Architecture of the CSD neuron. The neuron is marked by a flipout in the RN2-Flp, Tub-FRT-CD2-FRTGal4, UAS-mCD8GFP strain, resulting in GFP expression in a single CSD neuron. (a) Only one of the pair of CSD neurons is labeled with antibodies to GFP (green) and the brain neuropile is stained with mAbnc82 (red). 1 μm sections at appropriate levels are stacked to visualize the cell body and ipsilateral dendrites (arrows), the branches to the higher centers (asterisks), projections to the lateral protocerebrum (arrowheads) in both hemispheres, and the presynaptic terminals in the contralateral antennal lobe (demarcated by yellow dots). (b) A single CSDn visualized in the brain of the third instar larva. Dendritic arbors ramify in the ipsilateral lobe (white arrows), branch extensively at the ipsilateral higher centers (inset) and send only a few arbors on the contralateral side (yellow arrow). The terminal arbors are extensive within the contralateral antennal lobe (demarcated with dotted lines). (c) In the adult, the terminal arbors of the CSDn arborize within the contralateral lobe and also send a branch in the antennal commissure (yellow arrow) to the ipsilateral antennal lobe. (d-d") Nod::lacZ localization in the ipsilateral dendrites (arrowheads) is visualized by anti-β-galactosidase staining (d', d", red). Inset in (d-d") shows Nod::lacZ localization in an ipsilateral neurite (arrowhead). (e-g) RN2-Flp, Tub-FRT-CD2-FRTGal4, UAS-mCD8GFP/mb247-DsRed animal stained with antibodies against GFP and visualized in the green (GFP) and red (ds-red) channels of the confocal microscope. Branches exit the main trunk in both hemispheres (yellow and white asterisks) and traverse anterior to the mushroom bodies to terminate within the higher centers (arrowheads in (f)). (g) A few sections are stacked to show the arborization to the calyx from the contralateral branches (arrows); the arrowhead indicates the branchpoint to the calyx neurites. (h, i) Schematic diagrams of the CSD neuron showing its projection patterns in the adult (h) and the larvae (i). The arrow in (h) indicates the crossover of presynaptic terminals to the lobe ipsilateral to the soma. Ca, Calyx; LH, lateral horn. Scale bar in (d) inset = 5 μm; for all other figures = 10 μm.