Telencephalic-olfactory bulb ventricle wall organization in Austrolebias charrua: Cytoarchitecture, proliferation dynamics, neurogenesis and migration.

Adult neurogenesis participates in fish olfaction sensitivity in response to environmental challenges. Therefore, we investigated if several populations of stem/progenitor cells that are retained in the olfactory bulbs (OB) may constitute different neurogenic niches that support growth and functional demands. By electron microscopy and combination cell proliferation and lineage markers, we found that the telencephalic ventricle wall (VW) at OB level of Austrolebias charrua fish presents three neurogenic niches (transitional 1, medial 2 and ventral 3). The main cellular types described in other vertebrate neurogenic niches were identified (transient amplifying cells, stem cells and migrating neuroblasts). However, elongated vimentin/BLBP+ radial glia were the predominant cells in transitional and ventral zones. Use of halogenated thymidine analogs chloro- and iodo-deoxyuridine administered at different experimental times showed that both regions have the highest cell proliferation and migration rates. Zone 1 migration was toward the OB and telencephalon, whereas in zone 3, migration was directed toward the OB rostral portion constituting the equivalent of the mammal rostral migratory band. Medial zone (MZ) has fewer proliferating non-migrant cells that are the putative stem cells as indicated by short and long proliferation assays as well as cell lineage markers. Sparse migration observed suggests MZ may collaborate with VW growth. Scanning electron microscopy evidenced that the whole VW has only monociliated cells with remarkable differences in cilium length among regions. In OB there are monociliated cells with dwarf cilium whereas ventral telencephalon shows long cilium. Summarizing, we identified three neurogenic niches that might serve different functional purposes.