Active and Passive Antennal Movements during Visually Guided Steering in Flying Drosophila

Insects use feedback from a variety of sensory modalities, including mechanoreceptors on their antennae, to stabilize the direction and speed of flight. Like all arthropod appendages, antennae not only supply sensory information but may also be actively positioned by control muscles. However, how flying insects move their antennae during active turns and how such movements might influence steering responses are currently unknown. Here we examined the antennal movements of flying Drosophila during visually induced turns in a tethered flight arena. In response to both rotational and translational patterns of visual motion, Drosophila actively moved their antennae in a direction opposite to that of the visual motion. We also observed two types of passive antennal movements: small tonic deflections of the antenna and rapid oscillations at wing beat frequency. These passive movements are likely the result of wing-induced airflow and increased in magnitude when the angular distance between the wing and the antenna decreased. In response to rotational visual motion, increases in passive antennal movements appear to trigger a reflex that reduces the stroke amplitude of the contralateral wing, thereby enhancing the visually induced turn. Although the active antennal movements significantly increased antennal oscillation by bringing the arista closer to the wings, it did not significantly affect the turning response in our head-fixed, tethered flies. These results are consistent with the hypothesis that flying Drosophila use mechanosensory feedback to detect changes in the wing induced airflow during visually induced turns and that this feedback plays a role in regulating the magnitude of steering responses

Airborne chemical sensing with mobile robots

Airborne chemical sensing with mobile robots has been an active research areasince the beginning of the 1990s. This article presents a review of research work in this field,including gas distribution mapping, trail guidance, and the different subtasks of gas sourcelocalisation. Due to the difficulty of modelling gas distribution in a real world environmentwith currently available simulation techniques, we focus largely on experimental work and donot consider publications that are purely based on simulations

Direct inhibition of histamine receptors in the antennal lobe of Manduca sexta: Putative evidence for an olfactory corollary discharge circuit

Animals that plume track have developed navigational strategies that optimize the ability to track an odor to its source. This movement is an active part of the olfactory experience. For vertebrates, sniffing is also an active part of the olfactory experience that controls the speed and regularity of odor interactions with the olfactory receptors. This sniffing is coincident with locomotion throughout the environment and head movement back and forth across an odor plume. Similarly, moths actively beat their wings as they encounter odor plumes. In Manduca sexta, this wing beating influences speed and regularity of olfactory input in such a way that odor processing and perception are enhanced. While it is clear that the antennal lobe (AL) of M. sexta has evolved to process these naturally encountered olfactory stimuli, there may be a source of input that optimizes processing only when odor is sampled through wing beating. In other sensory systems, corollary discharge (CD) mechanisms have evolved to enhance sensory processing when the sensory input is caused by an animal\u27s own muscle movement, termed reafference. These CD circuits exhibit a functional neural connection, either direct or indirect, between the sensory system and the motor system that caused the reafference. In M. sexta, there is a candidate pair of histamine (HA) immunoreactive neurons that project from the mesothoracic ganglia to the ALs. The goal of this study was to functionally characterize the role of HA signaling within the AL of M. sexta using pharmacological injections and behavioral detection assays. Here we have shown that pharmacological disruption of normal histamine signaling within the AL reduces sensitivity. This provides the first functional characterization of an olfactory CD circuit that uses flight-motor information to mediate olfactory sensitivity

Glomerular input patterns in the mouse olfactory bulb evoked by retronasal odor stimuli

BACKGROUND: Odorant stimuli can access the olfactory epithelium either orthonasally, by inhalation through the external nares, or retronasally by reverse airflow from the oral cavity. There is evidence that odors perceived through these two routes can differ in quality and intensity. We were curious whether such differences might potentially have a neural basis in the peripheral mechanisms of odor coding. To explore this possibility, we compared olfactory receptor input to glomeruli in the dorsal olfactory bulb evoked by orthonasal and retronasal stimulation. Maps of glomerular response were acquired by optical imaging of transgenic mice expressing synaptopHluorin (spH), a fluorescent reporter of presynaptic activity, in olfactory nerve terminals. RESULTS: We found that retronasally delivered odorants were able to activate inputs to multiple glomeruli in the dorsal olfactory bulb. The retronasal responses were smaller than orthonasal responses to odorants delivered at comparable concentrations and flow rates, and they displayed higher thresholds and right-shifted dose–response curves. Glomerular maps of orthonasal and retronasal responses were usually well overlapped, with fewer total numbers of glomeruli in retronasal maps. However, maps at threshold could be quite distinct with little overlap. Retronasal responses were also more narrowly tuned to homologous series of aliphatic odorants of varying carbon chain length, with longer chain, more hydrophobic compounds evoking little or no response at comparable vapor levels. CONCLUSIONS: Several features of retronasal olfaction are possibly referable to the observed properties of glomerular odorant responses. The finding that retronasal responses are weaker and sparser than orthonasal responses is consistent with psychophysical studies showing lower sensitivity for retronasal olfaction in threshold and suprathreshold tests. The similarity and overlap of orthonasal and retronasal odor maps at suprathreshold concentrations agrees with generally similar perceived qualities for the same odorant stimuli administered by the two routes. However, divergence of maps near threshold is a potential factor in perceptual differences between orthonasal and retronasal olfaction. Narrower tuning of retronasal responses suggests that they may be less influenced by chromatographic adsorption effects

