Mark G. Baxter - US grants

The Behavioral Core (Core C) will perform behavioral analyses of rats and mice from three projects (Projects 2, 4, and 5) of the SCOR. Sleep apnea and sleep disruption cause cognitive impairments in humans. The Behavioral Core will examine the consequences of physiological and sleep manipulations on cognitive function in rats (Projects 2 and 4) and mice (Project 5). The tasks we use will test motor skills, spatial learning and memory, paired-associate learning, attention/vigilance, and working memory/executive function. As a Specific Aim of Core C we will develop and validate a modified version of a standard attentional task (the 5-choice serial reaction time task) as a test of vigilance and wakefulness in rats and mice.

The Behavioral Core (Core C) will perform behavioral analyses of rats and mice from three projects (Projects 2, 4, and 5) of the SCOR. Sleep apnea and sleep disruption cause cognitive impairments in humans. The Behavioral Core will examine the consequences of physiological and sleep manipulations on cognitive function in rats (Projects 2 and 4) and mice (Project 5). The tasks we use will test motor skills, spatial learning and memory, paired-associate learning, attention/vigilance, and working memory/executive function. As a Specific Aim of Core C we will develop and validate a modified version of a standard attentional task (the 5-choice serial reaction time task) as a test of vigilance and wakefulness in rats and mice.

DESCRIPTION (provided by applicant): General anesthetics may act as neurotoxins when given early in mammalian development. Experiments in rodents have demonstrated long-term impairments in cognition and social behavior after administration of general anesthetics early in life. General anesthetics are also neurotoxic to infant nonhuman primates, but their long-term effects on cognition and social behavior are not known. Retrospective studies in humans have shown that children who received more than one general anesthetic before the age of 4 are at a greater risk of learning disability. Thus, early neurotoxic insults from general anesthesia may result in long-term impacts on human cognitive development, but it is not possible to address this question directly in humans because randomized prospective studies are not possible and retrospective (observational) studies are subject to serious confounds: for example, children who need multiple general anesthetics early in life may differ in many ways from children who do not. Whether general anesthesia is neurotoxic to infants and children, and may result in long-term cognitive impairments, is one of the most critical questions in anesthesiology today. A nonhuman primate model of cognitive development after early exposure to anesthesia will address two key issues in establishing whether neurotoxicity of general anesthesia given early in life is cause for concern. First, the closer correspondence between neuroanatomy and cognitive development in nonhuman primates and humans increases the extent to which findings in the animal model can be translated to humans. Second, a nonhuman primate model of cognitive effects of early anesthetic exposure would provide a means to compare different anesthetic regimens, or potential treatments that could be given during or after anesthetic exposure to mitigate or reverse neurotoxic effects and subsequent cognitive impairments. We will test rhesus monkeys that have received three general anesthetics with sevoflurane (an inhalation anesthetic commonly used in pediatric anesthesiology) before their 6th week of life on cognitive and socioemotional tasks throughout their first three years of life, to track the effects of repeated postnatal anesthesia on cognitive and socioemotional development. This will provide data both on the effect of anesthesia on neurocognitive development, and on cognition and socioemotional behavior in juvenile monkeys at an age roughly corresponding to the onset of formal schooling in children. This work will provide a critical translational model for studying long-term effects of postnatal anesthesia on cognition and social behavior in nonhuman primates, which will be vital for assessing potential risks of anesthesia in pediatric populations, as well as for testing potential agents that may mitigate or eliminate this risk. PUBLIC HEALTH RELEVANCE: General anesthetics may cause brain damage when given early in development, resulting in long-term impairments that lead to learning disabilities and potentially other developmental disorders. Whether these effects of general anesthetics, which have been demonstrated mainly in laboratory rodents, are cause for concern in humans is not known. This project will test, using a nonhuman primate model with brain function much closer to that of humans, whether early exposure to general anesthesia is associated with long-term impairments in memory and socioemotional behavior, providing critical information about whether concern about anesthetic use in children is warranted.

