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Despite successful preclinical treatment studies to improve neurocognition in the Ts65Dn mouse model of Down syndrome, translation to humans has failed. This raises questions about the appropriateness of the Ts65Dn mouse as the gold standard. We used the novel Ts66Yah mouse that carries an extra chromosome and the identical segmental Mmu 16 trisomy as Ts65Dn without the Mmu 17 non- Hsa 21 orthologous region. Forebrains from embryonic day 18.5 Ts66Yah and Ts65Dn mice, along with euploid littermate controls, were used for gene expression and pathway analyses. Behavioral experiments were performed in neonatal and adult mice. Because male Ts66Yah mice are fertile, parent-of-origin transmission of the extra chromosome was studied. Forty-five protein-coding genes mapped to the Ts65Dn Mmu 17 non- Hsa 21 orthologous region; 71%–82% are expressed during forebrain development. Several of these genes are uniquely overexpressed in Ts65Dn embryonic forebrain, producing major differences in dysregulated genes and pathways. Despite these differences, the primary Mmu 16 trisomic effects were highly conserved in both models, resulting in commonly dysregulated disomic genes and pathways. Delays in motor development, communication, and olfactory spatial memory were present in Ts66Yah but more pronounced in Ts65Dn neonates. Adult Ts66Yah mice showed milder working memory deficits and sex-specific effects in exploratory behavior and spatial hippocampal memory, while long-term memory was preserved. Our findings suggest that triplication of the non- Hsa 21 orthologous Mmu 17 genes significantly contributes to the phenotype of the Ts65Dn mouse and may explain why preclinical trials that used this model have unsuccessfully translated to human therapies. [ABSTRACT FROM AUTHOR]

Down syndrome (DS) is the most common genetic disorder associated with intellectual disability. To study this syndrome, several mouse models have been developed. Among the most common is the Ts65Dn model, which mimics most of the alterations observed in DS. Ts65Dn mice, as humans with DS, show defects in the structure, density, and distribution of dendritic spines in the cerebral cortex and hippocampus. Fasudil is a potent inhibitor of the RhoA kinase pathway, which is involved in the formation and stabilization of dendritic spines. Our study analysed the effect of early chronic fasudil treatment on the alterations observed in the hippocampus of the Ts65Dn model. We observed that treating Ts65Dn mice with fasudil induced an increase in neural plasticity in the hippocampus: there was an increment in the expression of PSA-NCAM and BDNF, in the dendritic branching and spine density of granule neurons, as well as in cell proliferation and neurogenesis in the subgranular zone. Finally, the treatment reduced the unbalance between excitation and inhibition present in this model. Overall, early chronic treatment with fasudil increases cell plasticity and eliminates differences with euploid animals. • Fasudil treatment recovers dendritic trees in granule neurons of Ts65Dn mice. • Fasudil treatment increases spine density in granule neurons of Ts65Dn mice. • Fasudil treatment increases structural plasticity in the hippocampus of Ts65Dn mice. • Fasudil treatment recovers cell proliferation rate in dentate gyrus of Ts65Dn mice. • Fasudil infusion reduces the excess of inhibitory puncta in the hippocampus of Ts65Dn. [ABSTRACT FROM AUTHOR]

Abstract Down syndrome (DS) in humans is associated with differences of the central nervous system and oromotor development. DS also increases risks for pediatric feeding challenges, which sometimes involve the use of altered food consistencies. Therefore, experimental food consistency paradigms are of interest to oromotor investigations in mouse models of Down syndrome (DS). The present work reports impacts of an altered food consistency paradigm on the Ts65Dn and Dp(16)1Yey mouse models of DS, and sibling control mice. At weaning, Ts65Dn, Dp(16)1Yey and respective controls were assigned to receive either a hard food or a soft food (eight experimental groups, n = 8–10 per group). Two weeks later, mice were assessed for mastication speeds and then euthanized for muscle analysis. Soft food conditions were associated with significantly smaller weight gain (p =.003), significantly less volitional water intake through licking (p =.0001), and significant reductions in size of anterior digastric myofibers positive for myosin heavy chain isoform (MyHC) 2b (p =.049). Genotype was associated with significant differences in weight gain (p =.004), significant differences in mastication rate (p =.001), significant differences in a measure of anterior digastric muscle size (p =.03), and significant reductions in size of anterior digastric myofibers positive for MyHC 2a (p =.04). In multiple measures, the Ts65Dn model of DS was more affected than other genotype groups. Findings indicate a soft food consistency condition in mice is associated with significant reductions in weight gain and oromotor activity, and may impact digastric muscle. This suggests extended periods of food consistency modifications may have impacts that extend beyond their immediate roles in facilitating deglutition. Graphical abstract Unlabelled Image Highlights • A soft food consistency causes reduced weight gain in mouse models of Down syndrome and control mice. • A soft food consistency causes significant reductions in licking behavior. • Ts65Dn mice have slower mastication rates than other genotypes. • Both genotype and food consistency may impact digastric muscle. [ABSTRACT FROM AUTHOR]