Second-order conditioning in Drosophila

Animals possess the ability to associate neutral stimuli in their environment with both rewards and punishment. A conditioned stimulus (CS1) such as a smell or sound, can become associated with an unconditioned stimulus (US), such as a food reward, to elicit what is known as the conditioned response (CR). This type of learning is commonly referred to as classical conditioning or first-order conditioning (FOC). Second-order conditioning (SOC) is an extension of this type of association wherein a novel stimulus is introduced (CS2) and associated with a previously conditioning first-order stimulus (CS1). As a result, the organism may show an attraction or avoidance towards the novel stimulus (CS2) even though it was never directly paired with the original unconditioned stimulus (US). In nature, there is a potential for SOC in almost any circumstance involving exposure to a sequence of learned events. For example, honeybees often memorize complex navigational pathways by associating landmarks with the presence of flowers. While a house or a tree may not reward the insect with nectar, it can be associated with a series of stimuli that eventually lead to a beneficial reward. My work in this dissertation focuses on conclusively demonstrating SOC for the first time in Drosophila along with utilizing genetic and molecular techniques to in- vestigate the neuronal basis of this behavior. The fruit fly has numerous advantages underlying its usefulness as a model organism: its genome has been sequenced, it possesses a relatively short time of development, it can be easily subjected to genetic alterations, and it is studied by numerous laboratories around the world. Using an au- tomated, computer-controlled olfactory-based learning paradigm, I will demonstrate the ability of Drosophila to form these complex, higher-order memories initially be- lieved to be reserved only for the vertebrate learning model. In addition, I will show that Drosophila are also capable of conditioning in situations of complex odor presen- tations for both first- and second-order conditioning. Furthermore, through the use of a transgenic neuron silencing approach exclusive to the Drosophila animal model, I will examine whether previously studied neuronal circuits fulfill similar roles in both first- and second-order conditioning

Efficacy of a trickling system for ammonia, particulate matter, and odor removal from livestock production buildings

As the size of animal feeding operations increases, the air quality and odor challenges these operations face has received increasing attention. Airborne ammonia (NH3), due to the degradation of urea in manure storage, odors during the breakdown of manure during storage, and particulate matter (PM) emissions for barn ventilation all contribute to the air and odor challenges these operations face. Finding feasible solutions for dealing with these emissions from animal agriculture require continued implementation and evaluation of practical strategies. This thesis describes development of a trickling scrubber for removal of ammonia and odor emissions from barn ventilation air and evaluates its performance at both lab- and field-scales. Lab-scale NH3 removals ranged from 19% to 86% while odor removal varied from 21% to 78% depending on key operating parameters like trickling solution pH, air flow rate, and the age of the trickling solution. Lab-scale results indicated trickling solution should be periodically change every 5 to 7 days to keep the system effective and avoid saturating the trickling solution with ammonia. The field-scale measurements were carried out in a commercial swine barn located in central Iowa. The trickling system installed in the swine barn significantly reduce PM emissions with an average reduction of 66%, 78%, and 80% for PM2.5, PM10 and TSP, respectively. An odor removal efficiency of 33% was averaged during the study. Overall this work demonstrated that trickling scrubbers could provide high levels of odor control, but greater development and improved management strategies are required to consistently achieve high levels of performance