Cognitive aging in women is closely related to age-related changes in neuroendocrine systems, particulariy the loss of circulating ovarian steroid hormones that occurs in menopause. Surprising findings from the Women's Health Initiative Memory Study showed that hormone treatment (HT) begun long after the onset of menopause failed to improve cognition and may have been harmful. This contrasts with other studies indicating beneficial cognitive effects of HT begun soon after the onset of menopause. To reconcile these findings a 'window of opportunity'hypothesis has been proposed, such that there is a limited period of fime after menopause during which HT may improve cognifion. Because of other health risks associated with long-term HT including cardiovascular disease and cancer, current advice is for women to take a short course of HT at the onset of menopause and then disconfinue it. We will test, in a well-characterized animal model, whether beneficial cognitive effects of HT (on spatiotemporal working memory, visual recognition memory, and vulnerability to distraction) persist after discontinuation of HT, and whether they are sfill observed when HT is begun after a long delay post-menopause. In vivo neuroimaging analyses conducted concurrently with behavioral tesfing will measure neurobiological changes in parallel with cognitive ability. This study will test the 'window of opportunity'hypothesis explicitly, as well as whether cognitiye benefits can be maintained after withdrawal of HT. These studies will provide critical translational insights into how HT can improve cognitive outcomes of aging. RELEVANCE (See instructions): Hormone replacement therapy in women after menopause can improve brain funcfion, including memory. We will test, in an animal model, how the fiming of hormone therapy after menopause affects its ability to improve brain function, both in terms of whether therapy must begin soon after menopause to be effective, and whether its beneficial effects persist after therapy is discontinued. These studies will help us maintain best brain and memory function in women as they age.

DESCRIPTION (provided by applicant): The primary goal of this Program Project is to investigate interactions between the aging brain and female reproductive senescence. Early studies in young female rats demonstrated clearly that changes in circulating estrogen (E) levels affect cellular and molecular attributes of hypothalamic circuits as well as hippocampus, implicating E in modulating both reproductive neuroendocrine circuits and cognition. However, we now know that the aged brain reacts to E differently than the young brain, and we also know that the estrogen/aging interactions differ in important ways between rodents and nonhuman primates. The key to the next five years is to use both animal models to their best advantage to provide a neurobiological framework for the complex clinical issues surrounding the neurobiology of menopause and post-menopausal cognitive impairment. We will pursue a full spectrum analysis of the key issues; from signaling mechanisms of estrogen to an in-depth structural and functional assessment of the effects of estrogen on the circuits regulating reproductive function (hypothalamus), and cognition (hippocampus and prefrontal cortex). We will continue to reveal the neuronal signaling pathways activated by circulating E, as well as the molecular and synaptic basis for age related decline in E-induced synaptic plasticity. The rodent studies are particularly informative with respect to molecular mechanisms, and they have revealed several new targets of investigation for E signaling in hypothalamus, hippocampus and prefrontal cortex. The nonhuman primate studies reveal the neurobiological underpinnings of E-induced cognitive enhancement in aged monkeys, as well as the synaptic basis of cognitive resilience in the absence of E in young female monkeys. In addition, the nonhuman primate studies have highlighted the importance of prefrontal cortex and related cognitive functions as a target for E. Current studies in both the rat and nonhuman primate models are investigating the cognitive and neurobiological effects of different hormone treatment regimens. Proposed studies will investigate the window of opportunity hypothesis and the duration of beneficial effects after cessation of treatment. These results will provide critically important information on brain aging and will aid in the design of hormone treatments that provide maximal neurological benefits for post-menopausal women.

