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2014 Research Showcase
NB Abstracts
Abstract Title : Measures for quantifying the stability of spatial firing patterns in rodent hippocampal place cells
Abstract : It has been established that subsets of cells in the rodent hippocampus fire predominantly when the animal is in a specific region of its environment. Moreover, it has been shown that these spatial regions of high-density firing (or ?place fields?) form quickly when the animal is exposed to a new environment and persist after repeated exposure to the same environment. Thus, it has been proposed that the hippocampus provides a spatial map of the animal?s environment which is both learned and remembered. As a symptom of learning and memory, the stability of place fields over time has been quantified and compared under a variety of experimental manipulations. Most commonly, the stability of spatial firing has been quantified by taking the Pearson's correlation coefficient of spatial firing rates between two time periods. Experimentally, this approach has not been unfruitful. Mathematically, however, this measure only quantifies the extent to which the spatial firing rates between two time periods are linearly related, not the extent to which these rates are identical. Thus, important information regarding the stability of spatial firing has been lost. Here we propose several measures which might quantify stability in this stronger sense. We test these measures of strong stability in parallel with the traditional Pearson's correlation coefficient on simulated and experimental data and utilize statistical methods to quantify their success.
Advisor : FRED H. GAGE
Abstract Title : Does HDGF-related protein 3 Regulate Oligodendrocyte Myelination in the Central Nervous System?
Abstract : In the central nervous system, axons are myelinated by oligodendrocytes (OLs). However, though our understanding of OL biology is increasing, the signals that emanate from the axons and trigger myelination initiation are still poorly understood. Previous studies have found that HRP3II, a newly identified isoform of the hepatoma-derived growth factor (HDGF) family, shows peak expression in the axons of spinal motor neurons before and during the myelination period. Furthermore, overexpression of HRP3II increased Schwann cell proliferation and myelination, suggesting its importance for regulating the local pool of Schwann cells. Therefore, our goal is to determine whether HRP3II also plays a critical role in the myelination of neurons by OLs in the central nervous system (CNS) using a recently developed CNS myelination model. Mouse embryonic stem cell derived cortical neurons were cultured onto microfluidic devices. We overexpressed HRP3II using two different constructs: GFP-HRP3II Fusion Protein and GFP-HRP3II inner ribosomal entry site (IRES). After co-culturing the neurons with OLs, the devices were stained and imaged. We identified OLs based on their morphology and found that the average number of MBP+ OLs is significantly larger with both HRP3II overexpression constructs compared to controls, suggesting its role in the proliferation and/or maturation of OLs. After further quantitative analysis, we found that both overexpression constructs increase the percent of myelinated axons compared to the neurons containing normal levels of HRP3II; and this effect is not selective for GFP+ axons only, supporting the idea of some type of factor that can act at a distance.
Abstract Title : Reorganization of the Dentate Gyrus Neural Network in Medial Temporal Lobe Epilepsy and its effect on Learning and Memory
Abstract : Past research has proposed that the dentate gyrus (DG) plays an important part in pattern separation, the process of differentiating between similar inputs patterns, a network computation thought to be critical for episodic memory formation. Patients with medial temporal lobe epilepsy (MTLE), characterized by chronic seizures due to the lack of neuronal inhibition, exhibit memory deficits, which might be caused by the anatomical changes frequently characterized in the DG of these patients. These changes include synaptic reorganization of the neuronal network, and mossy fiber sprouting from principle neurons of the DG. Ongoing research in our lab has suggested that an increase in the anatomical reorganization of the DG is associated with a loss of pattern separation in epileptic animals. To further investigate the effects of this pathological reorganization on memory processing, I explored the impact a reorganized dentate network has on the ability of the DG to distinguish between two different novel environments. Local field potentials and extracellular action potentials were recorded from populations of dentate neurons while rats, with chronic epilepsy, were foraging for food in a series of familiar square and circular environments and then in a novel environment to test changes during learning. Comparisons of the rate and pattern of DG granule cell activity in control and epileptic animals were assessed and the differences/similarities were analyzed to determine whether there is a correlation between impairments in distinguishing novel environments and MTLE.
