1992 — 2005 |
Buck, Linda B |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Molecular Basis of Olfactory Discrimination @ Fred Hutchinson Cancer Research Center
DESCRIPTION: (Adapted from the Investigator's Abstract) The mammalian olfactory system has a dual function. On the one hand it mediates the detection and discrimination of a vast number of structurally diverse odorants that are perceived as having different odors. On the other, it mediates the detection of pheromones, chemicals released from animals that stimulate neuroendocrine alterations and stereotyped behaviors in members of the same species. In most mammals, olfactory ligands are sensed at two, functionally distinct sites: the nasal olfactory epithelium (OE), which detects odorants, and the vomeronasal organ (VNO), which is thought to be specialized to detect pheromones. The VNO has been implicated in a variety of pheromone effects in rodents, including stereotyped aggressive and mating behaviors, inhibitory and stimulatory effects on estrus cycle and the onset of puberty, and "pregnancy block," a pheromone effect that appears to involve chemical individuality cues that distinguish mice of different strains. Urine appears to be a source of many of these effects. However, very few pheromones have been chemically identified, and the mechanisms by which they are detected are not yet known. Three families of sensory receptors have been identified in the olfactory system: one family of about1000 odorant receptors (ORs), expressed in the OE, and two smaller families of receptors in the VNO, the V1Rs and V2Rs, with about35 and about140 members, respectively. All three families have characteristic features of G protein coupled receptors, and members of all three families are diverse, suggesting that each family detects a variety of ligands. The presence of two large families of receptors in the VNO raises a number of questions. One is why there are two distinct families of VNO receptors. Another is why there are so many. Does one family recognize pheromones, and the other individuality cues? Do the two families detect pheromones that elicit different effects? Are some V1Rs and V2Rs expressed in only males or females? The major aim of this proposal is to gain insight into the mechanisms underlying pheromone detection by characterizing the composition and structure of the mouse V1R and V2R gene families, their expression in the VNO of male, female and neonatal animals, and their ligand recognition properties.
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1994 — 1998 |
Buck, Linda B |
P01Activity Code Description: For the support of a broadly based, multidisciplinary, often long-term research program which has a specific major objective or a basic theme. A program project generally involves the organized efforts of relatively large groups, members of which are conducting research projects designed to elucidate the various aspects or components of this objective. Each research project is usually under the leadership of an established investigator. The grant can provide support for certain basic resources used by these groups in the program, including clinical components, the sharing of which facilitates the total research effort. A program project is directed toward a range of problems having a central research focus, in contrast to the usually narrower thrust of the traditional research project. Each project supported through this mechanism should contribute or be directly related to the common theme of the total research effort. These scientifically meritorious projects should demonstrate an essential element of unity and interdependence, i.e., a system of research activities and projects directed toward a well-defined research program goal. |
Expression Zones in Mammalian Olfactory Epithelium @ University of Maryland Baltimore
The mechanisms underlying perceptual acuity in the olfactory system are not well understood. We have identified a multigene family that codes for hundreds of diverse odorant receptors that are expressed by olfactory sensory neurons in the nasal cavity. We have recently obtained evidence that these receptors are expressed in distinct spatial patterns that may provide for an initial organization of incoming sensory information in the olfactory epithelium prior to its transmission to the olfactory bulb. It appears that the olfactory epithelium is divided into a limited number of odorant receptor expression zones. These zones are bilaterally symmetrical in the two nasal cavities and are the same in different individuals. Each receptor gene may be expressed in only one zone. However, many different receptor genes are expressed in the same zone and each gene is expressed in neurons that are scattered throughout the zone. It appears that the developing neuron, in choosing which receptor gene to express, may be confined to a strictly defined zonal gene set, but may select a member of that set via a stochastic mechanism. The proposed studies will investigate how the highly specified zonal organization of odorant receptor gene expression is achieved and examine the functional significance of this organization. An in vitro neurogenesis system will be used to determine whether zonal patterning is intrinsic to the olfactory epithelium or is imposed by the olfactory bulb via retrograde signals. In order to gain insight into the molecular mechanisms underlying zonal patterning, we will use chromosomal in situ hybridization to examine the genomic organization of the zonal gene sets. To identify molecules which act as zone specifiers, we will: l) examine whether zone specific sequence motifs are present in the 5' flanking sequences of odorant receptor genes and, if so, use these motifs to identify DNA binding proteins that recognize these motifs, 2) perform PCR reactions with degenerate primers to identify members of known families of DNA binding proteins that are differentially expressed in the different zones, 3) perform a broad search for zone specific RNAs using the differential RNA display method. Finally, in a series of collaborative studies, we will ask whether the odorant receptor expression zones behave as functional units when the olfactory epithelium is exposed to odorants. Together, these studies should provide a great deal of information about the functional significance of the expression zones and the molecular mechanisms by which they are specified. Since the mechanisms that are used to achieve the functional organization of the olfactory system are likely to be shared by other parts of the nervous system, these studies are likely to contribute to a broad understanding of nervous system development and function.
