Jeansok J. Kim - US grants

DESCRIPTION (provided by applicant): Memory impairments constitute a major problem in society. These occur naturally with aging and as a result of diseases (e.g., Alzheimer's disease), and are exacerbated by stress. The hippocampus, as part of a brain system necessary for the formation of stable declarative (or explicit) memory appears to be prominently susceptible to uncontrollable stress. Recent rodent studies demonstrate that stress interferes with learning of hippocarnpal-dependent spatial memory and alters the inducibility of long-term potentiation (LTP) and long-term depression (LTD)--two putative synaptic mechanisms of information storage-in the hippocampus. Other studies indicate that the amygdala is critically involved in coordinating stress-related behaviors and modulating hippocampal functioning. Our long-term goal is to understand the amygdalar mechanisms involved in mediating stress effects on hippocampal functioning.There are three specific aims of the project: (1) an IN VITRO ANALYSIS will investigate the role of the amygdala in mediating stress effects on hippocampal LTP/LTD; (2) a BEHAVIORAL ANALYSIS will examine the amygdalar mechanisms mediating stress-induced impairments in hippocampal-dependent spatial memory; and (3) a SINGLE UNIT ANALYSIS of hippocampal place cells will integrate stress effects on hippocampal plasticity and spatial memory. These related aims are designed to test our current working hypothesis that stress-induced alterations in hippocampal functioning are due to excessive activity exerted by the amygdala onto the hippocampus during stress.Data obtained from this project would be of significance (1) from a basic scientific perspective providing valuable information concerning how hippocampal plasticity might be regulated by naturalistic factors (such as stress) and the underlying mechanisms subserving stress effects on hippocampal functioning; and (2) from an applied perspective, providing important insights that will assist in developing therapeutic approaches to alleviate cognitive impairments associated with stress-induced ailments (such as anxiety, posttraumatic stress disorder, vascular dementia) that severely limit the quality of human life.

DESCRIPTION (provided by applicant): Stress contributes to myriad psychopathologies, including anxiety, depression, schizophrenia, and drug use relapse. A common thread binding these disorders appears to be the stress-associated alteration in cognitive processes, namely learning and memory. Considerable human and animal research has shown that the hippocampus, a brain structure necessary for the formation of stable declarative (or explicit) memory, is highly susceptible to stress. Rodent studies further indicate that stress impairs long-term potentiation (LTP), a leading candidate cellular mechanism of information storage, in the hippocampus. We have recently discovered that the amygdala plays a necessary, time-dependent role in the emergence of stress effects on hippocampal LTP and memory. Accordingly, we hypothesize that the amygdala is an important component of the central stress mechanism that regulates neurocognitive functioning. The long-term goal of this research is to construct a general experimental and theoretical basis for understanding how stress influences the hippocampus - from synaptic plasticity to neural activity to behavior - and incorporate this in a systems-level model that can organize existing data, predict new results, and generalize to other cognitive processes impacted by stress. There are four specific aims of the project: (1) an IN VITRO ANALYSIS will investigate the central stress mechanism altering hippocampal LTP;(2) a BEHAVIORAL ANALYSIS will determine the nature of central stress mechanism influencing hippocampal memory;(3) a SINGLE UNIT ANALYSIS will relate stress effects on specific behaviors with the activity of hippocampal neurons;and (4) GENERALIZATION OF THE MODEL will test whether the central stress mechanism identified in the first three aims is applicable to other types of learning and memory. Information generated from this project would be of significance (1) from a basic scientific perspective, providing valuable insights into the neuronal substrates underlying stress effects on neurocognition;and (2) from an applied perspective, providing testable hypotheses for explaining neurobiological changes that occur during stressful situations, thereby allowing insights into and treatment of various stress-related disorders that severely limit the quality of human life in today's increasingly hectic and long-living society.

