Browsing by Author "Stringer, Megan"

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    Can Epigallocatechin gallate (EGCG) Treatment Rescue Hippocampal-Dependent Cognitive Function in a Down Syndrome Mouse Model?
    (Office of the Vice Chancellor for Research, 2016-04-08) East, Audrey; Stringer, Megan; Abeysekera, Irushi; Goodlett, Charles R.; Roper, Randall J.
    Down Syndrome (DS) is caused by the trisomy of human chromosome 21 (Hsa21). Trisomy 21 can cause various behavioral, cognitive, learning and memory deficits. Deficits in hippocampal structure and function have been identified in mouse models of DS and are implicated in cognitive and learning impairments. Mouse models have suggested that deficits in cognitive function are associated with overexpression of Dyrk1a, a gene on Hsa21 found in three copies of individuals with DS. Dyrk1a is a gene that is involved in brain development and function. Ts65Dn DS model mice exhibit trisomy for approximately half of the genes on Hsa21 including Dyrk1a and exhibit cognitive and learning impairments. We are using Ts65Dn mice to test the effects of Epigallocatechin gallate (EGCG), a Dyrk1a inhibitor, on Dyrk1a activity and cognitive function. We hypothesize that EGCG will reduce Dyrk1a activity in the hippocampus and improve hippocampal-dependent spatial learning and memory in the Morris water maze place learning task in Ts65Dn mice. The mice were given daily EGCG treatment (200 mg/kg per day) by means of oral gavage beginning on postnatal day 54 and continuing throughout water maze testing (postnatal days 67-74). Measures of spatial learning included latency and path length to find a submerged platform during acquisition trials (postnatal days 67-73). Memory for the previously learned location of the platform was assessed on a probe trial (postnatal day 74) in which the platform was removed and the amount of time spent swimming in the area of the tank previously containing the platform was measured. These measures allowed us to analyze the mice’s ability to learn and remember the position of the platform and to spatially orient themselves. Preliminary data indicates that EGCG treatment may not be an effective treatment for the spatial learning and memory deficits evident in this mouse model of DS.
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    Correction of cerebellar movement related deficits by normalizing Dyrk1a copy number in the Ts65Dn mouse model for Down syndrome
    (Office of the Vice Chancellor for Research, 2016-04-08) Patel, Roshni; Stringer, Megan; Abeysekera, Irushi; Roper, Randall J.; Goodlett, Charles R.
    Elucidation of the underlying mechanisms involved in brain related deficits of Down syndrome (DS) would be useful for consideration of therapeutic interventions. Several DSspecific phenotypes have been hypothesized to be linked to altered expression or function of specific trisomic genes. One such gene of interest is D YRK1A , which has been implicated in behavioral functions of the hippocampus and cerebellum. The Ts65Dn mouse model for DS includes a triplication of D yrk1a in addition to a triplication of >100 other human chromosome 21 mouse orthologs. To evaluate the role of D yrk1a in cerebellar function, we have genetically normalized the D yrk1a copy number in otherwise trisomicTs65Dn mice and reduced D yrk1a copy number in otherwise euploid mice (2N) for a total of 3 alternative genetic doses of D yrk1a: EuploidDyrk1a +/+ , EuploidDyrk1a +/, Ts65DnDyrk1a +/+/+ , and Ts65DnDyrk1a +/+/. Cerebellar movementrelated function in these knockdown models is being assessed through a novel behavioral balance beam task. Additionally, levels of D yrk1a activity in the cerebellum for all genotypes were analyzed by HPLC. We have previously demonstrated that Ts65DnDyrk1a +/+/+ mice perform worse in the balance beam task in comparison to EuploidDyrk1a +/+ mice. Preliminary results of the current study do not indicate such a difference among Ts65DnDyrk1a +/+/+ mice in comparison to EuploidDyrk1a +/+ mice. We hypothesize that the lack of replication of the previous findings may be due to differences in postweaning housing environments. Mice in the previous study were singlehoused, whereas mice in the present study were grouphoused, which may help mitigate motor deficits in the trisomic mice. Additionally, current trends display a deficit in balance beam performance of both the EuploidDyrk1a +/and the Ts65DnDyrk1a +/+/groups, which suggests that reducing the copy number of D yrk1a by one may have detrimental effects on motor coordination. Concomitant analysis of the balance beam performances and Dyrk1a activity levels may indicate the sensitivity of the balance beam task to assess the role Dyrk1a activity in cerebellar function.
