Daniel W. Wesson, Ph.D. - US grants

Humans and other animals use odors to guide a variety of behaviors critical for survival. However, the neural mechanisms by which odor molecules in the environment are processed within the brain to yield perception are not resolved. Surprisingly, even a basic description of what types of odors are represented by one major olfactory structure, the olfactory tubercle (OT), is not available. Elucidating the role of the OT in olfaction will help clarify the process of olfactory perception. Therefore, the present proposal describes an experimental strategy aimed to elucidate the contributions of the OT to olfactory processing by combining neurophysiological, behavioral and computational methods in mice. It is predicted that OT neurons will display a unique representation and responsivity to odors in comparison to another primary olfactory cortex (the piriform cortex). Further, it is predicted that OT neuronal activity in response to odors will dramatically differ based upon behavioral state, including anticipation and reward-conditioning, thus positioning the OT as a link between perception and behaviorally-relevant processes. Together, these findings will enhance our understanding of information processing and, more specifically, how olfactory perception is formed within the brain. Broader impacts resulting from the proposed activity include the training of high school, undergraduate, and graduate students in core aspects of neurophysiology and behavioral neuroscience. The project will extend special effort to involve women and under-represented minorities. Furthermore, it will provide a mechanism to bridge ties between local (Cuyahoga county) high schools and colleges (Cleveland State U. and John Carroll U.) and the Case Western Reserve University (CWRU) by allowing students exposure to scientific training through aspects of this proposal.

? DESCRIPTION (provided by applicant): On a daily basis, sensory stimuli acquire learned values that inform our essential behaviors. Understanding the neural substrates for the emotional associations of stimuli, sometimes referred to as valence, will yield important insights into a wide range of human conditions. The mammalian olfactory system provides a simple model for understanding the neural mechanisms of stimulus valence. Second order neurons in the olfactory bulb distribute odor information into several secondary structures, including the olfactory tubercle (OT) and piriform cortex (PCX). Odor information at this stage is shaped and later transmitted into tertiary structures involved in reward, emotion, and learning, which in turn provide feedback upon the secondary structures. The present proposal seeks to address fundamental principles of odor valence coding in the OT and PCX, and in doing so will resolve major questions regarding the inter-regional processing and storage of stimulus valence. Experiments will be performed in rodents engaged in an operant olfactory task, along with simultaneous multi- electrode single-unit recordings, and in some cases, neural perturbations using chemical-genetics. Using this approach, we will determine whether secondary structures are specialized to code for odor valence (Aim 1). Next we will exploit the connectivity of secondary olfactory structures to determine the dependence of the OT and PCX upon each other for odor valence coding (Aim 2). Finally, we will determine if and how valence coding in the OT and PCX depends upon top-down modulation by a prominent tertiary association structure with known importance for valence (Aim 3). Together, these investigations will provide fundamental information on the mechanisms of odor information processing, the behavioral relevance of these coding schemes, and the critical interactions between secondary and tertiary olfactory structures.

Project Summary/Abstract Hyposmia, the reduced ability to smell, is very common in Parkinson?s disease (PD). Almost 90% of PD patients have hyposmia, which often develops about a decade before motor symptoms manifest. The pathology of PD is characterized by the presence of aggregated ?-synuclein in neurons across the brain; ?-Synuclein aggregation is believed to start in the olfactory brain regions, especially the olfactory bulb, and then spreads to other structures in the brain. The manifestation of the symptoms in PD is therefore believed to reflect the spreading of the pathology, explaining why olfactory deficits would manifest before other symptoms. In addition to ?-synuclein aggregation, there are other key processes that normally associate with PD ? neuronal death and neuroinflammation. There is, however, a fundamental gap in knowledge regarding the pathogenic mechanisms which cause hyposmia in PD. Thus, the objective of this multi-PI project is to establish how the progressive spreading of aggregated ?-synuclein from the olfactory bulb to other olfactory structures, and the associated neural cell death and neuroinflammation, trigger hyposmia. To this end, we will perform sophisticated measures of olfactory function (Wesson) in an experimental paradigm that we recently developed and which recreates spreading of ?-synuclein pathology across olfactory structures associated with olfactory deficits (Brundin). With this approach we will define the links between olfactory dysfunction and key underlying mechanisms of early PD, testing the hypothesis that ?- synuclein pathology progression from the olfactory bulb induces widespread neurodegeneration, protein aggregation, and neuroinflammation in the olfactory system, resulting in impaired olfaction. Specifically, we aim to demonstrate that ?-synuclein pathology affects odor information processing and to identify neuropathological underpinnings of these olfactory deficits. Further, we will test innovative approaches to modulate pathogenesis and to determine whether these interventions can improve olfactory function and/or stop the spreading of the pathology. These findings will provide fundamental information on the olfactory system and on how olfaction is impacted by specific neurodegenerative processes. We expect that our findings will eventually facilitate the development of therapeutic approaches to prevent the development of olfactory deficits associated with the spreading of ?-synuclein pathology across olfactory structures. Since these therapies should also prevent the spreading of ?- synuclein pathology to other brain regions, they have the potential to become disease-modifying interventions against PD.