• Ts65Dn and Dp(16)1Yey mice both have ultrasonic vocalization (USV) phenotypes. • More USV differences were found for Ts65Dn than for Dp(16)1Yey. • USV frequency parameters were lower for Ts65Dn and higher for Dp(16)1Yey mice. Down syndrome (DS) is a developmental disorder associated with a high incidence of challenges in vocal communication. DS can involve medical co-morbidities and structural social factors that may impact communication outcomes, which can present difficulties for the study of vocal communication challenges. Mouse models of DS may be used to study vocal communication differences associated with this syndrome and allow for greater control and consistency of environmental factors. Prior work has demonstrated differences in ultrasonic vocalization (USV) of the Ts65Dn mouse model of DS at a young adult age, however it is not known how USV characteristics are manifested at mature ages. Given that the aging process and age-related co-morbidities may also impact communication in DS, addressing this gap in knowledge may be of value for efforts to understand communication difficulties in DS across the lifespan. The current study hypothesized that the Ts65Dn and Dp(16)1Yey mouse models of DS would demonstrate differences in multiple measures of USV communication at a mature adult age of 5 months. Methods: Ts65Dn mice (n = 16) and euploid controls (n = 19), as well as Dp(16)1Yey mice (n = 20) and wild-type controls (n = 22), were evaluated at 5 months of age for USV production using a mating paradigm. Video footage of USV sessions were analyzed to quantify social behaviors of male mice during USV testing sessions. USV recordings were analyzed using Deepsqueak software to identify 10 vocalization types, which were quantified for 11 acoustic measures. Results: Ts65Dn, but not Dp(16)1Yey, showed significantly lower proportions of USVs classified as Step Up, Short, and Frequency Steps, and significantly higher proportions of USVs classified as Inverted U, than euploid controls. Both Ts65Dn and Dp(16)1Yey groups had significantly greater values for power and tonality for USVs than respective control groups. While Ts65Dn showed lower frequencies than controls, Dp(16)1Yey showed higher frequencies than controls. Finally, Ts65Dn showed reductions in a measure of complexity for some call types. No significant differences between genotype groups were identified in analysis of behaviors during testing sessions. Conclusion : While both Ts65Dn and Dp(16)1Yey show significant differences in USV measures at 5 months of age, of the two models, Ts65Dn shows a relatively greater numbers of differences. Characterization of communication phenotypes in mouse models of DS may be helpful in laying the foundation for future translational advances in the area of communication difficulties associated with DS. [ABSTRACT FROM AUTHOR]

This study was designed to investigate the brain proteome of the Ts65Dn mouse model of Down syndrome. We profiled the cerebellum and hippocampus proteomes of 6- and 12-month-old trisomic and disomic mice by difference gel electrophoresis. We quantified levels of 2082 protein spots and identified 272 (170 unique UniProt accessions) by mass spectrometry. Four identified proteins are encoded by genes trisomic in the Ts65Dn mouse. Three of these ( CRYZL11 , EZR , and SOD1 ) were elevated with p -value <0.05, and 2 proteins encoded by disomic genes ( MAPRE3 and PHB ) were reduced. Intergel comparisons based on age (6 vs. 12 months) and brain region (cerebellum vs. hippocampus) revealed numerous differences. Specifically, 132 identified proteins were different between age groups, and 141 identified proteins were different between the 2 brain regions. Our results suggest that compensatory mechanisms exist, which ameliorate the effect of trisomy in the Ts65Dn mice. Differences observed during aging may play a role in the accelerated deterioration of learning and memory seen in Ts65Dn mice. [ABSTRACT FROM AUTHOR]

