Flonicamid metabolite 4-trifluoromethylnicotinamide is a chordotonal organ modulator insecticide†

BACKGROUND

The selective aphicide flonicamid is known to cause symptoms in aphids that are like those of chordotonal organ TRPV channel modulator insecticides such as pymetrozine, pyrifluquinazon and afidopyropen. Flonicamid is classified by the Insecticide Resistance Action Committee as a chordotonal organ modulator with an undefined target site. However, although it has been shown not to act on TRPV channels, flonicamid's action on chordotonal organs has not been documented in the literature.

RESULTS

Flonicamid causes locusts to extend their hindlegs, indicating an action on the femoral chordotonal organ. In fruit flies, it abolishes negative gravitaxis behavior by disrupting transduction and mechanical amplification in antennal chordotonal neurons. Although flonicamid itself only weakly affects locust chordotonal organs, its major animal metabolite 4-trifluoromethylnicotinamide (TFNA-AM) potently stimulates both locust and fly chordotonal organs. Like pymetrozine, TFNA-AM rapidly increases Ca²⁺ in antennal chordotonal neurons in wild-type flies, but not iav¹ mutants, yet the effect is nonadditive with the TRPV channel agonist.

CONCLUSIONS

Flonicamid is a pro-insecticide form of TFNA-AM, a potent chordotonal organ modulator. The functional effects of TFNA-AM on chordotonal organs of locusts and flies are indistinguishable from those of the TRPV agonists pymetrozine, pyrifluquinazon and afidopyropen. Because our previous results indicate that TFNA-AM does not act directly on TRPV channels, we conclude that it acts upstream in a pathway that leads to TRPV channel activation. © 2022 Society of Chemical Industry.

A Markerless Pose Estimator Applicable to Limbless Animals

The analysis of kinematics, locomotion, and spatial tasks relies on the accurate detection of animal positions and pose. Pose and position can be assessed with video analysis programs, the “trackers.” Most available trackers represent animals as single points in space (no pose information available) or use markers to build a skeletal representation of pose. Markers are either physical objects attached to the body (white balls, stickers, or paint) or they are defined in silico using recognizable body structures (e.g., joints, limbs, color patterns). Physical markers often cannot be used if the animals are small, lack prominent body structures on which the markers can be placed, or live in environments such as aquatic ones that might detach the marker. Here, we introduce a marker-free pose-estimator (LACE Limbless Animal traCkEr) that builds the pose of the animal de novo from its contour. LACE detects the contour of the animal and derives the body mid-line, building a pseudo-skeleton by defining vertices and edges. By applying LACE to analyse the pose of larval Drosophila melanogaster and adult zebrafish, we illustrate that LACE allows to quantify, for example, genetic alterations of peristaltic movements and gender-specific locomotion patterns that are associated with different body shapes. As illustrated by these examples, LACE provides a versatile method for assessing position, pose and movement patterns, even in animals without limbs.

Visualization of naive and learned odor representations using in vivo calcium imaging and immunohistochemical bouton mapping of single Drosophila mushroom body neurons

This protocol enables the quantification of odor-evoked calcium activity in mushroom body Kenyon cells of the Drosophila melanogaster brain at the single bouton level. We also present subsequent characterization of naive and learned odor representations in the context of olfactory coding. This approach to analyzing the neuronal basis of associative learning provides a substrate for similar studies, perhaps in other animals, to probe the attributes of a neuronal memory trace at the level of synapses distributed across neurons.

For complete details on the use and execution of this protocol, please refer to Bilz et al. (2020).

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Neuronal activity is monitored in vivo at single synaptic bouton level in Drosophila

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Learning-induced modulation of calcium dynamics is visualized

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Congruence of odor responses is quantified across distributed synapses

Visualization of a Distributed Synaptic Memory Code in the Drosophila Brain

During associative conditioning, animals learn which sensory cues are predictive for positive or negative conditions. Because sensory cues are encoded by distributed neurons, one has to monitor plasticity across many synapses to capture how learned information is encoded. We analyzed synaptic boutons of Kenyon cells of the Drosophila mushroom body γ lobe, a brain structure that mediates olfactory learning. A fluorescent Ca²⁺ sensor was expressed in single Kenyon cells so that axonal boutons could be assigned to distinct cells and Ca²⁺ could be measured across many animals. Learning induced directed synaptic plasticity in specific compartments along the axons. Moreover, we show that odor-evoked Ca²⁺ dynamics across boutons decorrelate as a result of associative learning. Information theory indicates that learning renders the stimulus representation more distinct compared with naive stimuli. These data reveal that synaptic boutons rather than cells act as individually modifiable units, and coherence among them is a memory-encoding parameter.

