THE ARREST OF LUTEINIZING-HORMONE-RELEASING HORMONE NEURONAL MIGRATION IN THE GENETIC ARHINENCEPHALIC MOUSE EMBRYO (PDN PDN)/

From previous observations, it was suggested that non-attachment of th e olfactory nerve to the telencephalon blocked the induction of the ol factory bulbs in genetic arhinencephalic mouse embryos (Pdn/Pdn). The olfactory nerve ends in a tangle beneath the forebrain in these embryo s. From these observations, we speculated that the migration of lutein izing hormone-releasing hormone (LHRH) neurons might be disturbed in t he olfactory nerve. A mass of LHRH neurons was observed in the end of the olfactory nerve fibers, but LHRH neurons were found in the hypotha lamus in Pdn/Pdn embryos on day 16 of gestation. Narrow by-paths were found between the olfactory nerve and the forebrain, and the migration of LHRH neurons through these by-paths was observed in Pdn/Pdn embryo s on day 13 of gestation. From the reports that a gene deleted in the arhinencephalic syndrome (Kallmann's syndrome) shares homology with ne ural cell adhesion molecules (N-CAM), it was speculated that non-attac hment of the olfactory nerve in the Pdn/Pdn embryo might be associated with abnormalities of N-CAM. The axon fibers of the olfactory nerve r eacted specifically with anti-N-CAM IgG both in +/-(+/+ and/or Pdn/+) and Pdn/Pdn on day 11.5 and 12, but not on day 13 and 16 of gestation. The axon fibers of the olfactory nerve were positive to anti-N-CAM Ig G specifically just during the developmental period that the olfactory nerve fibers attached to the telencephalon. It is still not clear whe ther non-attachment of the olfactory nerve may be associated with N-CA M or not from the present observations.