Sheri Mizumori - US grants

Spatial abilities are often observed to decline as a result of normal aging in both humans and rats. In the interest of the future development of appropriate therapeutic treatments, it is necessary to understand the contribution of age-related changes in brain organization. The hippocampus is a particularly interesting structure for study in this regard because it is considered critical for the acquisition of new spatial information, and it appears particularly susceptible to age-associated pathological abnormalities. Thus, the prim,dry focus of this research is to understand the relationship between physiological properties of a senescent hippocampal formation and spatial performance in rats. Since synaptic activation within hippocampus is extensively modulated by different subcortical afferents (some of which are known to undergo significant changes with age), this research will also examine the possibility that age-related changes in subcortical inputs influence the accuracy with which the hippocampus represents spatial aspects if an environment. The specific goals of this proposal is to provide a comprehensive evaluation of the contributions of neural representations of space and movement in the hippocampus to impaired spatial performance by aged rats. This goal will be accomplished in two parts: First discharge of different populations of single hippocampal neurons will be correlated with specific behaviors and spatial cognitive skills of young and old animals. Also, possible age differences in factors such as attention to spatial cues will be considered in terms of age-related changes in choice accuracy and neurophysiological function. Part 2 of this proposal will assess the effects of age on subcortical modulation of hippocampal function by monitoring behavioral and physiological consequences of selective and reversible deafferentation in young and old rats performing a spatial memory task. Seven afferent structures will be examined. Temporary deafferentation will be achieved by microinjection of a local anesthetic (tetracaine) or a GABA agonist (muscimol) into afferent nuclei. Using an injection-recording procedure that was recently developed for this research, the immediate behavioral and physiological consequences of selective deafferentation, as well as recovery back to baseline conditions. will be observed. Afferent activation effects will be tested by local injection of glutamate or carbachol. In summary, these results should provide important insight into possible age-changes in the neural representation of information critical for accurate spatial behaviors.

9514880 Mizumori To study the process by which sensory-based, organism- centered spatial information is transformed into an allocentric coordinate system, we will examine the relative sensory and mnemonic contributions within individual tectolimbic structures to accurate navigation. This first step is essential in order to define target structures within the neural system of interest. The original specific aims also proposed to test the functional connectivity between the target brain structures so that we could begin to evaluate the dynamical interactions between structures. However, the latter specific aim has been eliminated. To facilitate comparisons between structures, these experiments will focus on one well studied form of navigational learning, visual spatial learning by rats on a radial maze. Comparison of the response properties of information representation in a variety of brain structures during a single behavior will allow future studies to begin to postulate the sort of dynamical interactions that must exist between brain areas if adaptive consequences of spatial processing are to be realized. In order to understand how organisms utilize the tectolimbic circuit in a behaviorally meaningful way, it is essential that we determine how this system affects the ongoing behavior of the animal. We hypothesize that striatal structures such as the nucleus accumbens and caudate nucleus serve to integrate hippocampal spatial information with nonspatial reward-related information to direct the initiation of voluntary behavior via efferents to the ventral pallidum, a critical structure for the direct control of voluntary behaviors. Together, the results of this neural system analysis will not only provide new and important insight into how multiple brain areas might act in concert during navigation, but our findings should also afford new opportunities to learn about neuroplastic mechanisms that might be available during normal spatia l learning. Single unit responses of the same 12 brain structures listed in the original proposal will be recorded as rats perform a nonspatial and spatial learning task on the radial maze. The structures selected comprise the tectolimbic and limbic striatal systems. Preliminary data show that it is possible to classify these various cell types as spatial or nonspatial, and that we can determine the relative mnemonic and sensory contribution of these cells to navigation. A memory function will be suggested if 1) there is protracted shaping of the correlate during acquisition of a spatial task, 2) if there is evidence for contextual dependency of the representation, and/or 3) if there is short term persistence of the representation in the absence of environmental (visual) cues. Exps. 1-3 will test these possibilities. Exp. 4 and 5 will evaluate the sensory-dependence of the representation by observing cell responses immediately after the removal of visual cues, and after scrambling of the cues. Vestibular sensory contributions will be assessed by rotating the center portion of the radial maze, then observing unit and behavioral responses (Exp. 6). Intramaze olfactory sensory influences on the spatial representations will be tested by observing unit responses to rotation of the entire maze (Exp. 7). Exp. 8 will investigate the role of voluntary movement to spatial representations. Finally, since accumbens cells are sensitive to differences in reward magnitude, Exps. 1-8 will take place using rewards of different magnitude.

