Cell turnover in the vomeronasal epithelium: Evidence for differential migration and maturation of subclasses of vomeronasal neurons in the adult opossum

Previous investigations of cell turnover in the mammalian vomeronasal senso ry epithelium (VN-SE) raised two issues. First, if, in addition to the alre ady demonstrated vertical migration, horizontal migration from the edges of the VN-SE participates in neuronal replacement. Second, whether or not mig ration and maturation is differential in upper and lower populations of vom eronasal neurons, since these two cell populations are chemically, physiolo gically, functionally, and perhaps evolutionarily different. By injecting b romodeoxyuridine (BrdU) into adult opossum (Monodelphis domestica) and perm itting different survival times, the pattern of distribution of BrdU-labele d cells was analyzed. No evidence of horizontal migration in neuronal repla cement was found. To investigate vertical migration and maturation of subcl asses of vomeronasal neurons, double immunohistochemistry of BrdU and marke rs of the lower (G(o alpha) protein) and upper [G(12 alpha) protein and olf actory marker protein (OICIP)] cell populations were performed. Three days after administration of BrdU, some mature neurons were observed in both low er and upper layers of the VN-SE, as demonstrated by coexpression of BrdU w ith G(o alpha) protein and OR IP, respectively. The data on vertical distri bution, however, indicate that most of the daughter cells enter the G(o alp ha)-protein-expressing zone of the VN-SE by day 5, whereas most daughter ce lls do not reach the G(12 alpha)-protein-expressing zone until day 7, sugge sting that these two populations mature at slightly different rates. These results are the first evidence of differential neurogenesis of subclasses o f vomeronasal neurons. (C) 2000 John Wiley & Sons, Inc. J Neurobiol 43: 50- 63, 2000.