Effect of graded nerve pressure injuries on motor function.
OBJECTIVE
The purpose of this study was to determine the minimum amount of nerve fibers required to maintain normal motor function after nerve injury in rats.


METHODS
The authors first confirmed that a common peroneal nerve injury caused more aggravating effects on lower limb motor function than tibial nerve injury, as assessed by the static sciatic index (SSI). Thereafter, rats were subjected to varying degrees of crush injury to the common peroneal nerve. At 48 hours after the injury, motor function was assessed using the SSI and slope-walking ability (with slope angles of 30° and 45°). The tibialis anterior muscle, a main muscle innervated by the common peroneal nerve, was removed. Muscle sections were co-labeled with neuronal class III β-tubulin polyclonal antibody to identify the presence of axons and Alexa Fluor 488-conjugated α-bungarotoxin to identify the presence of motor endplates.


RESULTS
The evaluation of neuromuscular innervation showed a correlation between SSI scores and ratios of residual axons (rs = 0.68, p < 0.01), and there was a statistically significant difference between slope-walking ability and ratios of residual axons (p < 0.01). Moreover, the ratios of residual axons in the nerve-crushed rats with normal motor function (SSI above -20) ranged from 36.5% to 88.7%, and those ratios in the success group with slope-walking angles of 30° and 45° ranged from 14.7% to 88.7% and from 39.8% to 88.7%, respectively.


CONCLUSIONS
In this study of rodents, less than half of the motor axons were sufficient to maintain normal motor function of the lower limb.
Department of Anatomy, Shinshu University School of Medicine, Matsumoto, Japan.
Mika
M
Karasawa
Department of Anatomy, Shinshu University School of Medicine, Matsumoto, Japan.
Kumiko
K
Yokouchi
Department of Anatomy, Shinshu University School of Medicine, Matsumoto, Japan.
Akira
A
Kakegawa
Department of Anatomy, Shinshu University School of Medicine, Matsumoto, Japan.
Kyutaro
K
Kawagishi
Department of Anatomy, Shinshu University School of Medicine, Matsumoto, Japan.
Tetsuji
T
Moriizumi
Department of Anatomy, Shinshu University School of Medicine, Matsumoto, Japan.
Nanae
N
Fukushima
D000818:Animals; D005260:Female; D051381:Rats; D001369:Axons / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology; D009048:Motor Skills / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation; D009409:Nerve Crush; D059348:Peripheral Nerve Injuries / Q000503:physiopathology; D010543:Peroneal Nerve / Q000293:injuries / Q000503:physiopathology; D017208:Rats, Wistar; D016138:Walking / Q000502:physiology; D003668:Pressure Ulcer / Q000503:physiopathology
SSI = static sciatic index; common peroneal nerve; crush injury; peripheral nerve; sciatic nerve; slope-walking; static sciatic index