PROJECT SUMMARY Basic fear research largely employs the Pavlovian fear conditioning paradigm in rodents. While this model systems approach simplifies behavioral and biological analyses of acquisition, maintenance and expression mechanisms of conditioned fear memories, fear conditioning studies cannot address the fact that animals and humans rely on a multitude of actions and decisions to survive the breadth of risky situations in the real world. Hence, there is a need to complement fear conditioning studies with ecologically-relevant fear research that can lead to novel translational insights. This renewal application will continue to employ and enhance our ?approach food-avoid predator? paradigm to investigate the naturalistic workings of the brain?s fear system. Specifically, in Aim 1, we will examine how rats adapt their fear responses, risk-assessment and foraging decisions to more realistic and diverse risky situations by simulating hidden versus visible threats and terrestrial versus aerial predators. We will also determine the functions of fear conditioning, which has never been analyzed in a naturalistic setting, under realistic prey-predator interaction scenarios. In Aim 2, we will utilize pharmacology, single unit recordings and optogenetics to further elaborate the neural mechanisms of fear in naturalistic risky conditions. Based on our earlier work, we hypothesize that the dorsal periaqueductal gray-amygdala pathway signals impending threats to elicit innate fear, that the reciprocal medial prefrontal cortex-amygdala circuits serve risk proximity assessment functions, and that the amygdala-hippocampal pathway provides the safety-danger boundary information for adaptive foraging decisions and strategies. This ethologically relevant project is significant (i) from a basic scientific perspective because it will advance a more naturalistic view of the fear system that will fill gaps in knowledge and predict new results, and (ii) from an applied perspective because it can lead to novel insights to develop more effective treatments for generalized anxiety, panic, phobia and posttraumatic stress disorders.

SUMMARY Recent work in our laboratory has shown that cyclic fear can prevail over entrainment of circadian rhythms by the light-dark (LD) cycle and lead to diurnal foraging and feeding in nocturnal rodents. When mice or rats are housed in a cage setup in which they need to leave a safe nesting area to access a foraging area for food and water, they forage and feed during the dark phase of the LD cycle. If the foraging area is rendered dangerous with random footshocks during the active dark phase, the animals? foraging and feeding activity shifts to the light phase. This switch to diurnal behavior represents the output of a circadian oscillator, which is entrained by the cyclic fear stimulus, and is dependent on an intact suprachiasmatic nucleus (SCN), where the master clock resides, and an intact amygdala, which encodes fear perception. Our working hypothesis for this proposal is that a circadian oscillator within the amygdala is entrained by cyclic fear and leads to a shift in the timing of foraging and feeding behavior. Specific Aim 1 will determine whether cyclic nocturnal fear entrains the circadian oscillators in the amygdala and/or the SCN in animals entrained to cyclic fear under LD or constant darkness (DD) conditions. Specific Aim 2 will determine whether cyclic fear can also entrain the circadian rhythms of foraging and feeding in female mice, and whether sex differences are explained by the ovarian hormone regulation. Specific Aim 3 will determine whether the evocation of fear by electrical or optogenetic stimulation of the basolateral amygdala (BLA) during the dark phase is sufficient to induce entrainment of feeding and foraging, and whether the activation of the BLA is necessary for fear entrainment by optogenetically inhibiting it while animals are exposed to the fear stimulus. This Aim will also assess whether in vitro optogenetic stimulation of the amygdala is sufficient to locally entrain the amygdala circadian oscillator. Specific Aim 4A,B will exploit region-specific KOs of the clock gene Bmal1 or global KOs of the clock genes Per1 and Per2 to determine whether canonical molecular clock of mammals is part of the fear-entrained oscillator. Aim 4C will assess whether amygdala-specific Bmal1 KOS fail to entrain to cyclic fear. Our finding that nocturnal fear entrains circadian rhythms indicates that limbic centers that encode fear are part of the circuitry that orchestrates circadian rhythms. It also provides a uniquely tractable system to unmask how the master circadian clock within the SCN and the amygdala integrate photic and fear cues to time complex behavioral processes. Circadian and sleep disorders are a hallmark of anxiety and fear disorders such as post- traumatic stress disorder; our findings could shed light into the neural mechanisms that link trauma to the regulation of sleep and circadian rhythms.

