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In Diptera, subsets of small retinotopic neurons provide a discrete channel from achromatic photoreceptors to large motion-sensitive neurons in the lobula complex. This pathway is distinguished by specific affinities of its neurons to antisera raised against glutamate, aspartate, gamma-aminobutyric acid (GABA), choline acetyltransferase (ChAT), and a N-methyl-D-aspartate type 1 receptor protein (NMDAR1). Large type 2 monopolar cells (L2) and type 1 amacrine cells, which in the external plexiform layer are postsynaptic to the achromatic photoreceptors R1-R6, express glutamate immunoreactivity as do directionally selective motion-sensitive tangential neurons of the lobula plate. L2 monopolar cells ending in the medulla are accompanied by terminals of a second efferent neuron T1, the dendrites of which match NMDAR1-immunoreactive profiles in the lamina. L2 and T1 endings visit ChAT and GABA-immunoreactive relays (transmedullary neurons) that terminate from the medulla in a special layer of the lobula containing the dendrites of directionally selective retinotopic T5 cells. T5 cells supply directionally selective wide-field neurons in the lobula plate. The present results suggest a circuit in which initial motion detection relies on interactions among amacrines and T1, and the subsequent convergence of T1 and L2 at transmedullary cell dendrites. Convergence of ChAT-immunoreactive and GABA-immunoreactive transmedullary neurons at T5 dendrites in the lobula, and the presence there of local GABA-immunoreactive interneurons, are suggested to provide excitatory and inhibitory elements for the computation of motion direction. A comparable immunocytological organization of aspartate- and glutamate-immunoreactive neurons in honeybees and cockroaches further suggests that neural arrangements providing directional motion vision in flies may have early evolutionary origins., (Copyright 2003 Wiley-Liss, Inc.)

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 betac lobe with its vertical branch alphac, 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 gamma lobe, are equipped with clawed dendritic specializations and are the structural homologues of clawed class II Kenyon cells supplying the gamma lobes in cockroaches and honey bees. Three intermediate divisions lie between the betac lobe and gamma lobe. These are, from the back towards the front, the beta lobe, the beta' lobe, and a narrow division between beta' and gamma called the beta" 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. Microsc. Res. Tech. 62:151-169, 2003., (Copyright 2003 Wiley-Liss, Inc.)