Hair cell loss as a function of age in the normal cochlea of the guinea pig.

The surface specimen technique was used to study both spiral organs of 28 normal guinea pigs of four age groups: less than 24 hours, 6 weeks, 3 months and 1 year. Damaged hair cells were recorded for the whole of each spiral organ on cochleograms. The mean percentage number of outer hair cells damaged per age group was found to increase as a power function of age. In the animals aged less than 24 hours the mean percentage of damaged outer hair cells was 0.45%; in the 6-week animals, 1.85%; in the 3-month animals, 3.19%; and in the 1-year animals, 6.82%. At all ages outer hair cell loss was maximal in the third row, and towards the apex of the cochlea. Inner hair cell loss was very slight, with a maximum of 9 damaged inner hair cells per cochlea.