Ionocytes in the olfactory epithelium of developing Raja clavata

Ionocytes, with morphological features and Na+/K(+)ATPase immunoreactivity typical of chloride cells, have been highlighted in the olfactory epithelium of some vertebrates. Because of their response to staining in histological sections they are named light-stained cells. Their role in olfaction or osmoregulation has not been clarified. In this work we wanted to detect, for the first time, the appearance of light-stained cells during development. We choose the skate Raja clavata as a model, since light-stained cells are widely present in elasmobranches more than in other vertebrate group. Embryos and juveniles, at different stages of development from 13 weeks after laying (11 weeks before hatching) to 24 weeks after hatching, were examined by histological and immunohistochemical methods. Our results exhibit that active light-stained cells are present since the 19 weeks after laying, about 9 weeks after the opening of the respiratory canals in the egg case and in concomitance with olfactory neuron maturation. Thus, we suggest for the light-stained cells a role in the olfactory processes and, in particular, in ionic regulation of the olfactory mucus.