PROJECT SUMMARY Substance abuse and misuse pose significant costs to society and represent a global disease burden. Relapse after a period of drug-free abstinence is one of the most profoundly debilitating aspects of addiction, occurring in 40?80% of individuals. Understanding the neurobiological mechanisms of drug taking and relapse will ultimately lead to better therapeutic interventions. The ventral striatum is a network of brain structures implicated in compulsive drug-seeking and includes the ventral pallidum, nucleus accumbens (NAc), and olfactory tubercle (OT). The OT, like the NAc, is a site of massive innervation of dopaminergic neuron terminals from the ventral tegmental area in the midbrain. Rodents self-administer psychoactive substances and electrical current into the OT, and more readily administer cocaine into the OT than even NAc. Further, our lab has uncovered that the activity of OT neurons robustly reflects reward-guided behaviors and rewards. Despite this evidence pointing towards a role for the OT in mediating reinforcement, little is known about the OT, and at present, the OT is not included in mainstream models of the reward system. The short-term goal of the parent project is to build off both our published and unpublished studies positioning the OT in the reward circuitry to determine mechanisms whereby the OT exerts control over cocaine seeking and taking. Our overall hypothesis is that there is a functional organization amongst ventral striatum subregions which influences drug seeking. The goal of this administrative supplement is to provide summer research opportunities to a NIDA research intern. The intern will engage in projects using in vivo physiological methods to demonstrate manners whereby OT neurons, including OT medium spiny neurons, represent drug seeking (Aim 2), and those projects employing cell-specific optogenetic methods to determine the regulation of reinforcement and drug-seeking by OT neurons (Aim 3). The results of this project will answer long-standing questions about the fundamental circuitry of the OT and its significance in the context of motivated behavior and drug-seeking. Together this project will contribute to our long-term goal of generating a more complete model of the brain's reward system.

E-cigarettes are increasingly used by teenagers, who are particularly vulnerable to the addictive properties of nicotine. With the exclusion of menthol, the use of flavor additives has been banned from traditional cigarettes, while e-cigarettes (e-cigs) are marketed in over 7,000 different flavors. We hypothesize that flavorants enhance nicotine reward through sensory and/or natural reward mechanisms. As a consequence, flavored e-cigs may promote nicotine experimentation, dependence, and eventually, the use of regular cigarettes. Despite the fact that the FDA has recently regulated the sales of flavored e-cigs to minors, no flavor ban has been implemented, and adolescents could still obtain flavored e-cig products through friends or unscrupulous sellers. Furthermore, understanding how flavors influence e-cig use is important for the implementation of regulatory rules that can reduce potential disease and death deriving from the consumption of this increasingly popular tobacco product. The overall goal of this application is to compare the rewarding and reinforcing properties of flavored vs. non-flavored e-cigs in adolescent and adult mice, and identify the neural substrates responsible for the enhancing effects of flavorants. Our hypothesis is that flavored e-cigs are more rewarding than non-flavored e-cigs and that flavor additives promote and sustain nicotine seeking in adolescents due to the combined influence of flavorants and nicotine on the ventral striatum. The first goal is to determine whether flavorants enhance adolescent nicotine reward and promote nicotine self- administration, and compare their effects in adult mice. The second goal is to understand how e-cig flavorants are encoded in the ventral striatum during acquisition of e-cigarette vapor preference and self-administration. The third goal is to determine whether exposure to e-cig flavorants alters synaptic plasticity in the ventral striatum and whether it modifies cellular responses to nicotine. Our experiments will combine behavioral approaches with tetrode recordings during behavior and brain slice electrophysiology to determine how e-cigarette nicotine vapor affects reward-associated brain areas, and whether flavorants (e.g. fruit or mint) have additive or synergistic effects.

Project Summary The striatum is an evolutionarily conserved structure involved in cognitive and limbic regulation of motor control. Striatal circuits are implicated in the initiation and execution of ethologically relevant motor output, ranging from exploratory actions to highly stereotyped motor patterns. Dysfunction of these circuits leads to motor control abnormalities that frequently manifest as excessive repetitive behaviors. Self-directed grooming, a highly stereotyped repetitive motor pattern, is observed in virtually all animals, serving vital functions in hygiene maintenance, thermoregulation, de-arousal, stress reduction, and social communication. Abnormally repetitive grooming is a central behavioral phenotype observed in numerous models for neurological and neuropsychiatric diseases. A better understanding of the neural control of grooming may thus yield fundamental insights into how the brain controls repetitive motor output in both normal and diseased conditions. Our preliminary work suggests that an understudied population of interneurons within the olfactory tubercle (OT; the most ventral part of the striatum), predominantly in the Islands of Calleja (IC), is involved in mediating this behavior. The striatum has a fairly uniform cellular composition, with ~95% of the neurons being spiny projection neurons (SPNs), classified as D1- or D2-type according to the dopamine receptors they express. One exception to this uniformity is the existence of evolutionarily conserved IC, clusters of densely- packed, GABAergic granule cells, which express the D3 dopamine receptor. By means of optogenetic manipulations, we have shown that activation of OT D3 neurons initiates robust grooming behavior via arrest of other alternative ongoing behaviors. In contrast, inactivation of these neurons halts ongoing grooming. These findings lead to the central hypothesis that OT D3 neurons play critical roles in controlling grooming behavior. Through an array of modern neuroscience approaches (optogenetics, ex vivo and in vivo electrophysiology, fiber photometry, neural circuit tracing, and behavior), we will pursue three specific aims to determine (1) in vivo activity patterns of OT D3 neurons and SPNs in grooming and other behaviors, (2) contributions of OT D3 neurons to grooming in relation to other brain regions, and (3) the effects of dopamine release into the OT on grooming behavior. Overall, this project will provide insights into the neural circuitry of the IC/OT D3 neurons and its role in neurobiological control of a highly important motor pattern.