Bruce S. McEwen - US grants

DESCRIPTION (provided by applicant): This project addresses cellular and molecular mechanisms by which estrogens (E) and progesterone (P) regulate synaptogenesis in the hippocampus. Synapse turnover occurs naturally during the 4-5d estrous cycle of the female rat by a mechanism that requires the activity of NMDA receptors. Synapse formation has been demonstrated on CAl neurons using Golgi technique, dye filling of cells, and electron microscopy (EM). We have established a new method for demonstrating E-induced synapse formation using radioimmunocytochemistry for synaptic and dendritic markers, which this project will utilize, along with gene microarrays, to discover E and P regulation of key molecules involved in synapse formation and maturation. As far as the site and mechanism for E regulation, inhibitory interneurons may play a pivotal role, as they express the ERa receptor subtype in cell nuclei. We will test the hypothesis that inhibitory interneurons govern the excitability of the pyramidal neurons upon which new synapses are formed, and that E transiently alters both GABA and BDNF activity and allows synapse formation to occur. However, we postulate that E regulates local events in dendrites and synapses of pyramidal neurons via non-nuclear ER sites coupled to second messengers. Using EM, we have found ERa in dendritic spines, presynaptic terminals and glial cell processes. This localization is consistent with a mechanism, demonstrated by others, involving E activation of second messengers. These actions may regulate, for example, the phosphorylation of proteins involved in dendritic protein synthesis and the activity of ion channels and receptors. We shall investigate E regulation of key second messenger intermediates such as Akt and CREB at the light and EM levels, using estrogen antagonists as tools to discriminate these effects from nuclear E actions. We shall also use light and EM to study actions of P in E-primed females, since P causes down-regulation of newly formed synapses within 12-24h by a mechanism that involves intracellular progestin receptors (PR). PR are not evident in cell nuclei of the rat at the light microscopic level, but are evident in dendrites and glial cells by EM. We have also characterized ER and PR in the mouse hippocampus and have obtained preliminary evidence for E-induction of a specific marker of dendritic spines that suggests that E may promote the maturation of synaptic connections in the mouse. We plan to use the power of mouse genetics by employing mice lacking ERa and ERb to provide more definitive information regarding the role of the two known intracellular ER types in these E effects.

Stress is accompanied by the activation of a number of endocrine secretions. Of these, adrenal glucocorticoids play a pivotal role as the principal regulators of the brain-pituitary response to stress and as agents which restore homeostatic balance and also protect the body from its own defense mechanisms such as inflammation and immune reactions. Though the body cannot long endure the absence of stress hormones, prolonged elevation of these hormones can have deleterious, even disastrous, effects such as increased susceptibility to infections and cancer. In addition the brain may also suffer in ways which are long-lasting and even permanent through glucocorticoid-induced neuronal loss and other long-term compensatory changes in neurochemical function which may influence mood and cognitive performance as well as the stress-response mechanism. This proposal investigates how prolonged stress and persistent and repeated elevation of glucocorticoid hormones alter neurochemistry of the principal adrenal steroid target area of the brain, the hippocampus, as well as of hormone sensitive areas of the limbic system and the frontal cortex. Having established glucocorticoid effects on glucocorticoid receptor levels, neurotransmitter receptor binding, cAMP formation stimulated by neurotransmitters, Synapsin I levels and mRNA and VIP levels and mRNA, we intend to investigate the degree to which effects of persistent and repeated glucocorticoid elevation (eg., 6-12 weeks duration) may be irreversible and reflect either the loss of cells or the compensatory response of the brain to cell loss. Finally, we shall determine whether the effects of repeated glucocorticoid elevation are cumulative or can be alleviated by periodic interruptions of stress hormone exposure. This work has relevance to degenerative brain diseases such as Alzheimer's endogenous depressive illness, and the study of persistent or chronic stress in loneliness, grieving, or isolation from normal life situations (eg., hostages, prisoners of war).

