Overview of the wiring diagram of the glomerular olfactory system of the larval Drosophila. A Schematic of the olfactory system of the larval Drosophila with EMreconstructed skeletons overlaid. The ORN cell bodies are housed in the dorsal organ ganglion, extend dendrites into the dome of the dorsal organ, and emit axons to the brain via the antennal nerve. Like in all insects, neuron cell bodies (circles) reside in the outer layer of the nervous system (grey), and project their arbors into the neuropil (white) where they form synapses. Also shown are the major classes of local neurons (Broad LNs, Picky LNs and Keystone) and the 2 classes of projection neurons (uPNs and mPNs). The arbors of the Broad LNs (black) specifically innervate the AL. LNs and mPN dendrites can extend into the subesophageal zone (SEZ), innervated by sensory neurons of other modalities. uPNs project to specific brain areas (mushroom body calyx and lateral horn; LH), and mPNs mostly project to other nearby brain areas. B The larva presents 21 unique olfactory glomeruli, each defined by a single ORN expressing a single or a unique pair of olfactory receptors. We reconstructed each ORN with a skeleton and annotated its synapses, here colored like the skeleton to better illustrate each glomerulus. See suppl. fig. 1 for individual renderings that aided in the identification of each unique ORN. C Summary connectivity table for the right antennal lobe with all major neuron classes (4 neuromodulatory neurons and the descending neuron from the brain were omitted), indicating the percent of postsynaptic sites of a column neuron contributed by a row neuron. For most neurons, the vast majority of their inputs originates in other neurons within the antennal lobe. In parentheses, the number of neurons that belong to each cell type. We show only connections with at least two synapses, consistently found among homologous identified neurons in both the left and right antennal lobes. Percentages between 0 and 0.5 are rounded down to 0. (Continues into the next page.)

Overview of the wiring diagram of the glomerular olfactory system of the larval Drosophila. A Schematic of the olfactory system of the larval Drosophila with EMreconstructed skeletons overlaid. The ORN cell bodies are housed in the dorsal organ ganglion, extend dendrites into the dome of the dorsal organ, and emit axons to the brain via the antennal nerve. Like in all insects, neuron cell bodies (circles) reside in the outer layer of the nervous system (grey), and project their arbors into the neuropil (white) where they form synapses. Also shown are the major classes of local neurons (Broad LNs, Picky LNs and Keystone) and the 2 classes of projection neurons (uPNs and mPNs). The arbors of the Broad LNs (black) specifically innervate the AL. LNs and mPN dendrites can extend into the subesophageal zone (SEZ), innervated by sensory neurons of other modalities. uPNs project to specific brain areas (mushroom body calyx and lateral horn; LH), and mPNs mostly project to other nearby brain areas. B The larva presents 21 unique olfactory glomeruli, each defined by a single ORN expressing a single or a unique pair of olfactory receptors. We reconstructed each ORN with a skeleton and annotated its synapses, here colored like the skeleton to better illustrate each glomerulus. See suppl. fig. 1 for individual renderings that aided in the identification of each unique ORN. C Summary connectivity table for the right antennal lobe with all major neuron classes (4 neuromodulatory neurons and the descending neuron from the brain were omitted), indicating the percent of postsynaptic sites of a column neuron contributed by a row neuron. For most neurons, the vast majority of their inputs originates in other neurons within the antennal lobe. In parentheses, the number of neurons that belong to each cell type. We show only connections with at least two synapses, consistently found among homologous identified neurons in both the left and right antennal lobes. Percentages between 0 and 0.5 are rounded down to 0. (Continues into the next page.)

Source publication
Preprint
Full-text available
The sense of smell enables animals to react to long-distance cues according to learned and innate valences. Here, we have mapped with electron microscopy the complete wiring diagram of the Drosophila larval antennal lobe, an olfactory neuropil similar to the vertebrate olfactory bulb. We found a canonical circuit with uniglomerular projection neuro...