Abstract Title : The Consequences of Voluntary Intermittent Ethanol Exposure During Adolescence on Adult Drinking
Abstract : Studies have shown that drinking during adolescence is a risk factor for alcohol related problems during adulthood1. The 2012 National Survey on Drug abuse and Health reported that current alcohol use among teens aged 12 to 17 was 12.9% and binge drinking was 7.25% 2. However, the mechanism by which early exposure to drinking leads to an increased risk for alcohol dependence in adults is not clear. Here we show that high degrees of voluntary drinking during adolescence can significantly enhance levels of alcohol self-administration during adulthood. In our study male Wistar rats were given a 2-bottle choice between 20% ethanol and water during adolescence to model voluntary drinking in adolescent humans. As adults, these rats as well as control rats, who did not have the opportunity to drink during adolescence, underwent operant lever press training to measure their motivation to drink alcohol as adults. We found that rats that voluntarily drank ethanol during their adolescence were significantly more likely to drink more ethanol when presented ethanol as adults than control animals. Similarly, significant differences were observed in the amount of alcohol consumed by each rat over all operant sessions between the control group, a subgroup of rats that only drank small amounts of ethanol during adolescence and a group that drank large amounts of ethanol during adolescence. This study shows that the voluntary consumption of alcohol during adolescence can have an impact on the amount of alcohol consumed during adulthood. Further research is needed in this model to identify the mechanisms mediating the increase in adult alcohol drinking. References: 1. Laucht, Manfred. ?Impact of age at first drink on vulnerability to alcohol-related problems: Testing the marker hypothesis in a prospective study of young adults? Journal of Psychiatric Research. Volume 43.15 (2009):1205-1212. 2. U.S. Department of Health and Human Services. Substance Abuse and Mental Health Services Administration. Results from the 2012 National Survey on Drug Use and Health: national findings.
Abstract Title : The Anatomical Changes Associated with Impaired Behavioral Pattern Separation in Chronic Model Temporal Lobe Epilepsy
Abstract : Pathological synchronization of electrical signals that result in involuntary body movement is known as seizure. Multiple consecutive seizures are known as epilepsy. A brain area with a recurrent circuit and thus is prone to epilepsy is the medial temporal lobe (MTL). Within the MTL, the hippocampus plays a role in episodic, working, and spatial memory. A specific sub region of the hippocampus, the dentate gyrus (DG), is known to support the process of pattern separation. This computation describes the ability of brain circuitry to distinguish between two similar, yet none-identical cues. Studies have shown that epilepsy may result in axonal sprouting and cell loss in the DG, suggesting that DG function may be perturbed due to epileptogenesis. Ongoing studies from our lab have suggested that behavioral pattern separation is impaired in a rat model of temporal lobe epilepsy. In this study, we hypothesize that the anatomical changes in the DG may be responsible for the behavioral deficit. To conduct our study, control Long-Evans male rats and rats with epileptogenesis (induced by a low-dose, i.p.- kainate injection) were tested for pattern separation on an 8 arm radial maze, and a behavioral deficit in the induced rats was observed. To test the correlation between axonal sprouting and behavioral deficit, the tissue from tested rats was Timm stained and microscopically visualized. To test the correlation between neuronal loss and behavioral deficit, immuno-histochemistry and stereology were used. Our results showed that neither sprouting nor cell loss in the dentate gyrus were associated with the behavioral deficit.
Advisor : DR. JOHN R. KELSOE JR., M.D.
Abstract Title : The Role of HTR7 Gene Regulation in Influencing SSRI Response in Bipolar Disorder
Abstract : Bipolar Disorder (BD) is a serious brain chemical disorder characterized by alternating euphoric and depressive states associated with suicidality. The disorder responds to medications belonging to the Selective Serotonin Reuptake Inhibitor (SSRI) family. Some BD patients respond well to SSRI therapy, others respond poorly. Currently, there is no method to pre-screen patients for SSRI response. Therefore, patients must endure medication trials followed by efficacy evaluation, which often delays effective treatment. In a previous study, Single Nucleotide Polymorphisms (SNPs) associated with SSRI response were genotyped in the HTR7 promoter region. In this study, two types of BD subjects were identified based on two criteria. The first criterion was either good or poor response to SSRI therapy. The second criterion was homozygotic alleles associated with the HTR7 promoter region, either a wild-type reference allele or an alternative one with a previously identified SNP. The two types of subjects were identified as either good responders homozygotic for the reference allele or poor responders homozygotic for the alternative allele. The hypothesis of this study is that there is a difference in HTR7 regulation in variations of the HTR7 promoter. In order to evaluate this difference, DNA fragments from both subject types were individually subcloned. These subclones were then evaluated by luciferase-based reporter assay for modulation of HTR7 gene expression. The results of this study will provide insight into a genetic link between Bipolar Disorder and SSRI response with a potential for future drug therapy pre-screening methods with a view to timely and effective treatment.
