Fig. 7: v-PNs expressing different 5-HTRs have divergent synaptic partners within the LH.
a overlap of AL (left) and LH (right) projections of the R24H08 (green) and R86G06 (cyan) v-PNs. Immunolabeling for N-Cadherin (dark blue) highlights neuropil. All scale bars = 20 µm. b Reconstruction of the v-PNs from the Hemibrain dataset that most closely resemble the R24H08 (v-PNR24; green) and R86G06 (v-PNR86; cyan) driver lines within AL and LH volumes. R24H08 v-PNs are shown in two shades of green to highlight the v-PNs predominantly innervating the VL2a glomerulus (dark green) and the DC3 glomerulus (light green). c Reconstruction of the axon terminals of the two v-PN groups within the LH. d Synapse fractions of the downstream LH neurons targeted by the candidate v-PNs from the R24H08 and R86G06 driver lines. LH output neurons (LHONs; lavender), LH local neurons (LHLNs; purple), LH centrifugal neurons (LHCENTs; pink). e Graph plot of the downstream synaptic targets of the v-PNR24 (green) and v-PNR86 (cyan) shows very little convergence, except for a single LHLN that is targeted by two v-PNR24 and all four v-PNR86 (black arrows). f Correlation matrix for the downstream partners of each v-PNR24 and v-PNR86 in the LH. Correlation values range between -1.0 (blue) and 1.0 (red). Green bar indicates individual v-PNR24 and blue bar indicates individual v-PNR86. The individual HemiBrain IDs used from top to bottom and left to right are 5813077810, 948834414, 1889883818, 1857143769, 1415825344, 791298858, 760264077, 729219639 and 698526273. g Schematic proposed model for the role of 5-HT in modulating v-PNs. v-PNs that express different 5-HT receptors (green = 5-HT1A/B, blue = 5-HT7) innervate partially overlapping combinations of glomeruli (left side, antennal lobes highlighted gray in brain reconstruction), thus participating in responses to partially overlapping sets of odors. v-PNs that express different 5-HT receptors project to different regions within the lateral horn (right side, lateral horns highlighted gray in brain reconstruction) and synapse upon different sets of lateral horn neurons (gray neurons within lateral horn). We propose that this enables 5-HT to differentially modulate (gray traces indicate before 5-HT, green/blue traces indicate effects of 5-HT) feedforward inhibition provided to separate output paths from the lateral horn. Brain meshes highlighting the antennal lobes and lateral horns were generated from the FAFB dataset26 on FlyWire25,113.
