Immunohistochemical localization of fibronectin-like protein in the inner ear of the developing gerbil and rat

Immunohistochemistry was used to demonstrate the distribution of fibronectin-like protein within the developing inner ear of two species of altricial rodents: gerbils and rats. While there were temporal differences between the two species, the developmental sequence of immunostaining was virtually identical. Most notably, in rats from embryonic day 18 through day 1 postpartum, and in gerbils from birth through day 4 postpartum, intense, discrete fibronectin-like immunoreactivity was observed in the cochlea immediately beneath the inner and outer hair cells, sites of active auditory nerve fiber growth and nerve-hair cell synaptogenesis at these ages. The results suggest that fibronectin is appropriately positioned spatially and temporally to play a significant role in promoting, guiding and/or maintaining neural innervation within the developing organ of Corti. The temporo-spatial pattern of immunostaining in Schwann cells and auditory (VIIIth cranial) nerve neurons implies that fibronectin also plays a significant role in the early formation of myelin. In non-neural elements of the cochlea, fibronectin is a major structural component within the basilar membrane at all of the developmental stages investigated.