2001 — 2003 |
Luscher, Bernhard |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Mapping the Neural Substrate of Anxiety @ Pennsylvania State University-Univ Park
DESCRIPTION: (provided by applicant) The objective of this proposal is to identify the neural substrates underlying trait anxiety. We have found that heterozygosity of the GABAA receptor y2 subunit gene leads to a subtle impairment of postsynaptic GABAA receptor function and trait anxiety in mice. The selective behavioral and cognitive deficits of y20/~ mice, together with established knowledge on the neural circuitry of conditioned fear and the regional distribution of the GABAA receptor deficit in =y2 0/+ mice, allow predictions as to which brain regions mediate trait anxiety. We hypothesize that GABAA receptor deficits in the cerebral cortex and/or hippocampus of y2 0/ mice lead to trait anxiety and that a GABAA receptor deficit that is confmed to these brain regions will result in trait anxiety-like behavior similar to the phenotype of =y2 0/+ mice. In order to map the brain regions that mediate trait anxiety, we have generated a mouse line that allows spatiotemporally restricted inactivation of the y2 subunit gene by means of the Cre/loxP system. Upon Cre induced inactivation of the y2 subunit gene, GABAA receptor function will be impaired in selective brain regions defined by the Cre expression pattern of tissue-specific Cre-transgenes or by stereotaxically applied Cre-encoding virus. Subsequently, stereotaxic injection of Cre-recombinant virus will be used to further characterize trait anxiety. These experiments will include determination of the critical stage during development during which GABAergic deficits lead to trait anxiety. In addition, we will determine whether the cognitive deficits associated with trait anxiety reflect alteration of the acquisition or expression of conditioned fear. The neural circuits that are implicated in the anxiolytic action of the benzodiazepines have considerable anatomical overlap with the proposed neural circuits of trait anxiety and are of therapeutic interest. To test this hypothesis, Cre-induced inactivation of the y2 subunit gene, which is essential for benzodizepine action, will be used to map the brain regions mediating the anxiolytic effect of benzodiazepines.
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2002 — 2006 |
Luscher, Bernhard |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Clustering and Synaptic Targeting of Gaba-a Receptors @ Pennsylvania State University-Univ Park
DESCRIPTION (provided by applicant): The long-term goal of our research is to unravel the mechanism regulating the clustering and postsynaptic targeting of g-aminobutyric acid type A (GABAA) receptors. These receptors are hetero-pentameric chloride channels and they mediate most inhibitory neurotransmission in the brain. GABAA receptor subtypes distinguished by their subunit composition are differentially expressed at the regional and cellular level. Differential localization of GABAA receptors is implicated in regulation of synaptic efficacy of GABAergic transmission and pathological changes in receptor localization are implicated in debilitating disorders such as epilepsy and anxiety. The factors and signaling pathways that determine receptor clustering and localization are largely unknown and shall be identified as part of this proposal. Most GABAA receptor subtypes are clustered at postsynaptic sites by a mechanism that requires the g2 subunit and the clustering protein gephyrin. Different a subunits might target receptors to different types of synapses. However, it is not known how GABAA receptors are linked to gephyrin and to the subsynaptic cytoskeleton. We hypothesize that synaptic localization is mediated at least in part by postsynaptic proteins that interact with cytoplasmic protein domains of the g2 subunit. To test this hypothesis we will map g2 subunit domains that mediate postsynaptic localization in neurons. Loss of the g2 subunit in vivo is associated with a reduced GABAA receptor channel conductance. It has been postulated that this reduced channel function during neural development might contribute to loss of GABAA receptor clusters in g2 subunit deficient neurons. Genetic approaches will be used to determine whether receptor activation is required for clustering of GABAA receptors. Finally, novel GABAA receptor binding proteins that interact with the g2 or a2 subunits will be analyzed with respect to their role in receptor clustering and localization. These studies will significantly advance our understanding of the regulation of GABAergic neurotransmission and identify new potential drug targets for the treatment of mental and neurological disorders such as anxiety and epilepsy.
