Neurotrophic interactions during in vitro development of the inner ear

The objective of this study was to explore the hypothesis that developing labyrinthine sensory receptors attract ingrowing neurites by chemotaxis. Cocultured otic explants which shared a single statoacoustic nerve (VIIIn) ganglion were explanted from 11-, 12.5-, and 14-day-old mouse embryos. Heterotypic ganglion explants consisted of 12-day-old otic explants which had their VIIIn replaced by a 10.5-day-old trigeminal nerve (Vn) ganglion. All cultures were grown to the equivalent of 20 days of gestation. Neurites of the (+) VIIIn explants grew into the sensory areas of both the (+) and (-) VIIIn cocultured explants. Neurites of the 14-day-old cocultured otic explants were only found in association with sensory areas within the (+) VIIIn explant. Neurites of nerve V of the heterotypic ganglion explants were found in association with the sensory areas of these otic explants. These results support the hypothesis that a limited period of chemotaxis (nonspecific in nature) is a possible mechanism for the establishment of the pattern of neurite ingrowth to the areas of the inner ear sensory receptors.