Istvan Mody - US grants

The goals of the proposed experiments are to obtain information about the basic mechanisms underlying long-term changes in the synaptic properties of mammalian CNS neurons. Such long-term alterations are thought to be responsible for the enduring enhancement in the efficacy of synaptic transmission underlying learning and memory formation. The present study will examine the role of intraneuronal Ca2+ homeostasis, in particular the contribution of Ca2+ sequestering organelles, to the control of synaptic excitability. Long-term potentiation (LTP), a use-dependent increase in synaptic efficacy critically linked to Ca2+, will serve as the model for plastic cellular alterations. The study will take advantage of the newly developed whole-cell patch clamp recording technique in conventional brain slice preparations. In addition to improving the quality and resolution of electrophysiological recordings, this technique is best suited for introducing chemicals and drugs into the neurons' internal environment. Whole-cell patch (current- and voltage-clamp) and extracellular recordings will be obtained in neurons of the rat hippocampal formation. Spontaneous or evoked excitatory or inhibitory postsynaptic currents will be recorded under various conditions of intraneuronal Ca2+ homeostasis. LTP will be induced by tetanic stimulation of afferent pathways. Considering the ubiquitous role of Ca2+ in regulating cellular function, the modulation of synaptic events by Ca2+ originating from Ca2+-sequencing organelles will be especially emphasised. This can be accomplished by studying how intraneuronally applied chemicals, which alter the release of Ca2+ from intracellular sequestering organelles, modify basal or long-term potentiated synaptic responses. Furthermore, the induction and maintenance phases of currents and fluctuations in steady excitatory current noise in potentiated neurons will permit the examination of long-term synaptic alterations at the single receptor/channel level. The study proposes to establish the nature of the relationship between intraneuronal Ca2+ homeostasis and the control of synaptic excitability intrinsic to the nervous system. The regulation of neuronal excitability by Ca2+ released from the neuronal endoplasmic reticulum or other Ca2+ sequestering organelles has not yet been investigated in detail. Only recently, by analogy to the function of the sarcoplasmic reticulum in muscle, studies have begun to stress the importance of Ca2+ buffering and release mechanisms in neurons. By extending these novel findings and examining previously unexplored aspects of intraneuronal Ca2+ homeostasis, the present experiments will provide a better understanding of the long-term regulation of neuronal function.

The goals of the proposed experiments are to obtain information about the basic mechanisms underlying long-term changes in the synaptic properties of mammalian CNS neurons. Such long-term alterations are thought to be responsible for the enduring enhancement in the efficacy of synaptic transmission underlying learning and memory formation. The present study will examine the role of intraneuronal Ca2+ homeostasis, in particular the contribution of Ca2+ sequestering organelles, to the control of synaptic excitability. Long-term potentiation (LTP), a use-dependent increase in synaptic efficacy critically linked to Ca2+, will serve as the model for plastic cellular alterations. The study will take advantage of the newly developed whole-cell patch clamp recording technique in conventional brain slice preparations. In addition to improving the quality and resolution of electrophysiological recordings, this technique is best suited for introducing chemicals and drugs into the neurons' internal environment. Whole-cell patch (current- and voltage-clamp) and extracellular recordings will be obtained in neurons of the rat hippocampal formation. Spontaneous or evoked excitatory or inhibitory postsynaptic currents will be recorded under various conditions of intraneuronal Ca2+ homeostasis. LTP will be induced by tetanic stimulation of afferent pathways. Considering the ubiquitous role of Ca2+ in regulating cellular function, the modulation of synaptic events by Ca2+ originating from Ca2+-sequencing organelles will be especially emphasised. This can be accomplished by studying how intraneuronally applied chemicals, which alter the release of Ca2+ from intracellular sequestering organelles, modify basal or long-term potentiated synaptic responses. Furthermore, the induction and maintenance phases of currents and fluctuations in steady excitatory current noise in potentiated neurons will permit the examination of long-term synaptic alterations at the single receptor/channel level. The study proposes to establish the nature of the relationship between intraneuronal Ca2+ homeostasis and the control of synaptic excitability intrinsic to the nervous system. The regulation of neuronal excitability by Ca2+ released from the neuronal endoplasmic reticulum or other Ca2+ sequestering organelles has not yet been investigated in detail. Only recently, by analogy to the function of the sarcoplasmic reticulum in muscle, studies have begun to stress the importance of Ca2+ buffering and release mechanisms in neurons. By extending these novel findings and examining previously unexplored aspects of intraneuronal Ca2+ homeostasis, the present experiments will provide a better understanding of the long-term regulation of neuronal function.

