FIG. 6.

Tacrine (THA) protects against neomycin-induced hair cell death in mouse utricle explants. Utricles were pretreated with 10 μM tacrine for 4 h, followed by 2 mM neomycin and THA for 24 h. Utricles were then fixed and labeled with antibodies against calmodulin (green) and calbindin (red). A Control utricle not treated with neomycin or THA. B Utricle pretreated with THA without neomycin exposure. Ten micromolar THA did not cause any hair cell loss. C Utricle without THA pretreatment, but treated with 2 mM neomycin demonstrates marked striolar and extrastriolar hair cell loss with a decrease in calmodulin and calbindin labeling. There is also an increase in cellular debris from dying hair cells. D Utricle pretreated with THA then treated with 2 mM neomycin demonstrates protection against hair cell loss. Scale bar in D = 20 μM and applies to all panels. E Hair cell survival is significantly increased (p < 0.01, one-way ANOVA) in both extrastriolar and striolar hair cells when utricles were pretreated with THA prior to neomycin (Neo+/THA+) compared to control utricles without THA pretreatment (Neo+/THA−). Bars represent the mean hair cell survival (% control) + 1 SEM (n = 11–15 utricles per group).