Browsing by Subject "Neuronal Plasticity"
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Item Activity-Dependent Regulation of Inhibition from Different Inhibitory Subtypes(2007-08-08) Bartley, Aundrea Frances; Gibson, Jay R.Neuronal activity, in the form of action potential firing, is critical in the maturation and maintenance of neocortical circuitry. A negative feedback mechanism by which neuronal circuits adapt to changing levels of average activity on a time scale of hours to days is known as homeostatic plasticity. At the simplest level, homeostatic adaptations occur to maintain firing rate of neurons at a particular set-point. To better understand homeostatic plasticity at the network level, one must understand the activity-dependent adaptations that occur in the different neocortical cells types. To this end, I examined the regulation of inhibitory neurons and their synapses. I used chronic pharmacological block of activity in a neocortical slice cultures to examine the role activity plays in regulating feedback inhibition defined by two biochemical inhibitory neuron subtypes - parvalbumin-positive (Parv+) and somatostatin-positive (Som+). The cellular and synaptic components of local feedback inhibition were examined. I found that chronic activity blockade caused the following: 1) an increase in the intrinsic excitability of Som+ neurons through the downregulation of 2 substhreshold currents. While not thoroughly examined in Parv+ neurons, a similar, but weaker, increase in excitability may occur in these neurons as well. These< changes are consistent with a homeostatic maintenance of firing rate in these neurons. 2) a differential regulation of monosynaptic inhibition based on subtype that was frequency dependent. At low frequency action potential firing, Parv+ mediated inhibitory drive was downregulated while Som+ was unchanged. Both subtypes were likely downregulated at high frequency firing. 3) an upregulation of excitatory drive onto both Parv+ and Som+ neurons. This was most dramatic at low frequency firing where both subtypes displayed an almost 3-fold increase. This is also consistent with homeostatic maintenance of firing rate in inhibitory neurons. 4) based on the above, a clear change in recurrent inhibition occurred at low frequency firing. First, net recurrent inhibition was increased for both subtypes, but the relative influence of the two changed, such that Som+ recurrent inhibition contributed more relative to that of Parv+ circuitry. At high frequency firing, a slight, but less resolvable, increase in net recurrent inhibition may have occurred in both subtypes without any change in relative contribution. 5) all of the synaptic changes were likely due to increases in presynaptic release probability and/or decreases in synapse number.Item Biochemical Characterization of Delta FosB(2006-12-19) Carle, Tiffany Lynn; Nestler, Eric J.; Phillips, Margaret A.; De Martino, George; Monteggia, LisaDeltaFosB, the truncated splice variant of FosB, is an important mediator of the long-term plasticity induced in brain by chronic exposure to many types of stimuli, such as repeated administration of drugs of abuse, stress, or compulsive running. Once induced, DeltaFosB persists in the brain for weeks or months following cessation of the chronic stimulus. In addition, DeltaFosB both activates and represses transcription. The biochemical basis of DeltaFosB's persistent expression and dual transcriptional regulation has remained unknown. Both the enhanced protein stability and transcriptional properties are unique to DeltaFosB, compared to FosB, and are critical for its role in neural plasticity. DeltaFosB lacks the C-terminal 101 amino acids of FosB as a result of alternative splicing. The purpose of this work is to biochemically characterize DeltaFosB relative to FosB, to determine how truncation of the FosB C-terminus directs its function. Here, I show that the FosB C-terminus contains two destabilizing elements that promote the degradation of FosB by both proteasome dependent and independent mechanisms. Pulse chase experiments of FosB C-terminal truncation mutants indicate that removal of these C-terminal degrons increases the FosB half-life ~5 fold and prevents its proteasome-mediated degradation and ubiquitylation, properties similar to FosB. These data indicate that alterative splicing specifically removes two