Basic research into the mechanisms of epilepsy has provided evidence consistent with highly conserved means of altered neuronal excitability regardless of the experimental model or species involved. The more fundamental the excitability change leading to epilepsy, the more conserved across species and models its underlying mechanism should be. The present study will compare three essential aspects of hippocampal neuronal excitability in three chronic cases of temporal lobe epilepsy (TLE): l) TLE patients, 2) limbic kindling, and 3) TLE induced by kainic acid (KA). The three major cellular alterations to be compared are: 1) long-term changes in the functioning of N-methyl-D-aspartate (NMDA) receptors; 2) the degree of excitatory synaptic drive onto interneurons following supragranular sprouting of mossy fibers, and 3) compensatory alterations in neuronal calcium homeostasis. The changes in NMDA channel function will be studied in cell-attached and excised patch clamp recordings in neurons acutely isolated from human TLE and kindled hippocampi. The sensitivity of the channels to second messengers, agonists, antagonists, magnesium, and zinc will be studied by analyzing steady-state channel openings and the kinetics of channel behavior following rapid agonist applications to membrane patches. The excitatory drive onto interneurons will be measured in the KA model known for its extensive but variable degree of mossy fiber sprouting. Its magnitude will be evaluated by measuring the effect of excitatory amino acid antagonists on inhibitory postsynaptic currents recorded in the whole- cell mode in brain slices, and will be correlated with the amount of mossy fiber sprouting determined in anatomical studies. Possible similarities between the handling of calcium by human TLE and kindled neurons will be explored in whole-cell recordings of calcium currents and simultaneous calcium imaging in acutely isolated human TLE and kindled dentate gyrus granule cells. The primary goal of the proposed experiments is to unravel common cellular and molecular events underlying the altered excitability of surviving neurons in TLE. Understanding the fundamental mechanisms how neurons can sustain epileptic discharges, how they remain in this state, and how their lasting change in excitability perturbs the rest of the brain region affected by epilepsy will lead to novel therapeutical approaches aimed at restoring normal excitability in epileptogenic structures.

The present proposal is aimed at uncovering the functional outcome of gamma-aminobutyric acid type A (GABA/A) receptor plasticity in hippocampal inhibitory synapses. The proposed experiments will also elucidate the pathological consequence of the plastic conversion of zinc (Zn2+)- insensitive synaptic GABA/A receptors into Zn2+-sensitive ones, shared by two experimental models of temporal lobe epilepsy. The general hypothesis is that kindling and pilocarpine-induced epilepsy are associated with critical subunit-specific plastic changes of synaptic GABA/A receptors in hippocampal neurons leading to a change in inhibitory function. Specifically, in dentate gyrus granule cells, these alterations result in an enhanced blocking action of the endogenous GABA/A receptor modulatory ZN2+, which upon its release from sprouted mossy fiber terminals will severely impair GABAergic inhibition. First, collaborative studies with other members of the Program Project will establish how, after pilocarpine treatment, the loss of alpha5 subunits from CA2/CA1 pyramidal cells translates into changes in the properties of inhibitory synapses. Through single-channel and whole-cell patch-clamp recordings in the two epilepsy models we will then establish the characteristics of synaptic GABA/A receptors typified by an altered Zn2+-sensitivity. With other Program Project members, subunit-specific antibodies will be used to probe the subunit composition on the altered receptors, and by reconstituting cloned subunits in expression systems, we will attempt to mimic the properties of native GABA/A receptors before and after the pathological plasticity. Furthermore, we will investigate the relationship between GABA/A receptor plasticity and the endogenous Zn2+ found in sprouted mossy fiber terminals. As Zn2+ can be released from these terminals during heightened neuronal activity, abnormally elevated extracellular Zn2+ levels may be present during hippocampal seizures. Because Zn2+ is a negative allosteric modulatory of some GABA/A receptors, a chronically enhanced Zn2+ release could by itself lead to GABA/A receptor plasticity. This hypothesis will be addressed by perfusing Zn2+, its chelators, and by experimentally reducing the amount of mossy fiber sprouting responsible for the excess Zn2+ delivery. Since Zn2+ may affect a variety of channels, other possible pre- and post-synaptic factors involved in the Zn2+-dependent regulation of GABA synapses will be explored. The proposed studies are expected to reveal critical aspects of long-term regulation of GABA synapses, leading to a better understanding of the pathological consequences of GABA/A receptor plasticity. Our findings could provide the basis for novel and rational therapeutical approaches against devastating psychiatric and neurodegenerative disorders including anxiety, stress, stroke, and epilepsy.

