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 the olfactory nerve to the telencephalon blocked the induction of the olfactory bulbs in genetic arhinencephalic mouse embryos (Pdn/Pdn). The olfactory nerve ends in a tangle beneath the forebrain in these embryos. From these observations, we speculated that the migration of luteinizing hormone-releasing hormone (LHRH) neurons might be disturbed in the olfactory nerve. A mass of LHRH neurons was observed in the end of the olfactory nerve fibers, but LHRH neurons were found in the hypothalamus 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 embryos on day 13 of gestation. From the reports that a gene deleted in the arhinencephalic syndrome (Kallmann's syndrome) shares homology with neural cell adhesion molecules (N-CAM), it was speculated that non-attachment of the olfactory nerve in the Pdn/Pdn embryo might be associated with abnormalities of N-CAM. The axon fibers of the olfactory nerve reacted 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 IgG specifically just during the developmental period that the olfactory nerve fibers attached to the telencephalon. It is still not clear whether non-attachment of the olfactory nerve may be associated with N-CAM or not from the present observations.