Morphological features of different regions in frog crista ampullaris (Rana esculenta).

The cellular organization of different regions of the crista epithelium from the frog posterior semicircular canal was studied by light, transmission and scanning microscopy. The sensory epithelium consists of hair cells surrounded by supporting cells and basal cells located close to the basement membrane. Three types of hair cells, namely club-like, cylindrical and pear-like cells differentially distributed along the crista could be recognized on the basis of their shape. Club-like cells are located only in the peripheral regions, cylindrical cells both in the central and in the peripheral regions, and pear-like cells appear segregated into the intermediate regions. Sensory cells of the central region are characterized by a ciliary apparatus consisting of stereocilia usually shorter--and in some cases less numerous--than those of cells of the other regions. The presence of large evaginations of the apical membrane of hair cells and of several vesicles of microexocytosis demonstrates that receptor cells have a considerable secretory activity. This secretory activity is also proven by the presence in the supranuclear region of hair cells of numerous Golgi complexes. Moreover, the presence of two kinds of Golgi complexes, one constituted by dilated cisternae containing a moderately electron-dense material and the other made up of flattened electron-transparent cisternae, suggests a diversified secretion of material by the hair cells. This heterogeneous material may provide substances important for cupula formation and the composition of the endolymph.