DESCRIPTION (adapted from applicant's abstract): The goal of this proposal is the continued characterization of fundamental and distinctive features of GABA receptor function and synapses of the mammalian CNS. In light of the known alterations of GABAergic inhibition in several neurological and psychiatric disorders, and of the GABA-related mechanism of action of numerous clinically used drugs such as anxiolytics, anesthetics and anticonvulsants, the proposed studies will considerably contribute to the understanding of inhibition and its alteration by drugs or neuronal activity. Each specific aim addresses a critical issue related to the regulation of GABAergic inhibition. These aims are: (1) to establish the specifics of the inhibitory control of interneurons, leading to understanding of the synchronous activation of GABA neuronal networks responsible for the timing of high frequency oscillations in the brain; (2) to gain insight into the cellular and molecular mechanisms which regulate GABA release and govern its synchrony; and (3) to uncover molecular alterations affecting the function of synaptic GABA-A receptors during tolerance and withdrawal after chronic BZ treatment. First, recordings from individual anatomically identified hippocampal interneurons will provide the first comprehensive combined physiological and anatomical fingerprinting of these cells. The findings are expected to explain the precise synaptic control of the interneuronal network, known as the critical clock for the high-frequency (gamma) oscillations in the cortex, in turn thought to underlie higher cortical function. Second, the study will probe pre- and postsynaptic factors, including GABA-B receptors and synaptic vesicle proteins, involved in the synchrony of GABA release. These factors are crucial for translating the high frequency discharges of interneurons into a precisely timed GABA release which tightly controls the activity of other interneurons and principal cells. The third part of the proposal will address BZ tolerance and withdrawal, a topic of considerable clinical relevance. We will examine the hypothesis that synaptic GABA receptor function is controlled by phosphorylation, and that alterations in this process may underlie BZ tolerance and withdrawal. The resulting insights into critical aspects of the short and long-term functioning of GABA synapses will lead to a better grasp of many clinical problems associated with alterations in inhibitory function including those of cognitive processes. A thorough understanding of the regulation of GABAergic inhibition may open novel therapeutical approaches aimed at devastating psychiatric and neurodegenerative disorders including anxiety, stress, stroke, and epilepsy.

Deposition of fibrillary beta-amyloid peptide (Abeta), the main component of amyloid plaques, is considered by most uccrent theories on Alzheimer's disease (AD) to be a key factor in the selective neuritic dystrophy and neuronal degeneration. Extracellular deposition of Abeta is thought to be one of the causes of AD pathology. The neural fibrillary tangles, cell loss, vascular damage, and dementia are presumed to follow as a direct result of this deposition. Accordingly, much of AD research focuses on understanding the molecular pathways for Abeta generation, on discovering factors affecting Abeta aggregation and deposition and on identifying the effects of Abeta at the cellular level. Most of our understanding concerning the effects of Abeta on cellular events is derived from research on cultured embryonic nerve cells, a preparation in an early stage of its maturation that cannot adequately resemble mature neurons that usually succumb to AD. In contrast, the preliminary experiments which will constitute the basis of the proposed studies, were obtained in acutely dissociated adult or aged hippocampal neurons. In these cells, intracellular second messenger- related pathways appear to mediate rapid cellular effects of Ab that may underlie some of the pathological consequences of the aggregated peptide. Acute exposure of the neurons to Abetas dramatically enhanced NMDA channel function through a modulatory pathway distinct from known effects of Abetas including elevated Ca2+ influx, liberation of free radicals, or activation of tachykinin receptors. Based on these findings, the present proposal will address the following hypothesis: intracellular second messenger pathways, including protein kinases or phosphatases, are activated by Abeta in adult or aged neurons. This project has four specific aims: 1) to identify protein kinases and phosphoprotein phosphatases activated or inhibited by Abeta; 2) to ascertain whether Abeta activates 2nd messenger systems common to other peptide receptors; 3) to determine the role and contribution of Ca2+ in the cellular and toxic actions of Abeta; and 4) to reveal the possible involvement of G-proteins and cyclic GMP in the cellular actions of Abeta. The study will use high resolution electrophysiological recordings in vitro in adult rodent CNS neurons, and in collaboration with Dr. Frautschy, it will assess the cellular damage produced by Abeta administration in vivo into the brains of mice null mutant for the intracellular Ca2+-binding proteins calbindin (CB) and parvalbumin (PV). By addressing the effects of Abeta on cellular second messenger functions in adult and aged nerve cells of the hippocampus and studying these novel actions of Abeta on cellular second messenger functions in adult and aged nerve cells of the hippocampus, and studying these novel actions on Abeta on NMDA channel activity in fully developed and aged neurons this proposal will identify intracellular second messenger pathways possibly involved in the actions of Abeta. An activation of second messenger cascades by Abeta may cause may lead, in the long run, to the neuronal dysfunction and the eventual degeneration associated with AD.

