Introduction: Hearing loss represents one of the most frequent human disabilities. Hair cells, the primary sound receptors located in the inner ear are extremely sensitive, but also very fragile. The destruction of these cells in humans or in any other mammal is not followed by replacement, and therefore a permanent hearing loss results. Material and Methods: Neonatal mousse CD1 (P0-6) were sacrificed according to the legal standards and ethics. After manual dissection of the cochleae, the entire spiral ganglion was dissected from the modiolus. The explants were treated with gentamicin, followed by incubation for 48 hours at 37°C.  Normal and damaged outer hair cells (OHC) or inner hair cells (IHC) were then counted to allow for statistical comparisons between groups. Results: A total of 20,100 outer hair cells from 64 cochleae and 4 groups were analyzed. At 3 mM of gentamicin the hair cells were almost complete damaged. The main type’s alteration in the damaged outer or inner hair cells was absence of hair. The mean difference between the damaged or not damaged OHC/IHC was statistically significant (p<0.001). Discussion: In our study we did not observe more damage in the basal cochlear turn when compared to the second turn. No statistically significant difference was found between the first cochlear turn of subjects on these groups, and turns 2 and 3, respectively. Conclusion: Progressive doses of gentamicin cause increased numbers of damaged outer and inner hair cells with absence of hair (the most frequent finding).


Hearing loss, Cochleae, Spiral ganglion, Ototoxic, Hair cells.