DESCRIPTION (Adapted from applicant's abstract): Relatively recent re-evaluations of the behavioral deficits of patients with basal ganglia dysfunction have revealed significant and striking cognitive impairments. These results were particularly surprising because for some time, the basal ganglia have been thought of as an extension of the motor control system. In an attempt to determine the precise cognitive consequence of basal ganglia (in particular striatum) compromise, animal researchers have focused on the contribution of the basal ganglia to learning and memory in rat and monkey. The rodent lesion literature suggests a selective role for the caudate stimulus-response or egocentric forms of learning (dissociating it from the context-based learning performed by rodent hippocampus), while the primate electrophysiological evidence supports a dual role for caudate in both stimulus-response and context-dependent learning. Here we present a potential resolution to the apparent discrepancy between response learning and contextual interpretations of the caudate nucleus. We propose that the caudate provides a response reference system to help define the goals of future actions that are deemed appropriate for the current context regardless of whether the specific task to be learned is stimulus-response in nature or involves the more flexible processing of context-dependent learning. In spatial learning, we argue that while the hippocampal sensory context system is important to allow the animal to organize sensory information in different ways, the caudate response referent system allows animals to quickly redefine response options as environmental demands change, the latter of which can play fundamental roles in many types of behavior. To distinguish between a strictly response theory and a response reference theory of caudate, the behavioral correlates of caudate single unit activity characterized as rats perform either a spatial context task, an egocentric response task, or a random forced choice task on a radial maze or a T-maze. Hippocampal place cell activity will be recorded simultaneously with the caudate activity to allow for direct analysis of the relative contributions of the two structures to different forms of learning. The possibility that dopamine regulates the learning-induced unit changes in caudate will be tested by looking at the effects of a dopamine neurotoxin unit-behavioral correlates. In this way, we not only address what unique role caudate has in different forms of learning, but also how the caudate may contribute to a larger neural circuit that allows organisms to ultimately have maximal flexibility in terms of sensory interpretations and response options.

DESCRIPTION (provided by applicant): Patients with basal ganglia dysfunction show significant and striking cognitive impairments. The specific contribution of striatum to learning, however, remains unclear: rodent lesion studies suggests a selective role in stimulus-response or egocentric forms of learning (dissociating it from context-based learning performed by hippocampus), while primate electrophysiological evidence supports a dual role for striatum in both stimulus-response and context-dependent learning. Nevertheless, comparison with studies of hippocampal-dependent memory supports a common view that multiple memory systems exist in brain. Our past work, however, shows that regardless of task, there is significant parallel representation in different brain structures. Given this parallel neural representation, it becomes of interest to know how different memory systems are coordinated. With this grant, we propose a novel perspective on this issue, which is to study how neuromodulators (e.g. dopamine) might bias the relative contributions of different neural systems to learning depending on current environmental demands. Aim 1 will determine the nature of neural representation by neurons in structures known to supply striatum and hippocampus with dopamine, the ventral tegmentum (VTA) and substantia nigra (SNc). Aim 2 will determine whether context-sensitivity of striatum and hippocampal neurons is due to VTA and/or SNc input by reversibly inactivating these structures while testing the context-sensitivity of striatal and hippocampal neurons. To determine whether the inactivation effects are due to dopamine disruption, we will apply D1 or D2 receptor antagonists, and then monitor the context-sensitivity of striatal and hippocampal neurons. Aim 3 will determine whether the context-sensitivity of single striatal and hippocampal unit records is reflective of a larger population response by evaluating the context sensitivity of the expression of the immediate-early gene cFos in striatum and hippocampus, by testing the effects of VTA or SNc inactivation on cFos expression in striatum and hippocampus, by testing pharmacologically a role for dopamine in context-induced cFos expression, and by directly comparing cFos activation patterns with single unit data recorded from the same animals. These studies should provide a strong test for the hypothesis that dopamine functions to regulate the relative contribution of striatum and hippocampus to different forms of learning.