? DESCRIPTION (provided by applicant): The proposed program on Research Training in the Neuroscience of Aging will provide predoctoral students in Neuroscience with an integrated training experience in the laboratories of nationally and internationally recognized faculty. The predoctoral training program builds on an exciting, translationally relevant curriculum taught in years one and two of graduate school that has been awarded NIH support through the Jointly Sponsored Predoctoral Early Stage T32 Training Program mechanism (T32 MH087004). The proposed new training program would be the first at Mount Sinai to focus specifically on the neuroscience of aging and age- related neurodegenerative disease (primarily Alzheimer's disease), complementing Mount Sinai's historical concentration and strength in research in these areas. Outstanding training faculty in the proposed program share common research interests in the mechanisms of brain function in health and disease, employing a diversity of experimental approaches and working at levels of analysis ranging from molecular neurobiology to human neuropsychology and neuroimaging. The training program specifically encourages participation of faculty mentors whose research grants directly focus on aging neuroscience research, while not excluding those whose research expertise is critically important for the interdisciplinary training we seek to impart. Through their course work, predoctoral trainees will have received a solid foundation in basic neurobiology and the pathophysiology of neurological and psychiatric disease, as well as biostatistics and the responsible conduct of research. Advanced coursework includes a seminar course on the biology of aging as well as focused elective courses in specific areas of neuroscience. Selection of a research mentor is made in a collaborative environment that actively promotes multidisciplinary, integrative research. Research training will also have a `work in progress' component, to foster important interdisciplinary interactions, hone presentation skills, and improve awareness of ethical issues. Using this approach, the program on Research Training in the Neuroscience of Aging will provide predoctoral students with the guidance and experimental tools, in the laboratories of our training faculty, to launch successful, productive, independent careers in aging research.

DESCRIPTION (provided by applicant): Elderly patients undergoing anesthesia and surgery frequently suffer from postoperative cognitive dysfunction (POCD) and postoperative delirium (PD). The cause of these entities is unknown; specifically it is unclear what part the anesthetics play in the development of POCD and PD. We hypothesize that elderly patient's cognitive capacities recover more slowly after receiving general anesthesia, perhaps because they have more limited cognitive reserve. A more prolonged recovery would confound diagnoses of POCD and PD and potentially puts patients who are discharged on the day of surgery at risk of not understanding postoperative instructions. The trajectory of postoperative cognitive recovery has never been explored and elderly participants have been explicitly not included in any type of emergence research. To explore this vital area we propose to study young and elderly volunteers with a combination of two state of the art neuropsychological tests (postoperative quality of recovery scale and the NIH Toolbox) and magnetic resonance imaging. Starting from baseline, we will determine multiple cognitive domains and resting state networks, treat the volunteers with general anesthesia, and then explore the recovery of the cognitive domains and alterations in functional networks. The data acquired in this project will have both clinical and theoretical relevance. Apart from distinguishing immediate drug effects from POCD and PD, characterization of the trajectory of cognitive recovery in the elderly could affect changes in clinical practice vis a vis the criteria we employ to determine, for example, hospital discharge in this population. Currently many elderly patients are (perhaps inappropriately) sent home on the day of surgery. Furthermore, characterization of the trajectory of recovery in this population would enable us to better educate our patients and those who help care for them as to the proper expectations and time course for their recovery from anesthesia. Most fundamentally, the trajectory at which various patients recover from anesthesia is the most unappreciated confounding factor in this debate on the direct and indirect effects of anesthetic drugs. The effects of the anesthesia itself are theoretically (and as we propose here, practically) separable from those due to surgery, by studying the former in the absence of the latter we can delineate the trajectory of cognitive recovery from anesthesia itself, developing an understanding that is currently lacking and yet necessary to understand POCD and PD in general.

Project Summary Impairments in cognitive functions that depend on the prefrontal cortex are a common feature of aging, as well as age-related diseases like Alzheimer's disease (AD). These impairments can reduce quality of life and interfere with daily activities including adherence to medication schedules, thereby resulting in additional effects that impact health in the elderly. A potential strategy to augment prefrontal cortex function is to selectively stimulate basal forebrain projections to the prefrontal cortex, increasing acetylcholine release in the dorsolateral prefrontal cortex and stimulating neuronal mechanisms that underlie normal working memory function. We propose to develop such a strategy in rhesus monkeys, and test its ability to improve cognition. This chemogenetic neuromodulation strategy will use a combination of two viruses: one retrogradely-transported vector containing Cre recombinase into dorsolateral prefrontal cortex and a second Cre-dependent DREADD into basal forebrain. This will selectively target basal forebrain neurons projecting to dorsolateral prefrontal cortex. Once this approach has been tested and validated, we will test whether stimulation of neurons of the primate basal forebrain that project to dorsolateral neocortex is effective in offsetting working memory impairment caused by pharmacological antagonism of acetylcholine. This will provide a critical test in a highly translationally-relevant model of the potential for a neurostimulation intervention, targeted at a discrete neuronal circuit, to improve age-related deficits in cognitive functions of the prefrontal cortex.