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2005 — 2009 |
Luscher, Bernhard |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Analysis of the Neural Substrate of Anxiety @ Pennsylvania State University-Univ Park
DESCRIPTION (provided by applicant): Trait anxiety describes a personality trait characterized by an elevated basal level of anxiety that represents a vulnerability factor for anxiety disorders and various forms of depression. Anxiety-disorders that afflict humans include generalized anxiety disorder (GAD), panic, diverse phobias and posttraumatic stress disorder (PTSD) which, together, are among the most frequent and costly psychiatric illnesses. The longterm goal of our research is to elucidate the molecular and cellular mechanisms underlying anxiety disorders. GABA-A receptors are widely recognized to hold a gatekeeper function in the modulation of anxiety state, especially in GAD and panic disorder. Mice with a heterozygous mutation of the GABA-A receptor gamma 2 subunit gene have been established as an animal model of that anxiety that exbits behavioral and cogntive deficits reminiscent of GAD in humans. Conditional deletion of this gene in pyramidal forebrain neurons during embryogenesis but not in adolescent mice leads to excessive trait anxiety in adults. In agreement with a developmental mechanism underlying trait anxiety, gamma 2 subunit heterozygous mice exhibit reduced hippocampal neurogenesis and serotonergic transmission. Based on these observations we hypothesize (I) that trait anxiety is due to the loss of specific types of hippocampal neurons during development. We further hypothesize (II) that the GABA-A receptor deficit leads to a deficit in serotonergic transmission that contributes to the manifestation of trait anxiety. We also predict (III) that treatment of young mutant mice with antidepressant and neurogenesis-enhancing drugs prevents development of trait anxiety in adults. Finally, (IV) we hypothesize that GABA-A receptor deficits in the hippocampus and cerebral cortex act independently of deficits in the amygdala to establish an anxiety-like phenotype. Together these studies will greatly advance our undestanding of the mechanism underlying anxiety and depressive disorders.
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2008 |
Luscher, Bernhard |
R56Activity Code Description: To provide limited interim research support based on the merit of a pending R01 application while applicant gathers additional data to revise a new or competing renewal application. This grant will underwrite highly meritorious applications that if given the opportunity to revise their application could meet IC recommended standards and would be missed opportunities if not funded. Interim funded ends when the applicant succeeds in obtaining an R01 or other competing award built on the R56 grant. These awards are not renewable. |
Protein Trafficking Regulating the Formation of Gabaergic Synapses @ Pennsylvania State University-Univ Park
Project Summary Neural inhibition by ?-aminobutyric acid (GABA) is vitally important for normal brain function as is evident from deficits in GABAergic transmission associated with a wide range of devastating neurological and psychiatric disorders including epilepsy, anxiety, mood disorders, mental retardation, and many others. Deficits in GABAergic transmission are commonly associated with deficits in expression, cellular distribution, or functional properties of GABA-A receptors. Here we focus on palmitoylation as a critically important mechanism that controls the trafficking of GABA-A receptors and the synaptic cell adhesion molecule neuroligin, which both are critically important for GABAergic inhibitory synaptic transmission. Our preliminary experiments show that the gamma2 subunit of GABA-A receptors and neuroligin 2 (NL2) are in vitro palmitoylated selectively by the same struturally related palmitoyltransferases, GODZ and SERZ-beta (also known as zDHHC3 and 7). Palmitoylation by these enzymes in postsynaptic neurons contributes to normal trafficking of GABA-A receptors, normal GABAergic innervation and normal function of GABAergic synapses. Moreover, accumulation of NL2 at synapses requires postsynaptic gamma2 subunit containing GABA-A receptors. Together, these preliminary findings lead us to propose the central hypothesis that GODZ/SERZ-[unreadable]-mediated palmitoylation and functional cooperativity between NL2 and GABA-A receptors play important roles in formation and postsynaptic differentiation of GABAergic inhibitory synapses. To further test this hypothesis we will i) test the function of GODD/SERZ-[unreadable] in palmitoylation and trafficking of GABA-A receptors, ii) test the function of GODD/SERZ-[unreadable] in palmitoylation and trafficking of NL2, and iii) analyze cooperativity between ?2 subunit-containing GABA-A receptors and NL2 in the formation of GABAergic synapses. Together these experiments will provide a thorough understanding of a mechanism that contributes to faithful apposition of GABAA receptors across form GABAergic terminals and thereby contributes to assembly and differentiation of GABAergic inhibitory synapses.
