Kristin Scott - US grants

DESCRIPTION (provided by applicant): The long-term objectives of this proposal are to increase understanding of taste recognition and taste perception. The proposed experiments will be conducted in the fruit fly, Drosophila melanogaster, an organism with a simple gustatory system and robust gustatory behaviors that is amenable to molecular, genetic and electrophysiological approaches. Taste recognition in Drosophila is mediated by sensory neurons on the proboscis, internal mouthparts, legs, wings, and ovipositor. Preliminary studies have characterized a large family of 56 candidate gustatory receptor genes (GRs) and revealed that each gustatory neuron expresses one or a few receptors. How are these different gustatory neurons represented in the brain? In the somatosensory and visual systems, sensory projections are segregated according to the location of the neuron in the periphery to provide a topographic map of stimulus position in the brain. In the olfactory system, projections are segregated according to the odorant receptor that the neuron expresses, such that the quality of an odor is mapped rather than its peripheral position. The proposed experiments are designed to determine the molecular and positional representations of tastes in the brain. The following aims are proposed: (1) to determine if gustatory projections are segregated according to the receptor they express; (2) to determine if they are segregated according to their location in the periphery; (3) to compare gustatory maps with mechanosensory maps; (4) to identify synaptic connections of gustatory neurons. The proposed experiments will provide insight into the logic of taste representations in the brain, with the ultimate aim of understanding how sensory perception is encoded in neural circuits.

[unreadable] DESCRIPTION (provided by applicant): Ion channels transduce changes in the extracellular environment into neural activity. The Degenerin/Epithelial sodium channel family of ion channels participates in fundamental processes in many organisms, from salt exchange in mammalian kidneys, mechanotransduction in C. elegans, and peptide sensing in snails. In Drosophila, there are 29 members of this gene family called pickpocket genes (ppk). The molecular, genetic, functional and behavioral assays available in Drosophila provide the opportunity to dissect the function of uncharacterized members of this gene family. In preliminary studies, two members of the ppk gene family have been identified that are exclusively expressed in sensory neurons in the adult Drosophila. The aim of this application is to elucidate their function. The experiments proposed will examine the ligands that are detected by ppk-containing cells, the cellular and behavioral phenotypes associated with loss of specific ppk genes, and response profiles of cells engineered to mis-express ppk ion channels. The proposed experiments will examine the hypothesis that ppk ion channels directly detect extracellular sensory cues. These studies will elucidate the biological role of ppk ion channels and determine the ligands that activate them. Because members of this ion channel family are associated with diverse human diseases, studies of ppk function are directly relevant to human health. PUBLIC HEALTH RELEVANCE: This research is relevant to public health because it examines the function of ion channels that are associated with human disease. Primary malfunctions in these channels underlie the pathophysiology of several important human diseases such as salt-sensitive hypertension and pseudohypoaldosteronism type I, and defects in these channels have been associated with cystic fibrosis and epilepsy. A basic understanding of the ligands that gate these ion channels may ultimately provide insight into human disease genes, with a direct impact on public health. [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Feeding regulation is essential to ensure that animals consume calories in proportion to their energy requirements. An imbalance of neuromodulatory systems that regulate feeding may result in obesity and eating disorders, with significant health-related consequences. The long-term objective of this proposal is to increase understanding of the molecular signaling pathways that regulate food intake and how they interact, crucial for devising rational approaches toward controlling obesity and eating disorders. The monoaminergeric neurotransmitters, dopamine and serotonin, oppositely regulate feeding. In mammals, dopamine promotes feeding and serotonin inhibits it. Preliminary studies of this proposal showed that dopamine and serotonin regulate feeding in the fruit fly Drosophila melanogaster and identified the dopaminergic neurons that promote feeding and serotonergic neurons that inhibit feeding. The relative simplicity of the fruit fly nervous system provides a tractable model to dissect how dopamine and serotonin oppositely regulate feeding. Aim 1 will examine whether the activity of serotonergic neurons bidirectionally controls feeding behavior in response to external gustatory cues and internal physiological state. Aim 2 will test the hypothesis that dopamine and serotonin act over short timescales to regulate feeding during a meal as well as over longer timescales to adjust feeding based on internal physiological state. Aim 3 will examine whether dopamine and serotonin are opponent signals that act on the same or different neurons to modulate feeding. The proposed molecular genetic, electrophysiological and behavioral approaches will provide a comprehensive analysis of dopamine and serotonin function that is difficult to achieve in other systems. These studies will provide insight into how the monoaminergic neurotransmitter systems exercise control over feeding and will significantly advance understanding of feeding modulation, an essential foundation relevant for human health and disease.

