Determinants of neurons-sensory receptor cell interaction during development of the inner ear.

Trophic interactions are best defined as interactions between nerves and other cells which initiate or control molecular modification in the other cells and/or neurons. Interactions between the neurons which compose the statoacoustic ganglion and the cells which become the hair cells of the inner ear sensory receptors occur during the development of these sensory receptors. The hypothesis that the program for sensory hair cell cytodifferentiation is intrinsic and does not require the extrinsic stimulus of neuronal interaction to trigger its expression is presented with supporting data from in vivo, in ovo and in vitro experiments. A second hypothesis pertaining to a mechanism for the ingrowth of statoacoustic ganglion dendrites to their appropriate target sites within the inner ear is presented with accompanying in vitro experiments as supporting evidence. This hypothesis proposes that the mechanism for guiding neuritic elements of the statoacoustic ganglion to their appropriate target tissues is that attractant fields are established by the differentiating sensory epithelia of the inner ear to which nerve growth cones of ingrowing afferent neurites are attracted.