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2001 — 2005 |
Buck, Linda B |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Molecular Analysis of Olfactory Sensory Imputs @ Fred Hutchinson Cancer Research Center
DESCRIPTION (From the Applicant's Abstract): The olfactory system resembles other sensory systems in its ability to translate sensory stimuli into distinct perceptions. However, it offers unique opportunities to use molecular approaches to elucidate how information is extracted from sensory stimuli and then organized in the brain to yield different perceptions. This opportunity stems from the finding that odorant detection is mediated by approximately 1000 different odorant receptors (ORs), which are expressed by olfactory sensor neurons (OSNs) in the nasal olfactory epithelium (OE). From the OE, signals are relayed through the olfactory bull (OB) and then the olfactory cortex (OC) to other brain areas. Each OSN expresses one OR gene. In the OE, 4 zones express different sets of ORs. OSNs expressing the same OR are scattered in one zone. However, their axons converge in a few specific OB glomeruli, generating a precise map of OR inputs. The functional significance of the patterning of the OE and OB is not yet understood, nor is it known how OR inputs are organized beyond the OB. Another important question is how information about diverse odorant structures is organized to yield different odor perceptions. Recently we found that different odorants are recognized by different combinations of ORs. A single odorant was recognized by both highly related and divergent ORs, and some ORs distinguished among odorants that differed by a single functional group whereas others did not. In the studies described in this proposal, we will further explore how olfactory information is obtained from odorant structures by the OR family. We will also examine how that information is organized in the olfactory system. We will first use a combination of calcium imaging of OSNs and single cell PCR to identify ORs for n-aliphatic odorants that have the same carbon chains, but a variety of different functional groups. We will then express each of the ORs in a cell line and further characterize their odorant specificities. Based on our previous findings, we expect to identify both highly related and divergent ORs, some of which will distinguish odorants that differ in functional group and others that will not. Using in situ hybridization, we will then ask whether there are correlations between the function of an OR, or its structure, and either zones in the OE or the particular arrangement of glomeruli in the OB. Finally, we will use gene targeting to generate mice that coexpress a transneuronal tracer with a single OR gene in order to determine how inputs from individual ORs are organized in the OC and whether inputs from ORs for odorants with different functional groups are targeted to specific cortical regions.
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2006 — 2010 |
Buck, Linda B |
P01Activity Code Description: For the support of a broadly based, multidisciplinary, often long-term research program which has a specific major objective or a basic theme. A program project generally involves the organized efforts of relatively large groups, members of which are conducting research projects designed to elucidate the various aspects or components of this objective. Each research project is usually under the leadership of an established investigator. The grant can provide support for certain basic resources used by these groups in the program, including clinical components, the sharing of which facilitates the total research effort. A program project is directed toward a range of problems having a central research focus, in contrast to the usually narrower thrust of the traditional research project. Each project supported through this mechanism should contribute or be directly related to the common theme of the total research effort. These scientifically meritorious projects should demonstrate an essential element of unity and interdependence, i.e., a system of research activities and projects directed toward a well-defined research program goal. |
Effects of Aging On the Olfactory Cortex
laboratory mouse; respiratory epithelium
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2008 — 2012 |
Buck, Linda B |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Molecular Mechanisms of Olfaction in Mammals @ Fred Hutchinson Cancer Research Center
DESCRIPTION (provided by applicant): In mammals, volatile odorants are detected by olfactory sensory neurons (OSNs) in the olfactory epithelium (OE) of the nose. In response to odorants, OSNs transmit signals to the olfactory bulb (OB) of the brain, which relays signals to the olfactory cortex (OC). The OC sends information to yet other brain areas involved in odor perception and the emotional and physiological effects of odors. Odorant detection in mice is mediated by ~1000 different odorant receptors (ORs), each expressed by a different subset of OSNs. ORs are used in a combinatorial manner to detect odorants, thereby allowing discrimination of a seemingly unlimited variety of odorants. However, we recently identified a second family of fourteen chemosensory receptors in the mouse OE. Genes encoding these receptors, called `trace amine-associated receptors' (TAARs) are present in mouse, human, and fish, and are found in both fish and mouse OE. Like ORs, individual mouse TAARs are expressed in unique subsets