Mechanism of injury process and regeneration of the vestibular organ after drug intoxication.

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The semicircular canal action potentials were recorded by changing potassium ion concentration. It turned out that the potentials stayd unchanged regardless whether or not the cupula is present, indicating the cupula does not serve as a barrier of ion to sensory cells. The action of streptomycin suflate (SM) on posture recovery was studied using adult bull frogs. SM intoxication resulted in various degrees of hair cell damage. Degree of posture recovery correlated well with the number of intact hair cell. The less the sensory cell damage, the better the posture recovery. The effect of SM on the regenerative process of the vestibular nerve was also studied. The vestibular nerve was sectioned in various conditions with intact endorgan or with SM intoxication. When the nerve was sectioned with the hair cells left intact, the nerve regenerated well and body balance recovered to normal in 8 to 9 weeks. However, when neural regeneration was blocked by inserting a piece of bone between the cut ends of nerve, recovery was incomplete. When the nerve was sectioned after damaging the hair cells, the nerve failed to regenerate and posture recovery was incomplete. These results suggest that the degree of posture recovery depends on hair cell function and neural regeneration. Furthermore, neural regeneration was strongly influenced by hair cell function. When the vestibular nerve was sectioned after complete posture recovery, the posture change was less and recovery time was shorter after the second neurectomy. This shows that in frogs central compensation could be easily established after the first neurectomy.