The Orphan Cytokine Receptor CRLF3 Emerged With the Origin of the Nervous System and Is a Neuroprotective Erythropoietin Receptor in Locusts

The orphan cytokine receptor-like factor 3 (CRLF3) was identified as a neuroprotective erythropoietin receptor in locust neurons and emerged with the evolution of the eumetazoan nervous system. Human CRLF3 belongs to class I helical cytokine receptors that mediate pleiotropic cellular reactions to injury and diverse physiological challenges. It is expressed in various tissues including the central nervous system but its ligand remains unidentified. A CRLF3 ortholog in the holometabolous beetle Tribolium castaneum was recently shown to induce anti-apoptotic mechanisms upon stimulation with human recombinant erythropoietin. To test the hypothesis that CRLF3 represents an ancient cell-protective receptor for erythropoietin-like cytokines, we investigated its presence across metazoan species. Furthermore, we examined CRLF3 expression and function in the hemimetabolous insect Locusta migratoria. Phylogenetic analysis of CRLF3 sequences indicated that CRLF3 is absent in Porifera, Placozoa and Ctenophora, all lacking the traditional nervous system. However, it is present in all major eumetazoan groups ranging from cnidarians over protostomians to mammals. The CRLF3 sequence is highly conserved and abundant amongst vertebrates. In contrast, relatively few invertebrates express CRLF3 and these sequences show greater variability, suggesting frequent loss due to low functional importance. In L. migratoria, we identified the transcript Lm-crlf3 by RACE-PCR and detected its expression in locust brain, skeletal muscle and hemocytes. These findings correspond to the ubiquitous expression of crlf3 in mammalian tissues. We demonstrate that the sole addition of double-stranded RNA to the culture medium (called soaking RNA interference) specifically interferes with protein expression in locust primary brain cell cultures. This technique was used to knock down Lm-crlf3 expression and to abolish its physiological function. We confirmed that recombinant human erythropoietin rescues locust brain neurons from hypoxia-induced apoptosis and showed that this neuroprotective effect is absent after knocking down Lm-crlf3. Our results affirm the erythropoietin-induced neuroprotective function of CRLF3 in a second insect species from a different taxonomic group. They suggest that the phylogenetically conserved CRLF3 receptor may function as a cell protective receptor for erythropoietin or a structurally related cytokine also in other animals including vertebrate and mammalian species.

Chromophore-Independent Roles of Opsin Apoproteins in Drosophila Mechanoreceptors

Rhodopsins, the major light-detecting molecules of animal visual systems [1], consist of opsin apoproteins that covalently bind a retinal chromophore with a conserved lysine residue [1, 2]. In addition to capturing photons, this chromophore contributes to rhodopsin maturation [3, 4], trafficking [3, 4], and stabilization [5], and defects in chromophore synthesis and recycling can cause dysfunction of the retina and dystrophy [6-9]. Indications that opsin apoproteins alone might have biological roles have come from archaebacteria and platyhelminths, which present opsin-like proteins that lack the chromophore binding site and are deemed to function independently of light [10, 11]. Light-independent sensory roles have been documented for Drosophila opsins [12-15], yet also these unconventional opsin functions are thought to require chromophore binding [12, 13, 15]. Unconjugated opsin apoproteins act as phospholipid scramblases in mammalian photoreceptor disks [16], yet chromophore-independent roles of opsin apoproteins outside of eyes have, to the best of our knowledge, hitherto not been described. Drosophila chordotonal mechanoreceptors require opsins [13, 15], and we find that their function remains uncompromised by nutrient carotenoid depletion. Disrupting carotenoid uptake and cleavage also left the mechanoreceptors unaffected, and manipulating the chromophore attachment site of the fly's major visual opsin Rh1 impaired photoreceptor, but not mechanoreceptor, function. Notwithstanding this chromophore independence, some proteins that process and recycle the chromophore in the retina are also required in mechanoreceptors, including visual cycle components that recycle the chromophore upon its photoisomerization. Our results thus establish biological function for unconjugated opsin apoproteins outside of eyes and, in addition, document chromophore-independent roles for chromophore pathway components.

