An ultrastructural and functional study of the inner ear after administration of hyaluronan into the middle ear of the guinea pig.

A single dose of hyaluronan, 19 mg/ml was administered into the right middle ear cavity of guinea pigs. The auditory function of the right ear was tested by recording the gross neural action potential (N1) before, directly after, and 28 days after the administration of hyaluronan. In a control group the right ear was sham-operated and the gross neural action potential (N1) was recorded twice; on the day of the sham operation and 28 days later. All animals were killed 28 days after the operation. All treated as well as sham-operated ears and every second intact ear were studied by scanning electron microscopy (SEM.) No ear had signs of hearing deterioration. Macroscopically, most of the hyaluronan was eliminated from the middle ear after 28 days. In the histological examination, pathological stereocilia were found in the apical turn of the cochlea in the ears to which hyaluronan was administered, the sham operated and the intact ears.