Representations of Reward and Movement in Drosophila Dopaminergic Neurons

The neuromodulator dopamine is known to influence both immediate and future behavior, motivating and invigorating an animal’s ongoing movement but also serving as a reinforcement signal to instruct learning. Yet it remains unclear whether this dual role of dopamine involves the same dopaminergic pathways. Although reward-responsive dopaminergic neurons display movement-related activity, debate continues as to what features of an individual’s experience these motor-correlates correspond and how they influence concurrent behavior. The mushroom body, a prominent neuropil in the brain of the fruit fly Drosophila melanogaster, is richly innervated by dopaminergic neurons that play an essential role in the formation of olfactory associations. While dopaminergic neurons respond to reward and punishment to drive associative learning, they have also been implicated in a number of adaptive behaviors and their activity correlates with the behavioral state of an animal and its coarse motor actions. Here, we take advantage of the concise circuit architecture of the Drosophila mushroom body to investigate the nature of motor-related signals in dopaminergic neurons that drive associative learning. In vivo functional imaging during naturalistic tethered locomotion reveals that the activity of different subsets of mushroom body dopaminergic neurons reflects distinct aspects of movement. To gain insight into what facets of an animal’s experience are represented by these movement-related signals, we employed a closed loop virtual reality paradigm to monitor neural activity as animals track an olfactory stimulus and are actively engaged in a goal-directed and sensory-motivated behavior. We discover that odor responses in dopaminergic neurons correlate with the extent to which an animal tracks upwind towards the fictive odor source. In different experimental contexts where distinct motor actions were required to track the odor, dopaminergic neurons become emergently linked to the behavioral metric most relevant for effective olfactory navigation. Subsets of dopaminergic neurons were correlated with the strength of upwind tracking regardless of the identity of the odor and remained so even after the satiety state of an animal was altered. We proceed to demonstrate that transient inhibition of dopaminergic neurons that are positively correlated with upwind tracking significantly diminishes the normal approach responses to an appetitive olfactory cue. Accordingly, activation of those same dopaminergic neurons enhances approach to an odor and even drives upwind tracking in clean air alone. Together, these results reveal that the same dopaminergic pathways that convey reinforcements to instruct learning also carry representations of an animal’s moment-by-moment movements and actively influence behavior. The complex activity patterns of mushroom body dopaminergic neurons therefore represent neither purely sensory nor motor variables but rather reflect the goal or motivation underlying an animal’s movements. Our data suggest a fundamental coupling between reinforcement signals and motivation-related locomotor representations within dopaminergic circuitry, drawing a striking parallel between the mushroom body dopaminergic neurons described here and the emerging understanding of mammalian dopaminergic pathways. The apparent conservation in dopaminergic neuromodulatory networks between mammals and insects suggests a shared logic for how neural circuits assign meaning to both sensory stimuli and motor actions to generate flexible and adaptive behavior

Cross-compartmental modulation and plasticity in the Drosophila mushroom body

The mushroom body (MB) is the site of odor association learning in Drosophila.  In the canonical model, there are two types of reinforcing dopamine neurons (DANs): one set for rewarding unconditioned stimuli (US), and one responding to aversive US.  When DANs are activated together with an odor (the conditioned stimulus, or CS), plasticity is induced in the downstream output neurons (MBONs).  We have identified a DAN (V1) that surprisingly responds preferentially to odors, and responds weakly or not at all to various classical US.  In order to explore the relationship between V1 odor responses and the established roles of the MB, I characterized the responses of DAN V1, and probed its relationship to odor-driven behavior, associative conditioning, and activity in other MB compartments. These data show that V1 receives recurrent input from identified MBONs, contributes to the activity of an MBON that enhances alerting behavior, and that its odor responses are modulated by conditioning. We therefore present the study of the alpha2 compartment, which V1 innervates, as the dissection of an atypical compartment of the MB, one that acts as a hub by which various information from other compartments and brain areas is integrated in order to alter a behavioral response to odor. This work furthers our understanding of the MB not simply as an engine of classical learning, but as a system of diverse interconnected modules that allow coordinated fine control of behavior

Orientation in space using the sense of smell

Several studies reported that respiration interacts with olfactory perception. Therefore, in the pilot study of this experiment series human breathing was investigated during an olfactory experiment. Breathing parameters (respiratory minute volume, respiratory amplitude, and breathing rate) were quantified in response to odor stimulation and olfactory imagery. We provide evidence that respiration changed during smelling and during olfactory imagery in comparison to the baseline condition. In conclusion, olfactory perception and olfactory imagery both have an impact on the human respiratory profile, which is hypothesized to be based on a common underlying mechanism named sniffing. Our findings underline that for certain aspects of olfactory research it may be necessary to control and/or monitor respiration during olfactory stimulation. The human ability to localize odors has been investigated in a limited number of studies, but the findings are contradictory. We hypothesized that this was mainly due to differential effects of olfactory and trigeminal stimulation. Only few substances excite selectively the olfactory system. One of them is hydrogen sulphide (H2S). In contrast, most odorants stimulate both olfactory and trigeminal receptors of the nasal mucosa. The main goal of this study was to test the human ability to localize substances, which excite the olfactory system selectively. For this purpose we performed localization experiment using low and high concentrations of the pure odorant H2S, the olfactory-trigeminal substance isoamyl acetate (IAA), and the trigeminal substance carbon dioxide (CO2). In preparation for the localization study a detection experiment was carried out to ensure that subjects perceived the applied stimuli consciously. The aim of the detection study was to quantify the human sensitivity in response to stimulation with H2S, IAA, and CO2. We tested healthy subjects using an event-related experimental design. The olfactory stimulation was performed using an olfactometer. The results showed that humans are able to detect H2S in low concentration (2 ppm) with moderate sensitivity, and possess a high sensitivity in response to stimulation with 8ppm H2S, 50% v/v CO2, and 17.5% v/v IAA. The localization experiment revealed that subjects can localize H2S neither in low nor in high concentrations. In contrast to that, subjects possess an ability to localize both IAA and CO2 stimuli. These results clearly demonstrate that humans are able to localize odorants which excite the trigeminal system, but they are not able to localize odors that stimulate the olfactory system exclusively, in spite of consciously perceiving the stimuli