of OSNs that express only that receptor, and OSNs with the same TAAR are dispersed within certain OE domains. These findings indicate that there are multiple subsets of OSNs that use different TAARs rather than ORs to detect chemosensory stimuli. Screening of TAARs with diverse odorants revealed ligands for several TAARs, all of which are small volatile amines. Strikingly, at least three mouse TAARs recognize amines found in urine. One detects a compound linked to stress while the other two detect compounds enriched in male versus female urine, one reportedly a pheromone. The evolutionary conservation of the TAAR family suggests that this family may have a chemosensory function distinct from ORs. Ligands identified for TAARs thus far hint at a function associated with the detection of social cues. In the proposed studies, we will further investigate the roles played by TAARs in the mouse. To identify compounds recognized by TAARs with unknown ligands, we will screen a wide variety of amines for activation of individual TAARs. We will also use calcium imaging of TAARs expressed in a cell line to ask whether most or all TAARs detect compounds in mouse urine and, if so, whether those compounds are differentially represented in the urine of mice of different genders, ages, or genetic backgrounds. We will then examine how TAAR signals are represented in the OB. First, we will use TAAR gene probes to examine to number and positions of glomeruli that receive input from individual TAARs. Next, we will use mice coexpressing axonal reporters with selected TAARs to determine whether or not there are TAAR-specific glomeruli. Then, we will use c-Fos to examine the responses of individual TAAR glomeruli to identified TAAR ligands as well as to mouse urine from different sources. Finally, we will prepare mice that coexpress a transneuronal tracer with single TAAR genes to investigate how TAAR signals are organized in the OC.Project Narrative The mechanisms that the brain uses to perceive the world around us and to learn and remember are unknown. We will investigate the mechanisms that underlie the sense of smell to gain insight into these questions.
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2016 — 2020 |
Buck, Linda B |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Mechanisms Underlying Innate Odor Fear @ Fred Hutchinson Cancer Research Center
? DESCRIPTION (provided by applicant): Defensive responses to danger are essential to survival and are seen throughout the animal kingdom, including in humans. In rodents, predator odors stimulate instinctive fear responses that include characteristic behaviors and increases in blood levels of stress hormones. The stress hormone response to predator odors and other stressors results from activation of the HPA (hypothalamic-pituitary-adrenal) axis, which involves a subset of corticotropin releasing hormone (CRH) neurons in the hypothalamus. In humans, as in rodents, stressful stimuli increase blood levels of stress hormones, suggesting the evolutionary conservation of mechanisms underlying physiological responses to fear and stress. Dysregulation of the HPA axis is seen in certain human psychiatric conditions, further suggesting that an understanding of the neural mechanisms that control stress hormones in rodents might ultimately provide insights relevant to human disease. The stereotyped nature of fear responses to predator odors in mice suggests the existence of genetically determined neural circuits that include olfactory receptors (ORs) in the nose that selectively detect those odors and specific subsets of brain neurons that receive signals from those receptors and generate their profound downstream effects on physiology and behavior. To gain insight into the molecular mechanisms and neural circuits that underlie stress hormone responses to predator odors, we propose to employ a combination of tools, including neural circuit tracing with neurotropic viruses that travel across one or multiple synapses, next generation RNA sequencing (RNA-Seq), high throughput screening, analyses of neural activity markers, and pharmacogenetic manipulation to activate or silence specific subsets of neurons. Using these tools, we will identify receptors in the nose that transmit signals to CRH neurons, identify odor molecules detected by those receptors, and determine whether the individual odor molecules stimulate stress hormone increases that mimic fear or instead block stress hormone increases, as it now appears some odors can do. To determine how the receptor signals are translated into specific responses by the brain, we will test the hypothesis that this is accomplished via the actions of specific subsets of neurons in the olfactory cortex and by selected non- olfactory brain areas that relay fear signals from the olfactory cortex to CRH neurons. To do this, we will investigate the locations of neurons in the olfactory cortex and other brain areas that are activated by predator odors and have the ability to transmit signals to CRH neurons. By activating and inhibiting neurons in specific areas, it will be possible to assess whether individual areas can either induce or suppress fear and whether those areas are required for the transmission of excitatory or inhibitory signals to CRH neurons that affect stress hormones. Together, these studies should provide significant insights into the molecular mechanisms and neural circuits that govern the profound impact of fear and stress-inducing odor stimuli on physiology.