Background Amyloid-β (Aβ), a hallmark of Alzheimer’s disease (AD), has long been a focus of basic and translation research in AD. Quantification and dissociation of the Aβ fractions in their soluble and insoluble forms, is a key factor in numerous AD studies. New method Here we provide a generalized sandwich-enzyme-linked-immuno-sorbent-assay (sELISA) protocol for quantification of human and murine Aβ 1-40 and Aβ 1-42 and dissociation of these peptides to their soluble-oligomeric and insoluble-fibrillar forms. Results We have validated the levels of soluble and insoluble Aβ 1-40 and Aβ 1-42 in the 5XFAD AD and the Ts65Dn Down-Syndrome (DS) mouse models in both the cortex, hippocampus and blood as follows: (1) blood levels of Aβ 1-40 and Aβ 1-42 are elevated in both mouse strains. (2) 5XFAD mice exhibit elevated soluble and insoluble Aβ 1-40 in cortical and hippocampal tissues, soluble Aβ 1-42 in the hippocampus, and insoluble Aβ 1-42i n both cortical and hippocampal tissues (3) Ts65Dn mice exhibit elevated levels of Aβ 1-40 in the cortex. Comparison with existing methods Several methodologies have been proposed for the high throughput measure of Aβ, including HPLC-mass-spectrometry, micro-immunoelectrodes, immunoprecipitation and ELISA. Although commercial sELISA kits are widely used, herein, we describe a more accessible and cost-effective in-house protocol enabling to measure either human or murine, soluble and insoluble Aβ 1-40 and Aβ 1-42 levels. Conclusions We provide a streamlined and accessible protocol for the assessment of soluble and insoluble Aβ 1-40 and Aβ 1-42 levels from mouse or human origins, enabling a higher accessibility for researchers in the field to generate reliable Aβ-related measurements. [ABSTRACT FROM AUTHOR]

Melatonin administered during adulthood induces beneficial effects on cognition and neuroprotection in the Ts65Dn (TS) mouse model of Down syndrome. Here, we investigated the effects of pre- and post-natal melatonin treatment on behavioral and cognitive abnormalities and on several neuromorphological alterations (hypocellularity, neurogenesis impairment and increased oxidative stress) that appear during the early developmental stages in TS mice. Pregnant TS females were orally treated with melatonin or vehicle from the time of conception until the weaning of the offspring, and the pups continued to receive the treatment from weaning until the age of 5 months. Melatonin administered during the pre- and post-natal periods did not improve the cognitive impairment of TS mice as measured by the Morris Water maze or fear conditioning tests. Histological alterations, such as decreased proliferation (Ki67+ cells) and hippocampal hypocellularity (DAPI+ cells), which are typical in TS mice, were not prevented by melatonin. However, melatonin partially regulated brain oxidative stress by modulating the activity of the primary antioxidant enzymes (superoxide dismutase in the cortex and catalase in the cortex and hippocampus) and slightly decreasing the levels of lipid peroxidation in the hippocampus of TS mice. These results show the inability of melatonin to prevent cognitive impairment in TS mice when it is administered at pre- and post-natal stages. Additionally, our findings suggest that to induce pro-cognitive effects in TS mice during the early stages of development, in addition to attenuating oxidative stress, therapies should aim to improve other altered processes, such as hippocampal neurogenesis and/or hypocellularity. [ABSTRACT FROM AUTHOR]

The Ts65Dn is a popular mouse model of Down syndrome (DS). It displays DS-relevant features of learning/memory deficits and age-related loss of functional markers in basal forebrain cholinergic neurons. Here we describe protein expression abnormalities in brain regions of 12-month-old male Ts65Dn mice. We show that the magnitudes of abnormalities of human chromosome 21 and non–human chromosome 21 orthologous proteins are greater at 12 months than at ∼6 months. Age-related exacerbations involve the number of components affected in the mechanistic target of rapamycin pathway, the levels of components of the mitogen-activated protein kinase pathway, and proteins associated with Alzheimer's disease. Among brain regions, the number of abnormalities in cerebellum decreased while the number in cortex greatly increased with age. The Ts65Dn is being used in preclinical evaluations of drugs for cognition in DS. Most commonly, drug evaluations are tested in ∼4- to 6-month-old mice. Data on age-related changes in magnitude and specificity of protein perturbations can be used to understand the molecular basis of changes in cognitive ability and to predict potential age-related specificities in drug efficacies. [ABSTRACT FROM AUTHOR]

