Larval and pupal development of the mushroom bodies in the honey bee, Apismellifera

The mushroom bodies are paired neuropils in the insect brain that act as mu ltimodal sensory integration centers and are involved in learning and memor y. Our studies, by using 5-bromo-2-deoxyuridine incorporation and the Feulg en technique, show that immediately before pupation, the brain of the devel oping honey bee (Apis mellifera) contains approximately 2,000 neuroblasts d evoted to the production oft;he mushroom body intrinsic neurons (Kenyon cel ls). These neuroblasts are descended from four clusters of 45 or fewer neur oblasts each already present in the newly hatched larva. Subpopulations of Kenyon cells, distinct in cytoarchitecture, position, and immunohistochemic al traits, are born at different, but overlapping, periods during the devel opment of the mushroom bodies, with the final complement of these neurons i n place by the mid-pupal stage. The mushroom bodies of the adult honey bee have a concentric arrangement of Kenyon cell types, with the outer layers b orn first and pushed to the periphery by later born neurons that remain nea rer the center of proliferation. This concentricity is further reflected in morphologic and immunohistochemical traits of the adult neurons, and is de monstrated clearly by the pattern of expression of Drosophila myocyte enhan cer factor 2 (DMEF2)-like immunoreactivity. This is the first comprehensive study of larval and pupal development of the honey bee mushroom bodies. Si milarities to patterns of neurogenesis observed in the mushroom bodies of o ther insects and in the vertebrate cerebral cortex are discussed. (C) 1999 Wiley-Liss, Inc.