Gamma-hydroxybutyrate is abused by humans occasionally or chronically due to its euphoric and sedative effects. An overdose of GHB can lead to a severe depression of the consciousness, seizures, vomiting and even death, while long-term abuse can be associated with a marked withdrawal syndrome. Thus, ingestion of GHB causes biological changes in the brain that may have major influence on the well-being of the individual. The goal of this proposal is to characterize specific alterations in the brain in a mouse model of GHB abuse. The fundamental hypothesis to be tested by the present proposal is that chronic GHB administration affects the mammalian brain through GHB effects via GABAB receptors. This causes behavioral alterations attributable to changes in physiological processes, such as neuronal firing and excitatory and inhibitory synaptic transmission. As GABAB receptors may be the major target of GHB action, the chronic effects of oral GHB should be dampened by GABAB receptor antagonists, or should be absent in animals where the GABAB receptor has been genetically ablated. Presently, changes in the CNS caused by GHB abuse are poorly understood. We propose a number of investigations relying on behavioral and electrophysiological examination of orally GHB-treated mice. Each of the three specific aims addresses critical features of the mechanism of action of GHB. The aims are 1) to determine the in vivo neuronal correlates of chronic, oral GHB-administration and withdrawal in wild-type mice and in GABAB receptor knockout mice; 2) to establish the cellular and neuronal network changes in the cerebral cortex in the mice after chronic, oral GHB- administration; and 3) to ascertain whether GABAB-receptor antagonists and GHB-receptor antagonist NCS-382 offer protection against the GHB-induced changes in behavior and cellular properties. To accomplish these goals, oral treatment with GHB will be carried out in mice subjected to behavioral and electrophysiological tests. Furthermore, high resolution electrophysiological recordings will be obtained from neurons identified with IR-DIC methods and anatomical reconstruction of the recorded cells. Selective GABAB receptor antagonists will be used, while the newly generated GABAB receptor knockout animals will serve as an advanced tool to test the involvement of GABAB receptors in these processes. The study is expected to yield novel and specific insights into the GHB-induced changes in the mammalian brain. By developing and characterizing a mouse model of GHB abuse, our study will open the possibility of further using genetically altered mice for studying the effects of GHB on the brain or other organs. Understanding the specific alterations that accompany GHB abuse will lead to a better grasp of the clinical problems associated with GHB ingestion, including acute intoxication, long-term abuse, and the GHB withdrawal syndrome.

DESCRIPTION: (Verbatim from the Applicant's Abstract) The goal of this proposal is to continue the characterization of fundamental and distinctive features of GABA receptor function and inhibitory mechanisms in the mammalian CNS. Alterations in GABAA receptor-mediated inhibition take place over the course of several neurological and psychiatric disorders, and numerous clinically used drugs including anxiolytics, anesthetics and anticonvulsants have GABAA receptor-dependent mechanisms of action. In light of this, the proposed studies will contribute to the understanding of inhibition and its alterations by neuronal activity, drugs or disease states. The proposal will characterize two distinct forms of GABAergic activity in central neurons: phasic inhibition mediated by activation of GABAA receptors at synapse, and tonic inhibition that is most likely generated by extrasynaptic receptors activated by ambient GABA present in the extracellular space. The central hypothesis to be tested is as follows: tonic and phasic GABAergic inhibition are separately generated and differently regulated in the central nervous system. Consequently, the two inhibitions perform distinct functions to control the excitability of individual neurons and of interconnected neuronal networks. Each specific aim addresses critical features of the two types of inhibition. These aims are: 1) to establish the differential pharmacology of the two types of inhibition; 2) to study their regulation by endogenous factors; 3) to resolve how the two inhibitions control the activity of interneurons; 4) to identify distinct subclasses of interneurons explicitly involved in producing one or the other type of inhibition; 5) to uncover the role played by the two types of inhibition in regulating the excitability of neuronal networks. To establish these goals, high resolution electrophysiological recordings will be obtained from neurons identified with IR-DIC and fluorescent methods. Light and electron microscopical investigations will address the specific anatomical properties and localization of the receptors and cells involved. Moreover, the study will use genetically altered mice that over- or under-express certain GABA receptors in specific neuronal populations. Other mutant mice have well-defined subclasses of interneuron expressing specific markers to facilitate their identification for electrophysiological recordings or for their specific photochemical ablation by exposure to UV light. The study is expected to yield novel and specific insights into the functioning of the GABAergic system in the brain. Understanding the role and the specific control of the two types of inhibition will lead to a better grasp of many clinical problems associated with alterations in inhibitory function including those underlying cognitive processes. A thorough knowledge of the regulation of GABAergic inhibition by endogenous factors and by specific drugs will open the possibility for novel therapies aimed at curing some devastating psychiatric and neurological disorders including anxiety, stress, stroke, and epilepsy.

