[Evaluation of turnover of olfactory epithelium in mice by using anti-BrdU monoclonal antibody].

Among nerve cells of vertebrates, the olfactory elements are uncommon in their capacity to turnover and to be replaced after injury. An autoradiographical and morphological observation has shown that degenerated olfactory nerve cells are reconstituted by a new population of neurons which originate from basal cells. However, an autoradiographic method requires a special isotope institute and it takes a long time for the final specimen to observe. Recently, a rapid technique without the radioisotope has been alternatively developed in which a thymidine analogue, 5-bromo-2'-deoxyuridine (BrdU), is incorporated into replicating DNA and subsequently localized using a specific monoclonal antibody. In the present study, cell dynamics of olfactory mucosa in mice were investigated by means of immunohistological technique. The results were as follows. 1. The labelled elements were concentrated at the basal layer of the epithelium, which were observed 5 hrs after the first injection of BrdU. 2. At 15 days after administration of BrdU, the labelled elements were located in the mid-layer of the epithelium, where can be recognized as the compartment of nerve cells. 3. After 30 days, the labelled cells disappeared from the epithelium. It indicates that the period of turnover in the olfactory epithelium of mice is within 30 days. 4. Fifteen days after axotomy of the olfactory nerves, two stained patterns which were numerously or sparsely labelled regions were observed. The former is considered that immature neurons predominantly exist, and the latter is the area which mature neurons abundantly locate. It is considered that this immunohistological approach is useful for the observation of the turnover of the olfactory epithelium.