IMMUNOCYTOCHEMICAL STUDY OF THE DIFFERENTIATION PROCESS OF THE SEPTALORGAN OF MASERA IN DEVELOPING RATS

The septal organ of Masera is a small patch of olfactory epithelium lo cated near the base of the nasal septum. Using the growth-associated p rotein B-50/GAP-43 as neuronal marker, we have studied the differentia tion process of this organ from the olfactory sheet in embryonic and n ewborn rats. Results show that the septal organ first appeared at embr yonic day 16. Even though it was included in the olfactory sheet, the presumptive septal organ could be distinguished by a higher density of B-50/GAP-43-positive neurons. Concomitantly to its morphological deve lopment, the septal organ progressively isolated from the main olfacto ry epithelium. This isolation resulted from the extension of a transit ional area which progressively lost its typical features of olfactory epithelium to become a putative respiratory epithelium in late embryon ic stages. Results strongly suggest that the septal organ should be a proper chemosensory system with its own time-course of development.