Abstract Title : Characterization of RNA binding protein with multiple splicing (RBPMS) as a marker for retinal ganglion cells.
Abstract : How can we identify the cellular impact of retinal disease? One challenge lies in accurately quantifying the loss of cells such as retinal ganglion cells (RGCs). This requires reliable markers that identify all the different subtypes of RGCs. Several studies investigating different RGC markers have been performed--but have yielded varying levels of success, due to inconsistent expression and specificity. The recently discovered RNA binding protein RBPMS appears to be a strong candidate as an RGC marker. To test its specificity and reliability, we performed immunostaining for RBPMS and Brn3a (the latter which labels a large percentage of RGCs), and compared them to retrogradely labeled RGCs. Previous studies demonstrate that retrograde labeling with Fluorogold yields approximately 99% labeling of RGCs. Our results, in comparison, indicate that RBPMS was expressed specifically in RGCs, and closely matched Fluorogold's labeling efficiency. This indicates that RBPMS is expressed in almost all RGCs, unlike Brn3a--which is expressed in only about 80% of RGCs. Thus, our studies provide strong evidence that RBPMS is a more reliable and specific marker for RGCs, compared to other commonly used markers.
Advisor : EDWARD KOO
Abstract Title : The effect of dentate gyrus-specific APP expression on neurogenesis
Abstract : The cognitive impairment seen in Alzheimer?s disease (AD) may be the result of decreased neurogenesis, the production of new neurons. Ongoing adult neurogenesis in the subgranular zone (SGZ) of the dentate gyrus (DG) in the hippocampus has been shown to contribute to hippocampal-dependent learning and memory. However, the effects of amyloid precursor protein (APP) and its cleavage product, amyloid β-peptide (Aβ), on neurogenesis remain unclear due to conflicting reports from both rodent and human studies. Previously established APP transgenic mouse models have over expression of APP in their whole brain, inducing generalized damage from systemic APP overload. Thus, it is difficult to separate direct APP- from Aβ-mediated effects. We generated a transgenic mouse model with site-specific and inducible human APP expression in the DG to study the vulnerability of this neuronal population to APP/Aβ-induced synaptic injury. Using Ki67 and BrdU labeling, we measured the prolif eration of neural stem and progenitor cells (NSPCs) in these mice. Six to eight month-old mice were found to have a decreased number of proliferating cells within the SGZ and decreased BrdU+ cells in the DG, suggesting reduced NSPC proliferation and/or survival. Additionally, ten-twelve month-old mice suffered from significantly reduced neuronal density within the DG compared to their wild-type litter-mates. However, tetracycline transactivator (tTA) toxicity, which was used for the inducible expression of APP in these mice, has been shown to induce DG-specific neurodegeneration. Thus, we are assessing whether the observed defect in NSPC proliferation is mediated by tTA expression and/or APP over-expression.
Advisor : JING WANG
Abstract Title : Neural Mechanism of Imprinting in Drosophila Melanogaster via Dopamine-ecdyson Receptors and 20-Hydroxy-Ecdyson
Abstract : During the critical period of an animal's life, usually earlier in stage, sensory cues that signal safety and food are quickly learned and encoded into the memories of young animals through modification of neurons in the sensory neural circuits. As a survival mechanism, imprinted sensory cues can guide and shape animals' preferences and behaviors. Our results demonstrate that Drosophila exhibits a robust firm of olfactory imprinting. Drosophila, when exposed to apple cider vinegar (ACV) soon after their eclosion, show enhanced attraction towards ACV, whereas control flies without any exposure to ACV show little or no attraction to ACV. Causality between neural plasticity and imprinted behavior has yet to be defined; what is the neural mechanism of olfactory imprinting? We found that dopamine-ecdyson receptors (DopEcR) in the sensory neurons play a critical role in the olfactory imprinting. In addition, older flies when fed with 20-Hydroxy ecdyson (20E) exhibit increased behavioral attraction towards ACV, suggesting that 20E concentration exerts its effect in fly behavior towards conditioned odorant. In conclusion, my work yielded insight into the cellular mechanism underlying olfactory imprinting.