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2018 — 2021 |
Buck, Linda B |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Mechanisms Underlying Olfactory Effects On Appetite @ Fred Hutchinson Cancer Research Center
Appetite is a basic drive that is essential to survival. The olfactory system can have potent effects on appetite in mammals, with certain odors stimulating appetite in humans, and either increasing or decreasing food intake and body weight in rodents. In the mouse, as in other mammals, olfactory sensory signals travel from olfactory sensory neurons in the nasal olfactory epithelium through the olfactory bulb to the olfactory cortex and then to other brain areas. Odorants are detected in the nose by ~1000 different odorant receptors (ORs), each expressed by a different subset of sensory neurons. Neurons with the same OR are scattered in one nasal spatial zone, but their axons converge in a few specific glomeruli in the olfactory bulb, creating a semi- stereotyped sensory map in which each glomerulus and its associated mitral and tufted relay neurons, which project to the cortex, appears dedicated to one OR. Signals from each glomerulus travel to multiple distinct areas of the olfactory cortex. How the vast array of sensory information generated by this organization might impact appetite is unexplored. To begin to investigate this question, we conducted preliminary studies on olfactory inputs to two subsets of neurons linked to appetite, both of which are located in the arcuate nucleus of the hypothalamus: AGRP (agouti related peptide) neurons, which can enhance appetite, and POMC (pro- opiomelanocortin) neurons, which can suppress appetite. We found that only some odors affect the activity of AGRP or POMC neurons and that different odors activate AGRP versus POMC neurons. Using a Pseudorabies virus (PRV) that travels retrogradely across multiple synapses, we found evidence for neurons upstream of AGRP and POMC neurons in the olfactory cortex, but only in certain olfactory cortical areas. These observations are consistent with the idea that some olfactory sensory inputs can have innate effects on appetite and that those effects involve genetically programmed neural circuits that convey signals from specific ORs in the nose through the olfactory system to hypothalamic neurons that regulate appetite. In the studies proposed in this application, we will test the hypotheses that 1) AGRP and POMC neurons can receive input from selected ORs that are similar among individuals and recognize odorants that affect the activity of the appetite neurons and appetite behaviors, 2) neurons within specific areas of the olfactory cortex can influence AGRP or POMC neuron activity and appetite-associated behaviors, and 3) odor-responsive neurons in other brain areas can relay signals from the olfactory cortex to AGRP or POMC neurons to modulate their activity and regulate behaviors associated with appetite. Together, these studies should provide significant new insights into the molecular mechanisms and neural circuits that govern the impact of olfactory sensory signals on appetite.
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2018 — 2021 |
Buck, Linda B |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Odor Blocking of Stress @ Fred Hutchinson Cancer Research Center
ABSTRACT The mammalian olfactory system detects a multitude of volatile chemicals perceived as scents. In animals, it also detects predator odorants that stimulate instinctive fear responses essential to survival. These defensive responses include increases in blood levels of stress hormones, which result from activation of the HPA (hypothalamic-pituitary-adrenal) axis. A small subset of corticotropin releasing hormone (CRH) neurons in the hypothalamus of the brain plays a key role in the HPA axis. Stressful stimuli increase blood levels of stress hormones in humans as well as in rodents, suggesting the evolutionary conservation of mechanisms underlying physiological responses to fear and stress. Moreover, chronic stress has been linked to some human diseases and dysregulation of the HPA axis is seen in certain human psychiatric conditions, further suggesting that an understanding of the neural mechanisms that control stress hormones in rodents might ultimately provide insights relevant to human disease. The stereotyped nature of stress hormone responses to predator odors in mice suggests the existence of genetically determined neural circuits that convey predator odor signals from the nose through higher olfactory areas to CRH neurons. Consistent with this idea, we recently discovered that a small brain area that occupies less than 5% of the olfactory cortex plays a key role in stress hormone responses to volatile predator odorants detected in the nose. Surprisingly, we and others have obtained evidence that certain common odorants can block stress hormone responses to a predator odor. Our studies further indicate that some odorants also block stress hormone responses to a potent non-olfactory stressor, physical restraint. We propose a series of experiments to investigate the neural circuit mechanisms underlying these unexpected effects of common odorants on stress. In the proposed studies, we will employ a combination of tools to investigate where and how common odorants act in the brain to modulate stress. These include the charting of neural pathways using neurotropic viruses that travel across one or multiple synapses, induction of Cre recombinase expression in stressor- and blocking odorant-responsive neurons, single cell transcriptome analysis to define neurons involved in stress responses and their blocking by common odorants, and chemogenetic and optogenetic silencing of subsets of neurons in specific brain areas. Together, these studies should provide important insights into how odors that appear innocuous can have profound modulatory influences on physiological responses to fear and stress that can be important to survival but, when dysregulated, can predispose to disease.
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