A Possible Embryonic Mechanism for the Establishment of Innervation of inner Ear Sensory Structures

The objective of this study was to explore the hypothesis (Van De Water, 1976) that differentiating sensory receptors of the inner ear may attract ingrowing neurites of the statoacoustic (VIIIn) ganglion by chemotaxis. Co-cultured embryonic inner ears which shared a single VIIIn ganglion were grown "in vitro" to the equivalent of 20 days gestation and then processed histologically to show both cytodifferentiation of sensory structures and the presence of neural elements. Specimens of both 11- and 12.5-day-old co-cultured otocysts showed that VIIIn ganglion neurites grew into sensory receptors of both(+) with and (-) without ganglion inner ear explants. Fourteen-day-old co-cultured inner ears revealed that only the (+) ganglion inner ear explants received VIIIn ganglion neurites into the sensory areas, and that neurites were not attracted into the (-) ganglion explants. The results were found to support the hypothesis of a limited period of chemotaxis as being a possible mechanism for the establishment of the pattern of innervation of inner ear sensory receptors by its VIIIn ganglion.