Jing W. Wang - US grants

DESCRIPTION (provided by applicant): The central nervous system is made from a limited number of microcircuit motifs. Our long-term goal is to unravel the general principles of the elementary microcircuits. In this study, we focus on the contribution of synaptic modulation to circuit function, sensory processing and animal behavior. GABA is the major inhibitory neurotransmitter in the central nervous system and plays a key role in synaptic modulation. GABA exerts its modulatory role via two distinct receptor systems, the fast ionotropic GABAA and the slow metabotropic GABAB receptors. There is good evidence from human clinical trials and animal experiments to suggest that GABAB receptor agonists reduce the craving for drugs such as cocaine, heroin, alcohol, and nicotine. The molecular cloning of GABAB receptors report a lack of heterogeneity, suggesting limited possibilities for selective interference with the GABAB receptors to avoid side effects in pharmacotherapy. Selection of alternative targets in the GABAB system could be aided by a deeper understanding of the GABAB receptor mediated synaptic modulation in basic neural circuits. GABAB receptor mediated synaptic modulation is the focus of this study. The anatomical simplicity and the power of genetics make Drosophila a particularly amenable system to investigate the contribution of synaptic modulation to circuit function as well as behavioral output. We have obtained evidence showing that Drosophila odorant receptor neurons express GABAB receptors and the activation of GABAB receptors causes presynaptic inhibition. We adopt a multidisciplinary approach that combines molecular genetics, behavioral studies, and optical imaging to study GABAB receptor mediated feedback inhibition in the olfactory system, and also its contribution to olfactory behaviors. Studies of such defined olfactory circuit should shed light on the general principles of synaptic modulation and feedback inhibition. These general principles should also guide target selection for future therapeutic interventions. PUBLIC HEALTH RELEVANCE There is good evidence from human clinical trials and animal experiments to suggest that GABAB receptor agonists reduce the craving for drugs such as cocaine, heroin, alcohol, and nicotine. However, a selective interference with the GABAB receptors without side effect is limited by the lack of receptor heterogeneity. The work of this proposal is basic science that seeks to reveal the mechanisms of the GABAB system in synaptic modulation and circuit function, creating a knowledge base from which alternative targets in the GABAB system can be evaluated for future therapeutic interventions.

DESCRIPTION (provided by applicant): Information about the external world arrives at our brain via sensory system. Sensory stimuli interact with receptor neurons in the periphery to generate sensation. Interpretation of the peripheral neural activity by the central circuitry leads to perception of the external world. What features of an animal's sensory world are relevant to behavior? How are the important sensory cues processed in the central brain to generate appropriate behavioral output? This proposal focuses on studying the neural representation of innately attractive and aversive odorants at the level of both primary and secondary sensory processing centers in an effort to uncover hard wired neural circuits that encode negative or positive valence in a simple model organism. The proposed experiments will be carried out in Drosophila, an organism with an anatomically simple olfactory system that is amenable to molecular and genetic manipulations, optical imaging technologies, and behavioral analysis. The experiments outlined here investigate the hypothesis that innately attractive and aversive odorants are encoded by separate labeled-line circuits. The goals of these experiments are: 1) to define key circuit elements at the level of the antennal lobe, a primary sensory processing center for olfaction, that mediate attraction or aversion to olfactory stimuli;2) to examine the representation of attractive and aversive odorants at higher brain center such as the mushroom body. These findings would then serve as a platform for launching a longer-term project directed at olfactory perception and decision- making at higher brain centers, where valence is assigned to stimuli encountered in the environment for appropriate motivated behaviors. PUBLIC HEALTH RELEVANCE: Drug addiction through neural circuit of reward signal has a profound impact on sensory perception. The work of this proposal is basic science that seeks to reveal the neural circuit underlying olfactory perception, creating a knowledge base from which potential neuron population can be evaluated for future therapeutic interventions of drug addiction.

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

During critical developmental stages, important environmental cues such as the face of one's mother or the smell of home are stored or "imprinted" into the memories of young animals. In this capacity, imprinting serves as an important survival mechanism and can have enduring effects on animal behaviors. Dr. Wang's laboratory has obtained evidence to demonstrate that the fruit fly Drosophila exhibits a robust form of olfactory imprinting. Exposure to a given odorant in early adulthood dramatically increases a fly's preference for that odorant at a later stage. Despite significant progress into the cellular and molecular mechanisms of olfactory imprinting in diverse species, causality between neural plasticity in specific neurons and olfactory imprinting behavior has been difficult to establish. The anatomical simplicity of Drosophila, coupled with sophisticated genetic tools for this model organism, confers unique advantages for studies linking neural activity to behavioral output. Dr. Wang and colleagues will use molecular genetics, behavioral studies, and optical imaging, to study olfactory imprinting in Drosophila. The proposed experiments aims to reveal the neural circuit underlying the imprinting behavior, which will yield insights into mechanisms of social attachment and development of individual preferences.

