Calbindin (CaBP 28 kDa) appearance and distribution during development of the mouse inner ear

Previous reports of the distribution of calbindin, a 28 kDa vitamin D-induced calcium-binding protein, in the mammalian peripheral vestibular system postulated that this protein was involved in the calcium-dependent mechanisms occurring in the hair cells and ganglion cells. In this study, we examined the possibility of a relationship between the presence of calbindin and neurotransmission by comparing calbindin appearance in the inner ear to the sequence of synaptogenesis. Calbindin distribution was studied by immunocytochemistry, in the developing mouse inner ear from gestational day 12 to postnatal day 40. During the early development, calbindin was localized in non-neuronal structures: Kolliker's organ, spiral limbus and crista supporting cells; and in cochlear and vestibular ganglion neurons and sensory cells. At later stages and in the adult, no reactivity was observed in the non-neuronal cell populations and only certain sensory and nerve cells remained stained: inner hair cells, outer hair cells, vestibular hair cells of the apex of the cristae and of the striola in the maculae, all Corti's ganglion neurons and some vestibular ganglion neurons. The sequence of appearance of calbindin immunoreactivity in the sensory and nerve cells was not completely parallel to the maturation sequence of the inner ear, especially synaptogenesis. The dual distribution of calbindin during development and its expression in specific sensory and nerve cells opens new perspectives on its role in the inner ear.