Wolf Huetteroth

The mushroom bodies (MBs), prominent paired neuropils of the insect brain, are multimodal sensory processing centers. In the MBs of Papilio xuthus , a flower‐foraging swallowtail butterfly with sophisticated color vision, the inner zone and the rim of the outer zone of the primary calyx receive prominent visual input. These two visual zones are spatially segregated from the outer zone that receives olfactory input. Sensory information is transmitted to the MB output sites (the lobes) via the pedunculus, but it remains unknown how the concentric modality organization of the calyx is transformed and represented in the spheroidal lobe neuropils in P. xuthus . To address this question, we investigated the architecture of the Papilio MBs in detail. Immunofluorescent staining and tracer injections into the MBs revealed the branching patterns of Kenyon cells (KCs), the MB intrinsic neurons, and several output pathways to other neuropils of the central brain. We newly defined the α/β, α′/β′, and γ lobes of the Papilio MBs following the nomenclature system commonly used in other insects. KCs conveying visual information extend axon‐like fibers to the α/β lobe (a large ventral division), while KCs conveying olfactory information send fibers to the α′/β′ lobe located between the α/β and γ lobes. These parallel sensory pathways in the MBs of P. xuthus were summarized as a three‐dimensional reconstruction of the MB subdivisions. Our study facilitates future physiological and functional studies of multisensory processing in the swallowtail butterfly brain.

Play-like behaviour (PLB) is pervasive across the animal kingdom, especially in vertebrate species. Invertebrate PLB has been restricted to social or object interaction. Here we examined individual PLB in the vinegar fly Drosophila melanogaster by providing voluntary access to a spinning platform – a carousel. We demonstrate that flies exhibit idiosyncratic carousel interactions that qualify as play-like behaviour. While some flies show spontaneous avoidance, others actively seek stimulation, engaging in repeated, prolonged visits to the carousel. We propose that flies voluntarily expose themselves to external forces to intentionally receive exafferent stimulation. Self stimulation provides an efficient way to improve self-perception via internal model training and can shape multisensory integration. One-Sentence Summary: Vinegar flies seek passive movement.

Animal behaviours are demonstrably governed by sensory stimulation, previous experience and internal states like hunger. With increasing hunger, priorities shift towards foraging and feeding. During foraging, flies are known to employ efficient path integration strategies. However, general long-term activity patterns for both hungry and satiated flies in conditions of foraging remain to be better understood. Similarly, little is known about how permanent contact chemosensory stimulation affects locomotion. To address these questions, we have developed a novel, simplistic fly activity tracking setup—the Panopticon. Using a 3D-printed Petri dish inset, our assay allows recording of walking behaviour, of several flies in parallel, with all arena surfaces covered by a uniform substrate layer. We tested two constellations of providing food: (i) in single patches and (ii) omnipresent within the substrate layer. Fly tracking is done with FIJI, further assessment, analysis and presentation is done with a custom-built MATLAB analysis framework. We find that starvation history leads to a long-lasting reduction in locomotion, as well as a delayed place preference for food patches which seems to be not driven by immediate hunger motivation.

Although animals switch to backward walking upon sensing an obstacle or danger in their path, the initiation and execution of backward locomotion is poorly understood. The discovery of Moonwalker Descending Neurons (MDNs), made Drosophila useful to study neural circuits underlying backward locomotion. MDNs were demonstrated to receive visual and mechanosensory inputs. However, whether other modalities converge onto MDNs and what are the neural circuits activating MDNs are unknown. We show that aversive but not appetitive olfactory input triggers MDN-mediated backward locomotion. We identify in each hemisphere, a single Moonwalker Subesophageal Zone neuron (MooSEZ), which triggers backward locomotion. MooSEZs act both upstream and in parallel to MDNs. Surprisingly, MooSEZs also respond mostly to aversive odor. Contrary to MDNs, blocking MooSEZs activity has little effect on odor-evoked backward locomotion. Thus, this work reveals another important modality input to MDNs in addition to a novel olfactory pathway and MDN-independent backward locomotion pathway.

Animal behaviours are demonstrably governed by sensory stimulation, previous experience and internal states like hunger. With increasing hunger, priorities shift towards foraging and feeding. During foraging, flies are known to employ efficient path integration strategies. However, general long-term activity patterns for both hungry and satiated flies in conditions of foraging remain to be better understood. Similarly, little is known about how chronic contact chemosensory stimulation affects locomotion. To address these questions, we have developed a novel, simplistic fly activity tracking setup – the Panopticon. Using a 3D-printed Petri dish inset, our assay allows recording of walking behaviour, of several flies in parallel, with all arena surfaces covered by a uniform substrate layer. We tested two constellations of providing food: i) in single patches, and ii) omnipresent within the substrate layer. Fly tracking is done with FIJI, further assessment, analysis and presentation is done with a custom-built MATLAB analysis framework. We find that starvation history leads to a long-lasting reduction in locomotion, as well as a delayed place preference for food patches not driven by immediate hunger motivation.

Value coding of external stimuli in general, and odor valence in particular, is crucial for survival. In flies, odor valence is thought to be coded by two types of neurons: mushroom body output neurons (MBONs) and lateral horn (LH) neurons. MBONs are classified as neurons that promote either attraction or aversion, but not both, and they are dynamically activated by upstream neurons. This dynamic activation updates the valence values. In contrast, LH neurons receive scaled, but non-dynamic, input from their upstream neurons. It remains unclear how such a non-dynamic system generates differential valence values. Recently, PD2a1/b1 LH neurons were demonstrated to promote approach behavior at low odor concentration in starved flies. Here, we demonstrate that at high odor concentrations, these same neurons contribute to avoidance in satiated flies. The contribution of PD2a1/b1 LH neurons to aversion is context dependent. It is diminished in starved flies, although PD2a1/b1 neural activity remains unchanged, and at lower odor concentration. In addition, PD2a1/b1 aversive effect develops over time. Thus, our results indicate that, even though PD2a1/b1 LH neurons transmit hard-wired output, their effect on valence can change. Taken together, we suggest that the valence model described for MBONs does not hold for LH neurons.