Contexts in source publication

Context 1
... the Drosophila larva, we find a similarly organized glomerular olfactory system of minimal numerical complexity ( Figure 1a). In this tractable system, each glomerulus is defined by a single, uniquely identifiable ORN [12,13], and almost all neurons throughout the nervous system are expected to be uniquely identifiable and stereotyped [14][15][16][17]. ...
Context 2
... and mPNs mostly project to other nearby brain areas. B The larva presents 21 unique olfactory glomeruli, each defined by a single ORN expressing a single or a unique pair of olfactory receptors. We reconstructed each ORN with a skeleton and annotated its synapses, here colored like the skeleton to better illustrate each glomerulus. See suppl. fig. 1 for individual renderings that aided in the identification of each unique ORN. C Summary connectivity table for the right antennal lobe with all major neuron classes (4 neuromodulatory neurons and the descending neuron from the brain were omitted), indicating the percent of postsynaptic sites of a column neuron contributed by a row ...
Context 3
... between 0 and 0.5 are rounded down to 0. (Continues into the next page.) Berck, Khandelwal et al., 2016 The wiring diagram of a glomerular olfactory system Figure 1: (Continued.) D Schematic of the innervation patterns of the main classes of LNs and PNs in the antennal lobe. ...
Context 4
... reconstructed from electron microscopy all synaptic partners of the 21 ORNs for both the left and right antennal lobes of a first instar larva (Figure 1b; Figure 1-figure supplement 1 and 2). Per side, we found 21 uniglomerular PNs (uPNs; one per glomerulus), 14 LNs, 14 multiglomerular PNs (mPNs), 4 neuromodulatory neurons, 6 subesophageal zone (SEZ) interneurons and 1 descending neuron (Figure 1c, d). ...
Context 5
... reconstructed from electron microscopy all synaptic partners of the 21 ORNs for both the left and right antennal lobes of a first instar larva (Figure 1b; Figure 1-figure supplement 1 and 2). Per side, we found 21 uniglomerular PNs (uPNs; one per glomerulus), 14 LNs, 14 multiglomerular PNs (mPNs), 4 neuromodulatory neurons, 6 subesophageal zone (SEZ) interneurons and 1 descending neuron (Figure 1c, d). These identified neurons present stereotyped connectivity when comparing the left and right antennal lobes. ...
Context 6
... we analyze this complete wiring diagram on the basis of the known function of circuit motifs in the adult fly and other organisms and known physiological properties and behavioral roles of identified larval neurons. We found two distinct circuit architectures structured around the two types of PNs: a uniglomerular system where each glomerulus participates in a repeated, canonical circuit, centered on its uPN [39]; and a multiglomerular system where all glomeruli are embedded in structured, hetereogeneous circuits read out by mPNs (Figure 1e; [19]). We also found that the inhibitory LNs structure a circuit that putatively implements a bistable inhibitory system. ...
Context 7
... mapped the wiring diagram of the first olfactory neuropil of the larva by reconstructing the left and right ORNs and all their synaptic partners. We used a complete volume of the central nervous system (CNS) of a first instar larva, imaged with serial section electron microscopy ( [17]; see methods for online image data availability; Figure 1-figure supplement 1). We reconstructed 160 neuronal arbors using the software CATMAID [40,41]. ...
Context 8
... 14 pairs of LNs originate in 5 different lineages (Figure 1-figure supplement 3). We assigned the same name to neurons of the same lineage, and numbered each when there is more than one per lineage. ...
Context 9
... selected names reminiscent of either their circuit role or anatomical feature, including "Broad" to refer to panglomerular arbors; "Picky" and "Choosy" for LNs of two different lineages (and different neurotransmitter; see below) with arbors innervating select subsets of glomeruli; "Keystone" for a single pair that mediate interactions between LNs of different circuits; and "Ventral LN" for a single pair of LNs with ventral cell bodies. We also determined the neurotransmitters of LNs that were previously unknown (Figure 2-figure supplement 1). We introduce the properties of each LN type below with the olfactory circuits that they participate in. ...