NSF support for this project will have broader impact at several levels. First, making inroads into understanding how early experience shapes behavioral preferences can elucidate basic principles that may seed and inform future efforts in the study of imprinting in other organisms. Second, experience gained by the participants of this proposal will be vital in incorporating modern imaging techniques and quantitative analysis into the undergraduate biological curriculum. Third, the support of this project will also provide opportunities to train a new generation of scientists in a multidisciplinary approach.

DESCRIPTION (provided by applicant): The modulation of behavior by basic physiological need is essential for animal survival. Relevant sensory stimuli are transformed by peripheral receptors into electrical signals to form an internal representation of the external world. Shaping sensory representation by internal physiological state of the organism could be an important mechanism to provide behavioral flexibility. In particular, hunger modulates feeding behavior in most animals to maintain energy homeostasis. Despite that olfaction makes important contribution to the perception of food quality, very little is known about how starvation alters olfactory representation. This proposal focuses on studying the hunger modulation in early olfactory processing. The proposed experiments will be carried out in Drosophila, an organism with an anatomically simple olfactory system that is amenable to molecular and genetic manipulations, optical imaging technologies, and behavioral analysis. The experiments outlined here investigate the hypotheses that insulin is a global satiety signal in the early olfactory system, and that both insulin and local neuropeptide signaling are integrated at specific sensory neurons to enable hunger modulation of olfactory sensitivity. The goals of these experiments are: 1) evaluating the hypothesis that insulin is a global metabolic signal for hunger modulation;2) investigating the role of local sNPF (a homolog of NPY in Drosophila) signaling in starvation-dependent presynaptic facilitation;3) investigating the role of local tachykinin signaling in starvation-dependent presynaptic inhibition. There is good evidence to suggest that this kind of hunger modulation in peripheral olfactory system is present in vertebrate systems. The notion that hunger modulation at the peripheral olfactory system is linked to insulin signaling has potential implication for therapeutic intervention of the seemingly unstoppable obesity epidemic trend in a large percentage of the population. PUBLIC HEALTH RELEVANCE: Obesity is a seemingly unstoppable epidemic that affects a large population. The work of this proposal is basic science that seeks to reveal the connection between olfaction and appetitive behavior. Defining the olfactory circuit that modulate feeding behavior will create a knowledge base from which potential molecular targets can be evaluated for future therapeutic interventions.

? DESCRIPTION (provided by applicant): Neural circuits are organized to elicit appropriate behavioral responses to environmental stimuli. Advancement in technologies allowing the visualization and manipulation of neural activity has made it possible to establish a causal relationship between circuit function and behavior. This proposal attempts to expand the repertoire of existing technologies by exploiting a unique feature of the NFAT molecule - calcium/calcineurin-dependent nuclear localization. In the novel activity reporter system named CaLexA, a truncated version of NFAT containing the necessary nuclear localization signal is fused to LexA to make the synthetic transcription factor LexA- NFAT. The resulting activity reporter system will detect not only persistent neural activity but phasic activity as well with hih sensitivity in freely moving, behaving animals. We have identified several state-of-the-art molecular technologies that will increase the signal- to-noise ratio of the CaLexA activity reporter system as well as add the ability to discriminate between phasic and sustained neural activity. In Aim 1, we will engineer new LexA-NFAT constructs to suppress unwanted background and enhance behaviorally relevant signal. In Aim 2, we will design new LexA-NFAT constructs that will allow the detection of transient calcium activity. In Aim 3, we will use optogenetics to generate precisely controlled patterns of neural activity so that calcium imaging and the CaLexA reporter system can be compared for their sensitivity and dynamic range to gain a full characterization of all the LexA-NFAT variants. The creation and characterization of these new CaLexA activity reporter systems will make available to the Drosophila neurobiology community a new set of tools for the study of neural circuits and behavior, and molecular designs that can be readily modified for other genetic model organisms.

Metabolic state has a profound impact on cognitive function and our perception of the external world. However, the mechanisms underlying behavioral changes during the transition from mild to severe starvation are poorly understood. Here, we propose to take advantage of the anatomical simplicity and genetic tractability of Drosophila to study how shifts in metabolic state shape olfactory circuit function and thus impact appetitive olfactory behavior. There are remarkable similarities between Drosophila and mammals in the organization and molecular regulation of olfactory systems, suggesting shared principles in the neurobiology of hunger. Elucidating how changes in olfactory neural circuits impact the perception of food quality and dietary selections may lead to a better understanding of factors that contribute to obesity as well as anorexia in the infirm and elderly. The experiments outlined here investigate the hypotheses that the decline of insulin, a global satiety signal, triggers local neuropeptide signaling to recruit distinct neuronal populations at different stages of starvation. The goals of these experiments are: 1) investigating the temporal expression pattern of sNPF receptors in different neuronal populations; 2) investigating the role of local sNPF (a homolog of NPY in Drosophila) signaling in modulating neuronal excitability in a higher order olfactory center; 3) Investigate changes across the broader gamma lobe MBON network.