destabilizing elements from FosB in order to generate a longer-lived transcription factor, DeltaFosB, in response to chronic perturbations to the brain. Truncation of the C-terminus from FosB also results in differing interaction partners for FosB and DeltaFosB that may contribute to the varying functions of each protein. Specifically, using co-immunoprecipitation assays both in vitro and in vivo, I determined that HDAC1 (histone deacetylase 1) is the preferential binding partner of DeltaFosB compared to FosB. These data suggest an intriguing hypothesis that DeltaFosB interactions with specific HATs and HDACs may be one mechanism by which DeltaFosB mediates both activating and repressive transcriptional activities. DeltaFosB is a unique transcription factor compared to its Fos family members. Truncation of the FosB C-terminal domain liberates DeltaFosB, enabling long-term protein stability and promoting specific interactions with protein partners that are critical for gene regulation important for neural plasticity.Item Brain-Region-Specific Contributions of FOXP1 to Autism and Intellectual Disability Phenotypes(2017-08-11) Araujo, Daniel John; Eisch, Amelia J.; Konopka, Genevieve; Powell, Craig M.; Volk, Lenora J.; Wu, Jiang I.Mutations and deletions in the transcription factor FOXP1 are causative for severe forms of autism spectrum disorder (ASD) that are often comorbid with intellectual disability (ID). FOXP1 is enriched throughout the brain, with strong expression in the pyramidal neurons of the neocortex, the CA1/CA2 subfields of the hippocampus, and the medium spiny neurons of the striatum. Understanding the role that FOXP1 plays within these brain regions could allow for management of ASD and ID symptoms. This doctoral dissertation leverages multidisciplinary techniques and Foxp1 mutant mouse models to ascertain the role of Foxp1 in the brain and its contribution to specific ASD- and ID-relevant phenotypes. In the first chapter of this dissertation, I review the literature on the characteristics, demographics, and shared genetic underpinnings of ASD and ID and I review the work linking FOXP1 to these disorders. Afterwards, I describe the regional transcriptome regulated by Foxp1 within the brain and I correlate alterations in the gene expression profile of the striatum with deficits in communication (Chapter 2). Briefly, I utilized RNA-sequencing performed on Foxp1 heterozygous knockout animals to uncover the genes regulated by Foxp1 within the neocortex, hippocampus, and striatum. I also recorded the early postnatal ultrasonic vocalizations (USVs) of these animals and I was able to correlate changes in the properties of striatal medium spiny neurons with deficits in USV production. Next, I move onto using a Foxp1 conditional knockout (Foxp1cKO) mouse model to ascertain the contributions of Foxp1 in the neocortex and the hippocampus to ASD and ID-related behaviors (Chapter 3). In brief, I show that total loss of Foxp1 in the pyramidal neurons of the neocortex and the CA1/2 hippocampal subfields results in social communication deficits as well as hyperactivity and anxiety-like behaviors. I also show that Foxp1cKO mice display gross impairments in hippocampal-based spatial-learning tasks and I correlate these deficits with alterations in the expression of genes involved in hippocampal physiology and synaptic plasticity. In my final chapter (Chapter 4), I consider the implications that these data have on our understanding of the role that Foxp1 plays within the brain and I suggest research strategies to answer the new questions that my findings have generated. I also discuss the implications that this research has on our understanding of ASD and ID pathophysiology in general and I recommend future directions for work focused on managing these disorders.Item Development of Neocortical Circuits: a Cell Autonomous Examination of mGluR5 and MEF2C(2015-04-08) Loerwald, Kristofer William; Johnson, Jane E.; Meeks, Julian P.; Powell, Craig M.; Huber, Kimberly M.; Gibson, Jay R.Development of neocortical circuits requires both genetic programs and sensory experience-dependent modification of synaptic function. The rules that dictate how synapses develop and respond to changing patterns of input influence both the emergence of receptive fields and the capacity for learning. In turn, the factors that determine the rules for synaptic