Lisa Stowers - US grants

DESCRIPTION (provided by applicant): Without the appropriate regulation of behavior such as aggression and mating, individuals cannot function in society. A growing number of Americans obtain therapeutic drugs to modify behavior, yet we have little understanding of the mechanisms and neuronal pathways that initiate behavioral responses. In mice, chemical cues called pheromones serve as signals between individuals to regulate their social behavior. Mouse pheromone response provides an experimentally approachable system to define the neuronal circuitry that regulates mammalian social behavior. The long-term goals of this proposal are to identify signals in the environment that influence behavior and their underlying molecular mechanisms. The mouse major urinary proteins (MUPs) family of genes displays characteristics consistent with a role in pheromone signaling. MUPs provide a molecular fingerprint of an individual's age, strain, and gender. MUPs display a hydrophobic binding pocket enabling them to be carrier proteins for pheromones. MUPs are expressed in secretory fluids with pheromone signaling activity and are excreted into the environment. Furthermore, MUPs co-purify with a bioactive fraction of urine that elicits social behavioral responses in mice. Based on these observations, the central hypothesis for the proposed research is that the MUPs are an integral component of pheromone signaling. To test this hypothesis the following specific aims are proposed: 1) Establish which MUPs are expressed in the liver, secreted into the urine, and transmitted between animals. 2) Define genetically the function of MUPs in pheromone signaling. 3) Define the function of liver specific MUPs in regulating social behavior. These aims will be tested using genomic and molecular genetic strategies to elucidate the extent to which MUPs function in pheromone signaling.

DESCRIPTION (provided by applicant): Neural information processing utilizes an unfathomable number of discrete circuits composed of seemingly similar neurons dedicated to specific and diverse tasks. Elucidation of the temporal activity, spatial organization, or molecular differences among neurons that lead to distinct perceptual, neuroendocrine, or behavioral outcomes is critical to the design of effective therapeutic intervention. The molecular-genetics revolution of the investigation of chemosensory-mediated behavior has provided the potential to identify, manipulate, and reveal the mechanisms that underlie individual neural circuits. Though great progress has been made in identifying groups of receptors and neurons that participate in chemosensory information coding we do not know the specific ligands and neural circuits that mediate any defined behavior in a mammalian model. The objective of this research is to identify the pheromone ligands, responding sensory neurons, and necessary neuronal circuits that mediate a specific social behavior in the mouse. 1) We will use a novel chemical capture method to chemically tag, enrich, and profile small molecules of any physicochemical class to identify the specific pheromones that encode a single defined behavior. 2) We expect that an individual behavior is mediated by a dedicated subset of chemosensory neurons. We will use calcium imaging combined with molecular and histochemical methods to define the sensory neurons that promote the behavior. 3) Social behavior in rodents is plastic; the age and gender of the receiving animal determines whether it will respond. We predict that neuronal pathways that are active in responding animals are inactive, not present, or spatially distinct from those activated in non-responding animals. We will analyze mice expressing a novel genetic reporter of cFos activation to define and manipulate the neural circuit underlying a single behavior. We expect that at the completion of these aims we will have made an important first step that will allow us to predictably activate social behavior in mice and therefore define at the cellular and molecular level underlying mechanisms of neural function and dysfunction.

DESCRIPTION (provided by applicant): Social behavior is evolutionarily conserved and highly stereotypic. Emission and detection of specialized chemosensory odorants appropriately regulates mouse social behavior through primary circuits that stimulate the amygdala and hypothalamus. Though chemosensory ligands are not thought to regulate human behavior, studies from stroke and trauma victims have revealed that the same subnuclei within the amygdala and hypothalamus that are activated by chemosensory ligands in the mouse function in humans to similarly generate social behavior. The precise subsets of neurons that generate stereotyped behavior are unknown in any species. We have now identified a protein family of 31 chemosensory ligands that promote stereotypic behavior. The objective of this research is to use this natural toolbox of chemosensory ligands to identify sensory receptors and neural circuits that generate stereotyped behavior. We will systematically manipulate, study, and mutate individuals of this large family of chemosensory ligands to comparatively test, evaluate, and advance our understanding of the organization of the sensory neurons, neural circuits, and central nuclei that generate behavior. 1) We will use calcium imaging to isolate specific neurons that detect these ligands and molecular analysis to identify candidate sensory receptors. 2) We will analyze and compare cFos activity in the brain following exposure each of our 31 ligands in order to identify the neural code associated with each ligand. 3) We will mutate our ligands through the generation of chimeras and rational protein design to selectively activate subsets of sensory neurons and investigate their ability to generate behavior. We expect that at the completion of these aims we will have made important steps towards elucidating the neuronal code that initiates innate behavior and enable us to define at the cellular and molecular level, underlying mechanisms of neural function and dysfunction.

This project was developed during a NSF Ideas Lab on "Cracking the Olfactory Code" and is jointly funded by the Chemistry of Life Processes program in the Chemistry Division, the Mathematical Biology program in the Division of Mathematical Sciences, the Physics of Living Systems program in the Physics Division, the Neural Systems Cluster in the Division of Integrative Organismal Systems, the Division of Biological Infrastructure, and the Division of Emerging Frontiers.

