EMBRYONIC (PSA) N-CAM REVEALS CHAINS OF MIGRATING NEUROBLASTS BETWEENTHE LATERAL VENTRICLE AND THE OLFACTORY-BULB OF ADULT MICE

In the brain of adult mice, cell division persists in the subventricul ar zone (SVZ) of the lateral ventricles. These SVZ cells migrate rostr ally 3-5 mm to the olfactory bulb, where they differentiate into neuro ns. We have investigated the distribution of PSA-N-CAM in the adult mo use forebrain. Immunoreactivity for PSA-N-CAM precisely reveals the mi gratory pathway of SVZ cells. This pathway of PSA-N-CAM positive cells starts in the lateral wall of the lateral ventricle, where immunoposi tive cells form weblike patterns. The PSA-N-CAM positive pathway exten ds rostrally between the corpus callosum and the striatum into the ant erior ventral telencephalon, and then into the core of the olfactory b ulb. Experiments in which [H-3]-thymidine was injected systemically in dicated that the majority of the dividing cells on the SVZ of the late ral ventricle and along the migratory pathway are positive to PSA-N-CA M or closely associated with PSA-N-CAM. Microinjection of [H-3]-thymid ine into the SVZ of the lateral ventricle to label a small patch of di viding SVZ cells shows that neuroblasts that migrated away from the in jection site are positive or are closely associated with other cells t hat are positive for PSA-N-CAM. Migrating cells are tethered together, forming long chains of immunopositive cells. The migratory pathway is formed by 30-40 of these immunopositive chains. Radially oriented ind ividual PSA-N-CAM positive cells were observed in the olfactory bulb. These cells seem to have broken away from chains of immunopositive cel ls in the core of the olfactory bulb and to be migrating to more super ficial layers. Little is known about the mechanisms of tangential migr ation during development and in adulthood. The cell-cell arrangement r evealed by PSA-N-CAM staining suggests new models for this form of neu ronal migration. PSA-N-CAM localization along the migratory pathway to the olfactory bulb suggests that in the adult brain this molecule pla ys a role in migration of neuronal precursors. (C) 1995 Wiley-Liss, In c.