Abstract Title : Role of Atypical Protein Kinases in Axon Regeneration
Abstract : The identification of cell intrinsic factors that can modulate the regenerative potential of both central and peripheral nerve axons is of particular interest for enhancing axon growth and functional recovery following traumatic injury to the nervous system. In this study, we identify a novel role for atypical protein kinase C isoforms PKM-ζ and aPKC-λ, which have recently been shown to regulate axon specification in developing neurons. Our experiments indicate that PKM-ζ and aPKC-λ may also regulate axon growth in adult neurons, making them potential targets for regenerative therapies. Overexpression or knockdown of PKM-ζ was tested in primary adult DRG cultures grown on growth permissive (laminin) or inhibitory (myelin) substrates, and neurite extension was quantified using automated image analysis. Overexpression of PKM-ζ reduced neurite extension on laminin, whereas knockdown of PKM-ζ enhanced neurite extension on myelin. These results suggest PKM-ζ is functioning as a negative regulator of neurite outgrowth in adult DRGS, as reduction of PKM-ζ allows for outgrowth of adult neurites in an inhibitory environment. Complementary experiments testing the effect of altering aPKC-λ expression levels in adult DRGs as well as in vivo experiments studying the role of PKM-ζ and aPKC-λ in axon regeneration after optic nerve injury are underway. These studies will help identify a functional role for PKM-ζ and aPKC-λ in enhancing axon regeneration in both the peripheral and central nervous systems, and assess their therapeutic potential for nervous system injuries.
Abstract Title : MEF2 in Neurons
Abstract : MEF2, along with various transcription factors, is known to govern important aspects of neural development and synaptic plasticity. Many target genes of such transcription factors have also been identified. Nevertheless, the genome-wide mechanisms that are directly regulated by MEF2 remain unclear. In this study, we attempted to confirm the target genes identified by ChIP-sequencing using RT-qPCR. Also, we have analyzed the genetic program and mechanisms of MEF2, a crucial regulator of activity-depended synapse development. Overall, our analyses suggest that the ubiquitously expressed transcription factor MEF2 regulates a broad and intricate transcriptional program in neurons that control synapse development.
Advisor : YISHI JIN
Abstract Title : Dissecting the nuclear import mechanisms of a bZip protein CEBP-1 and the function of importin proteins in the nervous system
Abstract : Axon regeneration is critical for functional recovery after nerve injury; however, the molecular mechanisms of this capability remain poorly understood. Caenorhabditis elegans is an excellent model organism in which to examine conserved molecular mechanisms involved in nerve regeneration. Recent studies have revealed the importance of a transcription factor known as CCAAT/enhancer-binding protein-1 (CEBP-1) in axon regeneration. We have proposed a tentative model that upon injury CEBP-1 undergoes retrograde transport to the nucleus, thereby triggering pro-regenerative pathways that accelerate axon regrowth. Supporting this idea, we have identified a member of the Importin alpha protein family as a putative binding partner of CEBP-1. Importin proteins regulate the retrograde transport of cargoes from the axon to the nucleus, allowing for the import of transcription factors into the nucleus. To better understand the mechanisms of injury signal transport from the injured site to the nucleus, we are examining the position of nuclear localization signals on the CEBP-1 protein itself. Moreover, we are investigating the relationships between CEBP-1 and various importin proteins, as well as the function of importin proteins in the nervous system. Understanding of the cellular and molecular mechanisms behind the function of CEBP-1 may lead to greater comprehension of the mechanisms involved in axon regeneration. As these functions are elucidated, insight may be gained as to their application in nerve regeneration across species.