Type-specific changes in fiber morphometry following denervation of canine extraocular muscle

To investigate the changes that occur in extraocular muscle morphometry following denervation, 12 beagles were subjected to intracranial section of the left oculomotor nerve. The inferior and medial rectus muscles were removed from both orbits of four dogs killed at each 4-week postoperative interval. Fiber diameters and fiber-type ratios of denervated muscles were compared with those from paired muscles in the normal orbit. We found significant, persistent atrophy of the singly innervated fibers in both the global and orbital layers of denervated extraocular muscle. The multiinnervated fibers were predominantly spared from denervation atrophy. We also found a significant increase in the proportion of multiinnervated fibers in the orbital layer only. These results suggest a relative neurotrophic independence of multiinnervated fibers in extraocular muscle.