Comparative study of immature and mature olfactory receptor cells in adult frogs

We describe a method to produce frog olfactory epithelium with a population of developmentally synchronized receptor cells suitable for electrophysiological studies. The epithelium is ablated with ZnSO4 and allowed to regenerate for 10 days. Generation of new cells is then blocked by continuous treatment with hydroxyurea. Since new receptor cells are generated beginning on the 6th day after ablation, it is reasonable to assume that receptor cells in the preparation originated between the 6th and 10th days following ablation. The age range of these cells would be no more than 5 days. The cells develop normally and in relative synchrony. Olfactory epithelia with developmentally synchronized receptor cells were used for a physiological study of response properties as a function of developmental age. Developmental stages of receptor cells were confirmed by fine-structure analysis. There were no differences in the polarities or shapes of electro-olfactograms (EOGs) recorded from olfactory epithelia composed of immature or mature receptor cells. However, amplitudes of the main negative components in EOGs recorded from epithelia composed of mature receptor cells were generally higher than those from epithelia composed of immature cells. The majority of immature olfactory receptor cells had low spontaneous activity or none at all. Mature olfactory receptor cells had a variety of frequencies of spontaneous activity ranging from less than one to more than 70 spikes/min. Extracellular single unit activity recordings showed that, contrary to what has been observed in rat embryos, olfactory receptor cells in regenerating epithelia of adult frogs do not go through a stage in which they respond to all odorants.