plasticity are defined by the proteins functioning at the synapse. This project investigates two proteins situated to have wide-reaching impacts on synaptic function. One of the challenges in detailing the roles a protein plays in regulating synapses is discerning not only its acute role on synaptic function, but also its long-term impact on circuit development. Therefore, studying how a protein is engaged by physiological patterns of input in vivo over an extended period of time will provide a broader picture of how it influences synaptic function and circuit development. mGluR5 has previously been implicated in several forms of plasticity that act to directly weaken synaptic function. In this document, I provide evidence that the net-effect of mGluR5 on synaptic function throughout the first few weeks of postnatal development is to promote synaptic input pathway strength, as demonstrated in 2 prominent and well-characterized input pathways to L2/3 pyramidal cells of barrel cortex. Furthermore, I demonstrate a possible role for mGluR5 in a homeostatic mechanism, offsetting the enhanced evoked synaptic input by suppressing both spontaneous transmission and intrinsic excitability. The transcription factor MEF2 also has established roles in regulating synaptic function. However, much less is known about the synaptic mechanisms through which MEF2 mediates its effects. Here, I implicate MEF2C as the critical MEF2 family member involved in regulating synaptic function in L2/3 pyramidal cells in barrel cortex, and provide potential synaptic and molecular mechanisms by which MEF2C regulates pathway input.Item Identification and Characterization of Novel Mechanisms of Functional and Structural Synapse Remodeling: Focus on Vav Guanine Nucleotide Exchange Factors and MEF2 Transcription Factors(2014-07-23) Hale, Carly Fenwick; Huber, Kimberly M.; Cowan, Christopher W.; Green, Carla B.; Kim, Tae-KyungProper development of synaptic connectivity is a dynamic process requiring formation, elimination, maintenance, and plasticity of synapses. During early postnatal development, excess synapses are formed in most neural circuits, which are subsequently pruned during adolescence in a sensory- and activity-dependent mechanism. The brain also exhibits experience-dependent synaptic modifications that may enhance or weaken functional synapse strength. Investigation of numerous neurodevelopmental and psychiatric disorders reveals dysfunctions in synapse formation and function; however, underlying molecular mechanisms remain poorly understood. In Part One of this study, I identify a novel role for Vav guanine nucleotide exchange factors (GEFs) in brain-derived neurotrophic factor (BDNF)-dependent synapse plasticity. BNDF and its receptor, TrkB, are well-established positive modulators of hippocampal long-term potentiation (LTP), and increasing evidence suggests that BDNF/TrkB facilitates LTP in part through the stimulation of Rho GTPases and subsequent F-actin remodeling and dendritic spine structural dynamics. I report that Vav-family GEFs are activated by BDNF/TrkB signaling, and are required for BDNF-induced Rac-GTP formation. Vav GEFs, which are enriched at hippocampal glutamatergic synapses, are necessary for rapid BDNF-induced dendritic spine growth and CA3-CA1 LTP. Furthermore, Vav2/3-deficient mice have impaired contextual fear conditioning, as well as reduced anxiety. Together, findings support a role for Vav-dependent F-actin dynamics in BDNF-stimulated dendritic spine head enlargement and LTP, and normal hippocampal-dependent learning and memory and anxiety in mice. Part Two of this study reports the identification of common MEF2 and FMRP mRNA targets that are required for MEF2-induced synapse elimination. The activity-dependent transcription factor myocyte enhancer factor 2 (MEF2) is a key negative regulator of excitatory synapse number, promoting synapse removal in neurons through a complex program of gene expression. The RNA binding protein and translational regulator fragile X mental retardation protein (FMRP) was recently identified as an essential downstream component of MEF2-induced synapse elimination, suggesting that these autism-linked proteins coordinate transcriptional and translational control of common transcripts to mediate proper synaptic connectivity. Using high throughput sequencing of RNA isolated by cross-linking immunoprecipitation (HITS-CLIP) of FMRP, I find a large overlap of MEF2-induced transcripts and FMRP-associated mRNAs, consistent with their shared roles in synapse elimination. More specifically, protocadherin 17 (Pcdh17) mRNA is induced by MEF2 and exhibits differential binding to FMRP following MEF2 activation. Reducing Pcdh17 alone does not alter basal synapse number, but reducing Pcdh17 levels blocks MEF2-induced dendritic spine elimination of hippocampal neurons. These data suggest that MEF2-induced synapse elimination requires Pcdh17 – a MEF2 target gene and FMRP-associated transcript.Item Investigating Experience-Dependent Plasticity in the Accessory Olfactory Bulb(2018-04-03) Cansler, Hillary Lauren; Roberts, Todd; Meeks, Julian P.; Huber, Kimberly M.; Monteggia, LisaChemosensory information processing in the mouse accessory olfactory system (AOS) guides the expression of social behavior. After salient chemosensory encounters, the accessory olfactory bulb (AOB) experiences changes in the balance of excitation and inhibition at reciprocal synapses between mitral cells (MCs) and local interneurons. The mechanisms underlying these changes remain controversial. Moreover, it remains unclear whether MC-interneuron plasticity is unique to specific behaviors, such as mating, or whether it is a more general feature of the AOB circuit. Here, we describe a population of AOB internal granule cells (IGCs) that upregulate expression of the immediate early gene Arc following the resident-intruder paradigm in an AOS-dependent manner. Targeted electrophysiological studies revealed that Arc-expressing IGCs in acute AOB slices from resident males displayed stronger excitation than non-expressing neighbors when sensory inputs are stimulated. The increased excitability of Arc-expressing IGCs was not correlated with changes in the strength or number of excitatory synapses with MCs, but was instead associated with increased intrinsic excitability and decreased HCN channel-mediated IH currents. Consistent with increased inhibition by IGCs, MCs responded to sensory input stimulation with decreased depolarization and spiking following resident-intruder encounters. Different populations of IGCs are activated following exposure to males and females, suggesting they are activated in an input-specific fashion. We also describe multiple behavioral paradigms that have been designed to assay social recognition following resident-intruder behavior in conjunction with in vivo manipulation of Arc-expressing IGCs. Together, these results reveal that non-mating behaviors drive AOB inhibitory plasticity, and indicate that increased MC inhibition involves intrinsic excitability changes in Arc-expressing interneurons.Item Locus Coeruleus-Dependent Dopamine Release in the Dorsal Hippocampus: Mechanisms and Modulation of Synaptic Plasticity(2019-12-02) Sonneborn, Alex Jay; Meeks, Julian P.; Huber, Kimberly M.; Kourrich, Said; Roberts, Todd; Greene, Robert W.Locus coeruleus (LC) neurons coordinate the overwhelming majority of norepinephrine (NE) signaling throughout the mammalian neocortex and hippocampus. Recent discoveries indicate that dopamine (DA), the biosynthetic precursor of NE, is also released from LC axons. These axons innervate most brain regions, and are especially prevalent in the rodent dorsal hippocampus, including area CA1. It was previously thought that the only supply of CA1 dopamine was the ventral tegmental area, but several recent studies have identified LC fibers as the main source of DA in this region. However, both the mechanism by which LC-DA is released, and whether or not it is released in sufficient quantities to influence DA-dependent processes in the hippocampus, remain unclear. These questions have major implications for theories concerning the molecular basis of learning, since the consolidation of episodic memories in CA1 requires activation of dopamine D1-like receptors. Therefore, the focus of this dissertation is to determine if LC-originating DA can modulate synaptic plasticity, and therefore learning and memory, in CA1 of the mouse hippocampus. We also sought to uncover the molecular mechanism of this LC-DA release. The following experiments study the effects of LC-dopamine on CA1 function using optogenetic, electrophysiological, pharmacological, and behavioral approaches. We show that optogenetically evoked LC-DA release is sufficient