Zinc is an essential trace element that is critical for a large number of structural proteins, enzymatic processes and transcription factors. In the brain, zinc ions are involved in synaptic transmission. The homeostasis of zinc is crucial for cell survival and function, and cells have developed a wide variety of systems to control zinc concentration. Alterations in free zinc concentration have been related with brain dysfunction. Down Syndrome individuals present alterations in free zinc concentration and in some of the proteins related with zinc homeostasis. We have analyzed the amount of free zinc and the zinc chelating protein metallothionein 3 in the astrocytes using primary cultures of the murine model Ts65Dn. We have observed a higher number of zinc positive spots in the cytoplasm of trisomic astrocytes but a decrease in the total concentration of total intracellular free zinc concentration (including the spots) respect to control astrocytes. Using FM1-43 staining, we found that the endocytic function remains unaltered. Therefore, a possible explanation for this lower concentration of free zinc could be the higher concentration of metallothionein 3 present in the cytoplasm of trisomic astrocytes. The blockade of metallothionein 3 expression using an specific siRNA induced an increase in the concentration of free zinc in basal conditions but failed to increase the uptake of zinc after incubation with zinc ions. [ABSTRACT FROM AUTHOR]

Abstract: Down syndrome (DS) is the leading cause of genetically defined intellectual disability. Although speech and language impairments are salient features of this disorder, the nature of these phenotypes and the degree to which they are exacerbated by concomitant oromotor dysfunction and/or hearing deficit are poorly understood. Mouse models like Ts65Dn, the most extensively used DS animal model, have been critical to understanding the genetic and developmental mechanisms that contribute to intellectual disability. In the present study, we characterized the properties of the ultrasonic vocalizations (USVs) emitted by Ts65Dn males during courtship episodes with female partners. USVs emitted by mice in this setting have been proposed to have some basic correlation to human speech. Data were collected and analyzed from 22 Ts65Dn mice and 22 of their euploid littermates. We found that both the minimum and maximum peak frequencies of Ts65Dn calls were lower than those produced by euploid mice, whereas the mean individual duration of “down” and “complex” syllable types was significantly longer. Peak, minimal and maximal, and the fundamental frequencies of short syllables generated by Ts65Dn mice were lower compared to those by euploid mice. Finally, Ts65Dn males made fewer multiple jumps calls during courtship and the mean total duration of their “arc”, “u”, and “complex” syllables was longer. We discuss the human correlates to these findings, their translational potential, and the limitations of this approach. To our knowledge, this is the first characterization of differences between adult Ts65Dn and euploid control mice with respect to USVs. [Copyright &y& Elsevier]

Background: Down syndrome is associated with significant failure in cognitive function. Our previous investigation revealed age-dependent degeneration of locus coeruleus, a major player in contextual learning, in the Ts65Dn mouse model of Down syndrome. We studied whether drugs already available for use in humans can be used to improve cognitive function in these mice. Methods: We studied the status of β adrenergic signaling in the dentate gyrus of the Ts65Dn mouse model of Down syndrome. Furthermore, we used fear conditioning to study learning and memory in these mice. Postmortem analyses included the analysis of synaptic density, dendritic arborization, and neurogenesis. Results: We found significant atrophy of dentate gyrus and failure of β adrenergic signaling in the hippocampus of Ts65Dn mice. Our behavioral analyses revealed that formoterol, a long-acting β2 adrenergic receptor agonist, caused significant improvement in the cognitive function in Ts65Dn mice. Postmortem analyses revealed that the use of formoterol was associated with a significant improvement in the synaptic density and increased complexity of newly born dentate granule neurons in the hippocampus of Ts65Dn mice. Conclusions: Our data suggest that targeting β2 adrenergic receptors is an effective strategy for restoring synaptic plasticity and cognitive function in these mice. Considering its widespread use in humans and positive effects on cognition in Ts65Dn mice, formoterol or similar β2 adrenergic receptor agonists with ability to cross the blood brain barrier might be attractive candidates for clinical trials to improve cognitive function in individuals with Down syndrome. [Copyright &y& Elsevier]

