The mushroom bodies of Drosophila melanogaster: An immunocytological and golgi study of Kenyon cell organization in the calyces and lobes

Golgi impregnations reveal a variety of dendritic morphologies amongst Kenyon cells in the mushroom bodies of Drosophila melanogaster. Different morphological types of Kenyon cells contribute axon-like processes to five divisions of the medial and vertical lobes. Four of these divisions have characteristic affinities to antibodies raised against aspartate, glutamate, and taurine. A newly described posterior subdivision of the medial lobe, here named the βc lobe with its vertical branch αc, comprises glutamatergic Kenyon cells that are probably homologous to glutamatergic Kenyon cells in the cockroach and honey bee, and are the last neurons to differentiate. The first neurons to differentiate, which supply the γ lobe, are equipped with clawed dendritic specializations and are the structural homologues of clawed class II Kenyon cells supplying the γ lobes in cockroaches and honey bees. Three intermediate divisions lie between the βc lobe and γ lobe. These are, from the back towards the front, the β lobe, the β′ lobe, and a narrow division between β′ and γ called the β″ lobe. The fused calyx of the Drosophila mushroom body is comparable to the double calyces of Hymenoptera, here exemplified by a basal taxon, Diprion pini. Further similarities between the hymenopteran calyces and those of Drosophila are suggested by the segregation of different types of Kenyon cell dendrites within the calyx neuropil. The organization of afferents from the antennal lobes also defines regions in the Drosophila calyx that may be homologous to the lip and basal ring regions of the honey bee calyces. As in honey bees, GABAergic processes densely invade Drosophila's calyces, which also contain a sparse but uniform distribution of octopaminergic elements.