Comparative Analysis of Neurogenesis in the Central Olfactory Pathway of Adult Decapod Crustaceans by In Vivo BrdU Labeling.

To examine the distribution of neurogenesis in the central olfactory pathway of adult decapod crustaceans, we labeled, in vivo, six species of decapod crustaceans representing most infraorders (shrimps, spiny lobsters, clawed lobsters, crayfish, hermit crabs, true crabs) with the proliferation marker 5-bromo-2'-deoxyuridine (BrdU). In all tested species a group of small, neuron-like nuclei in the lateral soma clusters of the brain was labeled; the lateral soma clusters are composed of the cell bodies of ascending olfactory projection neurons. In only a few instances did groups of BrdU-positive nuclei also occur in the other soma clusters of the central olfactory pathway. In the spiny lobster (Panulirus argus), a group of small neuron-like nuclei was labeled in the medial soma clusters containing the cell bodies of local interneurons of the olfactory deutocerebrum. In the hermit crab (Pagurus bernhardus), and the true crab (Cancer pagurus), a group of small neuron-like nuclei was labeled in soma clusters located in the eyestalks. These soma clusters probably contain the cell bodies of local interneurons of the hemiellipsoid bodies, to which the olfactory projection neurons ascend. These results indicate that neurogenesis occurs among olfactory projection neurons in the adult brain. Among the other neuronal types of the central olfactory pathway, however, neurogeneis is restricted to specific taxa. The persistence of neurogenesis among the different neuronal types of the central olfactory pathway throughout adult life suggests an enormous structural plasticity of brain circuitry that may enable the longlived decapod crustaceans to adapt to changing olfactory environments.