Abstract: Down syndrome (DS) is the most common genetic aberration leading to intellectual disability. DS results from an extra copy of the long arm of human chromosome 21 (HSA21) and the increased expression of trisomic genes due to gene dosage. While expression in DS and DS models has been studied extensively at the RNA level, much less is known about expression of trisomic genes at the protein level. We have used quantitative Western blotting with antibodies to 20 proteins encoded by HSA21 to assess trisomic protein expression in lymphoblastoid cell lines (LCLs) from patients with DS and in brains from two mouse models of DS. These antibodies have recently become available and the 20 proteins largely have not been investigated previously for their potential contributions to the phenotypic features of DS. Twelve proteins had detectable expression in LCLs and three, CCT8, MX1 and PWP2, showed elevated levels in LCLs derived from patients with DS compared with controls. Antibodies against 15 proteins detected bands of appropriate sizes in lysates from mouse brain cortex. Genes for 12 of these proteins are trisomic in the Tc1 mouse model of DS, but only SIM2 and ZNF295 showed elevated expression in Tc1 cortex when compared with controls. Genes for eight of the 15 proteins are trisomic in the Ts65Dn mouse model of DS, but only ZNF294 was over expressed in cortex. Comparison of trisomic gene expression at the protein level with previous reports at the mRNA level showed many inconsistencies. These may be caused by natural inter-individual variability, differences in the age of mice analyzed, or post-transcriptional regulation of gene dosage effects. These antibodies provide resources for further investigation of the molecular basis of intellectual disability in DS. [Copyright &y& Elsevier]

Abstract: The Ts65Dn mouse displays several phenotypic abnormalities that parallel characteristics found in Down syndrome. One important characteristic associated with Down syndrome is an increased incidence of early-onset Alzheimer''s disease. Since Alzheimer''s disease is characterized largely by progressive memory loss, it is of interest to study working memory in the Ts65Dn mouse. Previous research in our lab using a titrating, delayed matching-to-position schedule of reinforcement has demonstrated that young, adult male Ts65Dn mice do not display a working memory deficit when compared to age-matched littermate controls. However, there have been no studies examining the working memory of these mice as they age. Due to the correlation between Down syndrome and Alzheimer''s disease, and as part of a larger effort to further characterize the phenotype of the Ts65Dn mouse, the purpose of this study was to determine whether aged Ts65Dn mice possess a working memory deficit when compared to age-matched littermate controls. In order to study working memory, two groups of mice were trained under a titrating, delayed matching-to-position schedule of reinforcement. The first group was trained beginning at 3 months of age, and the second group began training at 15 months of age. Both groups were studied to 24 months of age. Initially, both groups of Ts65Dn mice performed at a lower level of accuracy than the control mice; however, this difference disappeared with further practice. The results from these lifespan studies indicate that the aged Ts65Dn mouse does not possess a working memory deficit when compared to age-matched controls. [Copyright &y& Elsevier]

Abstract: Down syndrome is the most common genetic disorder associated with mental retardation. Subjects and mice models for Down syndrome (such as Ts65Dn) show defects in the formation of neuronal networks in both the hippocampus and the cerebral cortex. The principal neurons display alterations in the morphology, density and distribution of dendritic spines in the cortex as well as in the hippocampus. Several evidences point to the possibility that the atrophy observed in principal neurons could be mediated by changes in their inhibitory inputs and, in fact, an imbalance between excitation and inhibition has been observed in Ts65Dn mice in these regions, which are crucial for learning and information processing. These animals have an increased density of interneurons in the primary somatosensory cortex, especially of those expressing calretinin and calbindin D-28k. Here, we have analysed the expression and distribution of several neuropeptides in the primary somatosensory cortex of Ts65Dn mice in order to investigate whether these subpopulations of interneurons are affected. We have observed an increase in the total density of somatostatin expressing interneurons and of those expressing VIP in layer IV in Ts65Dn mice. The typology of the somatostatin and VIP interneurons was unaltered as attested by the pattern of co-expression with other markers. Somatostatin immunoreactive neurons co-express mainly D-28k calbindin and VIP expressing interneurons maintain its pattern of co-expression with calcium binding proteins. These alterations, in case they were also present in subjects with Down syndrome, could be related to their impairment in cognitive profile and could be involved in the neurological defects observed in this disorder. [Copyright &y& Elsevier]

