Shock tunnel studies of scramjet phenomena

Commissioning of the new T4 shock tunnel at the University of Queensland implied that it was no longer necessary to focus the work of the research group about an annual test series conducted in the T3 shock tunnel in Canberra. Therefore, it has been possible to organize a group for work to proceed along lines such that particular personnel are associated with particular project areas. The format of this report consists of a series of reports on specific project areas, with a brief general introduction commenting on each report. The introduction is structured by project areas, with the title of the relevant report stated under the project area heading. The reports themselves follow in the order of the project area headings

Targeting trisomic treatments: optimizing Dyrk1a inhibition to improve Down syndrome deficits

Overexpression of Dual‐specificity tyrosine‐phosphorylated regulated kinase 1A (DYRK1A), located on human chromosome 21, may alter molecular processes linked to developmental deficits in Down syndrome (DS). Trisomic DYRK1A is a rational therapeutic target, and although reductions in Dyrk1a genetic dosage have shown improvements in trisomic mouse models, attempts to reduce Dyrk1a activity by pharmacological mechanisms and correct these DS‐associated phenotypes have been largely unsuccessful. Epigallocatechin‐3‐gallate (EGCG) inhibits DYRK1A activity in vitro and this action has been postulated to account for improvement of some DS‐associated phenotypes that have been reported in preclinical studies and clinical trials. However, the beneficial effects of EGCG are inconsistent and there is no direct evidence that any observed improvement actually occurs through Dyrk1a inhibition. Inconclusive outcomes likely reflect a lack of knowledge about the tissue‐specific patterns of spatial and temporal overexpression and elevated activity of Dyrk1a that may contribute to emerging DS traits during development. Emerging evidence indicates that Dyrk1a expression varies over the life span in DS mouse models, yet preclinical therapeutic treatments targeting Dyrk1a have largely not considered these developmental changes. Therapies intended to improve DS phenotypes through normalizing trisomic Dyrk1a need to optimize the timing and dose of treatment to match the spatiotemporal patterning of excessive Dyrk1a activity in relevant tissues. This will require more precise identification of developmental periods of vulnerability to enduring adverse effects of elevated Dyrk1a, representing the concurrence of increased Dyrk1a expression together with hypothesized tissue‐specific‐sensitive periods when Dyrk1a regulates cellular processes that shape the long‐term functional properties of the tissue. Future efforts targeting inhibition of trisomic Dyrk1a should identify these putative spatiotemporally specific developmental sensitive periods and determine whether normalizing Dyrk1a activity then can lead to improved outcomes in DS phenotypes

Low dose EGCG treatment beginning in adolescence does not improve cognitive impairment in a Down syndrome mouse model

Down syndrome (DS) or Trisomy 21 causes intellectual disabilities in humans and the Ts65Dn DS mouse model is deficient in learning and memory tasks. DYRK1A is triplicated in DS and Ts65Dn mice. Ts65Dn mice were given up to ~ 20 mg/kg/day epigallocatechin-3-gallate (EGCG), a Dyrk1a inhibitor, or water beginning on postnatal day 24 and continuing for three or seven weeks, and were tested on a series of behavioral and learning tasks, including a novel balance beam test. Ts65Dn as compared to control mice exhibited higher locomotor activity, impaired novel object recognition, impaired balance beam and decreased spatial learning and memory. Neither EGCG treatment improved performance of the Ts65Dn mice on these tasks. Ts65Dn mice had a non-significant increase in Dyrk1a activity in the hippocampus and cerebellum. Given the translational value of the Ts65Dn mouse model, further studies will be needed to identify the EGCG doses (and mechanisms) that may improve cognitive function

Effects of EGCG Treatment of Ts65Dn Down Syndrome Mice on a Balance Beam Task

poster abstractDown 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

Multivariate Concentric Square Field unveils behavioral exploratory categories of locomotor activity in mouse model of Down syndrome

poster abstractDown Syndrome (DS), trisomy 21(Ts21), is a genetic condition in which a third copy of chromosome 21 is present, and results in neurodevelopmental deficits including intellectual disability. DS has been modeled in mice; Ts65Dn mouse model displays many of the phenotypes associated with DS, including cognitive deficits. We previously studied behavioral phenotypes of Ts65Dn mice and observed significantly increased locomotor activity in a novel arena (an “open field”). In those studies, treatment of the Ts65Dn mice with ~10 mg/kg/day of epigallocatechin-3-gallate (EGCG), a selective inhibitor of the DYRK1A kinase (one of the genes implicated in the neurodevelopmental deficits in DS and in Ts65Dn mice), failed to attenuate hyperactivity. Locomotor activity in an open field is a basic measure of general exploration in a simple environment, and was only moderately sensitive to the hyperactivity of the Ts65Dn mice. The aim of the current study was to use a more advanced analysis of behavioral patterns of exploration in a more complex, multi-partitioned arena, termed the Multivariate Concentric Square Field (MCSF). The advantage of MCSF is that it provides more elaborate measures of exploratory behavior by examining different categories of exploration: general activity, exploratory activity, risk assessment, risk taking and shelter seeking behavior. Trisomic mice and euploid littermates were treated with a continuous high dose (~100 mg/kg/day) of EGCG or water (controls) beginning at weaning. At seven weeks of age, they were tested in the MCSF on two consecutive days. Our current results indicate that Ts65Dn mice displayed more exploratory behavior compared to controls, and the EGCG treatment may have normalized exploratory behavior toward that of controls. Identifying altered patterns of exploratory behavior in the Ts65Dn mouse and the normalizing effects of EGCG treatment may help provide a therapeutic approach to DS

Mock observations with the Millennium Simulation: cosmological downsizing and intermediate-redshift observations

Only by incorporating various forms of feedback can theories of galaxy formation reproduce the present-day luminosity function of galaxies. It has also been argued that such feedback processes might explain the counterintuitive behaviour of 'downsizing' witnessed since redshifts z ≃ 1–2. To examine this question, observations spanning 0.4 < z < 1.4 from the Deep Extragalactic Evolutionary Probe (DEEP)2/Palomar survey are compared with a suite of equivalent mock observations derived from the Millennium Simulation, populated with galaxies using the galform code. Although the model successfully reproduces the observed total mass function and the general trend of 'downsizing', it fails to accurately reproduce the colour distribution and type-dependent mass functions at all redshifts probed. This failure is shared by other semi-analytical models which collectively appear to 'over-quench' star formation in intermediate-mass systems. These mock lightcones are also a valuable tool for investigating the reliability of the observational results in terms of cosmic variance. Using variance estimates derived from the lightcones, we confirm the significance of the decline since z ∼ 1 in the observed number density of massive blue galaxies which, we argue, provides the bulk of the associated growth in the red sequence. We also assess the limitations arising from cosmic variance in terms of our ability to observe mass-dependent growth since z ∼ 1

Can Epigallocatechin gallate (EGCG) Treatment Rescue Hippocampal-Dependent Cognitive Function in a Down Syndrome Mouse Model?

poster abstractDown 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

Correction of cerebellar movement related deficits by normalizing Dyrk1a copy number in the Ts65Dn mouse model for Down syndrome

poster abstractElucidation 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

Effects of Increased Dosage EGCG Treatment on Cognitive Deficits in the Ts65Dn Down Syndrome Mouse Model

poster abstractDown 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

Effects of 50 mg/kg EGCG Treatment of Ts65Dn Down Syndrome Mice on Novel Object Recognition

poster abstractDown 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