Project Summary The vast majority of Alzheimer's disease (AD) cases are late-onset and it ss now widely believed that development of late-onset AD is the consequence of accumulated brain damage over many years. This process begins with the generation of abnormal oligomeric proteins (amyloid beta oligomers, A?Os) from misprocessed amyloid precursor protein. A?Os are toxic to synapses, and over time A?O buildup and synaptic damage lead to deposition of amyloid plaques and hyperphosphorylated tau protein causing neurofibrillary tangles and neuronal loss, the hallmarks of AD neuropathology. Despite tremendous resource investment, the translation of this mechanistic understanding of AD pathogenesis into new therapies for AD remains elusive. We propose the development of a nonhuman primate model of early AD pathogenesis based on exogenous administration of A?Os to middle-aged rhesus monkeys. Our extensive preliminary data show that a month of twice-weekly A?O administration causes synapse loss targeted to highly plastic thin dendritic spines, and neuroinflammation, changes that mirror what is thought to occur in the earliest prodromal phase of human AD. This model therefore addresses a key limitation of existing animal models of AD: it is based on the pathogenetic process thought to lead to the vast majority of human late-onset AD cases. Based on the acute effects of A?O administration on synaptic and glial markers in rhesus monkeys, we hypothesize that deficits in cognition and affect mirroring symptoms of AD in humans will develop over time in rhesus monkeys chronically treated with A?Os and relate to synaptic disease observed in postmortem histology. To test our hypothesis, rhesus monkeys treated with A?Os or a scrambled peptide control will complete cognitive and affective tasks sensitive to cortical and subcortical function. Our design provides detailed assessment of the time course of behavioral changes, and we will determine synaptic, neuronal, and glial markers in the brains of these monkeys concurrently with the emergence of behavioral deficits. Behavior will be tested in repeated cycles so that changes over time with increasing cumulative dose of A?Os can be determined. These experiments will provide a multi-faceted behavioral characterization of how synaptic dysfunction caused by A?O treatment impacts cognitive and affective behaviors dependent on multiple cortical and subcortical structures, and will let us develop A?O administration in rhesus monkeys as a model for testing interventions that may derail the progression of pathological cascades before full-blown AD develops, providing a new setting for developing treatments for an urgent public health problem.

Project Summary General anesthetics may act as neurotoxins in the developing mammalian nervous system and cause long-term neurobehavioral changes after exposure in infancy. Repeated exposure is particularly deleterious to the developing nervous system, and children who undergo more than one general anesthesia before the age of 4 are at an increased risk for substantial emotional and cognitive changes. It is therefore critical that preventative treatments be found. Studies in animal models have suggested that persistent anesthetic-induced changes such as neurotoxicity, gliotoxicity, loss of synapses and changes in mitochondrial structure may lead to long-term behavioral impairments. Early effects of anesthesia on mitochondria may be key to long-term impairments: protection of mitochondria from oxidative stress caused by free radical generation from general anesthetics eliminates subsequent cognitive impairment in adulthood in rodents. We have established a nonhuman primate model of early anesthetic exposure. In a previous award, we showed that infant rhesus monkeys that received multiple exposures of to the inhalation anesthetic sevoflurane, commonly used in pediatric anesthesia, showed long-term changes in socioemotional and cognitive development when tested later in development. In this new proposal, we will use that model to test the hypothesis that neonatal anesthesia exposure is associated with long-term changes in synaptic and mitochondrial structure in the primate brain, and that protection of mitochondria from oxidative stress at the time of anesthesia exposure mitigates or prevents subsequent changes in cognitive and socioemotional development. Specifically, in Aim 1 of this project, mitochondrial and synaptic structure in adulthood will be examined at the electron microscopic level in tissue prepared and banked from those subjects from the previous award. For Aim 2, infant rhesus macaques will be exposed to sevoflurane (3 exposures in the six weeks of life) in the presence of R(+)pramipexole, a mitochondrial protectant, or treated with vehicle and will be followed behaviorally for 2 years to assess sparing of neurobehavioral changes in the treated group. We will determine whether R(+)pramipexole treatment also protects against synaptic and mitochondrial changes in these monkeys. Together, results from these studies can provide a causal link between anesthetic exposure, mitochondrial dysfunction, and altered emotional and cognitive behavior in monkeys. They will also provide a first step towards improved anesthetic protocols and preventative treatments that will allow children to undergo safe surgery while minimizing unintended long-term effects on the brain and behavior.

