Changes of Hair Cell Number in the Vestibular Utricles of Guinea Pigs Following Transtympanic Injection of Gentamycin

ObjectiveTo observe the damage and recovery of the hair cell bundles in the vestibular utricles of guinea pig following transtympanic injection of gentamycin.MethodsGentamycin(GM) was injected transtympanically into both middle ears of piginented guinea pigs.The damage and recovery of hair cell bundles in the vestibular utricles were bilaterally examined by scanning electron microscopy (SEM).ResultThe recovery period in one ear of each animal was 4 days (Group Ⅰ)and the other was 4 weeks (Group Ⅱ).The utricles were apparently devoid of hair bundles from 4 days to 4 weeks of postinjection period,the density of mature hair bundles was (19.79±7.76) per 1000 μm 2.Howerer,immature hair bundles in multiple stages of development could be indentified after 4 weeks of recovery,while their density decreased to (13.69±6.9) per 1000 μm 2.Typically regenerated small hair bundles were recognized as a single kinocilium as well as shorter and thinner stereocilia with relatively small cell apexes.The most important characteristic was that the stereocilia in a new bundle were almost similar in height.Quantitative observations indicated that total hair bundles survived from GM damage were decreasing in number within 4 days to 4 weeks after recovery.On the contrary,the density of small hair bundles in Group Ⅱ(4.95±4.76) per 1000 μm 2.increased significantly as compared with that in Group Ⅰ(1.76±2.21) per 1000 μm 2.ConclusionThe mammalian inner ear may be capable of regenerating new hair cell bundles in vestibular epithelia after GM ototoxicity.