Correcting locomotion dependent observation biases in thermal preference of Drosophila

Sensing environmental temperatures is essential for the survival of ectothermic organisms. In Drosophila, two of the most used methodologies to study temperature preferences (T_P) and the genes involved in thermosensation are two-choice assays and temperature gradients. Whereas two-choice assays reveal a relative T_P, temperature gradients can identify the absolute T_p. One drawback of gradients is that small ectothermic animals are susceptible to cold-trapping: a physiological inability to move at the cold area of the gradient. Often cold-trapping cannot be avoided, biasing the resulting T_P to lower temperatures. Two mathematical models were previously developed to correct for cold-trapping. These models, however, focus on group behaviour which can lead to overestimation of cold-trapping due to group aggregation. Here we present a mathematical model that simulates the behaviour of individual Drosophila in temperature gradients. The model takes the spatial dimension and temperature difference of the gradient into account, as well as the rearing temperature of the flies. Furthermore, it allows the quantification of cold-trapping and reveals unbiased T_P. Additionally, our model reveals that flies have a range of tolerable temperatures, and this measure is more informative about the behaviour than commonly used T_P. Online simulation is hosted at http://igloo.uni-goettingen.de. The code can be accessed at https://github.com/zerotonin/igloo.

Saccadic movement strategy in a semiaquatic species - the harbour seal (Phoca vitulina)

Moving animals can estimate the distance of visual objects from image shift on their retina (optic flow) created during translational, but not rotational movements. To facilitate this distance estimation, many terrestrial and flying animals perform saccadic movements, thereby temporally separating translational and rotational movements, keeping rotation times short. In this study, we analysed whether a semiaquatic mammal, the harbour seal, also adopts a saccadic movement strategy. We recorded the seals' normal swimming pattern with video cameras and analysed head and body movements. The swimming seals indeed minimized rotation times by saccadic head and body turns, with top rotation speeds exceeding 350 deg s^-1 which leads to an increase of translational movements. Saccades occurred during both types of locomotion of the seals' intermittent swimming mode: active propulsion and gliding. In conclusion, harbour seals share the saccadic movement strategy of terrestrial animals. Whether this movement strategy is adopted to facilitate distance estimation from optic flow or serves a different function will be a topic of future research.

Saccadic Movement Strategy in Common Cuttlefish (Sepia officinalis)

Most moving animals segregate their locomotion trajectories in short burst like rotations and prolonged translations, to enhance distance information from optic flow, as only translational, but not rotational optic flow holds distance information. Underwater, optic flow is a valuable source of information as it is in the terrestrial habitat, however, so far, it has gained only little attention. To extend the knowledge on underwater optic flow perception and use, we filmed the movement pattern of six common cuttlefish (Sepia officinalis) with a high speed camera in this study. In the subsequent analysis, the center of mass of the cuttlefish body was manually traced to gain thrust, slip, and yaw of the cuttlefish movements over time. Cuttlefish indeed performed short rotations, saccades, with rotational velocities up to 343°/s. They clearly separated rotations from translations in line with the saccadic movement strategy documented for animals inhabiting the terrestrial habitat as well as for the semiaquatic harbor seals before. However, this separation only occurred during fin motion. In contrast, during jet propelled swimming, the separation between rotational and translational movements and thus probably distance estimation on the basis of the optic flow field is abolished in favor of high movement velocities. In conclusion, this study provides first evidence that an aquatic invertebrate, the cuttlefish, adopts a saccadic movement strategy depending on the behavioral context that could enhance the information gained from optic flow.