to activate D1/D5 receptors (D1/5R) on CA1 pyramidal neurons and modulate synaptic potentiation at Schaffer collateral synapses, a necessary step for the consolidation of learning. In accordance with this, we find that LC-specific knockdown of DA synthesis can block learning at the behavioral level (Chapter 2). We also demonstrate that one possible LC-DA release mechanism is reverse transport through the norepinephrine transporter (NET), and advance the idea that presynaptic NMDA receptors on LC terminals may play a role in this release. Furthermore, as DA and NE should be co-released in dorsal CA1, we show that they act together to enhance synaptic strength (Chapter 3). Since LC activity is known to be involved in attention and memory, our results contribute new insight into how the LC can link attentional processes to memory formation at the molecular, circuit, and behavioral levels (Chapter 4).Item Magnetic Resonance Imaging of Plastic Changes in the Human Brain Following a Motor Task(2012-11-06) Tung, Kuang-Chi 1970-; Huber, Kimberly M.; Gardner, Kevin H.; Malloy, Craig R.Brain plasticity forms the basis of many of our daily functions including memory and learning. Evidence of brain plasticity in humans mostly consists of morphological and functional changes following days, weeks, or years of specific usage. On a time scale of minutes, on the other hand, it is not yet clear whether such changes are detectable and what the nature of these changes is. If detected and understood, then these changes have the potential of becoming diagnostic or predictive parameters towards treatments or therapies. The experiments I performed showed that significant changes in brain’s organization can be detected within a single session using functional MRI technique. Here human volunteers were subject to a 23-minute button-press motor task and their resting-state brain activity before and after the task was assessed with functional connectivity MRI (fcMRI). It was found that, compared to the pre-task resting period, the post-task resting fcMRI revealed a significantly higher cross-correlation coefficient (CC) between left and right motor cortices. These changes were region-specific and required the motor task to take place as sham control study did not show CC changes. Furthermore, the amplitude of fcMRI signal fluctuation (AF) also demonstrated an increase in the post-task period compared to pre-task. These changes were observed using both right-hand-only task and two-hand task, and were demonstrated in two separate subject cohorts. The left-hand task group did not show significant changes in motor cortex CC. The recovery time-course of these changes was also investigated, and it was found that the CC change lasted for about 5 minutes while the AF change lasted for at least 15 minutes. Voxel-wise analysis revealed that pre/post-task differences were also observed in auditory cortex, visual areas, and thalamus. Finally, network analysis showed that simple motor tasks result in the strengthening of functional connectivity between these areas. My data suggest that elevated CC and AF in fcMRI may be potentially used as markers for brain plasticity. Further, these imaging parameters can be used to delineate network wide changes in the brain by the task.Item Mechanisms of Synapse Depression in Response to Postsynaptic Patterned Burst Firing(2016-11-28) Chang, Chia-Wei; Kim, Tae-Kyung; Huber, Kimberly M.; Gibson, Jay R.; Roberts, Todd; Lin, WeichunNeuronal activity and experience stimulate synapse pruning (Zuo et al 2005b) to refine neuronal circuits during early postnatal development (Hua & Smith 2004), and are critical for learning and memory (Fu & Zuo 2011). Previous studies suggest that the activity-dependent transcription factor Myocyte Enhancer Factor 2 (MEF2) prunes functional and structural excitatory synapses in hippocampal and striatal neurons (Flavell et al 2006, Pulipparacharuvil et al 2008), findings that have been correlated with a role for MEF2 in behaviors, including memory formation (Barbosa et al 2008, Cole et al 2012, Dietrich 2013). Here, I report the use of a physiologically-relevant neuronal activity paradigm to study MEF2 transcriptional activity and function in the hippocampus. Utilizing optogenetics and biolistics, a method to sparsely express genes in neurons, I precisely controlled both activity and gene expression in a