Figure 9. Main calyx (CA).

The dendrites of 1757 KCs of the α/β, α′/β′, and γ cell types define the CA. (A) The pie chart shows a breakdown of the inputs to these KCs. The largest source of input is from 129 uniglomerular olfactory projection neurons as judged by synapse number (uPNs; 63.6% of total input to the KCs); the number of synapses is indicated for each uPN cell type. Additional olfactory sensory input is provided by 23 multiglomerular projection neurons (mPNs). Information about temperature is provided by both 35 mPNs (th_mPN) and 19 uPNs (th_uPN). The next most prominent inputs are KC-to-KC synapses within the CA (11.9%), from APL (9.5%; see Figure 3—figure supplement 1A) and from MB-C1 (4.6%; see Figure 3—figure supplement 1H). Smaller sources of input are indicated by the numbered sectors: 1, a group of nine neurons previously described as ‘centrifugal’ neurons (Bates et al., 2020a) that innervate both CA and LH (1.3%). 2, MB-CP2 (1.0%); 3, PPL201 (see Figure 3—figure supplement 1G). The remaining 3.4% is provided by 31 other neurons (blue). (B) An image of the CA showing the locations of olfactory PN and thermo PN synapses onto KCs. The green dots representing thermo PN olfactory input synapses are of larger diameter to allow better visibility in the presence of the larger number of gray dots representing olfactory input synapses. Note the thermo PN inputs are located in the anterior and at the periphery of the CA, corresponding to the position of α′/β′ap1 and γt KC dendrites. The inset shows the orientation of the image. (C) Inputs from olfactory PNs are shown color-coded based on the type of olfactory information they are thought to convey (see Bates et al., 2020b): 1, fruity; 2, plant matter; 3, animal matter; 4, wasp pheromone; 5, insect alarm pheromone; 6, yeasty; 7, alcoholic fermentation; 8, decaying fruit; 9, pheromonal; 10, egg-laying related; 11, geosmin.

Figure 9—figure supplement 1. Distribution of the termini of olfactory PNs in the CA.

(A-A′′) MB images showing the orientation of the CA (blue) in panels B-E′′: (A) frontal view, (A′) top view, and (A′′) side view. (B-B′′) Four individual DL2d uniglomerular PNs (uPNs), each shown in a different color, innervate the CA, shown in faint gray. The axons of individual PNs split into two to three branches, each terminating in a large bouton that forms part of a highly stereotyped ‘claw-like’ connection with KCs (F; Figure 9—video 1). DL2d PNs terminate primarily in the anterior-lateral CA. (C-C′′) Synaptic connections, color-coded to correspond to the PNs in B-B′′, from DL2d PNs onto KCs. (D-D′′) DM1 and DC1 are shown; these uniglomerular PNs are unusual in that there is only a single cell of each type per brain hemisphere. Both DM1 and DC1 have widely distributed boutons, which occupy non-overlapping areas of the CA (Jeanne et al., 2018); DM1’s boutons are more dorsal and DC1’s more ventral. (E-E′′) Synaptic connections from the DM1 and DC1 PNs onto KCs, color-coded by PN type. (F) An example PN-to-KC synapse with a claw-like structure. DA1 lPN (1734350908; green) connects to KCγm (600356751; Figure 9—video 1; orange); note how the KC dendrite wraps around the PN bouton. Presynaptic sites of the PN and postsynaptic sites of the KC are shown in yellow and gray , respectively. (G–H) Distribution of the axons of DL2d, DM1 and DC1 in the LH and CA. (G) The four DL2d PNs innervate the middle of the LH. Note their axons terminate in the same area of the LH, but lack the large terminal boutons seen in the CA. (H) DM1 and DC1 axons remain segregated in the LH.

Figure 9—figure supplement 2. Spatial arrangement in the CA of synaptic input from different PN groups.

The synaptic terminals of PNs in the CA are shown. PNs that convey distinct types of olfactory information are shown separately as indicated. (A-A′) MB images indicating the orientation of the figures shown in remaining panels: (A) frontal view and (A′) top view. The CA is shaded blue. (B-B′). Synapses KCs receive from all the olfactory PN groups that are shown individually in panel C-H′. (C-C′) PNs that convey the presence of geosmin and insect alarm pheromone, both highly aversive odors, are clustered. (D-D′) PNs that convey pheromones and odors involved in egg-laying site selection occupy the center and periphery of the CA, respectively. (E-E′) PNs that convey fruity and plant matter information are distributed in the dorsal part of the CA. (F-F′) PNs that convey yeasty and alcoholic fermentation odors are distributed widely across the CA. (G-G′) PNs that convey wasp pheromone and animal matter information. (H, H′) PNs that convey decaying fruit information.

Figure 9—figure supplement 3. Gustatory input to a subset of KCs.

The PN, VP5+Z adPN, has been reported to receive sensory input with mixed modalities, with hygrosensory input from the VP5 glomerulus in the AL and gustatory input from the SEZ (Marin et al., 2020). We found that it connects to 16 KCs that extend a portion of their dendritic arbors outside the main CA. (A) Eleven γm KCs connect at three locations to the axon of VP5+Z adPN, just anterior to the main CA (indicated by yellow arrowheads), forming a total of 140 synapses. The same 11 γm KCs also have dendritic claws inside the CA (their dendrites are dark blue where they lie outside the CA and faint blue where they lie within the CA) where they receive input from many olfactory PN types; their synapses from VP5+Z adPN do not have a claw-like structure. VP5+Z adPN is the top PN input to these KCs. (B) Connections from VP5+Z adPN to other KC types are shown: three KCγd/s4 (purple, n = 30); two KCα/βp (blue, n = 13) and two KCα’/β’ap1 (green, n = 12). (C) Top 10 downstream targets of VP5+Z adPN by neuron type. Note that the 11 γm KCs are its top target. In addition to the neurons shown, two DNs are prominent downstream targets: DNp44 (542751938) with 52 synapses and DNg30 (571346836) with 33 synaspes. (D) VP5+Z adPN in the hemibrain (left: front view, right: side view) with presynaptic sites shown in yellow and postsynaptic sites in gray. Note the SEZ is not in the hemibrain volume and its putative position is indicated below the dashed lines, which mark the ventral extent of the hemibrain volume. (E) VP5+Z adPN traced in FAFB, with its complete dendrite in the SEZ where it receives strong input from gustatory receptor neurons (S. Engert and K. Scott, personal communication). The same two views as in panel D are shown; presynaptic (yellow) and postsynaptic (gray) sites are indicated.

Figure 9—video 1. Introduction to γ main KCs.

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