figure supplement 1: Electron microscopy view of the antennal lobe of Drosophila larva. A Cross-section of the antennal lobe, with dorsal up and lateral to the left. Notice most of the antennal lobe is wrapped by glial cells (darker profiles), but these do not fully enclose it (not shown), opening towards the SEZ (bottom right). Individual glomeruli are not wrapped in glia like in other insects [79], but glia do separate the antennal lobe from the neuronal somas and from nearby neuropils. ALT, antennal lobe tract. Corresponds to serial section 648 in the online volume, at bottom left (right antennal lobe from anterior view). B Magnification of the box in A, showing an axon terminal of the 24a ORN synapsing onto the 24a uPN and multiple LNs. The dendrite of the 24a PN contains mitochondria, vesicles and presynaptic sites (magenta arrows), synapsing in this section onto e.g. one of the two Keystone LNs among others. The ORN axon bouton hosts multiple synapses (red arrows) with prominent ribbons or T-bars. The ORN boutons are packed with vesicles, giving them a darker appearance than surrounding PN and LN neurites; also contain numerous mitochondria (not shown in this image). Only some LNs are labeled for clarity; all neurites in this image were reconstructed. Blue arrows point to synapses of labeled LNs.

figure supplement 1: Electron microscopy view of the antennal lobe of Drosophila larva. A Cross-section of the antennal lobe, with dorsal up and lateral to the left. Notice most of the antennal lobe is wrapped by glial cells (darker profiles), but these do not fully enclose it (not shown), opening towards the SEZ (bottom right). Individual glomeruli are not wrapped in glia like in other insects [79], but glia do separate the antennal lobe from the neuronal somas and from nearby neuropils. ALT, antennal lobe tract. Corresponds to serial section 648 in the online volume, at bottom left (right antennal lobe from anterior view). B Magnification of the box in A, showing an axon terminal of the 24a ORN synapsing onto the 24a uPN and multiple LNs. The dendrite of the 24a PN contains mitochondria, vesicles and presynaptic sites (magenta arrows), synapsing in this section onto e.g. one of the two Keystone LNs among others. The ORN axon bouton hosts multiple synapses (red arrows) with prominent ribbons or T-bars. The ORN boutons are packed with vesicles, giving them a darker appearance than surrounding PN and LN neurites; also contain numerous mitochondria (not shown in this image). Only some LNs are labeled for clarity; all neurites in this image were reconstructed. Blue arrows point to synapses of labeled LNs.

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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...

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... 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. ...
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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. ...
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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.