Postnatal expression of the alpha-thyroid hormone receptor in the rat cochlea.

Thyroid hormone receptors belong to the superfamily of nuclear receptors which are expressed in many tissues. Reduced levels of thyroid hormones in acquired or congenital hypothyroidism can lead to hearing loss which may be irreversible. In this study we investigated immunohistochemically the postnatal distribution of the triiodothyronine alpha receptor in the rat cochlea. Cell regions of high sensitivity towards thyroid hormones should have a high density of thyroid hormone receptors. Strong immunoreactivity for the alpha-thyroid hormone receptor was observed in spiral ganglion cells as well as inner and outer hair cells of the cochlea. Staining could be detected during all stages investigated from the first postnatal day up to day 30 and exhibited mainly a nuclear pattern. These observations suggest that spiral ganglion cells and hair cells are target regions of thyroid hormones in the adult and developing cochlea. Thyroid hormones could thus play an important role in the maturation of the inner ear.