DESCRIPTION (provided by applicant): A prominent theory argues that DA cells generate predictive signals for impending reward and/or they signal when reinforcement contingencies change. It is argued here that by taking a more dynamic and broad systems view of DA's contribution to cognition, we can better understand the significance of DA function;we need to consider not only how DA regulates plasticity in efferent structures, but also how DA neurons themselves are regulated by experience. Studies from the last grant period provide compelling evidence that DA function is context-dependent. The present proposal includes four Specific Aims that will allow us to test the hypothesis that context regulation of DA neuronal signaling of reward information is derived from a combination of inputs from existing memory and decision making systems of the prefrontal cortex (PFC) and context evaluation by hippocampus (HPC). PFC and HPC are thought to impact the timing of the DA reward signal relative to salient cues by experience-dependent gating of sensory information to DA neurons via the tegmentum. This work incorporates a combination of 1) high density single unit recording so that we can understand (relative to DA signals) the neural codes within the PFC, HPC, and two tegmental areas, the pedunculopontine nucleus (PPTg) and the lateral dorsal tegmental nucleus (LDTg), 2) reversible inactivation of brain structures to test for functional connectivity between regions of interest, and 3) behavioral genetic analysis to identify the role of the NMDA system in DA regulation. Aim 1 will determine the nature of neural representation in structures that regulate DA activity: PPTg, LDTg, HPC and PFC. Aim 2 will determine whether the context-sensitivity of DA neurons in the ventral tegmental area (VTA) and the substantia nigra (SNc) is due to PPTg, LDT, HPC, or PFC input. Aim 3 will determine whether context-sensitivity of PPTg, LDTg and PFC neural representations is ultimately derived from HPC or PFC. Aim 4 will test whether it is the glutamate (NMDA) component of the afferent input that regulates burst firing by DA cells by testing these cellular properties in freely behaving mice that are selectively missing NR1 receptors on DA cells. Broad Significance: Understanding how context information regulates signaling by DA neurons is of fundamental importance for therapeutic development in cases of drug relapse, Parkinson's disease, and normal age associated decline in learning. PUBLIC HEALTH RELEVANCE: Malfunction of the dopamine system has been implicated in many disorders (e.g. Parkinson's disease) and maladaptive conditions (e.g. drug addiction and juvenile delinquency). This work proposes to delineate how memory systems of the brain modify the neural codes of dopamine neurons, allowing for new therapeutic interventions to be developed.

Project Description In order to solve the most challenging public health issues, the scientific community needs creative and diverse scientific solutions. As innovation is enhanced when a diverse set of investigators examine a scientific problem, retention of highly skilled scientists from underrepresented groups is critical. Neuroscience assistant professors and postdoctoral scholars from diverse and underrepresented backgrounds, including racial and ethnic minorities, people with disabilities, and people from disadvantaged backgrounds, face three major challenges in their career development. First, comprehensive professional development at these career stages is often overlooked, leaving early career neuroscientists underserved and lacking skills critical for advancement to tenure. Second, people from underrepresented backgrounds are often at higher risk of leaving science due to inequitable access to peer networks, mentors, and advice on how to succeed in faculty careers. Third, they may lack role models for exposure to potential career paths. To fill these gaps, we propose to create BRAINS: Broadening the Representation of Academic Investigators in NeuroSciences, a national program to accelerate and improve the career advancement of neuroscience postdoctoral researchers and assistant professors from underrepresented groups. The BRAINS program creates unique, life- transforming experiences for 50 neuroscientists. BRAINS participants will become more dedicated to their scientific career, better able to direct their careers, and more likely to achieve success in academic neuroscience. The BRAINS program goal is to increase engagement and retention of academic early-career neuroscientists from underrepresented groups by reducing isolation; providing tips, tools, and skills development to prepare for tenure track success; and increasing career self-efficacy. This goal will be met via three synergistic BRAINS activities: A) National Symposia; B) facilitated Peer Mentoring Circles; and C) Invent Your Career teams. The synergism among all these components will: 1. Increase the diversity of neuroscience faculty by providing mentoring, training and skills to under- represented postdoctoral scholars and assistant professors in the neurosciences so they have increased access to resources, feelings of preparedness, and sense of community and connectivity. 2. Reduce isolation of neuroscience postdoctoral scholars and assistant professors from underrepresented groups through the establishment of long-standing peer networks and informal mentoring relationships. 3. Increase career self-efficacy so postdoctoral scholars and assistant professors from underrepresented groups in the neurosciences will have more productive and satisfying careers.

BRAINS Project Description Retention of highly skilled scientists from diverse and underrepresented groups is critical for creating the diverse leadership necessary for innovation in neuroscience. Unfortunately, individuals from underrepresented groups often have higher turnover rates due to a greater sense of isolation and inequitable access to networks, mentors, and key resources that affect career success. Neuroscience postdoctoral researchers and assistant professors from diverse and underrepresented backgrounds (including racial and ethnic minorities and people with disabilities) are not immune to these issues. BRAINS: Broadening the Representation of Academic Investigators in NeuroScience adopts novel approaches to diversify neuroscience such that career advancement and retention of post-Ph.D., early-career neuroscientists from underrepresented groups (URGs: racial and ethnic minorities and persons with disabilities) are increased. BRAINS explicitly seeks to plug the neuroscience early career leaky pipeline by offering a novel professional development program that addresses factors known to impact persistence and career decisions of individuals from URGs in science. Such factors include one's sense of belonging and self-efficacy, the belief in one's ability to perform particular behaviors to produce a specific outcome. BRAINS intentionally targets talented neuroscientists considered at risk for leaving science and academia due to lack of professional support and career self-efficacy. BRAINS has already significantly impacted the career self-efficacy, career satisfaction, and sense of belonging of 56 participants. BRAINS will next enhance the breadth and depth of its impact by tripling the number of neuroscientists participating in the program, and by introducing formal cross- cohort activities that deepen the program's influence on participants' career advancement. Specifically, BRAINS' increased impact on the leaky pipeline will occur by 1. Expanding the longitudinal evaluation of all prior BRAINS participants and non-selected applicants, and growing the program by adding two new cohorts of BRAINS Fellows. 2. Foster additional synergistic networks, career skills, and the leadership potential of BRAINS Fellows through new cross-cohort activities. 3. Broadening BRAINS' reach amongst early-career neuroscientists from URGs by introducing a BRAINS Affiliates Program.

