Effects of immediate and delayed facial-facial nerve suture on rat facial muscle.
OBJECTIVE
To investigate regeneration of the mimic musculature after delayed facial nerve repair.


METHODS
In 30 rats the facial nerve on the right side was resected and immediately repaired with an end-to-end anastomosis. The entire levator labii muscle was removed on the right side and histochemically and morphometrically analyzed at 7, 14, 21, 28, 90 and 180 days after immediate nerve repair. In a further 20 rats, reinnervation was performed after 4 weeks in a further operation and the muscle was assessed at 14, 28, 90 and 180 days. Seven muscles of four normal rats were used as controls.


RESULTS
Three muscle fiber types could be identified by comparative histochemical analysis of two enzymes of succinate dehydrogenase (SDH) and m-ATPase: oxidative glycolytic (FOG) fibers, fast glycolytic (FG) fibers and intermediate muscle fibers that were designated SDH-INT. The number of fibers and the frequency distribution of single-fiber cross-sectional areas were determined for each type of fiber. No significant difference in the cross-sectional area of all fiber types was noted after 180 days when comparing immediate and delayed end-to-end sutures. In contrast, comparison of the fiber-type composition showed a significant increase in the number of FG fibers in the delayed suture, at the expense of FOG fibers. After immediate reinnervation the muscle approximately attained its natural fiber-type composition, whereas after delayed reinnervation the muscle showed an overall loss of oxidative capacity and differentiation towards phasic activity.


CONCLUSIONS
Changes in fiber-type composition following delayed nerve suture are irreversible and have specific effects on the precise function of the muscle. Immediate nerve repair improves axonal reinnervation.
Constantinidis
Jannis
J
Department of Otorhinolaryngology, University of Erlangen-Nuremberg, Erlangen, Germany. jannis.constantinidis@hno.imed.uni-erlangen.de
Akbarian
Arasch
A
Steinhart
Helmut
H
Iro
Heinrich
H
Mautes
Angelika
A
D000818:Animals; D004195:Disease Models, Animal; D005154:Facial Nerve / Q000503:physiopathology / Q000601:surgery*; D009121:Muscle Denervation; D018485:Muscle Fibers, Skeletal / Q000473:pathology*; D018482:Muscle, Skeletal / Q000294:innervation* / Q000473:pathology* / Q000503:physiopathology; D009416:Nerve Regeneration / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013536:Suture Techniques; D013997:Time Factors