Context 10
... Drosophila larva, this system is reduced to a single ORN and a single uPN per glomerulus [13,39,47]. With one exception (35a, which has 2 bilateral uPNs), our EM-reconstructed wiring diagram is in complete agreement with these findings (Figure 1b, 3a). Most of the larval uPNs project to both the MB and the LH (Figure 3a), like in the adult fly [3,48]. ...
Context 11
... insects (adult fly, bee, locust) and in vertebrates, the excitation of glomeruli is under control of inhibitory LNs that mediate functions such as gain control, which define an expanded dynamic range of uPN responses to odors [10,27,[51][52][53]. We found that most non-sensory inputs to the larval uPNs ( Figure 1c) are from a set of 5 panglomerular, axonless, and GABAergic [18] neurons that we named Broad LNs (Figure 3b, c; Fig- ure 3-figure supplement 1). These 5 Broad LNs also account for most inputs onto the ORN axons ( fig. ...
Context 12
... insects (adult fly, bee, locust) and in vertebrates, the excitation of glomeruli is under control of inhibitory LNs that mediate functions such as gain control, which define an expanded dynamic range of uPN responses to odors [10,27,[51][52][53]. We found that most non-sensory inputs to the larval uPNs ( Figure 1c) are from a set of 5 panglomerular, axonless, and GABAergic [18] neurons that we named Broad LNs (Figure 3b, c; Fig- ure 3-figure supplement 1). These 5 Broad LNs also account for most inputs onto the ORN axons ( fig. ...
Context 13
... dynamic range of uPN responses to odors [10,27,[51][52][53]. We found that most non-sensory inputs to the larval uPNs ( Figure 1c) are from a set of 5 panglomerular, axonless, and GABAergic [18] neurons that we named Broad LNs (Figure 3b, c; Fig- ure 3-figure supplement 1). These 5 Broad LNs also account for most inputs onto the ORN axons ( fig. 1c), therefore being prime candidates for mediating both intra-and interglomerular presynaptic inhibition (onto ORNs) as observed in the adult fly with morphologically equivalent cells [10,[53][54][55], and in the larva ...
Context 14
... their role in pre-and postsynaptic inhibition of ORNs and uPNs respectively, the Broad LNs synapse onto all neurons of the system, including other LNs and mPNs ( Figure 1c, Figure 2). Therefore Broad LNs may be defining a specific dynamic range for the entire antennal lobe, enabling the system to remain responsive to changes in odorant intensities within a wide range. ...
Context 15
... GABAergic cell type, that we call the Choosy LNs (two neurons; Figure 1c . CC-BY-NC-ND 4.0 International license certified by peer review) is the author/funder. ...
Context 16
... 2 of [19]). The difference in neurotransmitter is consistent with Picky LNs deriving from a different lineage than Choosy LNs (Figure 1-figure supplement 3). In addition, the two Choosy LNs present indistinguishable connectivity, whereas each Picky LN has its own preferred synaptic partners (see Supplementary File 1 and 2). ...
Context 17
... is because the main synaptic target of Picky LN 0 ( Figure 2) is a bilateral, axonless, GABAergic LN called Keystone (Figure 5a; Figure 2-figure supplement 1), which in turn strongly synapses onto the Broad LN Trio-a major provider of presynaptic inhibition (Figure 5b). Interestingly, Keystone is also a major provider of presynaptic inhibition, but selectively avoids some glomeruli (Figure 5c; Figure 3-figure supplement 1). Therefore the wiring diagram predicts that these two parallel systems for presynaptic inhibition can directly and strongly inhibit each other ( Figure 5b): homogeneous across all glomeruli when provided by the Broad LN Trio, and heterogeneous when provided by Keystone (Figure 5c). ...
