Doublecortin expression in the adult rat telencephalon

Doublecortin (DCX) is a protein required for normal neuronal migration in t he developing cerebral cortex, where it is widely expressed in both radiall y and tangentially migrating neuroblasts. Moreover, it has been observed in the adult rostral migratory stream, which contains the neuronal precursors traveling to the olfactory bulb. We have performed DCX immunocytochemistry in the adult rat brain to identify precisely the neuronal populations expr essing this protein. Our observations confirm the presence of DCX immunorea ctive cells with the characteristic morphology of migrating neuroblasts in the subventricular zone, rostral migratory stream and the main and accessor y olfactory bulbs. We have also found putative migratory cells expressing D CX in regions were no adult neuronal migration has been described, as the c orpus callosum, the piriform cortex layer III/endopiriform nucleus and the striatum. Surprisingly, many cells with the phenotype of differentiated neu rons were DCX immunoreactive; e.g. certain granule neurons in the hilar bor der of the granular layer of the dentate gyrus, some neuronal types in the piriform cortex layer II, granule and periglomerular neurons in the main an d accessory olfactory bulbs, and isolated cells in the striatum. Almost all DCX immunoreactive cells also express the polysialylated form of neural ce ll adhesion molecule and have a similar distribution to rat collapsin recep tor-mediated protein-4, two molecules involved in neuronal structural plast icity. Given these results, we hypothesize that DCX expression in different iated neurons could be related to its capacity for microtubule reorganizati on and that this fact could be linked to axonal outgrowth or synaptogenesis .