Project Summary Although accumulating evidence in humans points to improvements in emotional life with age, even in the context of physical and cognitive health challenges, the mechanisms that support those improvements are largely unknown. One possibility is that aspects of the social environment and social relationships guard against deleterious aging effects and thus promote wellbeing. Understanding the interplay between social environment and cognitive, affective, and neurobehavioral health outcomes across the lifespan is critical for developing effective interventions for people who suffer from the deleterious effects of aging, including depression and loneliness. Nevertheless, it is not ethical to manipulate humans? social relationships in order to test causal hypotheses. To address this mechanistic question, we capitalize on a robust animal model of human social, cognitive, affective, and neurobehavioral aging ? the rhesus monkey ? in order evaluate whether robust social environments and high-quality relationships promote and protect healthy affective, cognitive, and neurobehavioral aging while restrictions of the social environment compromise it. Additionally, we evaluate whether social interventions, namely increasing access to high quality social partners, may improve cognitive, affective, and neurobehavioral outcomes once they have been compromised by aging processes. We will restrict and then rejuvenate the social environment in both young and aged monkeys, and measure neurobehavioral function (cognition, affect, and neuroimaging measures of brain structure and function) concurrently with these manipulations. In this way, this program of work represents a critical first step in determining the mechanistic impact of social environment on neurobehavioral aging in addition to evaluating a potential intervention that could benefit individuals who have experienced unhealthy aging.

Alzheimer?s disease (AD) is a devastating condition that affects more than 5 million Americans, with a total annual cost of more than $300 billion predicted in 2020. Currently there are no effective treatments to counteract or slow the progression of AD, with promising findings in rodents failing to translate into successful therapies for patients. Monkey models may provide a more powerful translational model. The goal of this proposal is to characterize a monkey model of tau pathology in AD. This is responsive to RFA-AG-21-003 requesting proposals that target the ?development, characterization, and validation of suitable new or unconventional mammalian non-murine models of AD that may represent improved translational potential by better replicating pathological features of the disease?. With respect to nonhuman primate (NHP) models of AD, the RFA states explicitly that ?NHP have a very high translational value because of their close relationship to humans in terms of phylogeny, genetics, physiology, cognition, emotion, and social behavior?. In this proposal we describe initial findings in a tau-based monkey model of AD and propose a program to fully develop and validate the model by three PIs who have decades of experience on aging and neurodegeneration in NHP models. We have targeted the highly vulnerable entorhinal cortex (ERC) for unilateral infusions of an adeno-associated virus expressing a double tau mutation known to cause tau-related dementia in humans (AAV-P301L/S320F) and characterized neuropathology at 3 and 6 months after viral injection in NHPs. This causes extensive and progressive neuroinflammation and tau-based neuropathology, including end-stage neurofibrillary tangles, in ERC and in hippocampal and neocortical targets of ERC. Preliminary PET imaging in these monkeys displays robust phospho-tau accumulation in the hippocampus. The progressive time course relative to the time of vector injection is a great strength in terms of using this model for therapeutic development. These early studies demonstrate the potential for this model to replicate pathological features of AD in the monkey brain and to capture aspects of pathology that have not been well-modeled in rodents. We propose to do a full, rigorous characterization of this model, including long-term behavioral assessment, in vivo imaging, fluid biomarker assessment, and microscopic analyses. Full characterization of this model, will provide a platform to test therapeutic agents at different points in the disease process.