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2009 — 2010 |
Luscher, Bernhard |
RC1Activity Code Description: NIH Challenge Grants in Health and Science Research |
Use of a Mouse Model of Anxious Depression to Assess the Safety of Pediatric Anti @ Pennsylvania State University-Univ Park
DESCRIPTION (provided by applicant): This application addresses broad challenge area (15) Translational Science and specific challenge topic 15-MH-101, Effects of Psychotropic Medications on Neurodevelopment and Behavior in Animal Models". Antidepressants and anxiolytics are increasingly prescribed to pediatric patients at progressively younger ages and often for extended periods of time. These drugs act upon neurobiological substrates that undergo profound structural and functional changes from embryogenesis to childhood and adolescence, raising concerns for detrimental drug effects on brain development. In particular, treatment of children and adolescents with antidepressant drugs such as fluoxetine may result in increased suicidal behavior and lethality. Moreover, experiments in mice indicate that administration of fluoxetine during postnatal developmental stages corresponding to the last trimester of human development leads to behavior indicative of heightened anxiety and emotionality in adulthood. These effects are reminiscent of detrimental behavioral effects observed upon treatment of young mice with diazepam, a prototype benzodiazepine that potentiates the function of GABA via GABA-A receptors. Indeed, accumulating evidence suggests that antidepressants such as fluoxetine may exert their effect in part by modulation of GABAergic transmission. Fluoxetine and diazepam therefore might ultimately affect the developing nervous system through common mechanisms that call for a direct comparison. Postnatal brain development involves progressive, neural activity-dependent and function-specific maturation of GABAergic circuits, which at the cellular level includes a switch from mostly depolarizing function of GABA-A receptors to mostly hyperpolarizing effects. This developmental mechanism has been proposed to define temporal boundaries for critical periods of activity-dependent functional maturation that applies universally to most if not all brain functions. Evidence that such mechanisms might apply to the neurobiological substrate of anxiety and mood disorders is available from GABA-A receptor gamma2 subunit heterozygous mice (gamma2 mice), which have been established as an animal model of anxious depression that includes cognitive, behavioral, cellular, and endocrine characteristics associated with anxiety and mood disorders in patients. Importantly, analyses of conditional gamma2 mice suggest that the behavioral and other abnormalities in these mice are mediated by a developmental GABA-A receptor deficit. Interestingly, while diazepam administered to young mice has anxiogenic-like effects on adult behavior in wildtype (WT) mice, similar treatment of young gamma 2 mice is neutral or has anxiolytic like effects. These findings suggest that gamma2 mice exhibit GABAergic deficits in a critical period of neural plasticity in neural circuits relevant for anxiety and depressive- like behavior. Conversely, drug induced potentiation of GABAergic transmission of an otherwise normally developing brain negatively affects proper maturation of the same circuits. Given that fluoxetine and diazepam administered to young WT mice have similar anxiogenic-like effects on behavior in adulthood, we hypothesize that the two drugs interfere similarly with maturation of GABAergic circuits that are relevant for anxiety and depression-related behavior. To further address the mechanism of potentially detrimental developmental effects of fluoxetine and diazepam we here propose to i) determine and compare the postnatal developmental windows during which these two drugs affect behavior of WT and GABAAR gamma2 subunit heterozygous mice in adulthood. In addition, we will analyze and compare the developmental effects of these drugs on diverse molecular and cellular markers that are altered in gamma 2 mice and are implicated in anxiety and depression-related behavior. These studies will alert to potentially detrimental effects of antidepressant and anxiolytic drug on the developing postnatal brain and will help to delineate detrimental from neutral or possibly beneficial drug effects on brain development. In addition, they may advance the design and safety of antidepressant and anxiolytic therapies directed specifically at pediatric and adolescent patients. PUBLIC HEALTH RELEVANCE: Antidepressants, anxiolytics and other psychotropic medications are increasingly prescribed to pediatric patients at progressively younger age and often for extended periods of time. These drugs act upon neurobiological substrates that undergo profound structural and functional changes during childhood and adolescence, yet their mechanisms of action in the developing nervous system are largely unknown. We here take advantage of a mouse model of anxious depression to assess molecular, cellular, endocrine and behavioral consequences of antidepressant drug treatment in young animals representative of pedriatic patients. These studies will alert to potentially detrimental effects of antidepressant and anxiolytic drug on the developing postnatal brain and will help to delineate detrimental from neutral or possibly beneficial drug effects on brain development. In addition, they may advance the design and safety of antidepressant and anxiolytic therapies directed specifically at pediatric and adolescent patients.
