Figure 1. Introduction to lobula columnar (LC) neurons.

Schematics (A–C) and confocal images (D–K) show the lobula and adjacent parts of the visual system. (A,D,G,H) Horizontal sections. (B,E,I,J) Anterior views. (C,F,K) Cross-section views of the lobula. Some subregions of the optic lobe (Me, Medulla; Lp, Lobula plate; Lo, Lobula) and central brain (AOTu, Anterior Optic Tubercle; PVLP, Posterior Ventrolateral Protocerebrum; PLP, Posterior Lateral Protocerebrum) are indicated in selected panels. Dendrites of individual LC neurons (red and blue cells in the schematics and red, blue and green cells in J,K) span only part of the visual field. As populations, the neurons of a given LC cell type cover most or all of the lobula (F), though LC neurons with regionally restricted lobula arbors also exist (e.g. LC14 (Otsuna and Ito, 2006), see Figure 1—figure supplement 1). LC neurons receive feed forward visual inputs from photoreceptors in the retina via a series of optic lobe interneurons (a few lamina neurons, in brown, and transmedullary neurons [Tm], in green, are illustrated as examples in [A]). This places LC neurons at least 2–3 synapses downstream of the photoreceptors. The majority of LC neurons projects to distinct target regions in the central brain called optic glomeruli; some of these are illustrated in (A) and (B) and also visible as distinct structures in the anti-Brp pattern in the images in (D) and (E). Most optic glomeruli are located in the PVLP and the adjacent more posterior PLP. The more dorsal AOTu (illustrated in [B]) is considered a specialized optic glomerulus. For a more detailed map of optic glomeruli see Figure 3. Confocal images show either populations of neurons (D–I) or individual cells labeled using Multicolor FlpOut (MCFO) (Nern et al., 2015) (J,K). LC cell types shown are LC17 (D,G,H) and LC16 (E,F,I–K). Population labeling (D–I) was with split-GAL4 driven expression of a membrane marker (green; myr::smFLAG, using pJFRC225-5XUAS-IVS-myr::smFLAG in VK00005) with a presynaptic marker also shown [magenta; synaptotagmin-HA, using pJFRC51-3XUAS-IVS-syt::smHA in su(Hw)attP1] in (D,E) and by itself in (H). A neuropil marker (anti-Brp) is included in grey in (D–F,K) and neuropil regions are also in grey in the schematics. Images in (D,E,G–J) were generated using brains that were computationally aligned to a template brain using the anti-Brp pattern as reference. The anti-Brp pattern in (D,E) is that of the standard brain used for alignment. Images in (D–K) show projection images of different views of three-dimensional image stacks; these were generated in either Fiji (http://fiji.sc/) (D,E,G–J) or Vaa3D (Peng et al., 2010) (F,K). Scale bars represent 20 µm.

DOI: http://dx.doi.org/10.7554/eLife.21022.003

Figure 1—figure supplement 1. Examples of additional LC cell types and similar neurons.

These cell types were not selected for further analyses in this study since they did not project to glomerular target regions in the ventrolateral central brain, covered only part of the lobula as cell populations or are VPNs of a different optic lobe region. (A,B) LC14 cells, which project to the contralateral lobula, have been previously described (Hassan et al., 2000; Otsuna and Ito, 2006). LC14 is the name used by Otsuna and Ito; some closely related cells, here named LC14b, project to the contralateral medulla in addition to the lobula (Hassan et al., 2000; Langen et al., 2013). LC19 (C) and LC23 (D) are newly identified cell types that project to the contralateral (LC19) or both the ipsi- and contralateral (LC23) central brain. LC19 and LC23 neurons have cell bodies in the cell body rind between optic lobe and central brain near the dorsal tip of the lobula neuropile. LC19 arbors in the lobula are located mainly in layers Lo5 and Lo6, those of LC23 neurons primarily in layers Lo2 and Lo4 (see Figure 5—figure supplement 1 for details of lobula stratification). LC19 processes are present across the entire lobula; those of LC23 appear to cover only the anterior, not the posterior lobula. Images show projection views (generated in Vaa3D) of MCFO labeled neurons together with the anti-Brp neuropil marker (grey). (E) An example of a columnar lobula plate VPN (LPC1) also identified by others (Panser et al., 2016). LPC1 cells have cell bodies in the lobula plate cortex. Their processes in the lobula plate are mainly in lobula plate layer Lp2. (A), (B) and (C) show multiple cells; (D) and (E) segmented single cells. Scale bar represents 50 µm.

DOI: http://dx.doi.org/10.7554/eLife.21022.004