Abstract: Trisomy 21, also referred to Down syndrome (DS), is the most common genetic cause of mental retardation, affecting 1 each 800–1000 newborn children all over the world. DS is a complex disease, determined by an extra copy of human chromosome 21 that causes an imbalanced gene dose effect. The syntenies that exist between mouse chromosomes 10, 16, and 17 and human chromosome 21 offer the opportunity for a genotype–phenotype correlation and several mouse models of DS have been developed to improve our knowledge about cognitive disabilities and brain alterations. We present here the different murine models available up to now and we discuss the neural alterations that have been described in these strains. The largest amount of studies involved the so called Ts65Dn mouse showing early alterations of nitrergic, noradrenergic and cholinergic systems at the level of the basal forebrain. Neurogenesis and spine formations are decreased in the hippocampus, as well as the whole size of the cerebellum and the number of granule cells. [Copyright &y& Elsevier]

Background: Trisomy 21 or Down syndrome (DS) is the most frequent genetic cause of mental retardation. There is limited insight into the biological basis for the cognitive and motor deficits in DS. Because the striatum plays a key role in the regulation and learning of voluntary movements and in cognitive processes, our study was aimed at investigating striatal synaptic transmission and plasticity in a well-accepted genetic model of DS. Methods: Electrophysiological recordings were performed in a corticostriatal slice preparation from trisomic (Ts65Dn) and wild-type mice. Synaptic properties and plasticity, long-term potentiation (LTP) and long-term depression (LTD), were investigated. Results: The basal electrophysiological properties of striatal principal spiny neurons and cholinergic interneurons were spared in the Ts65Dn mouse model of DS. Striatal principal spiny neurons from Ts65Dn mice maintained their ability to undergo LTP and LTD. Conversely, LTP was lost in striatal cholinergic interneurons of Ts65Dn mice. The loss of LTP in striatal cholinergic interneurons of Ts65Dn mice was accompanied by a severe impairment of endogenous cholinergic signaling within the striatum. Conclusions: The intrastriatal cholinergic system that was thought to be spared in DS is functionally altered in the Ts65Dn genetic model of DS. Altered cholinergic transmission might play a critical role in the pathophysiology of motor and cognitive deficits in DS, leading to an abnormal processing of neuronal inputs within the basal ganglia. Targeting striatal cholinergic transmission might represent a new therapeutic strategy in DS. [Copyright &y& Elsevier]

Abstract: The Ts65Dn mouse is partly trisomic at chromosome 16 and is considered to be a valid mouse model of human Down syndrome. Prior research using an incremental repeated acquisition (IRA) schedule of reinforcement has revealed that there is a significant learning deficit in young, adult Ts65Dn mice compared to littermate controls. The purpose of this study was to examine whether this deficit changes during the life-span of these mice. In order to determine if changes in the deficit were caused by motoric or motivational deficiencies, a second group of mice was trained to respond under a performance version of the task (IRA-P). The IRA-P task required the same motor responses to produce the reinforcer, but no learning or acquisition was required. Data collected under the IRA task demonstrated that there was a significant learning impairment that persisted up to 24 months of age in the Ts65Dn mice compared to littermate controls. There was a significant decrease in the rate of responding and the number of milk presentations earned by the Ts65Dn mice after 19 months of age. However, during this time, response accuracy, which is independent of mobility and possibly motivation, did not decrease. Under the IRA-P schedule, there was no decrease observed in the number of milk presentations of either line as they aged, but the trend in the rate of responding of the Ts65Dn mice was similarly declining as the rate of responding observed in the Ts65Dn mice under the IRA task. These data indicate that the ability to learn in Ts65Dn mice does not decline with age as measured by the IRA task and suggests that perhaps Ts65Dn mice do not exhibit the same early onset Alzheimer''s disease phenotype that is typically seen in human patients. [Copyright &y& Elsevier]

Abstract: Ts65Dn mice are a genetic model for Down syndrome. Among others, these mice have cerebellar pathology features which parallel those seen in Down syndrome patients. Both individuals with Down syndrome and Ts65Dn mice have reduced cerebellar volume and numbers of granule and Purkinje cells. In this report, we describe morphological abnormalities of axons of Purkinje cells in the cerebellum of Ts65Dn mice, by using anti-calbindin immunocytochemistry. A consistent number of Purkinje cells shows axons bearing giant varicosities along their transit through the granular layer. The cerebellar arbor vitae made by fasciculated Purkinje cell axons has a patchy appearance, some tracks being devoid of calbindin staining. The infraganglionic plexus, formed by recurrent collaterals of Purkinje cell axons, has enormously increased density, which is evidence for a compensatory reaction to degeneration of distal segments of axons. These alterations are accompanied by strong glial reaction as evidenced by GFAP immunocytochemistry. Moreover, the alterations are more consistent in the anterior lobules of the vermis and intermediate cortex. The axonal pathology of Purkinje cells may explain the impairment in cerebellar functions observed in Ts65Dn mice at the adulthood. [Copyright &y& Elsevier]

