Neurogenesis in the central olfactory pathway of adult decapod crustaceans.

Based on the previous findings that the number of olfactory projection neurons increases continuously in adult shore crabs, Carcinus maenas, and that this increase is associated with the presence of 5-bromo-2-deoxyuridine (BrdU)-positive, proliferating cells in the appropriate soma clusters (lateral soma clusters), we studied the further fate of these proliferating cells and the presence of apparent adult neurogenesis throughout the central olfactory pathway of diverse species of decapod crustaceans. Double labeling experiments combining biocytin-backfills and in vivo BrdU labeling as well as BrdU labeling with extended survival times (1 month) indicate that the cells proliferating in the lateral soma clusters of adult Carcinus undergo neuronal differentiation in about 3-4 weeks. In vivo BrdU labeling of different species representing important taxa of decapod crustaceans (shrimps, spiny lobsters, clawed lobsters, crayfish) revealed that neurogenesis among olfactory projection neurons is a constitutive feature of the adult decapod brain. In contrast, adult neurogenesis of the other neuron types present in the central olfactory pathway occurs in a taxon-specific manner and appears to be related to the development and reduction of accessory lobes throughout decapod phylogeny.