Fig. 5.
Diversity and anatomical tiling properties of the large-field neuronal constituents of the fan-shaped body (FB). a Schematic frontal section of a brain hemisphere at central level, visualizing the FB and surrounding neuropil compartments, as well as lineages with neurons that provide large-field arbors in the FB. Lineages with somata located in the anterior brain are shown on the left and those with somata in the posterior brain on the right. Somata clusters are represented by colored circles with the names of the corresponding lineage next to them. Position of circles roughly coincide with the location of somata clusters in the brain. The projection envelope of a lineage, rendered in the same vivid color as its soma cluster, is divided into a dendritic part that innervates the fan-shaped body input domain (FBID) located in the lateral protocerebrum (SLP/SIP/SMP/CRE/LAL), and an axonal part covering certain layers of the FB. For example, neurons of DPMpl2 (dark green) project to the FB dorsal layers 5–9 and have dendrites in the posterior half of the FB input domain. Distinguished are five “major” lineages that contribute the large majority of FB large-field neurons (BAmv1, DALcl2v, CP2d, DPMpl2, DM6), represented by thick lines for input/output, from the remainder of “minor” lineages shown by thin lines. A second system of muted colors, independent of the vivid colors marking lineages and their projections, is employed to visualize the topographical correlation between input domain and FB output layer. Neurons innervating dorsal layers of the FB tend to have dendrites at more posterior locations in the FBID (see also panel c). b Plots of axonal arbors of FB-innervating neurons schematically shown in (a), presented in anterior view. ExR neuronal arbors are rendered in Fig. 3. c Plots of complete arbors of four of the five major lineages (BAmv1, DALcl2v, CP2d, DPMpl2) in lateral view (anterior to the right, dorsal up). Within each lineage, neurons ending in a specific FB layer are rendered in the same color. For all four lineages, neurons innervating the more dorsal layers (purple-light green-magenta-cyan) have dendritic arbors in the posterior FBID (SLP, SIP). Axonal arborization in the central FB layers (4, 5) correlates with dendritic arborization in the CRE; axonal arborization in the ventral layers (2, 3) with dendritic arborization in the antero-ventral FB input domain (SMP, posterior CRE, LAL). An exception is layer 1, innervated by a group of BAmv1 and CP2d neurons, that is correlated with dendritic endings in the most posterior FBID (arrows). d Sunburst plot visualizing lineages of origin of large-field FB neurons (inner circle) and their break-down into individual neuron types as defined in the hemibrain (outer circle). The size of each sector depicts the number of input synapses onto these neurons/lineages from lateral neuropil compartments. e Heatmap depicting input from mushroom body output neurons (MBONs) onto FB large-field neurons. Overall, large numbers of neurons of extremely diverse lineage associations (more than 30 lineages of origin; not shown) provide input to the large-field dendrites in the FBID. However, if filtered for specific subtypes of input neurons, like the MBONs presented in this heatmap, only a few lineages (e.g., BAmas1, CP2v, DALv2, DAMd1) provide the bulk of synapses to select FB large-field neuron groups. For abbreviations see Table 1