Neuroligins Nlg2 and Nlg4 Affect Social Behavior in Drosophila melanogaster

The genome of Drosophila melanogaster includes homologs to approximately one-third of the currently known human disease genes. Flies and humans share many biological processes, including the principles of information processing by excitable neurons, synaptic transmission, and the chemical signals involved in intercellular communication. Studies on the molecular and behavioral impact of genetic risk factors of human neuro-developmental disorders [autism spectrum disorders (ASDs), schizophrenia, attention deficit hyperactivity disorders, and Tourette syndrome] increasingly use the well-studied social behavior of D. melanogaster, an organism that is amenable to a large variety of genetic manipulations. Neuroligins (Nlgs) are a family of phylogenetically conserved postsynaptic adhesion molecules present (among others) in nematodes, insects, and mammals. Impaired function of Nlgs (particularly of Nlg 3 and 4) has been associated with ASDs in humans and impaired social and communication behavior in mice. Making use of a set of behavioral and social assays, we, here, analyzed the impact of two Drosophila Nlgs, Dnlg2 and Dnlg4, which are differentially expressed at excitatory and inhibitory central nervous synapses, respectively. Both Nlgs seem to be associated with diurnal activity and social behavior. Even though deficiencies in Dnlg2 and Dnlg4 appeared to have no effects on sensory or motor systems, they differentially impacted on social interactions, suggesting that social behavior is distinctly regulated by these Nlgs.

Saccadic body turns in walking Drosophila

Drosophila melanogaster structures its optic flow during flight by interspersing translational movements with abrupt body rotations. Whether these “body saccades” are accompanied by steering movements of the head is a matter of debate. By tracking single flies moving freely in an arena, we now discovered that walking Drosophila also perform saccades. Movement analysis revealed that the flies separate rotational from translational movements by quickly turning their bodies by 15 degrees within a tenth of a second. Although walking flies moved their heads by up to 20 degrees about their bodies, their heads moved with the bodies during saccadic turns. This saccadic strategy contrasts with the head saccades reported for e.g., blowflies and honeybees, presumably reflecting optical constraints: modeling revealed that head saccades as described for these latter insects would hardly affect the retinal input in Drosophila because of the lower acuity of its compound eye. The absence of head saccades in Drosophila was associated with the absence of haltere oscillations, which seem to guide head movements in other flies. In addition to adding new twists to Drosophila walking behavior, our analysis shows that Drosophila does not turn its head relative to its body when turning during walking.

Motor patterns during active electrosensory acquisition

Motor patterns displayed during active electrosensory acquisition of information seem to be an essential part of a sensory strategy by which weakly electric fish actively generate and shape sensory flow. These active sensing strategies are expected to adaptively optimize ongoing behavior with respect to either motor efficiency or sensory information gained. The tight link between the motor domain and sensory perception in active electrolocation make weakly electric fish like Gnathonemus petersii an ideal system for studying sensory-motor interactions in the form of active sensing strategies. Analyzing the movements and electric signals of solitary fish during unrestrained exploration of objects in the dark, we here present the first formal quantification of motor patterns used by fish during electrolocation. Based on a cluster analysis of the kinematic values we categorized the basic units of motion. These were then analyzed for their associative grouping to identify and extract short coherent chains of behavior. This enabled the description of sensory behavior on different levels of complexity: from single movements, over short behaviors to more complex behavioral sequences during which the kinematics alter between different behaviors. We present detailed data for three classified patterns and provide evidence that these can be considered as motor components of active sensing strategies. In accordance with the idea of active sensing strategies, we found categorical motor patterns to be modified by the sensory context. In addition these motor patterns were linked with changes in the temporal sampling in form of differing electric organ discharge frequencies and differing spatial distributions. The ability to detect such strategies quantitatively will allow future research to investigate the impact of such behaviors on sensing.