This award supports cooperative research in neuroendocrinology between Dr. Bruce McEwen of the Rockefeller University and Dr. Alexandro De Nicola at the Institute of Biology and Experimental Medicine in Buenos Aires, Argentina. This work will identify the characteristics of and the degree of overlap between two receptor systems for steroid hormones in the brain. Understanding the communication between steroidal receptors is important to interpreting interactions between other neurotransmitters and receptors. The use of new molecular biological methodology will lead to new advances in brain neuroscience. The principal investigators have a history of previous successful collaboration and a former student of Dr. De Nicola, Dr. Coirini, is now a post-doc in Dr. McEwen's laboratory. Both laboratories are well equipped for their part of the research and therefore significant contributions can be made by both sides in investigating the regulation of mineralocorticoid receptors by glucocorticoids and the regulation of glucocorticoid receptors by mineralocorticoids. Also, the levels of these hormones and how the binding activity is affected by the regulation will be determined. This work will continue a productive four-year collaboration.

9802428 McEwen This Americas Program award will fund a two-year cooperative research project between Dr. Bruce McEwen, Rockefeller University, and Dr. Alejandro F. de Nicola, Instituto de Biologia y Medicina Experimental, Buenos Aires, Argentina, on regulation and control of salt appetite. Salt appetite is associated with an important homeostatic, motivated behavior, and serves as a model for studying appetites and appetitive behaviors. These studies will provide insights into the neural basis of motivational states and behavior. Using state of the art techniques linking molecular biology and classical physiological approaches, the colaborators will focus on the amygdala as an important target area for mineralocorticoid induction of salt appetite. In situ hybridization histochemistry will be utilized to further investigate the role of adrenal steroid receptors. The project will address important, unanswered questions on the fundamental function of the brain in the regulation of fluid metabolism. This collaboration will combine the expertise of the US side in neurosciences and molecular biology, with the expertise of the Argentinean side in in physiology, pharmacology and neuroendocrinology. ***

minority institution research support; secondary schools;

9503716 McEwen This U.S.-Argentina Cooperative Research grant will support the collaborative research of Dr. Alejandro de Nicola of Argentina (Instituto de Biologia y Medicina Experimental) and Dr. Bruce McEwen of the U.S. (Rockefeller University) to investigate the role of Na,K-ATPase in the amygdala in the control of salt appetite in the rat caused by injections of deoxycorticosterone (DOC). The effects of the mineralocorticoid agonist, aldosterone, as well as the glucocorticoid receptor agonist, Ru 28362, on the amygdala and hippocampus will also be studied. The laboratories of both Drs. de Nicola and McEwen are well established and recognized for the high quality of research which has come out of them. The questions proposed generate much interest in the scientific community; in particular, the neural basis of steroid control of salt appetite in rats is recognized as an important problem. Both in Argentina and in New York, young scientists will be given an opportunity, as part of this grant, to participate in an important area of research in well-equipped laboratories. ***

IBN-9511349 and 9528213 Blanchard, D. C. and McEwen, Bruce Social stress is a common and enduring feature of life with important behavioral and physiological effects. A multidisciplinary research collaboration between the Laboratory of Behavioral Neurobiology at the University of Hawaii and the Laboratory of Neuroendocrinology at Rockefeller University is aimed at description and analysis of these effects. Previous work indicates that single, two-week stress periods can produce increased defensive behavior and decreased social and reproductive behavior; higher levels of stress hormones and impairment of mechanisms that normally limit stress hormone action; and widespread changes in brain neurochemical systems. Although these changes are beginning to provide insights into the dynamics of the physiological and behavioral response to chronic social stress, completed studies have measured only a single time point in the process. The proposed program will investigate the development of stress-related behavioral and physiological changes over time, and will determine the persistence of stress effects following single or multiple periods of chronic social stress. In addition, individual differences will be examined as determinants of responsivity to social stress. The proposed program will thus draw upon the different approaches and expertise of these two research groups to provide a uniquely comprehensive description and analysis of the effects of social stress in an ecologically appropriate situation.

