Jim Fadel - US grants

[unreadable] DESCRIPTION (provided by applicant): This proposal explores differences in temperament (anxiety) and gene expression (NPY) patterns in the amygdala as examples of endophenotypes that may contribute to ethanol consumption. Alcohol abuse and dependence is a complex disorder resulting from gene-environment interactions, but the genes encoding neuropeptide Y (NPY) or its receptor appear to confer risk for alcohol dependence in clinical and preclinical studies. This proposal expands our earlier studies and will explore the causative relationship between gene expression of NPY in the amygdala, an anxious behavioral phenotype, and ethanol consumption using the inherent phenotypic variation in anxiety seen in a rat model. The amygdala plays a critical role in anxiety-related behaviors and the anxiolytic effects of NPY may be mediated through the amygdala. Our previous studies have shown that rats with an anxious or nonanxious phenotype, defined using exploration of the elevated plus maze, display differences in ethanol preference. Changing NPY expression in amygdala also shifts ethanol preference, but only in anxious rats. Given the evidence that amygdala NPY levels regulate anxiety-related responses, the present application examines the hypothesis that NPY gene expression levels in the amygdala determine the anxiety phenotype of an individual, and low NPY levels may predispose animals for greater ethanol consumption based on this anxious phenotype. Aim 1 examines if altered NPY expression in amygdala changes anxiety state and subsequently modifies ethanol consumption in a two bottle self-administration procedure. This aim will develop lentivirus-mediated gene transfer methodologies to more directly test if lowering NPY expression in the amygdala enhances anxiety and thereby promotes ethanol consumption and/or if enhanced amygdala NPY gene expression is anxiolytic and thereby reduces ethanol preference. This Aim also characterizes anxiety phenotypes using additional behavioral models. Aim 2 will examine ethanol consumption in anxious and non-anxious phenotypes using a limited access model. This limited access method will allow more efficient screening of gene targets for development of therapeutic strategies to combat alcohol dependence. Aim 3 will examine if the pattern of neuronal activation in the amygdala (and other regions) differs with elevated plus maze exposure in the anxious and non-anxious phenotypes, and if NPY neurons are activated by ethanol injection or ethanol consumption during a limited access period. Combined with viral vector methods characterized in this developmental R21 grant these studies will lead to better characterization of specific aspects of the anxiety phenotypes regulated by NPY gene expression in the amygdala, and a better understanding of how these differences in anxiety phenotype and NPY gene expression predict ethanol consumption. [unreadable] [unreadable] Public Health Relevance: Although stress and anxiety contribute to alcohol consumption and abuse, the brain systems that predispose certain individuals to abuse alcohol and how alcohol relieves anxiety states remains unknown. The present studies use animal models to elucidate how the genes expressed in the brain region underlying emotional behaviors, namely the amygdala, control individual responses in an anxiety-provoking situation and if these same processes contribute to the alcohol consumption. The studies will provide a better understanding of how individual differences in gene expression underlie the interaction between stress and alcohol abuse, and may lead to novel targets to combat the growing problem of alcohol consumption in adolescents and adult populations. [unreadable] [unreadable] [unreadable]