Context 18
... non-ORN sensory neurons are the top inputs of Keystone and do not synapse onto any other olfactory LN. In contrast, ORNs that synapse onto Keystone also synapse onto the Broad LN Trio (Figure 3-figure supplement 1), suggesting a role for non-ORN sensory inputs in tilting the balance towards Keystone and therefore the heterogeneous state. However, the subset of ORNs that also synapse onto Picky LN 0 ( Figure 4c) could oppose the effect of the non-ORN sensory neurons by inhibiting Keystone and therefore disinhibiting the Broad LN Trio. ...
Context 19
... only other provider of panglomerular presynaptic inhibition is the Broad LN Duet, which is the main provider of panglomerular postsynaptic inhibition. These neurons may operate similarly in both states given that they are inhibited by both Keystone and Broad LN Trio (Figure 1c). The higher fraction of inputs from Broad LN Trio onto Duet might be compensated by the fact that the Trio LNs inhibit each other (Figure 3e, 5b), whereas the two Keystone LNs do not (Figure 5b). ...
Context 20
... we found evidence that an individual glomerulus can have a global effect on the olfactory system. All LNs (except Picky LN 3) receive inputs from Ventral LN ( Figure 1c, Figure 3-figure supplement 1), an interneuron of unknown neurotransmitter, which is primarily driven by the 13a glomerulus. This suggest that 13a, an ORN sensitive to alcohols [35], could potentially alter the overall olfactory processing. ...
Context 21
... Khandelwal et al., 2016 The wiring diagram of a glomerular olfactory system Figure 1-figure supplement 2: A single, identified ORN for each glomerulus in the antennal lobe of the first instar larva. Each panel shows an EM-reconstructed arbor of an ORN (colored) over the background of a Broad LN Duet (grey). ...
Context 22
... the left, all ORNs of each half of the antennal lobe are rendered together. The orientation (lateral to the left, dorsal up) and relative position of each ORN has been chosen to exactly match the arrangement in the supplementary figure 1 of Masuda-Nakagawa et al. 2009, where each individual ORN was identified and labeled with GFP using genetic driver lines. ...

Citations

... While the number of neurons that were targeted in our tested lines varies from one to seven pairs on average, and sometimes more, in the case when the lines label multiple neuron types, intersectional strategies can be used to further refine the expression patterns. In the larva, a volume of electron microscope data has been acquired and more than 60% of the nervous system has been reconstructed through collaborative efforts [10,21,22,24,25,27,29,[47][48][49]. The synaptic partners of the identified candidate neurons can therefore be further reconstructed in the electron microscopy volume. ...
Article
Full-text available
Nervous systems have the ability to select appropriate actions and action sequences in response to sensory cues. The circuit mechanisms by which nervous systems achieve choice, stability and transitions between behaviors are still incompletely understood. To identify neurons and brain areas involved in controlling these processes, we combined a large-scale neuronal inactivation screen with automated action detection in response to a mechanosensory cue in Drosophila larva. We analyzed behaviors from 2.9x10⁵ larvae and identified 66 candidate lines for mechanosensory responses out of which 25 for competitive interactions between actions. We further characterize in detail the neurons in these lines and analyzed their connectivity using electron microscopy. We found the neurons in the mechanosensory network are located in different regions of the nervous system consistent with a distributed model of sensorimotor decision-making. These findings provide the basis for understanding how selection and transition between behaviors are controlled by the nervous system.