The mammalian sense of smell is arguably the most complex sensory system in the animal kingdom. Hundreds of olfactory receptors are deployed to detect a vast array of chemicals with exquisite sensitivity in complex environments. This collaborative project combines biochemistry, neurobiology, genomics, mathematics and new technologies to understand how the mammalian olfactory system detects, encodes and extracts meaning from chemical stimuli. The goals of this project are to: (1) elucidate fundamental neural mechanisms for how chemical sensation turns into the perception of a smell; (2) produce a vast array of scientific resources to olfactory scientists; (3) provide valuable information for broader audiences, including for molecular evolution, chemical ecology, and flavor and fragrance communities; (4) establish new technologies and mathematical frameworks to study biological systems; and (5) facilitate applied chemical sensing technologies for environmental monitoring, food safety, and homeland security. The project also offers training opportunities from the high school to the postdoctoral trainee level, and educational opportunities and outreach through partnerships with local science museums as well as science learning centers and their media outlets.

This project's efforts are organized around three aims that focus on how information about odor identity and odor valence (attractiveness/aversiveness) is encoded at the level of olfactory receptors (Aim 1); within the olfactory bulb, where odor information is first processed (Aim 2); and the cortical amygdala, where odor codes may integrate with other information streams (Aim 3). Completion of the project entails the development and use a broad array of innovative approaches that include mapping all human and mouse odorant receptors to the chemicals they bind, defining the innate valence of these chemicals using behavioral assays, mapping all odorant receptor projections to the olfactory bulb, functionally characterizing their neural representations in the olfactory bulb and cortical amygdala, and using novel mathematical approaches to understand the underlying structure of odor coding and olfactory neural circuits at the level of sensory neurons, olfactory bulb glomeruli, and amygdala. Progress towards each aim involves close collaborations between team members with diverse expertise, including molecular biology, behavioral neuroscience, in vivo functional imaging, and mathematical and theoretical analysis of complex datasets. The multidisciplinary strategy implemented here promises to lead to an integrated and comprehensive understanding of how mammals sense and make sense of their chemical environments.

The aims of this proposal will determine mechanisms by which the internal state of stress alters neural activity. Even the most logical and brilliant can suddenly turn incoherent when riddled with anxiety. Strikingly, twenty percent of adult Americans suffer from debilitating stress. The inability to faithfully find stress-responsive neurons throughout the brain has stalled the field's ability to discover the mechanisms of precisely how stress impacts neurons to alter behavior. What is needed is a robust experimental platform for us and others to reliably use as a model to investigate how the internal state of stress alters neural function and behavior. Our preliminary data indicates that the state of stress silences subsets of neural activity in easily identified, well defined subsets of mouse olfactory sensory neurons. Stress silencing of neural activity has a black and white effect on behavior; if an individual cannot sense an odor cue they do not appropriately respond to the environment. In itself, this is surprising because it has been thought that the olfactory system is just a passive sensory collector vacuuming up environmental cues and passing that information to the brain. Instead, our preliminary data reveals that olfactory sensory neurons are capable of responding to an individual's current stress state, and that this response inhibits the sensation of olfactory stimulus. In order to determine how sensory neuronal activity is inhibited by the state of stress in both the main and accessory olfactory systems we will 1) elucidate the stress signals from the adrenal glands that are detected by olfactory sensory neurons, 2) identify the receptors on the olfactory sensory neurons that detect stress signals, and 3) determine the molecular mechanisms that enable stress to silence sensory neurons. Completion of these aims will open up new horizons to study the scope of function of olfaction. More broadly, this work will provide a molecular solution for us and others to use as a template for mechanistic study of the action of stress hormones throughout the more complicated brain. We anticipate that these results will precipitate new understanding of how sensory systems, the brain, and the body collectively generate behavior.    

Project Summary How does the brain transform sensory information into complex behavior? The objective of this proposal is to identify the relevant neurons across the brain that are necessary to produce a relatively simple motivated behavior to study and identify fundamental principles underlying coding. Sensory-to-behavior circuits must contain a variety of neural computations such as those that determine the identity and meaning of the sensed cues, gauge internal state, remember previous experience, and command muscle action. However, without knowing all of the parts of a model circuit, studying where and how these computations occur has proven difficult. Currently, complete circuit structure underlying most behaviors is largely unknown, and no complete model circuit has been traversed through the mouse limbic system. Therefore, study of neural coding relies on investigation of single brain regions, such as subdivisions of the amygdala or hypothalamus. Such focus may be akin to blind men touching different parts of an elephant; without perceiving the entirety, interpretation may become distorted. Here we propose that sensation-to-motivated-behavior employs an entire circuit and its study as a whole will accelerate understanding. We will overcome this bottleneck by leveraging the systematic control of the mouse?s olfactory system to elicit urine-marking behavior as an ideal model circuit. Upon smelling females, male mice are motivated to intentionally deposit copious urine marks to advertise their sexual availability. To investigate how this motivated circuit encodes behavior, we will 1) identify a complete, sensory-to-muscle, anatomic circuit that generates behavior, 2) determine the activity patterns of the relevant neurons in relationship to the behavior and to each other, and 3) determine the neural logic across the circuit that integrates internal state and experience. Completion of these aims will provide a unified picture of how a simple motivated behavior is coded in the brain. We expect that it will also provide the experimental means to identify and assign order and structure of basic known and unexpected principles that underlie how information is represented, altered, and integrated as it journeys from initial olfactory sensation to ultimate muscle activity. Once completed, both the approach and resulting knowledge will provide solutions for us and others to use as a template for the mechanistic study of the logic of sensory-to-behavior across other more complex motivated circuits. We anticipate that full knowledge of the parts and activity patterns the complete circuit will provide a crucial first step to understanding of how sensory systems, the brain, and the body collectively generate behavior.