Species-Specific Flight Styles of Flies are Reflected in the Response Dynamics of a Homolog Motion-Sensitive Neuron

Hoverflies and blowflies have distinctly different flight styles. Yet, both species have been shown to structure their flight behavior in a way that facilitates extraction of 3D information from the image flow on the retina (optic flow). Neuronal candidates to analyze the optic flow are the tangential cells in the third optical ganglion - the lobula complex. These neurons are directionally selective and integrate the optic flow over large parts of the visual field. Homolog tangential cells in hoverflies and blowflies have a similar morphology. Because blowflies and hoverflies have similar neuronal layout but distinctly different flight behaviors, they are an ideal substrate to pinpoint potential neuronal adaptations to the different flight styles. In this article we describe the relationship between locomotion behavior and motion vision on three different levels: (1) We compare the different flight styles based on the categorization of flight behavior into prototypical movements. (2) We measure the species-specific dynamics of the optic flow under naturalistic flight conditions. We found the translational optic flow of both species to be very different. (3) We describe possible adaptations of a homolog motion-sensitive neuron. We stimulate this cell in blowflies (Calliphora) and hoverflies (Eristalis) with naturalistic optic flow generated by both species during free flight. The characterized hoverfly tangential cell responds faster to transient changes in the optic flow than its blowfly homolog. It is discussed whether and how the different dynamical response properties aid optic flow analysis.

A syntax of hoverfly flight prototypes

Hoverflies such as Eristalis tenax Linnaeus are known for their distinctive flight style. They can hover on the same spot for several seconds and then burst into movement in apparently any possible direction. In order to determine a quantitative and structured description of complex flight manoeuvres, we searched for a set of repeatedly occurring prototypical movements (PMs) and a set of rules for their ordering. PMs were identified by applying clustering algorithms to the translational and rotational velocities of the body of Eristalis during free-flight sequences. This approach led to nine stable and reliable PMs, and thus provided a tremendous reduction in the complexity of behavioural description. This set of PMs together with the probabilities of transition between them constitute a syntactical description of flight behaviour. The PMs themselves can be roughly segregated into fast rotational turns (saccades) and a variety of distinct translational movements (intersaccadic intervals). We interpret this segregation as reflecting an active sensing strategy which facilitates the extraction of spatial information from retinal image displacements. Detailed analysis of saccades shows that they are performed around all rotational axes individually and in all possible combinations. We found the probability of occurrence of a given saccade type to depend on parameters such as the angle between the long body axis and the direction of flight.

Gaze strategy in the free flying zebra finch (Taeniopygia guttata)

Fast moving animals depend on cues derived from the optic flow on their retina. Optic flow from translational locomotion includes information about the three-dimensional composition of the environment, while optic flow experienced during a rotational self motion does not. Thus, a saccadic gaze strategy that segregates rotations from translational movements during locomotion will facilitate extraction of spatial information from the visual input. We analysed whether birds use such a strategy by highspeed video recording zebra finches from two directions during an obstacle avoidance task. Each frame of the recording was examined to derive position and orientation of the beak in three-dimensional space. The data show that in all flights the head orientation was shifted in a saccadic fashion and was kept straight between saccades. Therefore, birds use a gaze strategy that actively stabilizes their gaze during translation to simplify optic flow based navigation. This is the first evidence of birds actively optimizing optic flow during flight.

Neural mechanisms underlying target detection in a dragonfly centrifugal neuron

Visual identification of targets is an important task for many animals searching for prey or conspecifics. Dragonflies utilize specialized optics in the dorsal acute zone, accompanied by higher-order visual neurons in the lobula complex, and descending neural pathways tuned to the motion of small targets. While recent studies describe the physiology of insect small target motion detector (STMD) neurons, little is known about the mechanisms that underlie their exquisite sensitivity to target motion. Lobula plate tangential cells (LPTCs), a group of neurons in dipteran flies selective for wide-field motion, have been shown to take input from local motion detectors consistent with the classic correlation model developed by Hassenstein and Reichardt in the 1950s. We have tested the hypothesis that similar mechanisms underlie the response of dragonfly STMDs. We show that an anatomically characterized centrifugal STMD neuron (CSTMD1) gives responses that depend strongly on target contrast, a clear prediction of the correlation model. Target stimuli are more complex in spatiotemporal terms than the sinusoidal grating patterns used to study LPTCs, so we used a correlation-based computer model to predict response tuning to velocity and width of moving targets. We show that increasing target width in the direction of travel causes a shift in response tuning to higher velocities, consistent with our model. Finally, we show how the morphology of CSTMD1 allows for impressive spatial interactions when more than one target is present in the visual field.