[unreadable] DESCRIPTION (provided by applicant): The aging U.S. population has resulted in substantial increases in resources allocated to the prevention and treatment of age-related neurodegenerative conditions. Normal cognitive and homeostatic functions are major determinants of the capacity for independence and quality of life in the elderly. A growing body of data suggests that changes in homeostatic function, such as unexplained weight loss late in life, frequently precedes and may predict subsequent development of mild cognitive impairment or Alzheimer's disease. An intriguing hypothesis - based in part on the heuristic observation that proper behavioral responses to homeostatic challenges, such as food or water deprivation, entail a cognitive component - is that age-related changes in homeostatic function and cognitive decline may be mechanistically linked. This hypothesis is supported by studies showing clear anatomical connections between certain hypothalamic regions classically associated with homeostatic function and rostral brain regions, such as the basal forebrain cholinergic system (BFCS), that play crucial roles in cognition. Impairment of cognitive abilities dependent on the integrity of the cholinergic system is an early and consistent feature of age-related dementias, even in the absence of frank loss of cholinergic neurons, suggesting that changes in the afferent regulation of the BFCS may underlie some types of age-related cognitive decline. We have recently described a dense innervation of the BFCS by hypothalamic orexin/hypocretin neurons and shown that this input is dramatically reduced in aged animals. Orexins play prominent roles in multiple aspects of homeostasis but the conditions that activate orexin inputs to the basal forebrain and the functional implications of these interactions are largely unknown. Here, we propose a multi-level (neurochemical, anatomical, behavioral, genetic) approach to elucidate the role of orexin-cholinergic interactions in responses to homeostatic challenges and age-related cognitive decline. Aim 1 will combine lesion and pharmacological approaches to determine the role of orexin peptides in cortical acetylcholine release. Aim 2 will examine the role of orexin-ACh interactions in age-related deficits in activation of the BFCS as well as the ability of ectopic administration of orexins via direct intracranial administration or by lentiviral- mediated gene transfer to restore normal cholinergic function. Aim 3 will determine age-related effects of intra-basalis administration of orexins on attentional function. Collectively, these experiments will comprise a systematic description of the importance of orexin-acetylcholine interactions in arousal and how alterations in these interactions may contribute to age-related deficits in cognitive function and motivated behavior. The results of these studies will have important implications for understanding the basis of age- related cognitive decline and may suggest novel therapeutic targets for the treatment of these disorders. PUBLIC HEALTH RELEVANCE Compelling clinical data now indicate that Alzheimer's disease and other age-related dementias are often preceded by metabolic disturbances, including unexplained weight loss, years prior to diagnosis of frank dementia. Our novel hypothesis is that some aspects of homeostatic changes and cognitive decline may be mechanistically linked at the neural systems level. Accordingly, these studies are designed to investigate how the hypothalamus regulates the basal forebrain cholinergic system and how these interactions change with aging. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Anxiety and affective disorders represent an important clinical problem, yet our understanding of the disorders and the drugs used to treat them remains limited. Brain imaging studies show amygdala changes in patients with these disorders. The present studies use a multifaceted approach to elucidate how amygdalar opioid systems regulate anxiety and fear-related processes. These studies will enhance our understanding of amygdala circuits that control distinct aspects of anxiety and fear by comparing several anxiety-evoking stimuli, and elucidate the specific role of mu opioid receptors (MOR) in these different responses. Since our previous studies suggested that mu opioid receptors (MOR) and enkephalin in the amygdala can modulate basal anxiety responses and the actions of benzodiazepine anxiolytic drugs, the proposed studies will examine how MOR receptors modulate amygdalar circuitry to alter these anxiety-related responses. We hypothesize that distinct neuronal circuits are activated by different conditioned and unconditioned anxiety-evoking situations, and that presynaptic MOR receptors localized in specific amygdalar neurocircuits regulate changes in amygdala glutamate and GABA release to shift anxiety-related responses in a context-dependent manner. Four anxiety-evoking tests, including the elevated plus maze (unpredictable threat), predator odor-induced defensive burying (specific threat), restraint stress (psychogenic stimulus) and cue- conditioned freezing (learned fear), will be compared in these studies. Aim 1 uses virus-mediated gene transfer to examine if decreasing the expression of MOR in the amygdala alters anxiety-related behaviors and/or endocrine responses to restraint stress, and if selectively targeting these decreases to pyramidal neurons of the basolateral amygdala produces the same effects. Aim 2 uses cFos immunoreactivity to compare the cellular phenotype(s) activated by distinct anxiety-evoking situations, the localization of MOR in these activated neuron populations, and if activation patterns are altered by decreasing amygdala MOR expression. Aim 3 uses in vivo microdialysis in the amygdala to assess 1) if MOR activation alters GABA or glutamate efflux, 2) if anxiety-evoking situations induce release of enkephalin, GABA, or glutamate, and 3) if decreasing MOR expression modifies MOR-induced or anxiety-induced release of GABA or glutamate. The studies will enhance our understanding of how the amygdala and the opioid system regulate anxiety responses, and could provide novel therapeutic strategies for treating affective and anxiety-related disorders. Since opioid systems in the amygdala are modified during chronic pain states and altered by drugs of abuse, the results of these studies will also enhance our understanding of the neural basis of heightened anxiety states seen in chronic pain patients or during withdrawal from opiates, benzodiazepines, and alcohol. Anxiety disorders are the most common mental illness and affect more than19 million US adults, yet our understanding of these disorders and the drugs used to treat them remains limited. The present studies use animal models to elucidate how the circuitry in the brain region underlying emotional behaviors, namely the amygdala, controls responses in three different anxiety-evoking situations. The focus on endogenous morphine-like chemicals (opioids) could lead to new treatment strategies for anxiety disorders, and increase our understanding of why chronic pain states or withdrawal from prescribed or abused opioid drugs lead to increased anxiety.

