Regeneration of the eighth cranial nerve. II. Physiologic verification in the bullfrog

Two experiments were performed to document the functional capacity of the regenerated eighth cranial nerve. In experiment 1, the eighth cranial nerve was sectioned preganglionically and allowed to regenerate in a group of bullfrogs with normal contralateral eighth nerve and labyrinth. Posture and reflex to lateral tilt were measured preoperatively and postoperatively for a minimum of 3 months. Similar measures were performed in a second group of bullfrogs in which the eighth nerve had been destroyed by ganglionectomy and in a third with peripheral labyrinthectomies. In experiment 2, the eighth nerve was sectioned and allowed to regenerate in bullfrogs in which the contralateral nerve had previously been destroyed. Posture and reflex to lateral tilt were measured as in experiment 1. Similar measures were performed in a group of bullfrogs that had undergone bilateral nerve destruction. Regeneration of the eighth cranial nerve in bullfrogs in both experiments was documented histologically by labeling the regenerated fibers with horseradish peroxidase (HRP). In both experiments, posture recovered completely only in the bullfrogs in which the eighth cranial nerve was allowed to regenerate. Reflex to lateral tilt recovered more rapidly in the bullfrogs with regenerated nerves than in any of the other bullfrogs.