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2012 — 2013 |
Luscher, Bernhard |
R21Activity Code Description: To encourage the development of new research activities in categorical program areas. (Support generally is restricted in level of support and in time.) |
A Novel Developmental Mouse Model of Major Depressive Disorder @ Pennsylvania State University-Univ Park
DESCRIPTION (provided by applicant): Anxiety Disorders and Major Depressive Disorder (MDD) are among the most prevalent and debilitating psychiatric syndromes. They exhibit extensive comorbidity and overlapping genetic origins, yet their molecular etiology and functional interrelationship are poorly understood. The vulnerability for both types of disorders i greatly exacerbated in early life, indicating that they are primarily developmental disorders. Mounting evidence points to a causal role of deficits in GABAergic transmission for both types of disorders. In particular, MDD is accompanied by reduced function and loss of GABAergic interneurons, reduced GABA concentration most pronounced in the melancholic subtype of MDD, and alterations in the subunit composition of the principal GABA receptors (GABAARs). Moreover, extensive analyses of GABAAR y2 subunit heterozygous mice by our lab suggest that modest developmental deficits in GABAergic transmission through these receptors may be causal for MDD. These mice exhibit behavioral, cognitive and cellular alterations expected of such a model, including endocrine and pharmacologic characteristics of melancholic MDD. Importantly, conditional gene ablation experiments indicate a postnatal developmental origin of this phenotype. Here we propose to use pharmacological manipulation of GABAergic transmission during postnatal development to generate a novel non-genetic mouse model of MDD that uniquely i) mimics a developmental etiology of MDD, ii) allows separation of depression-related from anxiety-related pathology, and iii) leads to a permanent/stable phenotype in adulthood that is amenable to investigation across disciplines (behavioral, cognitive, molecular, neuroanatomical, pharmacological, etc.). Preliminary experiment indicate that treatment of mice with diazepam (DZP) between postnatal day (P)10 and P21 leads selectively to increased anxiety-like behavior. By contrast, DZP treatment from P29-35 leads to selectively increased immobility under stressful conditions, which is the inverse of a pharmacological antidepressant-like effect. Thus, we hypothesize that anxiety- and depression- related behavioral traits are independently controlled by similar mechanisms during distinct postnatal developmental critical periods. We propose to establish P29-35 DZP treated mice as a novel and unique mouse model of MDD that is suited to monitor the developmental molecular sequelae underlying vulnerability to MDD in adulthood, and to distinguish the molecular etiology of MDD from that of heightened anxiety. In Aim 1 we will more fully establish the depressive like behavioral, endocrine and pharmacologic phenotype of P29-35 DZP treated mice. In Aim 2 we will use transcriptome analyses of the cingulate cortex of P10-24 and P29-35 DZP treated mice to compare the molecular signature of anxious vs. depressive like brain states. The work proposed will lay the foundation for an in depth analysis of the developmental mechanism underlying vulnerability to MDD.