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    Deficits in a Radial-Arm Maze Spatial Pattern Separation Task and Cell Proliferation in a Mouse Model for Down Syndrome
    (Office of the Vice Chancellor for Research, 2016-04-08) Stringer, Megan; Podila, Himabindu; Dalman, Noriel; East, Audrey; Roper, Randall J.; Goodlett, Charles R.
    Down syndrome (DS) is caused by three copies of human chromosome 21 (Hsa21) and results in an array of phenotypes including intellectual disability. Ts65Dn mice have three copies of ~50% of the genes on Hsa21 and display many phenotypes associated with DS, including cognitive deficits. DYRK1A is found in three copies in humans with Trisomy 21 and in Ts65Dn mice, and is involved in a number of critical pathways including CNS development. Epigallocatechin-3-gallate (EGCG), the main polyphenol in green tea, inhibits Dyrk1a activity. We have shown that a three-week EGCG treatment normalizes skeletal abnormalities in Ts65Dn mice, yet did not rescue deficits in the Morris water maze spatial learning task or novel object recognition. The current study investigated deficits in a radial arm maze pattern separation task in Ts65Dn mice. Pattern separation requires differentiation between similar memories acquired during learning; distinguishing between these similar memories is thought to depend on distinctive encoding in the hippocampus. Pattern separation has been linked to functional activity of newly generated granule cells in the dentate gyrus. Recent studies in Ts65Dn mice have reported significant reductions in adult hippocampal neurogenesis, and after EGCG treatment, enhanced hippocampal neurogenesis. Thus, it was hypothesized that Ts65Dn mice would be impaired in the pattern separation task, and that EGCG would alleviate the pattern separation deficits seen in trisomic mice, in association with increased adult hippocampal neurogenesis. Beginning on postnatal day 75, mice were trained on a radial arm maze-delayed non-matching-to-place pattern separation task. Euploid mice performed significantly better over training than Ts65Dn mice, including better performance at each of the three separations. EGCG did not significantly alleviate the pattern separation deficits in Ts65Dn mice. The euploid controls had significantly more BrdU labeled cells than Ts65Dn mice, however, EGCG does not appear to increase proliferation of the hippocampal neuroprogenitor cells.
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    The Effect of 200mg/kg EGCG Oral Gavage Treatment on the Cerebellar-Dependent Behavior in a Down Syndrome Mouse Model
    (Office of the Vice Chancellor for Research, 2016-04-08) Dalman, Noriel; Stringer, Megan; Abeysekera, Irushi; East, Audrey; Patel, Roshni; Roper, Randall J.; Goodlett, Charles R.
    Trisomy 21 (Ts21) causes deficits in motor and cognitive ability that are hallmark phenotypes in Down syndrome (DS). The Ts65Dn mouse model of DS has about 50% of the orthologous genes that are triplicated from human chromosome 21, including the Dual specificity tyrosinephosphorylation-regulated kinase 1A (Dyrk1A) gene. Three copies of Dyrk1A have been implicated in the motor and cognitive deficits and altered cerebellar structure and function may contribute these impairments in Ts65Dn mice. Epigallocatechin 3-gallate (EGCG) is a catechin found in green tea and an inhibitor of Dyrk1A activity. We hypothesize that a 200mg/kg EGCG treatment given by oral gavage will inhibit Dyrk1A activity in the cerebellum of Ts65Dn mice and rescue deficits in motor coordination while performing the balance beam task. Evidence of improvement in this task would be observed as a reduction of paw slips as the animal traverses across beams of varying widths. In previous studies, EGCG treatment was placed in the animal’s water to be consumed but EGCG rapidly degrades in solution and it is difficult to control treatment doses via treatment in drinking water, due to each animal’s consumption behavior. This study utilized a daily oral gavage treatment of EGCG to control the dose and limits loss due to degradation. Results to date indicate that the Ts65Dn mice show deficits on the balance beam task relative to the euploid mice, particularly at the narrowest beam width used. The EGCG treatment does not appear to improve the performance of the Ts65Dn mice, though the lack of observed effects of EGCG may be due to the relatively low numbers of Ts65Dn-EGCG treated mice that have completed testing so far. One notable trend is that we will continue to test additional mice to gain sufficient power to determine conclusively whether EGCG improves motor coordination performance in Ts65Dn mice.