PROJECT SUMMARY While the existence of multiple memory systems in the brain is generally accepted, it is not known how these different systems interact to result in continuously adaptive memory-guided behaviors and decisions. Recent results clearly show that particular combinations of memory-related brain systems show synchronized neural activity (at the population level, for example at the theta frequency) in a task-dependent way. Yet the informational and behavioral significance of such co-modulation of neural activity in not known perhaps in part because such measures are not temporally or informationally refine enough to reveal the significance of this interaction. This proposal aims to develop a novel paradigm for determining whether a specific type of information in one brain area can provide a signal to a connected memory structure to engage or disengage in its well-known memory-related function. Specifically, Aim 1 will test the causal relationship between neural signatures of planned behaviors in hippocampus and the regulation of working memory/action selection by the medial prefrontal cortex. Also, the subsequent impact of this neural directive on future action selection, as well as on future hippocampal place field integrity, will be examined. It is postulated that prefrontal cortex normally stabilizes place fields which in turn should enable rats to more quickly adapt to changing task conditions. Disruption of such prefrontal function, especially during the operation of working memory, should destabilize place fields and EEG phenomena that rely on fully function place fields. In addition, impaired choice accuracy is predicted. Aim 2 proposes to build on the exciting idea that hippocampal theta oscillates between periods of memory encoding and memory retrieval. The same open loop system that was developed in Aim 1 will be used to disrupt selectively working memory encoding or retrieval functions of the medial prefrontal cortex when encoding or retrieval are detected in hippocampus. The general prediction is that disrupting encoding in the prefrontal cortex will disproportionately impair the initial learning behavioral and neural processes relative to behavioral and neural processes that go on after learning has taken place. The combined results will provide new insight into the informational nature of communication between hippocampus and the prefrontal cortex. Also the closed loop paradigm can serve as an innovative and new model for studying the functional interactions between other memory and behavioral systems of the brain, which in turn can have tremendous clinical and therapeutic benefits. It may be possible to interfere with (in cases of unwanted specific associations) or facilitate (in cases of deficient desired associations) specific types of learning or learned associations that characterize a number of mental disorders.

PROJECT SUMMARY Since hippocampal (HPC) neural activity does not reliably and accurately predict future choices in context- dependent tasks, experience-dependent and intentional behaviors must be enabled downstream of HPC, perhaps where information about one?s internal state (e.g. level of motivation, stress, and emotion) has an opportunity to bias cortical instructions for future behaviors. Indeed often one may ?know? what to do in a given situation, yet the condition of one?s internal state often prevent even desired responses from occurring. The present application tests the novel hypothesis that the lateral habenula (LHb) is pivotally important for determining the expression of HPC/mPFC-dependent memory and decisions because it integrates current internal state information with HPC/mPFC output to enable (or not) responses (60). This hypothesis is not predicted by the more common but narrower view that LHb directs choice behavior because it signals negative task conditions (11,23-26). AIM 1 will test whether interactions across the HPC-mPFC- LHb circuit are necessary to perform accurately on a HPC and mPFC-dependent spatial delayed alternation task that requires flexible decision making. Exp. 1: Since there are no known direct connections between HPC and LHb, their interactions will be studied using an established (muscimol-induced) disconnection paradigm. Preliminary data show that HPC-LHb interactions are necessary for accurate performance on the delayed alternation task. Exp. 2: Direct connections between mPFC and LHb have been described (4). Thus, optical inhibition of mPFC terminals in LHb will test the necessity of mPFC-LHb interactions for accurate task performance. Aim 2 will characterize the nature of HPC-LHb theta coherence during spatial delayed alternation task performance. Then we will determine the relative contributions of memory (via mPFC input) and internal state information (via lateral hypothalamus, or LH, input) to HPC-LHb coherence. Coordinated theta phase and power relationships across structures will be studied to better understand the direction of information flow, and the nature of information shared during bouts of theta coherence. Using the same animals, we will then determine the relative influence of memory system input (via PFC) and internal state input (via LH) on HPC-LHb theta coherence using retroviral and optogenetic methods. In summary, this R21 application seeks ?proof of concept? evidence for a novel hypothesis that could lead to new therapeutic approaches to improve lateral habenula-mediated disorders of behavioral control.