The primary goal of this project is to investigate the cellular and molecular mechanisms through which adrenal steroids mediate their behavioral actions on the control of sodium appetite. Adrenal steroids act upon the brain to arouse sodium appetite and do so by activating the brain angiotensin system as well as by suppressing inhibitory neuropeptide systems such as oxytocin (OT) and the tachykinins (TKs). These effects are mediated by genomic mechanisms involving mineralocorticoid and glucocorticoid receptors that are expressed throughout the brain acting in concert with non-genomic mechanisms. We have uncovered a novel, nongenomic action of adrenal steroids in the amygdala that has focussed our attention on this brain region, as well as upon the GABA-benzodiazepine receptor system. The interrelated Specific Aims are intended to elaborate on the genomic and non-genomic mechanisms of adrenal steroid action in terms of the neuropeptide systems and the GABA-benzodiazepine system and their interactions with each other in the arousal of sodium appetite. The Specific Aims investigate: 1) Genomic control of salt appetite involving mineralocorticoid and glucocorticoid receptors using the antisense technique; 2) Non-genomic control of salt appetite in the amygdala of the rat brain using local application of steroids and benzodiazepine agonists and antagonists; 3) Involvement of genomic control of the expression of key neuropeptides that are either excitatory or inhibitory for salt appetite; 4) Interaction of genomic and non-genomic mechanisms at the level of neuropeptides and GABAa receptors. Specific hypotheses to be tested include the notion that a genomic mechanism involving mineralocorticoid receptors maintains key components of the GABAa and neuropeptide systems in a state where the non-genomic actions can take place. Another hypothesis is that the non-genomic steroid action involves steroid metabolism to products that act directly upon the GABAa receptor to increase its efficacy. This research is relevant to understanding the role of behavioral and neural control of dietary salt intake, which contributes to the establishment and maintenance of hypertension.

McEwen IBN-9815480 Social stress is a common and enduring feature of life with important behavioral and physiological effects. A multidisciplinary research collaboration between the Laboratory of Behavioral Neurobiology at the University of Hawaii and the Laboratory of Neuroendocrinology at the Rockefeller University is aimed at description and analysis of these effects. Previous work with laboratory rodents indicates that single, two-week stress periods can produce a variety of potentially damaging changes, including: increased defensive behavior and decreased social and sexual behavior; higher levels of stress hormones and impairment of brain mechanisms that normally limit stress hormone action; impairment of brain and peripheral mechanisms of male sex hormone production; and widespread changes in brain neurochemical systems. Work in an initial granting period has begun to outline the time course of these changes and to describe their permanence or reversibility; crucial factors in understanding the dynamics of the stress cascade. The proposed program will undertake a fine-grained analysis of the development of stress effects by using behavioral, brain system, and hormone measures taken at closely spaced intervals. This will enable comparison of the relative time course of these changes, enabling the creation of more precise hypotheses concerning the relationships among these phenomena. A second focus will involve the role of male sex hormones in the development of dominance-subordination relationships and in modulating the stress responses of subordinate males. The final focus of the proposed work is on analysis of the role of previous (early or recent) stressful experience in modulating or exacerbating the response to subordination. These studies, using an ecologically appropriate model, will provide detailed information in several areas that are crucial in understanding the mammalian stress response and its widespread behavioral and physiolog ical consequences.