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    Effects of 50 mg/kg EGCG Treatment of Ts65Dn Down Syndrome Mice on Novel Object Recognition
    (Office of the Vice Chancellor for Research, 2016-04-08) Stringer, Megan; Roper, Randall J.; Goodlett, Charles R.; Delgado Taboada, Maria Fatima
    Down syndrome (DS) is caused by trisomy of chromosome 21, and affects 1/700 live births. DYRK1A, a gene found in three copies in humans with DS and Ts65Dn DS mice, has been linked to alterations in morphology and function of the brain resulting in cognitive impairment. Epigallocatechin-3-gallate (EGCG), an inhibitor of DYRK1A activity, has been proposed as a possible treatment. Using the Ts65Dn DS mouse model, we examined the effects of EGCG treatment on on hippocampal dependent learning and memory using a novel object recognition task (NOR). A previous study analyzing the effects of EGCG at a concentration 30mg/kg/day showed that there was no genotype or treatment effect in the NOR task when treatment is continuous through testing. In this study, the mice were given 50 mg/kg/day EGCG or water via their drinking water starting at 3 weeks of age. The mice were handled two days before testing and then underwent a series of behavioral tests including NOR. They underwent testing at 3 weeks and 7 weeks of treatment. Treatment was continuous throughout behavioral testing. NOR consists of a box with the objects placed diagonally from each other. The mice underwent 3 days of testing with 15 minute sessions per day consisting of habituation, exposure, and test day, all of which were recorded and analyzed to determine time spent exploring novel object in relation to familiar. The amount of time spent at each object was scored by three independent scorers, blind to genotype and treatment. We observed no genotype or treatment effect at either the 3 or 7 week test results, which is consistent with our past results. A higher dose, along with a more sensitive test of recognition memory, may be needed in order to show a treatment effect on the Ts65Dn mice.
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    Effects of EGCG Treatment of Ts65Dn Down Syndrome Mice on a Balance Beam Task
    (Office of the Vice Chancellor for Research, 2015-04-17) Taboada, Maria Fatima Delgado; Stringer, Megan; Roper, Randall J.; Goodlett, Charles R.
    Down syndrome (DS) is caused by trisomy of chromosome 21, and affects 1/700 live births. DS results in about 80 clinical phenotypes, including cognitive impairment. DYRK1A, a chromosome 21 gene, has been linked to alterations in morphology and function of the brain resulting in cognitive impairment. Epigallocatechin-3-gallate (EGCG), an inhibitor of DYRK1A activity, has been proposed as a possible treatment for cognitive deficits seen in individuals with DS. Using the Ts65Dn DS mouse model, we examined the effects of EGCG treatment on cerebellum dependent tasks using a balance beam test. We hypothesized that treatment with EGCG would improve Ts65Dn performance on the balance beam. In a first experiment, mice were given a dose of ~30 mg/kg/day EGCG, which showed no significant improvement in the balance beam task. In a second experiment, mice were given a dose of 100 mg/kg/day EGCG or water (control) starting at 3 weeks of age. The mice were handled two days before testing and then underwent a series of behavioral tasks including the balance beam test. The mice traversed three beams of differing widths (12, 9 and 6 mm), and three consecutive trials for each were recorded for further analysis. The balance beam recordings were scored by three independent scorers, blind to genotype and treatment, and the number of hind paw slips for each trial were scored. Our preliminary results indicate that the Ts65Dn mice are impaired at this task and have more hind paw slips compared to euploid controls. A larger number of animals should help to distinguish any differences in Ts65Dn mice due to EGCG treatment.
