Morphological differences in skeletal muscle atrophy of rats with motor nerve and/or sensory nerve injury

Abstract

Skeletal muscle atrophy occurs after denervation. The present study dissected the rat left ventral root and dorsal root at L4-6 or the sciatic nerve to establish a model of simple motor nerve injury, sensory nerve injury or mixed nerve injury. Results showed that with prolonged denervation time, rats with simple motor nerve injury, sensory nerve injury or mixed nerve injury exhibited abnormal behavior, reduced wet weight of the left gastrocnemius muscle, decreased diameter and cross-sectional area and altered ultrastructure of muscle cells, as well as decreased cross-sectional area and increased gray scale of the gastrocnemius muscle motor end plate. Moreover, at the same time point, the pathological changes were most severe in mixed nerve injury, followed by simple motor nerve injury, and the changes in simple sensory nerve injury were the mildest. These findings indicate that normal skeletal muscle morphology is maintained by intact innervation. Motor nerve injury resulted in larger damage to skeletal muscle and more severe atrophy than sensory nerve injury. Thus, reconstruction of motor nerves should be considered first in the clinical treatment of skeletal muscle atrophy caused by denervation.

Keywords: motor end plate; muscular atrophy; neural regeneration; rats; simple nerve injury; ultrastructure.

Figure 1

Gross morphology of rat gastrocnemius muscle atrophy. The denervated gastrocnemius muscle progressively atrophied after nerve injury. The ventral root transection group exhibited moderate muscle atrophy, the dorsal root transection group exhibited mild muscle atrophy and the sciatic nerve transection group exhibited severe muscle atrophy.

Figure 2

Morphology of rat gastrocnemius muscle (hematoxylin-eosin staining, light microscope, × 100). The size of gastrocnemius muscle cells gradually diminished in all rats after injury and reached the minimal value after 10 weeks in the sciatic nerve transection group. The cell diameter and cross-section area were the largest in the dorsal root transection group.

Figure 3

Morphology of the rat gastrocnemius muscle (uranyl acetate-lead citrate staining, light microscope, × 8 000; blue arrow, muscle cell nuclei; red arrow, muscle satellite cell nuclei). The ultrastructure of the gastrocnemius muscle cells exhibited similar changes in the three groups after nerve injury. With prolonged injury time, mitochondrial swelling, disorderly myofilaments and sarcomeres, shortened cristae, expanded sarcoplasmic reticulum, reduced glycogen granules, and enlarged nuclei were observed. In addition, myofilaments and sarcomeres broke, fused or disappeared, and mitochondria became vacuolated.

Figure 4

Rat gastrocnemius muscle motor end plate (acetylcholine esterase staining, light microscope, × 100). With prolonged denervation time, the changes in motor end-plate cross-sectional area and gray scale were similar in the ventral and dorsal root transection groups, i.e. the motor end-plate cross-sectional area gradually decreased, but the mean gray scale gradually increased, but these changes were not evident in the sciatic nerve transection group.