Glial fibrillary acidic protein-like immunoreactivity in the human fetal inner ear

The distribution of glial fibrillary acidic protein (GFAP)-like immunoreactivity (IR) was analyzed in the human fetal inner ear using immunohistochemical techniques. In the 11-week-old human fetal cochlea, nerve fibers labelled with GFAP had reached the basilar membrane, but innervation stained by antisera against GFAP to the hair cells reached only as far as the basal coil. In the 11-week-old human fetal vestibular organs, little GFAP-IR was present in the epithelia. In 14- and 15-week-old human fetal cochleae, rich immunoreactive neural networks were observed, including the inner spiral bundle. Many immunoreactive sites were found below inner hair cells in all coils. Outer spiral bundles in the first, second and third rows in the basal coil were labelled, but the outer spiral bundle in the third row in the apical coil was not stained by the antisera. In the macula utriculi, many heavily stained sites and a rich immunoreactive network in the sensory epithelium were labelled, while considerably fewer positive nerve fibers and sites were present in the sensory epithelia in the macula utriculi and cristae ampullares. These results suggest that GFAP-IR is a very useful marker of differentiation of Schwann cells in the peripheral nerve in the human inner ear.