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    Effects of EGCG treatment on deficits in a radial-arm maze spatial pattern separation task in a Down syndrome mouse model
    (Office of the Vice Chancellor for Research, 2015-04-17) Stringer, Megan; Stancombe, Kailey; Gainey, Sean; Sheikh, Zahir; Abeysekera, Irushi; Goodlett, Charles R.; Roper, Randall J.
    Down syndrome (DS) is caused by three copies of human chromosome 21 (Hsa 21) and results in a constellation of phenotypes that include intellectual disability. Ts65Dn mice, the most extensively studied model of DS, have three copies of approximately half the genes on Hsa 21 and display many of the phenotypes associated with DS, including cognitive deficits. DYRK1A is found in three copies in humans with Trisomy 21 and has increased expression in a number of tissues. Dyrk1a is also found in three copies in Ts65Dn mice, and has been shown to be involved in a number of critical pathways including CNS development and osteoclastogenesis. Epigallocatechin-3-gallate (EGCG), the main polyphenol found in green tea, is an inhibitor of Dyrk1a activity. We have previously shown that a three week treatment with EGCG normalizes skeletal abnormalities in Ts65Dn mice. Previous work has found that Ts65Dn mice are significantly impaired in several hippocampal-dependent tasks, including the Morris water maze and novel object recognition. Another hippocampal-dependent process, pattern separation, is the ability to differentiate between similar memories acquired during learning. Distinctive encoding of these similar memories in hippocampal formation is thought to be necessary to distinguish between them. Experimental reductions in adult neurogenesis have produced impairments in pattern separation performance. Given that recent studies in Ts65Dn mice have reported significant reductions in adult hippocampal neurogenesis, we hypothesize that Ts65Dn mice will be impaired in the pattern separation task. Furthermore, we hypothesize that treating Ts65Dn mice with EGCG throughout task learning would improve performance to control levels. A radial arm maze-delayed non-matching-toplace pattern separation task with three different degrees of spatial separation is used. Preliminary data suggests that, in contrast to control mice, Ts65Dn mice do not improve their performance over training.
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    Effects of Epigallocatechin-3-gallate Treatment on Cognitive Deficits in a Down Syndrome Mouse Model
    (Office of the Vice Chancellor for Research, 2014-04-11) Dhillon, Hardeep; Abeysekera, Irushi S.; Stringer, Megan
    Down syndrome (DS) is caused by three copies of human chromosome 21 (Hsa21) and results in a constellation of phenotypes that include intellectual disability (ID) and skeletal abnormalities. Ts65Dn mice, the most extensively studied model of DS, have three copies of approximately half the genes on Hsa21 and display many DS related phenotypes including skeletal and ID deficits. DYRK1A is found in three copies both in humans with DS and in Ts65Dn mice; DYRK1A has increased expression in humans with DS and is involved in a number of critical pathways including CNS development and osteoclastogenesis. Epigallcatechin-3-gallate (EGCG), the main polyphenolic compound found in green tea, inhibits Dyrk1a activity, and we have shown previously that a three-week treatment with EGCG during adolescence normalizes some skeletal abnormalities in Ts65Dn mice. The current study tested the hypothesis that a similar 3-week treatment with EGCG will also rescue cognitive deficits observed in Ts65Dn mice. Trisomic mice and euploid littermates were given EGCG or water (control) for three weeks during adolescence. Following termination of the treatment, the mice were tested sequentially (over 5 weeks) on locomotor activity (two daily 30-min sessions in an activity chamber), novel object recognition (NOR) memory, acquisition of delayed non-matching to place (DNMP) spatial working memory in a tmaze, or spatial learning and memory in the Morris water maze (MWM). Results to date indicate that Ts65Dn mice exhibit deficits in the learning and memory tasks compared to controls, but the 3-week EGCG treatment did not significantly improve their performance.We hypothesize that for EGCG to be effective for improving cognitive deficits of the Ts65Dn mice, it needs to be present in the brain during the behavioral testing period; our ongoing studies are testing this with continuous EGCG treatment throughout the behavioral testing process.