DESCRIPTION (provided by applicant): This proposal will continue to elucidate the regulation of neuronal function by calcium-binding proteins (CBPs) including calmodulin (CaM)-dependent second messenger systems. Calcium (Ca2+), one of the most important cellular signals, can control events with timings as diverse as neurotransmitter release and neuronal degeneration. Yet, the dynamics of its interactions with CBPs are little known, least of all at the time-scale needed to resolve its distinct roles in neuronal signaling The proposed studies will provide detailed insights into the functioning of endogenous neuronal Ca2+ -buffers, their interactions and competition for Ca2+ with Ca2+ effector systems, and their combined roles in determining the specific vulnerability of central neurons. The main hypothesis is as follows: the roles of neuronal CBPs as intracellular Ca2+ buffers or as competitors for specific Ca2+-dependent regulatory events are defined by their unique Ca2+-binding kinetics. In turn, the distinct kinetics and selective interactions of CBPs with Ca2+-effector systems are responsible for their diverse roles in regulating neuronal excitability, synaptic integration, and selective neuronal vulnerability. This hypothesis will be addressed in the following specific aims: 1) to resolve the Ca2+-binding kinetics of three neuronal CBPs including calbindin-D28K (CB28K) Parvalbumin (PV), and calretinin (CR) at or near physiological conditions; 2) to determine the physiological Ca2+-binding kinetics of substrate-free CaM, and of CaM bound to some effectors including the Ca2+/CAM-dependent protein kinase II (CaMK II), the Ca2+/CaM-dependent serine (Ser)/threonine (Thr) phosphatase calcineurin (CN), and the CaM-binding domain of the SK2 CA2+ dependent potassium (K+) channel; 3) to ascertain the role of CB28K in neuronal Ca2+ handling and in short-term plasticity at specific synapses; 4) to determine how CR alters neuronal excitability and short-term plasticity at synapses between mossy cells and granule cells of the hippocampal formation; 5) to uncover the relationship between the vulnerability of murine mossy cells and their CR content. These five aims will be accomplished by measuring Ca2+-binding to CBPs after ultra-fast photolysis of caged Ca2+ followed by computing the binding rate constants through compartmental kinetic modeling. High-resolution electrophysiological recordings combined with measurements of intracellular Ca2+ dynamics at the sub-millisecond time-scale will be done in identified neurons of brain slices prepared from mice with genetically altered levels of CBPs. For the first time, the physiological Ca2+-binding properties of CBPs will be linked to their functions as Ca2+ buffers, regulators of cellular excitability, and determinants of selective neuronal vulnerability. Understanding the precise relationship between intracellular Ca+ -binding and Ca2+ effector mechanisms will uncover the complex involvement of Ca2+ in the triad of neuronal excitability, plasticity, and vulnerability. This triad is critical in severe neurological maladies including ischemia/stroke neurodegenerative disorders, and epilepsy.

The goal of the present proposal is to gain insight into the mechanisms governing homeostatic neuronal plasticity caused by lasting changes in the GAB Aergic inhibition of central neurons. The equilibrium between excitation (E) and inhibition (I) in the CNS (the E/I balance) is widely accepted to depend on the fine-tuning of its individual components, thus preventing it from tipping over. The overall hypothesis of this proposal can be summarized as follows: changes specifically affecting one of the two types of GABAergic inhibition (phasic/synaptic and tonic/extrasynaptic) will result in well-defined homeostatic changes in the other type of inhibition and in the intrinsic and synaptic excitation of neurons. The end result will be an overall change in excitability capable of balancing out the offset inhibition. Distinct changes in the two functionally separate types of inhibition are expected to differentially offset the E/I balance resulting in markedly different compensatory inhibitory and excitatory alterations. Experimentally, the two types of inhibition will be independently altered by pharmacological, molecular biological or genetic means. The resulting offset in the E/I balance will be studied using high resolution electrophysiological recordings in long-term organotypic slice cultures and acute brain slices obtained from mice. Other experimental approaches will include collaborative anatomical, immunocytochemical, pharmacological, and molecular biological techniques. Homeostatic alterations in the E/I balance will be addressed in a highly specific manner using appropriate knockin and knockout mice for specific GABAA receptor (GABAAR) subunits and second messenger systems. The proposed studies will further our understanding of the physiological plasticity in the CNS, and will help form the basis for therapeutical advances rationally aimed at preventing pathological plasticity of GABAARs. Awareness of the excitatory inertia following withdrawal from allosteric GABAAR modulators, knowledge about the site of action and plasticity of neurosteroids, BZ and alcohol, and a fundamental understanding of homeostatic inhibitory plasticity will advance drug discovery for the treatment of many severely incapacitating neurological and psychiatric disorders with known involvement of the GABA system. Our findings could provide the basis for novel and rationally targeted therapeutical approaches for the cure of anxiety, stress, benzodiazepine withdrawal, and epilepsy.

DESCRIPTION (provided by applicant): Specific learning disabilities are the most common neurological complication in children with neurofibromatosis type I (NF1), a disorder affecting 1/4000 people world-wide. This genetic disease is caused by mutations in the NF1 gene which encodes neurofibromin, a Ras GTPase activating protein that is highly expressed in the brain. Our studies of mice mutant for the neurofibromin gene (Nf1+/- ) indicated that these mutants showed enhanced GABAA-mediated inhibition, deficits in long-term potentiation (LTP) and in spatial learning. In this application we propose to test the hypotheses that the spatial learning deficits of mice with an heterozygous-null germ-line Nf1 mutation (Nf1+/- mice), that model closely the human condition, are due to enhanced inhibition (either because of pre- or post-synaptic changes) that leads to deficits in LTP and subsequently to abnormalities in learning. We propose to pin-point both the cellular mechanism by which the Nf1+/- mutation affects inhibition, plasticity and learning and the brain region(s) affected by this mutation. To accomplish this we will use transgenic mice with cell-type (inhibitory or excitatory neurons) restricted deletions of Nf1, Adeno-Associated Virus type 2 Cre-recombinase (AAV-Cre) driven and region-specific (hippocampus, prefrontal cortex) deletions of Nf1, as well as a number of pharmacological, electrophysiological and behavioral tools. The specific aims of this proposal are: SPECIFIC AIM #1 - To determine whether deletions of Nf1 in either hippocampus or prefrontal cortex can account for the learning deficits of the Nf1 mutant mice. SPECIFIC AIM #2- To determine the critical cellular locus for neurofibromin's role in learning and memory. SPECIFIC AIM #3 - To determine how neurofibromin affects GABA-mediated inhibition and LTP. Although there is a great deal of data that implicate Ras/MAPK signaling in plasticity and learning, it is still unclear how this signaling pathway modulates these complex processes. The studies proposed here will further our understanding of the role of neurofibromin/Ras/MAPK signaling in the modulation of GABA-mediated inhibition, LTP and learning. Importantly, they will also be crucial for developing targeted treatments for the debilitating learning disabilities associated with Neurofibromatosis Type I.

