Histochemical, microchemical (microprobe) and organ culture approaches to the study of auditory development.
Cochlear development has been studied by means of biochemistry/histochemistry (Na+/K+-ATPase, adenylate cyclase, 2-deoxy-D-glucose and phospholipids), the energy dispersive X-ray microanalysis technique and organ culture of the mammalian inner ear. A high level of Na+/K+-ATPase and adenylate cyclase occurs in the stria vascularis and has been cytochemically demonstrated at the contraluminal side of marginal cell membranes. An increase in the adenylate cyclase content occurs approximately one day before and in parallel with the rise of the potassium content in endolymph. These processes are preceded by an ultrastructural differentiation of the stria vascularis but appear prior to the rapid increase of the endolymphatic potential. The functional activity of the developing/differentiating cochlea is reflected by increased levels of 2-deoxy-D-glucose first during the postnatal morphologic maturation of the organ of Corti and the stria vascularis approximately 1 week after birth, and, later during the maturation of cochlear potentials 10-14 days after birth. Organ culture of the embryonic inner ear is a suitable tool for studies on early (embryonic) morphologic development, neural induction, fate-mapping, epithelio-mesenchymal interactions and neurotrophic interactions. Concerning postnatal inner ear structures, organ culture has focused on development of afferent nerve fibres. The isolated organ is deprived of efferent fibres of central origin.