Sugars are essential nutrients that allow animals to derive energy from the environment to survive, as individuals and as species. Gustatory receptors on sensory neurons directly detect sugars in potential food sources, allowing animals to assess nutrient value. Sugar detection by the gustatory system drives innate feeding behaviors, arguing that the inherent value of sugars is embedded in innate circuits set up in development and refined over evolution. In addition, sugars are critical to animal survival and serve as rewarding stimuli that impart positive valence to other cues for learned associations. The long-term objective of this proposal is to gain insight into the taste pathways that detect sugars, to determine how these essential compounds promote feeding and act as reward signals. Aim 1 will examine taste processing pathways from sensory detection to feeding initiation, using behavioral, functional, and anatomical studies of several neurons in the circuit. These studies will provide insight into how taste detection and internal state are integrated in neural circuits to arrive at feeding decisions and to carry them out. Aim 2 will examine how sugar taste detection serves as a reward to impart positive valence onto other associated cues. These studies will test the hypothesis that there are two pathways that convey different aspects of reward, one taste-specific pathway and one pathway that relays a broader environmental context. These studies will determine how sugar sensory activation is transformed into the rewarding qualities of sweet taste in the memory system. The proposed molecular genetic, cellular and functional approaches will provide a comprehensive analysis of taste processing that is difficult to achieve in other systems. These studies will provide insight into how gustatory information is processed in the brain and an essential foundation for understanding insect feeding, relevant to limiting the spread of insect-borne disease.

Understanding the human brain remains one of the great challenges of modern science. The scope of disciplines required to understand brain structure and function - chemistry, molecular biology, structural biology, biophysics, electrical engineering, computational science, cognitive science and psychology - to say nothing of the fields of inquiry and exploration that are influenced by this understanding, such as religion, art, music, philosophy, sociology and literature, is far-reaching. The sheer scale of the cells contained in the human brain, in contemplating the vast number of neurons, some 80 billion, and the hundreds to thousands of connections that each neuron forms with other neurons, along with the additional 80 billion non-neuronal support cells, makes for a daunting parts list to catalog. And yet, beyond just a static picture of the arrangement of these various cells into ensembles and networks, the dynamic information flow between these cells, the electrical and chemical impulses that underpin the very essence of human existence - sensation, thought, emotion, cognition - represent not just an additional layer of complexity, but, at its core, a deep mystery to be unraveled and explored. To push back at this frontier requires new thoughts, new tools, new techniques, and new interpretations that will almost certainly come from teams of scientists working across disciplines to bring new approaches that are more than the sum of their parts. This project will develop and apply new methods for non-invasively measuring electrical signals underlying brain cell communication.

This award establishes a NeuroNex Innovation Project at the University of California, Berkeley, which will develop chemical-genetic methods to measure neuronal activity in a non-invasive, high-throughput, high-fidelity manner across multiple length scales, at high speed, and in multiple species with molecular precision. The team will optically read-out neuronal activity by directly imaging changes in membrane voltage with bright, sensitive, chemically-synthesized voltage-sensitive fluorophores. The voltage-sensitive fluorophore make use of photoinduced electron transfer (PeT) as a voltage-sensing trigger to provide fast, sensitive, non-disruptive optical recordings in neurons. In this project, pairing of PeT-based voltage-sensitive dyes with genetic targeting methods to enable optical voltage sensing with sub-cellular and sub-millisecond resolution in intact animal brains will be conducted. This NeuroNex Innovation Award is part of the BRAIN Initiative and NSF's Understanding the Brain activities.