DESCRIPTION (provided by applicant): The goal of the proposed studies is to address fundamental processes underlying the changes in neuronal excitability in the female brain during periods of altered steroid hormone levels. We will explore the mechanisms governing changes in GABAergic inhibition during the ovarian cycle, pregnancy, and during the interaction between stress and the ovarian cycle. Our experiments will focus on the regulation of GABAAR expression and function by progesterone and its neurosteroid metabolites. We recently demonstrated dynamic, ovarian cycle-linked modifications in specific GABAAR expression and function, while others have shown the same receptors to parallel ovarian cycle changes in the periaqueductal grey matter or to be upregulated in a steroid withdrawal model of PMS. During diestrus in mice when levels of progesterone and of progesterone-derivatives neurosteroids are elevated, there is an increased expression: of the GABAAR 6 subunits in hippocampal neurons and an increase in GABAAR 6 subunit-mediated tonic inhibition in dentate gyrus granule cells (DGGCs). This increase in GABAAR 6 subunits corresponds to a period of lowered seizure susceptibility and anxiety. The specific aims of this project will extend these Findings to the study of GABAAR alterations during pregnancy/postpartum and to the interactions between stress and the ovarian cycle. The fractional contributions of progesterone and its derivatives to the regulation of GABAAR expression and function will be addressed and possible molecular mechanisms (local receptor synthesis and receptor internalization) underlying the changes affecting the GABAergic system will be studied. A novel mouse model of postpartum depression will constitute a unique opportunity to begin to study fundamental neuronal mechanisms underlying this psychiatric disorder affecting nearly 10% of women in early motherhood. Our general hypothesis is that physiological and pathological changes in endogenous steroid hormones in the female brain alter neuronal excitability by producing hormonal state-dependent changes in specific neurotransmitter receptor systems. The focus of the present proposal is GABAergic inhibition in general, and specifically the tonic inhibition mediated by 6 subunit-containing GABAARs, which are the preferred, if not the sole, site mediating neurosteroid sensitivity in the CNS. The project will address the role of endogenous progesterone in GABAAR expression and function in female mice and will identify mechanisms underlying steroid hormone-linked changes in GABAARs by using a variety of molecular biological, biochemical, electrophysiological and behavioral approaches. Our studies are relevant to understanding the pathology of several psychiatric and neurological disorders including pre-menstrual dysphoric disorder (PMDD), catamenial epilepsy, and postpartum depression that are all linked to alterations in hormone levels in women. Uncovering events controlling the hormone-mediated regulation of GABAARs in females will lead to novel and potentially more effective therapeutic targets for treating and ultimately preventing these neurological and psychiatric disorders, while opening the way for fresh approaches to functional and clinical studies in humans.

DESCRIPTION (provided by applicant): According to the World Health Organization (WHO), epilepsies affect over 50 million people worldwide. This brain disorder affects not only the sufferers but also their families and indirectly the entire community. The approximately 2.5 million epileptics in the US, with 150-200,000 cases added each year, constitute an annual economic burden of ~$14 billion. Temporal lobe epilepsy (TLE) is the most common form of pharmaco- resistant epilepsies and is associated with significant morbidity and mortality due to recurrent and unpredictable seizures. In the civilian population, there is a good correlation between the occurrence of a neurological insult earlier in life (head trauma, status epilepticus, stroke, inflammation, etc.) and the development of TLE after a latent period. In addition to civilians, the incidence of posttraumatic epilepsy may increase drastically in the returning US veterans from Iraq and Afghanistan because the shock wave originating from Improvised Explosive Devices produces a novel type of brain injury including vascular damage. With evidence of brain injury in 61% of returning soldiers exposed to blasts, subsequent posttraumatic epilepsy is likely to reach unprecedented proportions in this population. The transition from brain insult to chronic epilepsy is termed epileptogenesis. In the absence of mechanistic insights into epileptogenesis, there is no rational pharmacological approach to its prevention. Conventional antiepileptic drugs (AEDs) are ineffective in preventing the conversion of a normal brain into an epileptic brain following a precipitating insult. The present proposal will address the major gap in our knowledge about the process of epileptogenesis by examining the common underlying mechanism at the cellular and circuit level of three different types of insult to the brain. It will identify specific neurons and circuits, and it will test whether these neuronal elements are necessary and sufficient for the progression to TLE following various insults. There is already some circumstantial evidence that neurons born in the adult brain are involved in this process. Our central hypothesis is that the key elements in epileptogenesis, leading to TLE following a precipitating brain insult, are a group of dentate gyrus granule cells that were caught by the insult at the most plastic stage of their development. This constitutes a new conceptual model of epileptogenesis and is fully testable using innovative novel optogenetic and chemical-molecular biological approaches to activate or inactivate specific neurons at specific times during the process of epileptogenesis. Moreover, electrophysiological and pharmacological studies will identify the distinguishing properties of these cells and circuits. Their specific fingerprints can then be used to develop novel pharmacological or gene therapy tools that will stop these critical neural elements from producing chronic epilepsy after a brain insult. The new discoveries will facilitate the translation of our basic findings into clinical practice.