single neuron to study the cell-autonomous role of MEF2 in response to specific neuronal firing patterns. In my study, I demonstrate that postsynaptic burst firing, physiologically-relevant activity commonly observed in hippocampal CA1 pyramidal neurons, stimulates transcriptional activation of endogenous MEF2A and MEF2D transcription factors. I find that burst firing for 1 hr (which I refer to as 'brief' stimulation) elicits MEF2-dependent synapse depression. Although we hypothesized that the depression event was the result of synapse elimination, due to MEF2's known role as a negative regulator of excitatory synapse number (Flavell et al 2006, Pfeiffer et al 2010, Tsai et al 2012), surprisingly, we discovered that depression induced by brief stimulation was caused by silencing of synapses. Among potentially MEF2A/D-regulated genes, Arc was robustly induced by brief postsynaptic burst firing via activation of endogenous MEF2A/D. In contrast, chronic (24 hr) postsynaptic burst firing promotes an elimination of synapses that occurs independently of MEF2A/D. Overall, these results demonstrate the activation of MEF2 in response to physiological patterns of neural activity, and demonstrate that brief and chronic activity stimulate distinct mechanisms of synapse depression - MEF2-dependent synapse silencing, and MEF2-independent synapse elimination.Item Novel Roles for the Activity-Regulated Genes Arc and Npas4 in Stress- and Cocaine-Induced Plasticity(2016-04-18) Kumar, Jaswinder Singh; Huber, Kimberly M.; Cowan, Christopher W.; Olson, Eric N.; Zinn, Andrew R.Mood, anxiety, and substance abuse disorders are chronic medical illnesses that contribute significantly to morbidity and mortality worldwide. Currently, these conditions are treated symptomatically using pharmacological and psychotherapeutic approaches; however, the efficacy of these modalities is limited by the dearth of understanding of neurobiological mechanisms underlying mental illness. The high rate of mortality associated with mood, anxiety, and substance abuse disorders is compounded by their shared comorbidity, warranting an investigation into potential shared pathophysiological mechanisms. Studies from human patients and rodent models suggest that these mechanisms may be attributed to disrupted structural and functional plasticity in brain regions involved in mood, reward, and motivation, including the nucleus accumbens (NAc) and medial prefrontal cortex (mPFC). However, the molecules and signaling pathways within these structures that regulate these behaviors, and how they are dysregulated in pathological psychiatric conditions, have yet to be fully identified and characterized. Here, we focus on two key proteins that participate in activity-dependent synaptic plasticity, the neuronal Per Arnt Sim Domain protein 4 (NPAS4) and the activity-regulated cytoskeleton-associated protein (Arc). We utilize a series of ethologically relevant behavioral paradigms to identify Arc and NPAS4 as two important mediators of stress, anxiety, and addiction-related behaviors. Npas4 and Arc, two activity-regulated genes, are robustly induced by stressful, anxiogenic stimuli. Loss of either gene confers an antidepressant and anxiolytic response in mice, and these behavioral phenotypes are mediated by local function of these two proteins in limbic forebrain regions. In a related study, we ask whether loss of Arc influences behavioral responses to cocaine administration. We find that Arc knockout (KO) animals exhibit increased sensitivity to the locomotor activating and rewarding effects of cocaine, and these two phenotypes are associated with a selective increase in synaptic strength in the NAc. Taken together, our results highlight a heretofore-unidentified role for Arc and NPAS4 in stress- and anxiety-like behaviors, as well as Arc in cocaine-related behavioral adaptations. We propose that these two molecules play a vital role in regulating synaptic and behavioral plasticity evoked by exposure to stress and drugs of abuse, likely via experience-dependent synaptic remodeling.Item Rapid Protein Translation Governs Persistent Changes in AMPAR Trafficking in a Form of Long-Term Synaptic Plasticity(2010-05-14) Waung, Maggie Wai-Ming; Huber, Kimberly M.Activation of group 1 metabotropic glutamate receptors (mGluRs) induces long-term depression of glutamatergic synapses (mGluR-LTD). Postsynaptic