Sensory protection of rat muscle spindles following peripheral nerve injury and reinnervation.
BACKGROUND
Skeletal muscle structure and function are dependent on intact innervation. Prolonged muscle denervation results in irreversible muscle fiber atrophy, connective tissue hyperplasia, and deterioration of muscle spindles, specialized sensory receptors necessary for proper skeletal muscle function. The protective effect of temporary sensory innervation on denervated muscle, before motor nerve repair, has been shown in the rat. Sensory-protected muscles exhibit less fiber atrophy and connective tissue hyperplasia and maintain greater functional capacity than denervated muscles. The purpose of this study was to determine whether temporary sensory innervation also protects muscle spindles from degeneration.


METHODS
Rat tibial nerve was transected and repaired with either the saphenous or the original transected nerve. Negative controls remained denervated. After 3 to 6 months, the electrophysiologic response of the nerve to stretch in the rat gastrocnemius muscle was measured (n = 3 per group). After the animals were euthanized, the gastrocnemius muscle was removed, sectioned, stained, and examined for spindle number (n = 3 per group) and morphology (one rat per group). Immunohistochemical assessment of muscle spindle innervation was examined in four additional animals.


RESULTS
Significant deterioration of muscle spindles was seen in denervated muscle, whereas in muscle reinnervated with the tibial or the saphenous nerve, spindle number and morphology were improved. Histologic and functional evidence of spindle reinnervation by the sensory nerve was obtained.


CONCLUSIONS
These findings add to the known means by which motor or sensory nerves exert protective effects on denervated muscle, and further promote the use of sensory protection for improving the outcome after peripheral nerve injury.
Elsohemy
Amal
A
Hamilton, Ontario, Canada From the Department of Psychiatry and Behavioral Neurosciences, the Department of Pathology and Molecular Medicine, and the Division of Plastic Surgery, Department of Surgery, McMaster University.
Butler
Richard
R
Bain
James R
JR
Fahnestock
Margaret
M
D000704:Analysis of Variance; D000818:Animals; D004195:Disease Models, Animal; D004576:Electromyography; D007150:Immunohistochemistry; D009121:Muscle Denervation; D009470:Muscle Spindles / Q000294:innervation* / Q000473:pathology; D018482:Muscle, Skeletal / Q000294:innervation* / Q000473:pathology; D009416:Nerve Regeneration / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology; D059348:Peripheral Nerve Injuries; D010525:Peripheral Nerves / Q000473:pathology; D011336:Probability; D011897:Random Allocation; D051381:Rats; D011917:Rats, Inbred Lew; D020127:Recovery of Function; D012684:Sensory Thresholds; D013979:Tibial Nerve / Q000293:injuries* / Q000601:surgery