DESCRIPTION (provided by applicant): Schizophrenia is associated with a reduction in GABA synthesis in a subpopulation of cortical interneurons that express the calcium-binding protein, parvalbumin (PV). These inhibitory interneurons display fast-spiking properties and target the perisomatic domain and axon initial segment of excitatory pyramidal neurons, thus enabling exquisite control over their spike timing. A deficit in such perisomatic inhibition in schizophrenia is likely to contribute to the impairments of fast cortical network synchronization and higher cognitive processing, which are key features of this disabling mental disorder. Another distinguishing characteristic of cortical PV interneurons are the dense aggregates of extracellular matrix molecules that ensheath their somata and primary processes, appearing as perineuronal nets (PNNs). The formation and degradation of these PNNs are activity-dependent, but their function and modulation in schizophrenia remain unknown. Our hypotheses are that 1) PV interneuron plasticity in schizophrenia is related to structural remodeling of PNNs, and 2) dysfunction of reciprocal inhibition between PV interneurons, possibly secondary to the altered structure of PNNs, is a key component of GABAergic deficits in schizophrenia. We will use two recently characterized transgenic mouse models of schizophrenia: the tamoxifen-inducible expression of the dominant-negative DISC1 C-terminal fragment (DISC1-cc) in 1-CaMKII expressing neurons and the selective knockout of NMDA receptors in forebrain GABAergic interneurons (Ppp1r2-Cre x NR1loxP/loxP mice). The ultrastructure of PNNs surrounding afferent terminals on PV interneurons will be determined using stimulated emission depletion (STED) super-resolution microscopy (nanoscopy) in fixed tissue. A deficiency in the inhibitory output of cortical PV interneurons in schizophrenia is thought to lead to hyperactivity and hyposynchrony of excitatory pyramidal neurons, and contribute to deficits in cognitive function. PV interneurons also show dense reciprocal connectivity, but the possible pathophysiology of such mutual inhibition remains unexplored. Patch-clamp recordings from PV interneurons in vitro will elucidate how these multiple modes of reciprocal GABAergic signaling and intrinsic membrane properties are modified in mouse models of schizophrenia. We propose that remodeling of the PNNs surrounding PV interneurons, and the erosion of compartmentalized synaptic and extrasynaptic GABAergic signaling pathways are critical components of the cortical network disinhibition in schizophrenia. Understanding how the multiple facets of GABAergic inhibition are disturbed in schizophrenia is essential for the rational design of GABAergic therapeutics. Moreover, elucidating the particular role of PNNs in both the function and dysfunction of PV interneurons should inspire new treatment strategies targeting the proteases responsible for PNN degradation. PUBLIC HEALTH RELEVANCE: Schizophrenia is a debilitating mental disorder that affects ~2.4 million Americans, and ~1% of the world's adult population. This syndrome is thought to arise through an interaction of multiple genetic and environmental factors during brain development, leading to a persistent dysfunction of dopaminergic, glutamatergic, GABAergic and cholinergic neurotransmitter systems into adulthood. Current monoaminergic treatments for schizophrenia are most effective in treating positive symptoms, comprising hallucinations and/or delusions. However, such antipsychotics yield little amelioration of the burden of negative symptoms and cognitive impairments, which may have the greatest impact on patients' long-term social and occupational abilities. It has been suggested that cognitive dysfunction in schizophrenia might be more intimately linked with deficits in cortical GABAergic transmission. There is great potential for addressing such dysfunction, as GABAA receptors display a high degree of heterogeneity in subunit composition, which is reflected in distinct patterns of expression across cell types and brain regions, and confers the opportunity for selective pharmacological modulation. The rational design of GABAergic therapeutics, though, will require a more detailed understanding of how functional imbalances in the multiple facets of GABAA receptor-mediated signaling contribute to schizophrenic symptoms.