PROJECT SUMMARY The natural process of aging is also the leading risk factor for Alzheimer?s disease (AD), a prevalent form of dementia that has devastating effects on the quality of human life and health care costs. As cognitive functions progressively deteriorate with AD, a neurobiological understanding of how AD alters brain cells and their circuit functions is one of the great challenges facing modern biomedical research with broad implications for advancing the nation?s health as well as stimulating the economy. Considerable human and animal AD research has focused on relating ?physical? (macroscopic, microscopic) changes in the brain with destructive loss of memory (i.e., anterograde and retrograde amnesias). In contrast, significantly less is known about the impact of AD on other cognitive functioning, such as risky decision-making which plays pervasive role in daily life, and how AD-afflicted neurons operate in ?real-time? as cognitive functioning is taking place. The primary goal of this application is to understand the dynamics of prelimbic cortex-hippocampus (PL-HPC) circuit functions in decision-making in a murine model of AD, utilizing an ecologically-relevant behavioral paradigm. We will test the general hypothesis that AD causes coordinated PL-HPC neural activities and risky decision- making abilities to decline as a function of the amyloid plaque accumulation in the two structures. There are two specific aims of the project: (1) an ETHOBEHAVIORAL ANALYSIS will investigate the scope of amyloid plaque effects on the animal?s ability to discern safety-danger boundary and make optimal risky foraging decisions; and (2) a SYSTEMS-LEVEL ANALYSIS will determine the neural synchrony in the PL-HPC network as AD mice perform risky foraging and also probe whether decision-making deficits can be alleviated by optogenetic intervention. Information generated from this project would be of significance (1) from a basic scientific perspective because it will provide novel data pertaining to AD-associated changes neural coding and decision-making; and (2) from an applied perspective because it provides a new avenue of naturalistic-based preclinical research that can potentially lead to developing successful treatments of AD-related declines in cognitive functions.

PROJECT SUMMARY Circadian rhythms are 24-hour biological cycles, and are evident as both behavioral and physiological outputs of biological clocks distributed throughout the brain and peripheral organs. In mammals, coordination between rhythms and clocks is attained primarily by the function of a master clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus, which is in turn entrained to the light- dark (LD) cycle. When mice need to leave a nesting area and access a foraging area for food and water, they primarily forage and feed during the dark phase of the LD cycle. However, when uncued footshocks occur randomly in the foraging area during the active dark phase, activity shifts to the light phase resulting in avoidance of the dangerous environment. Behavioral rhythms can also be shifted by uncued footshocks applied with a 24-h cycle in constant darkness (DD), but not if these shocks are cued by a tone. After both LD and DD exposure to cyclic unpredictable fear, the rhythms of foraging and feeding persist upon removal of all cyclic environmental time cues, indicating that these rhythms are the output of a fear-entrained oscillator. The Aims of our funded R01 Award are to identify the location of this oscillator and its underlying molecular mechanism, and to determine whether cyclic-fear entrainment differs between female and male mice. Experiments in the parent award test our underlying hypothesis that a circadian oscillator in the amygdala, relying on the canonical clock gene transcriptional-translational loop, is entrained by fear, leading to a shift in foraging and feeding activity. This Supplement proposal seeks to extend these goals in three experimental Specific Aims, which will serve as the framework for graduate training of Asad Beck, a graduate student of African American descent, at the University of Washington Graduate Program in Neuroscience. Specific Aim 1 will determine whether the recall of the circadian time-stamped contextual fear memory of the foraging area is sufficient to reinstate light phase foraging and feeding even in the absence of actual fear. The second Aim will determine whether sleep architecture during the first stages of exposure to nocturnal fear, which is predictive of how effective contextual fear learing is, predicts the speed of entrainment to nocturnal fear. Finally, the third Aim will characterize the sleep architecture in fear-entrained animals, which in animals entrained to nocturnal fear under an LD cycle should reflect the internal misalignment between SCN master clock and circadian oscillators within fear-coding centers. Our proposal also includes a thorough mentoring plan for Asad Beck. A detailed timeline for the 2.5 years of funding is intended to thoroughly train the candidate to accomplish the following goals: acquire quantitative and computational skills, develop mentoring abilities, develop critical thinking, written and oral communication skills, and establish a sense of self-confidence compatible with a leadership role. The mentoring plan takes advantage of the ample resources available for graduate training at the Program in Neurocience and the University of Washington as a whole.