Experimental study on recovery mechanism of body balance after vestibular damage

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Behavioral change after Gentamicin(. -GM)intoxication and vestibular neurectomy was studied using bull frogs. Intralabyrinthine injection of GM resulted in tilting posture according to the degree of the damage to the utricular macula. This, tilting developed as the time lapsed. The vestibular nerve was cut peripherally to the vestibular ganglion. The frog also sustained tilting toward the operated side by about 30 degrees. This tilting disappeared and the frog returned to normal posture over the period of 4-9 weeks. Microscopically the sectioned nerve well regenerated and the sensory epithelia was normal. This result indicates that both reactivation of the endorgan and central compensatory mechanism play an essential role in postural recovery after vestibular neurectomy. Based upon this finding following experiments were done. In experiment I, the right vestibular nerve was again cut after postural recovery. The tilting angle was smaller and the recovery period was shorter than the 1st neurectomy. Central compensation achieved in the right side is possibly responsible for this phenomenon. . In experiment II, the left nerve was cut after postural recovery. The tilting angle toward the left was greater than that of the 1st neurectomy. In experiment III, the frog under-went bilateral neurectomy, and a piece of the bone was inserted into the cut ends of the right nerve to inhibit neural regeneration. The frog slowly developed tilting toward the right side. This is possibly due to reactivated function of the left utricle, which resulted in vestibular imbalance at the peripheral level.