Neuronal loss after transsection of the facial nerve: A morphological and neurophysiological study in monkeys

Functional recovery after nerve lesions seems to depend on peripheral as we ll as central factors. To investigate the central neuronal loss after trans section of a pure motor nerve. the middle branch of the facial nerve on one side was transsected and immediately repaired microsurgically by epineural suturing. After a period of 6-15 months, a quantitative neurophysiological recording was made to estimate muscle response. A nerve tracer was injecte d into the mimic muscles innervated by the nerve to label the surviving mot or neurons within the facial nucleus. The opposite side was used as the con trol in all cares. After the regenerative period. a mean loss of 15% of the total cell number was observed within the facial nucleus compared with the opposite side. The cell loss comprised all types of neurons. This amount o f neuronal loss was followed by an even greater loss of muscle response whe n a quantitative neurophysiological recording was made after nerve regenera tion. The results are discussed in relation to loss of nerve elements after nerve lesions and its effect on functional recovery.