? DESCRIPTION (provided by applicant): The aging U.S. population has led to substantial increases in resources allocated to the prevention and treatment of age-related neurodegenerative conditions, including disorders of cognitive decline. Alterations in homeostatic functions such as energy balance and sleep patterns are also frequently seen in the elderly and these changes often precede and predict subsequent cognitive decline. A novel hypothesis is that some of these seemingly disparate manifestations of age-related deficits may share underlying neurobiological mechanisms; that is, brain regions that are involved in homeostasis regulate the activity of neurotransmitter systems and brain regions that mediate the appropriate behavioral and cognitive responses to physiological challenges, and these interactions may be impacted in aging. We have shown that aging is associated with loss of hypothalamic hypocretin/orexin neurons-a cell population that regulates energy balance and sleep/wake stability. Because hypocretin/orexin neurons also regulate neurotransmission in brain regions that underlie several aspects of attention, learning and memory we hypothesize that these neuropeptides link physiological function with age-related cognitive decline. The testable corollary to this hypothesis is that upregulation of the orexin/hypocretin system in aging will allow for preservation or restoration of these functions. In Aim 1 we will combine DREADD (designer receptors exclusively activated by designer drugs) and in vivo neurochemical approaches to determine the effect of acute orexin/hypocretin activation or inhibition on behavior and neurotransmission in several relevant brain regions. In Aim 2 we will use virus-mediated gene transfer and to perform chronic manipulations of the orexin/hypocretin system in a longitudinal animal model of aging. We will examine how these manipulations alter food and water intake, body composition and markers of neurotransmitter systems and neuronal activation. In Aim 3 we will test the hypothesis that the hypocretin/orexin system supports attentional performance across the life span using both acute and chronic manipulations of hypocretin/orexin transmission. Collectively, these studies will implicate the orexin/hypocretin system as a major contributing factor in cognitive and homeostatic manifestations of age-related neural dysfunction, and suggest a potential new target for development of therapies that prevent, delay or ameliorate age-related cognitive decline.

Non-technical Abstract

Feeding is an essential activity for the maintenance of life, and its regulation is associated with multiple brain mechanisms that work together to ensure that animals eat appropriately. The complexity of these interactions has presented challenges to our efforts to fully appreciate the neural basis of food intake. However, before we can understand that complexity we must first identify the individual brain circuits that regulate food intake. The main goal of this project is therefore to use advanced genetic and anatomical approaches to identify a novel circuit that contributes to the control of feeding behavior. Identifying this circuit will ultimately allow us to determine how it works together with other feeding circuits that we already know more about to regulate a complex behavior critical for animal survival. In achieving that goal the work will not only increase our understanding of fundamental principles associated with how the brain regulates behavior, but may also lead to unexpected insights into feeding disorders and the chronic medical conditions associated with them that create considerable economic and social burdens, nationally and globally. In addition, this project includes a Summer Internship Program that will provide an integrated research experience for undergraduate students, particularly students who will be recruited from populations that are under-represented in science and medicine. These research experiences will provide such students with experiential learning opportunities that will create a foundation for future success in biomedical or basic research science.

Technical Abstract

Many studies agree that leptin controls food intake through activation of hypothalamic leptin receptors (LepRs). In addition, recent reports have examined the participation of extra-hypothalamic LepRs. In this regard, we have identified neurons in the rat raphe nuclei that are activated by leptin. Intra raphe administration of leptin increases pSTAT3 expression in discrete serotonergic neurons and suppresses food intake. Using optogenetic approaches, we were able to inhibit feeding behavior when the raphe neurons responsive to leptin were photo-stimulated, and we showed that intra-raphe leptin increases hypothalamic 5-HT levels.zpur overarching hypothesis is therefore that, in addition to direct hypothalamic actions, leptin powerfully regulates food intake by activating LepRs located in the raphe nuclei, thus stimulating 5-HT release in the hypothalamic nuclei where 5-HT exerts anorectic effect. The current project will test this hypothesis by studying the functional anatomical serotonergic connections between the raphe and the hypothalamic nuclei, measuring in vivo 5-HT release in the hypothalamic nuclei that receive serotonergic terminals following optogenetic stimulation of leptin responsive neurons of the raphe nuclei; and identifying the phenotype of the hypothalamic neurons that are activated by leptin-stimulated serotonin release. The idea that leptin is acting at multiple target sites including serotonergic neurons in the raphe will advance our understanding of the regulation of feeding behavior. This research will also be used to provide in-depth research opportunities for students from a nearby liberal arts college, particularly students from under-represented populations.