... In the adult Drosophila, DAN neurons show context and state movement related responses [32], while midbrain dopaminergic neurons in vertebrates were shown to be involved in movement initiation [33]. Thus, these dopaminergic neurons could be modulating the activity of higher-order centers in the mushroom body depending on the multisensory context or animal's behavioral states [34] and thus could contribute to the sensorimotor decision-making (to turn or not to turn and which way to turn) during navigation in different modalities Studying the neural basis of navigation in a genetically modifiable Drosophila larva has many advantages as neuronal activity can be manipulated, the connections between neurons determined by EM reconstruction [22,24,28,[35][36][37][38][39][40] and patterns of neuronal activity correlated with behaviors. The identified sparse and single neuron type lines in this study are excellent starting point for further studying the circuit mechanism underlying navigational decision-making by combining quantitative behavioral analysis with optogenetics and the monitoring of neuronal activity in a behaving animal [41]. ...
Preprint
Small animals use sensory information to navigate their environment in order to reach more favorable conditions. in gradients of light, temperature, odors and CO 2 , Drosophila larvae alternate periods of runs and turns, regulating the frequency size and direction of turns, to move in a favorable direction. Whether larvae use the same strategies when navigating in response to somatosensory input is unknown. Further, while many of the sensory neurons that mediate navigation behaviors have been described, where and how these navigational strategies are implemented in the central nervous system and controlled by neuronal circuit elements is not well known. Here we characterize for the first time the navigational strategies of Drosophila larvae in gradients of air-current speeds using high-throughput behavioral assays and quantitative behavioral analysis. We find that larvae extend runs towards favorable directions and shorten runs in unfavorable directions, and that larvae regulate both the direction and amplitudes of turns. These results suggest similar central decision-making mechanisms underlie navigation behaviors in somatosensory and other sensory modalities. By silencing the activity of individual neurons and very sparse expression patterns (2 or 3 neuron types), we further identify the sensory neurons and circuit elements in the ventral nerve cord and brain of the larva required for navigational decisions during anemotaxis. The phenotypes of these central neurons are consistent with a mechanism where the increase of the turning rate in unfavorable conditions and decrease in turning rate in favorable conditions are independently controlled. In addition, we find phenotypes that suggest that the decisions of whether and which way to turn are controlled independently. Our study reveals that different neuronal modules in the nerve cord and brain mediate different aspects of navigational decision making. The neurons identified in our screen provide a basis for future detailed mechanistic understanding of the circuit principles of navigational decisionmaking.
... However, the recent advent of advanced techniques to target, label and monitor physiological input and output has made Drosophila an excellent model to investigate the neurobiological basis of behaviors and the development of neural circuits [18][19][20][21][22][23][24]. Furthermore, serial section Transmission Electron Microscopy (ssTEM) maps of neural connectivity [25][26][27][28][29][30][31] and advanced computational 'ethomic' approaches to establish behavioral categories [32][33][34] will greatly aid future investigations. ...
Preprint
Full-text available
Drosophila larval crawling is an attractive system to study patterned motor output at the level of animal behavior. Larval crawling consists of waves of muscle contractions generating forward or reverse locomotion. In addition, larvae undergo additional behaviors including head casts, turning, and feeding. It is likely that some neurons are used in all these behaviors (e.g. motor neurons), but the identity (or even existence) of neurons dedicated to specific aspects of behavior is unclear. To identify neurons that regulate specific aspects of larval locomotion, we performed a genetic screen to identify neurons that, when activated, could elicit distinct motor programs. We used 165 Janelia CRM-Gal4 lines – chosen for sparse neuronal expression – to express the warmth-inducible neuronal activator TrpA1 and screened for locomotor defects. The primary screen measured forward locomotion velocity, and we identified 63 lines that had locomotion velocities significantly slower than controls following TrpA1 activation (28°C). A secondary screen was performed on these lines, revealing multiple discrete behavioral phenotypes including slow forward locomotion, excessive reverse locomotion, excessive turning, excessive feeding, immobile, rigid paralysis, and delayed paralysis. While many of the Gal4 lines had motor, sensory, or muscle expression that may account for some or all of the phenotype, some lines showed specific expression in a sparse pattern of interneurons. Our results show that distinct motor programs utilize distinct subsets of interneurons, and provide an entry point for characterizing interneurons governing different elements of the larval motor program.