Changes in conformation of stereocilia in hair cells of the rat spiral organ of corti after 6-hydroxydopamine as revealed by scanning electron microscopy

Newborn rats were chemically sympathectomized by injection of 6-hydroxydopamine every day from day 1 to day 7, then every 5th day from day 10 until they were sacrificed. Litter mats left untreated or injected with the vehicle only (asorbic acid or physiological saline) were used as controls. Animals were sacrificed on days 15, 22, 30 and 34 by intracardiac perfusion with glutaraldehyde-paraformaldehyde in Millonig buffer, and their cochlease were dissected and prepared for scanning electron microscopy Stereocilia of outer and of inner hair cells were generally upright and not clumped in the 15-day-old treated rats. At 22 days, some of the outer hair cells were clumped and the tips of the hairs showed a tendency to stick to shreds of the tectorial membrane. Hairs of the inner hair cells were elongated and often in disarray. At 30 days, the changes in conformation of the hairs of both inner and outer hair cells had progresses, especially apically. Hairs of the outer hair cells were clumped, sometimes missing, and frequently bent over as though lacking stiffness. Tips of the hair were often firmly attached to shreds of the tectorial membrane. Hairs of the inner hair cells were thread-like and in disarray The only known effect of 6-hydroxydopamine under the experimental condition used here is the destruction of the peripheral adrenergic nervous system. Thus, present findings are interpreted to indicate that loss of sympathetic fibers to the internal ear results in changes in fluid and/or ion balance, perhaps due to an interference with protein metabolism, secondarily causing abnormalities in stereocilia. It is of interest that present results mimic in some respects the early effects of ototoxic drugs