The goal of this research is to develop miniaturized, low-cost, and smart microfluidic biochips that can perform "epigenetics in a drop". Such a platform will revolutionize data acquisition for molecular biology studies. The knowledge gained from applying molecular biology protocols to microfluidic biochips will facilitate the understanding of diseases such as cancer, and knowledge about epigenetic modifications in cells from inheritance will broaden the understanding of disease development. The results from this research will also be applicable to quantitative analysis protocols such as gene expression analysis. This project will foster multi-disciplinary education for engineering students and it has the potential to pave the way for new high-tech companies.

This research has been structured as an interdisciplinary collaboration between investigators with complementary expertise in design automation and system architecture for microfluidics, digital microfluidics technology, and molecular biology. It will lead to an integrated 5-layer system architecture for the seamless on-chip execution of complex biochemical protocols. Breakthroughs in design automation will enable real-time decision-making based on prescribed decision criteria; such a design will allow a diverse collection of protocol paths to be traversed. Research objectives include system design and optimization methods to support quantitative analysis protocols, demonstration of biomolecular protocols on microfluidic biochips, and evaluation of design automation solutions using test cases extracted from benchtop implementation of biomolecular protocols.

Feeding decisions are tightly regulated based on internal needs. Signals of hunger and thirst are detected by interoceptive neurons that promote specific consumption to restore homeostasis. Although generally considered independently, recent studies have demonstrated that interactions between hunger and thirst drives are important to coordinate competing needs. The aim of this proposal is to examine how food and water consumption is coordinately regulated, using the well developed Drosophila system as a model. These studies will evaluate how multiple internal signals are integrated within a neuron to regulate activity and how the activity of a single set of neurons regulates two opponent behaviors. This research takes advantage of established behavioral assays for water and sucrose consumption in Drosophila, molecular genetics to rapidly manipulate genes and neural function, single-cell electrophysiology for precise measurements of signal integration, and large-scale calcium imaging approaches to study network interactions. Specific Aim 1 will examine how signals of hunger and thirst modulate activity of interoceptive neurons, providing insight into how multiple signals are integrated within a neuron over time. Specific Aim 2 will characterize neurons downstream of the interoceptive neurons to examine how activity is transmitted to circuits to oppositely regulate two behaviors. Specific Aim 3 will determine how interoceptive neurons alter the responses in taste sensorimotor circuits to examine how internal states generate plastic changes in feeding networks. The proposed efforts will determine how internal signals of nutritional state are integrated across time to coordinate feeding decisions. The long-term objective of this work is to provide insight into how neuromodulators regulate circuits and behavior over long timescales, a basic problem in neuroscience relevant across systems.

Project Summary: Natural sensory inputs are typically complex, and often combine multiple modalities. Human speech, for example, combines auditory signals with visual cues, such as facial expressions, that inform the interpretation of the spoken words. As individual sensory pathways only provide a partial representation of the sensory information available, selecting the context-appropriate behavioral response to a multimodal stimulus often requires integrating information across modalities. How do neural circuits perform this fundamental computation? Our current understanding of sensory processing is predominantly built upon studies that have focused on single sensory modalities, working into the brain beginning from sensory receptors. As a result, we have a deep understanding of peripheral circuit computations in many different experimental contexts. However, working inward, cell-type by cell-type, has left our understanding of the circuits and computational principles that link sensation to action incomplete. Moreover, experimental strategies that focus exclusively on single sensory modalities cannot, by design, lead to insights into how the unified percepts that guide behavior can be assembled from information emerging in separate sensory processing streams. Here we leverage whole-brain imaging and advanced computational approaches to establish the fruit fly Drosophila as a model system for uncovering fundamental principles underpinning multisensory integration. This proposal has three goals. First, we will optimize whole-brain imaging in this experimental system, and use this technology to comprehensively characterize population dynamics underpinning the sensations of vision, mechanosensation and taste. Second, we will systematically quantify circuit interactions between these sensory modalities and across-animal variability, testing computational models of statistical inference, and identifying the algorithmic bases of multimodal integration. Third, we will link population dynamics to the response properties of single cell-types, providing a powerful path to characterizing circuit and synaptic mechanisms. Taken together, by developing and applying improved methods for large-scale monitoring of neural activity, combined with computational modeling and quantitative analysis, this project will greatly expand our understanding of sensory processing mechanisms across the brain.