PROJECT SUMMARY/ABSTRACT The long-term goal of this project is to determine the molecular mechanisms by which sex-determining genes and reproductive hormones differentially regulate olfactory sensitivity in males and females. In humans, olfactory performance is highly dependent on age and sex; women generally outperform men in smell identification, and men are more prone to olfactory impairment as they age. Similarly, in other animal species, select groups of odorant receptor neurons (ORNs), such as those important for pheromone detection, exhibit sexually dimorphic characteristics as animals reach the age of sexual maturity. However, the mechanisms underlying sexually-dimorphic neurophysiology are poorly understood.The research outlined here takes advantage of the powerful genetic toolkit of the Drosophila olfactory system to address this complex question. In this proposal, the first aim is to determine the generality of age-dependent sensitization in courtship- promoting ORNs. The hypothesis that all courtship-promoting ORNs in males undergo age-dependent sensitization will be tested using genetic, pharmacological, and functional imaging approaches. The second aim proposes a genetic analysis of downstream effector molecules that enhance olfactory sensitivity in the courtship-promoting ORNs. Finally, the third aim will test the hypothesis that a reproductive hormone promotes age-dependent sensitization through its interaction with a male-specific transcription factor. Results from these studies are expected to yield critical mechanistic insights into how sex-determining genes and reproductive hormones jointly regulate sensory neurophysiology and olfactory processing. These insights may have implications in understanding sexually dimorphic neurophysiology and sex-specific proclivities for certain neurodegenerative diseases.

Epigenetic regulation of gene expression is associated with long-lasting behavioral changes in animal models and humans. In response to environmental cues, epigenetic programs regulate gene expression in matured neurons via chromatin modifications and DNA methylation resulting in enduring neurophysiological changes. There is mounting evidence to implicate the involvement of dysfunctional epigenetic programs in many cognitive and neuropsychiatric disorders. However, establishing a causal link between epigenetic mechanism and neuronal properties that underlie behavioral adaptation in complex nervous systems has been difficult, mainly due to the paucity of behaviorally relevant neural and genetic substrates that are targeted by epigenetic regulation. Our goal is to determine the epigenetic basis of sensory experience-dependent changes in neurophysiology and behavior. We take advantage of the anatomical simplicity and the powerful genetic toolkit of the Drosophila olfactory receptor neurons (ORNs) involved in courtship behaviors, and the well- established Drosophila male courtship behavior, a robust ritualistic behavior governed by a single gene, fruitlessM (fruM) expressed in approximately 2000 interconnected neurons. Our pilot experiments and recent studies show that olfactory experience enhances the response of the Or47b and Ir84a ORNs in males and male courtship behavior. We also have linked olfactory receptor (OR) signaling through calcium, and histone acetyl transferase p300 to the expression of the transcriptional factor fruM as a molecular mechanism by which olfactory experience regulates neurophysiology and behavior. We hypothesize that fly and food odors in the environment lead to chromatin dependent changes in fruM transcription in sensory neurons to modify neurophysiology and courtship behavior with olfactory experience. To test this, we will first determine the effect of chromatin modulation by p300 on reprogramming neurophysiology and behavior. Next, we will characterize the molecular mechanisms by which olfactory experience and chromatin modulates fruM expression. Finally, we will determine the transcriptional and chromatin changes in ORNs with olfactory experience. .

PROJECT SUMMARY/ABSTRACT The long-term goal of this project is to uncover how the gut-brain axis regulates appetite in a nutrient-specific manner. In mammals, enteroendocrine cells in the gastrointestinal tract release a repertoire neuropeptides to regulate food intake. However, it is not clear how nutrients are represented by gut neuropeptides. The research outlined here takes advantage of the anatomical simplicity and the powerful genetic toolkit of the Drosophila to address the questions of how macronutrients ? carbohydrates, amino acids and fatty acids ? are transformed into a neuropeptide code and how nutritional information is processed to regulate appetite. The proposed study focuses on gut neuropeptide ? what macronutrients they represent (Aim 1) and whether they are anorexigenic hormones (Aim 2). In Aim 3, we will test the hypothesis that the level of an anorexigenic hormone represents not only the quantity but also the quality of amino acids. Results from these studies are expected to establish a neuropeptide code for macronutrients providing mechanistic insights into how food intake is regulated in a nutrient-specific manner. These insights are highly relevant to human health as reducing food intake by designed diets could provide a new avenue to fight the obesity epidemic