DESCRIPTION (Adapted from applicant's abstract): McEwen and colleagues have recently found that granule neurons are replaced in the dentate gyrus (DG) of the adult brain and that this occurs not only in rodents but also in tree shrews and primates. Moreover, they found that acute and chronic stress inhibit neurogenesis in the DG. The amygdala exerts an important influence on excitability and long-term potentiation (LTP) in the DG, and both the amygdala and DG are targets for stress and contain receptors for stress hormones. The central hypothesis of Project 4 is that stressors facilitate mechanisms subserving fear in the arnygdala and inhibit neurogenesis in granule neurons of the DG, both acutely and chronically; moreover, chronic stress results in decreased DG volume and altered connectivity and function that impairs the ability of the hippocampus to participate in context-dependent fear. The sequence of studies is as follows. First, in collaboration with LeDoux (Project 1), amygdala and DG LTP will be explored, especially focusing on amygdala influences on DG LTP. Next, also with LeDoux (Project 1), we plan to investigate the effects of restraint stress and contextual fear conditioning on DG neurogenesis. Third, in collaboration with LeDoux (Project 1) and the Quantitative Morphology Core, the effects of repeated stress on DG neurogenesis and structure will be examined in relation to the amygdala and fear. Fourth, in collaboration with Morrison (Project 3), the effects of stress and glucocorticoid manipulations on the expression and distribution of NMDA and other excitatory amino acid receptors in the DG will be determined. Based upon the neurogenesis findings, we plan to determine if turnover of DG neurons affects stability of fear conditioning, again in collaboration with LeDoux (Project 1). Concurrently, with these studies, and based upon our initial results, we plan to assess changes in DG gene expression during contextual fear conditioning. Finally, in collaboration with Mony de Leon of NYU, and later in conjunction with Silbersweig, Stern, and Gorman (Project 2), we plan to investigate the anatomical basis of hippocampal atrophy in the human brain with MRI and eventually compare this with animal brain MRI, in particular, establishing and validating methods for measuring DG volume.

DESCRIPTION (provided by applicant): The goal of the proposed research network will be to identify opportunities for later-life reversibility/remediation of phenotypes associated with early life adversity (ELA) by bringing together an international group of senior and junior scientists to foster and facilitate the interdisciplinary research needed to stimulate rapid advances in this field. The network will: (a) promote needed increases in scientific knowledge regarding the array of processes and pathways through which different ELAs (e.g., low socio-economic status [SES], stressful experiences, poor parent-child relationships, maternal nutrition and lifestyle) may similarly or differentially impact later life health and well-being, and (b) leverage evidence from (a) to promote development and evaluation of novel later-life interventions to reverse/reduce risk processes related to ELAs. Specific aims for this network will be to: (1). Build capacity to advance interdisciplinary research exploring the potential for midlife reversibility of or/compensation for risks conferred by ELA by convening biannual international, interdisciplinary meetings of researchers with expertise spanning animal and human research and a shared interest in collaborative work to: (a) foster better understanding of the life-course mechanisms/pathways linking ELA to trajectories of later life health and well-being; (b) develop and test later-life interventions to reduce or even completely reverse risks to health and well-being associated with ELA, and (c) identify resource needs to advance this agenda and devise strategies for their development. (2). Support new research on reversibility/remediation through seed/pilot funding; (3). Bring new researchers into the field by offering opportunities for engagement in network activities, including (a) collaborations on pilot or other projects, (b) participation in network meetings/workshops as affiliated researchers, and (c) funded internships with network researchers; and (4). Pursue active out-reach through dissemination and engagement with the broader research community through: (a) a network website; (b) annual network workshops or symposia at various professional meetings that include disciplinary interests in life-course influences on early adversity, and (c) publishing one or more articles or a special issue on the potential for later-life reversibility/remediation for ELA, focued on potential bio-behavioral or other targets and promising intervention approaches. In accomplishing these aims, the proposed network will (a) contribute significantly to promoting needed theoretical and empirical work to clarify how major ELAs impact adult health and well-being, including addressing unanswered questions regarding the mediators and moderators of these influences at different life- stages and (b) support and promote the interdisciplinary collaborations needed to develop effective interventions for mid- and later life adults that can remediate/reverse and therefore to ameliorate effects of early life adversity.