endocytosis of ionotropic α-amino-5-hydroxy-3-methyl-4-isoxazole propionic acid receptors (AMPARs) accompanies mGluR-LTD, and long-term decreases in AMPAR surface expression most likely mediate this form of synaptic plasticity. In support of this idea, both mGluR-LTD and decreases in AMPA receptors require rapid protein synthesis in dendrites. To understand how newly synthesized proteins maintain decreases in AMPAR surface expression, we examined how mGluRs persistently alter AMPAR trafficking. Using biochemical and immunocytochemical methods in dissociated rat hippocampal cultures, we find that brief activation of mGluRs by the group 1 mGluR selective agonist, DHPG, results in a rapid (10 min) increase in AMPAR endocytosis rate that persists for at least one hour after the removal of agonist. This persistent increase in endocytosis rate is blocked by the protein synthesis inhibitor anisomycin, suggesting that components of the endocytosis machinery are synthesized and necessary for mGluR-LTD. In contrast, treatment of cultures with NMDA, which induces NMDA receptor-dependent LTD causes a long-term (60 min) decrease in AMPAR surface expression, but does not persistently increase endocytosis rate. Recent work has implicated activity-regulated cytoskeletal associated protein (Arc) in the regulation of AMPAR endocytosis through its interactions with endophilin and dynamin, and Arc mRNA is induced in hippocampal CA1 dendrites following behavioral activity. However, little is known about how Arc is locally synthesized at synapses or whether its local synthesis contributes to synaptic plasticity. We find that DHPG induces rapid increases in local and synaptic dendritic Arc protein expression within 10 minutes in hippocampal neurons. Knockdown of Arc by lentiviral delivery of short-hairpin RNA increases basal surface AMPAR expression and synaptic transmission as measured by mEPSC amplitude. Arc knockdown blocks mGluR-induced decreases in surface AMPARs, AMPAR endocytosis as well as mGluR-LTD. Acute inhibition of new Arc translation with antisense nucleotides also blocks mGluR-induced persistent changes in AMPAR trafficking and mGluR-LTD. The involvement of rapid Arc synthesis in mGluR regulation of synaptic function provides a link between behavior-driven neuronal activity and plasticity at the synapse.Item The Role of KIBRA in Synaptic Plasticity Across Age(2021-05-01T05:00:00.000Z) Mendoza, Matthew Lee; Meeks, Julian P.; Huber, Kimberly M.; Green, Carla B.; Terman, Jonathan R.; Volk, Lenora J.Over the last four decades, neurobiology has gained valuable insight into the cellular and molecular mechanisms of learning and memory. However, a complete understanding of how we learn and remember information remains at the frontier of neuroscience research. In particular, the molecular bases for age-dependent changes in our capacity to learn and remember are poorly understood. Identifying the neural basis of age-dependent changes in learning and memory will not only provide crucial insights into the pathological mechanisms underlying progressive neurological disorders but also guide neurodevelopmentally informed educational strategies and legal policies. Synaptic plasticity, expressed as persistent increases (long-term potentiation, LTP) or decreases (long-term depression, LTD) in synaptic strength is thought to be a key cellular mechanism underlying cognitive functions such as learning and memory. AMPA-type glutamate receptors mediate the vast majority of fast-excitatory synaptic transmission in the central nervous system, and dynamic AMPA receptor trafficking is critical for many forms of synaptic plasticity. The coordinated movement of AMPA receptors into and out of a synapse is regulated by interactions with multiple proteins including the synaptic scaffold KIBRA (Kidney and Brain Protein). Previous evidence indicates that KIBRA and it's respective binding partners are associated with age-emergent neurological diseases such as Tourette, Schizophrenia, Alzheimer's, and Autism Spectrum Disorders. While there is a growing body of human literature implicating KIBRA in learning and memory, KIBRA's molecular function and contribution to cognitive maturation remains poorly understood. Therefore, this dissertation was designed to focus on the role of KIBRA in synaptic plasticity and AMPA receptor trafficking across the juvenile and adult brain. In