DESCRIPTION (provided by applicant): A large portion of the estimated $2.2 trillion stroke-related costs estimated in the U.S. between 2005 and 2050 pertains to the cost of care during the recovery period after the brain trauma, which in turn is highly correlated with the level of disability. These figures point to the urgency of improving post stroke neurorehabilitation, particularly since there are no drugs available, nor are there any in the pipeline, to facilitate functional recovery after stroke. Until recently, only few studies focused on the basic mechanisms and potential improvement of post stroke functional recovery. Previous findings from our laboratory, and some promising human data about non-invasive brain stimulation in recovering stroke patients, point to an imbalance between excitatory/inhibitory cortical circuits as a major obstacle in post stroke functional recovery. We will use a mouse model of stroke to examine how the outcome of brain stimulation after the injury can be improved. Photothrombotic stroke will be induced in the motor cortices of mice using a novel stroke model developed for focal ischemia induction in awake freely moving animals. We will test the hypothesis that the modulation of a highly specific component of the affected cortical microcircuits will provide the best outcome on functional recovery after stroke. Four different transgenic mouse lines will be used for specific optogenetic manipulations of excitatory and inhibitory cortical microcircuits in the peri-infarct region, or in the equivalent cortical area on the contralateral hemisphere. 1) Cortical pyramidal cells will be stimulated in the peri-infarct zone to test the effects of ipsilesonal stimulation of excitatory circuits; 2) The activity of inhibitory GABAergic cells will be suppresse in the peri-infarct zone to reduce the enhanced inhibition observed after stroke, previously shown by our lab to obstruct the path to functional recovery; 3) Peri-infarct glial cells will be stimulated to test whether impaired glial activity and a secondarily reduced GABA uptake may contribute to the observed enhancement in inhibition and the ensuing delayed functional recovery; 4) Contralateral to the infarct, GABAergic cells will be stimulated to dampen the output of the healthy motor cortex which may act to lower the activity of the lesioned side. Optical stimulation will be carried out for 5 days after stroke induction in daily 1-hour sessions, based o protocols of non-invasive, but non-specific brain simulation in human subjects. In addition to more traditional measures of functional motor recovery in mice, we will use a novel automated measurement of the mouse's movements on an air-supported sphere, which can be subjected to better quantification than previously used measures of motor recovery. By introducing novel approaches in stroke induction, stimulation therapy, and outcome metrics, the project addresses scientific questions related to the enormous economical and health burdens of stroke in both the U.S. and worldwide. The project will also identify specific target systems for promoting rehabilitation in the clinical practice, to result in a healthier life and an earlier functional reovery of stroke victims.

? DESCRIPTION (provided by applicant): Changing levels of the ovarian hormones 17?-estradiol (E2) and progesterone (PROG), together with their neuroactive metabolites, have essential actions on the central nervous system (CNS). Many of the CNS effects involve memory and mood disorders such as those found in women after menopause, or the cognitive and psychiatric symptoms frequently present during specific stages of the menstrual cycle. Yet, little is known about how large swings in ovarian hormone levels affect the coordination of neuronal ensembles in the brain during behavior and how particular abnormalities may ensue at the cellular or molecular level. This proposal focuses on the function of parvalbumin-positive (PV+) interneurons (INs) as collective mediators of cognitive and emotional states associated with altered ovarian hormone levels. These cells and the networks they control are critically involved in sharp-wave ripples (SPW-R) and ?-oscillations (30-120 Hz), brain rhythms essential for memory recall, cognition, and information processing. We hypothesize that E2 and PROG act on PV+INs through distinct mechanisms to alter SPW-R, ?-oscillatory activity, and/or phase-amplitude coupling between ? (5-10 Hz) and ?-oscillations. Two novel mechanisms will be investigated: the function of ? subunit- containing ?-amino-butyric-acid receptors (?-GABAARs) of PV+INs as a target for PROG-derived neurosteroids (NS); and the signaling cascade formed by the G-protein coupled E2 receptor (GPER-1) ? neuregulin 1 (NRG-1) ? endothelial growth factor receptor tyrosine kinase (ErbB4), for E2. Two periods of ovarian hormonal alterations will be examined in mice. The first is the physiological ovarian cycle in which E2 and PROG levels rapidly swing up and down over a typical cycle period of 4-6 days. The second is a genuine model of human menopause in mice, that is, the selective attrition of small primordial and primary ovarian follicles by the industrial chemical 4-vinylcyclohexene diepoxide (VCD) that has negligible effects on other tissues. These studies will provide the experimental underpinnings of the first comprehensive and unifying model of ovarian hormone action on neuronal oscillations underlying cognition and working memory. Sophisticated electrophysiological and optogenetic experiments in vivo and in vitro, genetic manipulations, pharmacological approaches never before tested for effects on neuronal ensembles, and morphological/immunohistochemical studies carried out for the first time in this context will converge in the proposal. This multifaceted and novel approach is expected to provide unique insights into the actions of ovarian hormonal changes on the female brain. The studies have a high translational potential as they will shed light on possible treatments for millions suffering from menstrual cycle-related neurological and psychiatric dysfunction (pre-menstrual syndrome, PMS, and pre-menstrual dysphoric disorder, PMDD), and may provide explanation for the cognitive decline and high prevalence of sporadic Alzheimer's disease (AD) in post-menopausal women.