Immunohistochemistry and histochemistry of the inner ear gelatinous membranes and statoconia of the chick (Gallus domesticus).

This study was undertaken to investigate whether the gelatinous membranes (GMs) of the chick (Gallus domesticus) inner ear contain glycoproteins and proteoglycans, as is the case in mammals, and whether or not the relative concentrations of glycoproteins and proteoglycans change during development. We used electron-microscopic histochemistry with tannic acid, Alcian blue and ruthenium red and immunoperoxidase with monoclonal antibodies to fibronectin and keratan sulfate. Both techniques were applied to material from newly hatched chicks in various developmental stages. In hatchlings, tannic acid, which precipitates mainly proteoglycans, stained the mineralizing GMs of the utricle, saccule and lagenar macula darker than it did the nonmineralizing GMs of the cristae and tectorial membrane of the basilar papilla, while Alcian blue and ruthenium red stained all GMs in the vestibule and basilar papilla almost to the same degree. Antikeratan sulfate (a proteoglycan marker) stained the GMs intensively, while antifibronectin (glycoprotein monoclonal marker) stained them less intensively. In the mineralizing GMs of the embryos, the immunoreactivity (density) of keratan sulfate almost doubles between days 7 (stages 31) and 21 (stage 46), while the density of fibronectin does not seem to change as much. Different concentrations of glycoproteins and proteoglycans in each GM may impart to it the capacity to remain unmineralized, as is the case for cupulae of the vestibule and tectorial membrane of the basilar papilla, or mineralized, as is the case for the statoconial membrane of the maculae.