Chapter 1, I review the pertinent literature to frame the overall trajectory of this dissertation. Next, in Chapter 2, using novel inducible and conditional KIBRA knock mice, I show that KIBRA acutely influences hippocampal LTP selectively in the adult brain, but not the juvenile brain. These adult-specific deficits in LTP were associated with a reduction in the basal and activity-dependent expression of AMPA receptors and AMPA receptor complex interactors. In Chapter 3, I examine KIBRA's role in LTD. Contrary to published results in conventional KIBRA KO mice on a hybrid C57Bl6N/FVB background, we show that acute manipulation of KIBRA on a C57Bl6N background does not influence hippocampal LTD. Lastly, I show that acute reduction of KIBRA influences GluA2 phosphorylation at S880, which might restrict the recycling of internalized AMPA receptors. Taken together, my data suggest that KIBRA preferentially influences LTP as opposed to LTD. KIBRA's role in LTP is selective to the adult hippocampus and loss of KIBRA reduces the expression and trafficking of AMPA receptors. In Chapter 4, I discuss the implication of this work and layout future directions.Item Transcriptional Mechanisms Underlying Neuronal Activity-Dependent Plasticity(2016-11-21) Schaukowitch, Katie Marie; Huber, Kimberly M.; Johnson, Jane E.; Tamminga, Carol; Kraus, W. LeeImpairment in learning and memory is a well-established cognitive symptom that is manifested in many psychiatric diseases including autism and schizophrenia. Studies have shown that long-lasting memory formation is mediated by rapid changes in nuclear gene expression in response to learning-induced sensory experience. Despite these findings, there is a significant gap in our knowledge as to how sensory information is precisely translated into specific transcriptional outputs. Recently, a class of long noncoding RNAs that are transcribed bidirectionally from the enhancers of activity-dependent genes in neurons (eRNAs) has been identified. My first project studied the function of eRNAs of two immediate early genes Activity-regulated cytoskeletal protein (Arc) and Growth arrest and DNA-damage-inducible, beta (Gadd45b), which have been implicated in mediating synaptic plasticity. Using a knockdown approach, we found that eRNAs are necessary for the full induction of their target genes in response to membrane depolarization. eRNAs specifically regulate the early elongation stage of transcription by allowing for efficient release of paused RNA polymerase II (RNAPII) from the promoters of activity-regulated genes. Knockdown of eRNAs results in the retention of an RNAPII pausing factor, Negative Elongation Factor (NELF), at the target gene promoter. eRNAs directly bind to NELF during stimulated conditions, suggesting that eRNAs interact with NELF to facilitate its release from the promoter, thus resulting in efficient and precisely timed gene activation. These data define a new role for the spatiotemporally controlled expression of regulatory RNAs in the experience-dependent gene expression network. My second project aimed to identify the transcriptional program activated when activity levels are suppressed. Homeostatic scaling allows neurons to maintain stable activity patterns by globally altering their synaptic strength in response to changing activity levels. Decreasing activity leads to an upregulation in synaptic strength, as seen by increases in AMPA mediated mEPSCs. It was previously shown that the increase in mEPSC amplitude could be blocked by a transcription inhibitor, suggesting that transcription is necessary for the scaling response. However, little is known about the genes directly regulated by activity suppression or the signaling mechanisms underlying the transcriptional control. Using RNA-Seq, we identified nearly 100 genes that were specifically upregulated in response to activity suppression. Neuronal pentraxin-1 (Nptx1), previously shown to promote AMPAR clustering, was increased ~3 fold, and knockdown of this gene blocked the increase in mEPSC amplitudes. SRF is a key transcription factor in regulating Nptx1 induction, which is calcium-dependent, indicating the existence of an active pathway to control transcription. Taken together, this study defines a novel transcriptional program that is able to sense the absence of activity and coordinate the global increase in synaptic strength.