons.
Sakuta
Naoki
N
Department of Orthopaedic Surgery, Institute of Clinical Medicine, University of Tsukuba, 1-1-1 Tennodai, Ibaraki 305-8577, Japan. sakuta@ipu.ac.jp
Sasaki
Sei-Ichi
S
Ochiai
Naoyuki
N
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001917:Brachial Plexus / Q000293:injuries; D002415:Cats; D005260:Female; D005552:Forelimb / Q000502:physiology; D007367:Intercostal Nerves / Q000601:surgery*; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation*; D009138:Musculocutaneous Nerve / Q000601:surgery*; D016067:Nerve Transfer