In this investigation, the electrophysiology and pathology of denervated orbicularis oculi muscles have been studied in dogs during chronic electrical stimulation. The orbicularis oculi muscles were unilaterally denervated in 8 dogs, and 4 of these muscles were directly stimulated on a daily basis for 75 days. No difference in minimum stimulus intensities evoking orbicularis oculi muscle twitch contraction appeared between denervated treated and nontreated muscles. A significant reduction of minimum stimulus intensities evoking upper eyelid complete closure (blink), however, was found in the denervated treated muscles between 10 and 30 days (p < 0.01). At 28 and 75 days, orbicularis oculi muscle biopsies showed no difference in muscle fiber diameter between denervated treated and nontreated muscles. At 75 days, type II muscle fiber distribution, however, was significantly increased in denervated treated muscles compared with denervated nontreated muscles (p < 0.01). These findings of orbicularis oculi muscle electrophysiology were consistent with a transient reversal of denervation changes by electrical stimulation, partially supported by muscle biopsies.
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