Abstract
Background We have demonstrated that the native motor zone (NMZ) within a muscle is an ideal
target for performing nerve-muscle-endplate band grafting (NMEG) to restore motor
function of a denervated muscle. This study was designed to determine spatiotemporal
alterations of the myofibers, motor endplates (MEPs), and axons in the NMZ of long-term
denervated muscles for exploring if NMEG-NMZ technique would have the potential for
delayed reinnervation.
Methods Sternomastoid (SM) muscles of adult female Sprague-Dawley rats (n = 21) were experimentally denervated and denervation-induced changes in muscle weight,
myofiber size, MEPs, and intramuscular nerve axons were evaluated histomorphometrically
and immunohistochemically at the end of 3, 6, and 9 months after denervation. The
values obtained from the ipsilateral normal side served as control.
Results The denervated SM muscles exhibited a progressive reduction in muscle weight (38%,
31%, and 19% of the control) and fiber diameter (52%, 40%, and 28% of the control)
for 3-, 6-, and 9-month denervation, respectively. The denervated MEPs were still
detectable even 9 months after denervation. The mean number of the denervated MEPs
was 79%, 65%, and 43% of the control in the 3-, 6-, and 9-month denervated SM, respectively.
Degenerated axons in the denervated muscles became fragmented.
Conclusions Persistence of MEPs in the long-term denervated SM suggests that some surgeries targeting
the MEPs such as NMEG-NMZ technique should be effective for delayed reinnervation.
However, more work is needed to develop strategies for preservation of muscle mass
and MEPs after denervation.
Keywords
denervation - peripheral nerve injury - motor endplate - acetylcholine receptor -
muscle atrophy - native motor zone