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2013 — 2017 |
Luscher, Bernhard |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Gabaergic Control of Depression Related Brain States @ Pennsylvania State University-Univ Park
DESCRIPTION (provided by applicant): Major depressive disorder (MDD) is a leading cause of total disability with inadequate treatment options and unresolved etiology. However, increasing evidence suggests that genetic and environmental vulnerabilities may converge on deficits of GABAergic transmission as a possible, causative core symptom of MDD. Other lines of research point to changes in glutamatergic transmission as being associated with MDD. In particular, subanesthetic doses of the NMDAR antagonist ketamin have rapid and lasting antidepressant effects even in otherwise drug-resistant forms of MDD, pointing to altered function of NMDA receptors. We have established GABA-A receptor gamma2 subunit heterozygous mice as an animal model with excellent construct, face and predictive validity of partially drug resistant MDD. Preliminary data show that GABA-A receptor deficits in gamma2 subunit heterozygous cultures result in markedly reduced expression and function of glutamate receptors. Treatment of mutant cultures with ketamine results in reversal of these deficits. Conversely, mice with GABA-A receptor deficit delimited to forebrain interneurons show a robust antidepressant-like phenotype. We here address the overall hypothesis that MDD is caused by reduced synaptic input from select subtypes of cortical and hippocampal GABAergic interneurons to pyramidal cells. The ensuing GABAergic deficit and altered E/I imbalance, through adaptive mechanisms results in reduced expression and function of ionotropic glutamate receptors, along with reduced functional connectivity of neurons. Transient treatment with NMDA receptor antagonists such as ketamine reverses these deficits and, following dissociation of the drug from the receptor, restores normal glutamatergic transmission. To address this hypothesis we will analyze ketamine-induced changes in expression and function of glutamate receptors and behavior in cultured neurons, brain slices and mice, respectively. We will further test whether chronic treatment with currently used antidepressants has similar effects on glutamatergic transmission. Lastly, we will use genetic deletion of the gamma2 subunit gene in small subsets of interneurons to identify interneuron subclasses that control depression-related behavior. Collectively, our proposal will contribute a major conceptual advance in understanding of the substrate of major depression as well as AD action.
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2018 — 2019 |
Luscher, Bernhard |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Elucidating the Neuronal Substrate of a Stress-Resilient Brain State @ Pennsylvania State University-Univ Park
Modified Project Summary/Abstract Section Major depressive disorder (MDD) is a leading cause of total disability with inadequate treatment options and unresolved underlying biology. However, diverse environmental stressors are widely recognized as major culprits in the etiology of MDD Mounting evidence suggests that environmental stressors and other causes of MDD converge on a reduced ratio of GABAergic and glutamatergic synaptic transmission (E/I ratio), while antidepressant therapies appear to act over time to augment GABAergic transmission and reverse such imbalances. In support of such mechanisms we have generated mice with enhanced GABAergic transmission by disinhibiting somatostatin positive GABAergic interneurons through conditional deletion of the gamma2 subunit of GABA(A) receptors selectively from these interneurons. Indeed, SSTCre:gamma2(f/f) mice exhibit a robust antidepressant- and anxiolytic-like phenotype, along with reduced phosphorylation of the eukaryotic elongation factor 2 (eEF2), which serves as a recognized biochemical endpoint of ketamine and other rapid-acting antidepressants. Here we propose to extend this line of experimentation and assess whether SSTCre:gamma2(f/f) mice are also resilient to the detrimental effects of chronic stress. Male and female SSTCre:gamma2(f/f) will be subjected to a 6-week uncontrolled chronic mild stress (UCMs) paradigm or stress-free control conditions and then examined for resilience to stress with respect to changes in emotional behavior (Specific Aim 1), biochemical markers indicative of antidepressant drug action (Specific Aim2), cellular changes indicative of detrimental effects of stress (Specific Aim 3) and synaptic/functional changes that are normally observed after stress (Specific Aim 4).
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