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    Effects of Increased Dosage EGCG Treatment on Cognitive Deficits in the Ts65Dn Down Syndrome Mouse Model
    (Office of the Vice Chancellor for Research, 2015-04-17) Dhillon, Hardeep; Abeysekera, Irushi; Stringer, Megan; Goodlett, Charles R.; Roper, Randall J.
    Down syndrome (DS), caused by trisomy of human chromosome 21 (Hsa21), is the leading genetic cause of cognitive impairment and results in a constellation of phenotypes. Although symptomatic and therapeutic treatments exist for some DS phenotypes, treatments generally do not address the genetic etiology. The Ts65Dn mouse model, which contains a triplication of approximately half the gene orthologs of Hsa21, exhibits hippocampal learning and memory deficits as well as cerebellar motor and spatial deficits similar to those present in individuals with DS. DYRK1A, one of the genes overexpressed in DS, has been identified as a potential cause of cognitive impairment; therefore normalization of DYRK1A activity may be a valid form of treatment. We have shown that Epigallocatechin-3-gallate (EGCG), a major polyphenol of green tea, can rescue skeletal deficits found in the Ts65Dn mouse model at a low dosage. When this same low dosage was used to rescue behavioral deficits, however, it was ineffective. We hypothesize that high dose EGCG treatment lasting throughout the behavioral testing period will rescue the cognitive deficits observed in Ts65Dn mice. Trisomic mice and euploid littermates were given EGCG or water (control) for 7 weeks while being tested sequentially on novel object recognition (NOR) and Morris water maze (MWM). Our current data set shows that Ts65Dn mice exhibit deficits in learning and memory; further data will be collected in order to identify the effect of EGCG. Data showing pure EGCG as being ineffective will suggest the importance adding a supplemental compound, while data showing pure EGCG as an effective form of treatment will strongly support use of EGCG in translational studies in individuals with Down syndrome.
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    The Effects on Novel Object Recognition by Genetic Reduction of Dyrk1a to Normal Levels in Otherwise Trisomic Ts65Dn Down Syndrome Mice
    (Office of the Vice Chancellor for Research, 2016-04-08) Parker, Abigail; Stringer, Megan; Goodlett, Charles R.; Roper, Randall J.
    Down syndrome (DS) is caused by the triplication of chromosome 21 (Hsa21) in humans and is the leading genetic cause of intellectual disability. Ts65Dn mice are used as a model of Down syndrome, with about half of the genes in three copies of those triplicated on Hsa21 in individuals with DS. Overexpression of Dyrk1a, a gene found to be triplicated in both individuals with DS and Ts65Dn mice, has been linked to learning and memory deficits. Mice are naturally drawn to novel objects. As such, the Novel Object Recognition (NOR) test can be used to determine if Ts65Dn as compared to normal mice are impaired in discriminating novel objects from previously explored objects. In our current study, Ts65Dn mice with two copies of Dyrk1a were compared to Ts65Dn and euploid mice using the NOR task. We hypothesize that Ts65Dn, Dyrk1a+/- mice would perform as well as euploid mice on the NOR task, given that they both have two copies of Dyrk1a. Our preliminary results indicate that a genotype effect between trisomic mice and euploid mice is not observed. Additionally, Ts65Dn control mice and euploid control mice have a higher discrimination ratio than their Dyrk1a knockdown counterparts. These results indicate that overexpression of Dyrk1a may not be entirely responsible for deficits in learning and memory.