Abstract: Down syndrome (DS) results from triplication of the whole or distal part of human chromosome 21. Persons with DS suffer from deficits in learning and memory and cognitive functions in general, and, starting from early development, their brains show dendritic and spine structural alterations and cell loss. These defects concern many cortical brain regions as well as the hippocampus, which is known to play a critical role in memory and cognition. Most of these abnormalities are reproduced in the mouse model Ts65Dn, which is partially trisomic for the mouse chromosome 16 that is homologous to a portion of human chromosome 21. Thus, Ts65Dn is widely utilized as an animal model of DS. To better understand the molecular defects underlying the cognitive and particularly the memory impairments of DS, we investigated whether the expression of several molecules known to play critical roles in long-term synaptic plasticity and long-term memory in a variety of species is dysregulated in either the neonatal brain or adult hippocampus of Ts65Dn mice. We found abnormal expression of the synaptic proteins synaptophysin, microtubule-associated protein 2 (MAP2) and cyclin-dependent kinase 5 (CDK5) and of the neurotrophin-3 (NT-3). Both the neonatal brain and adult hippocampus revealed significant abnormalities. These results suggest that a dysregulation in the expression of neurotrophins as well as proteins involved in synaptic development and plasticity may play a potential role in the neural pathology of DS in humans. [Copyright &y& Elsevier]

Abstract: Down syndrome (DS) is the leading non-heritable cause of mental retardation and is due to the effects of an extra chromosome 21. Mouse models of DS have been developed which parallel many of the cognitive and behavioral deficits of DS individuals. Of these, Ts65Dn mice show abnormal hippocampal properties including learning and memory deficits, altered synaptic plasticity and irregular dendritic spines. We assessed synaptic function of cultured postnatal Ts65Dn hippocampal neurons through examination of spontaneous miniature excitatory post-synaptic currents (mEPSCs) and compared them to those from diploid neurons. Averaged amplitudes and frequency of mEPSC events were similar to diploid suggesting presynaptic function is not overtly disrupted in Ts65Dn hippocampal neurons. However, both averaged decay and rise times (10–90% of peak) were significantly faster (∼20% for both rise and decay) in Ts65Dn neurons compared to diploid. The distribution of both decay and rise times, indicates global scaling of all percentile groups and is independent of amplitude suggesting normal electrotonic filtering in spite of abnormal expression of GIRK2 channel in Ts65Dn mouse. Western blot analysis suggests overexpression of GluR4 subunit of AMPA receptors which may contribute to faster mEPSC in Ts65Dn neurons. Intrinsic synaptic properties influenced by genetics or epigenetics factors in Ts65Dn postnatal cultured neurons are therefore disrupted and may contribute to the cognitive deficits associated with DS. [Copyright &y& Elsevier]

Abstract: Ts65Dn mice, like individuals with Down syndrome (DS), demonstrate a functional dissociation between explicit and implicit forms of memory, showing selective impairment in explicit or declarative learning tasks. Here, we explored Ts65Dn explicit memory deficits further by evaluating the ability of these mice to assimilate the temporal and spatial contexts under which previously novel objects had been encountered. We found that Ts65Dn mice could in fact form contextual representations of objects over the course of a few hours, contrary to their inability to discriminate object novelty over a more prolonged period of 24h. These results suggest that Ts65Dn mice might have particular difficulties in declarative tasks requiring long-term memory, presenting an especially important putative therapeutic target for pre-clinical and clinical DS research. [Copyright &y& Elsevier]

Abstract: The most commonly used model of Down syndrome, the Ts65Dn (TS) mouse, is trisomic for most of the region of MMU16 that is homologous to HSA21. This mouse shares many phenotypic characteristics with people with Down syndrome including behavioral and cognitive alterations. The objective of this study was to analyze the ability of two drugs that improve cognition in different experimental models, the acetylcholinesterase inhibitor donepezil and the non-competitive GABAA antagonist pentylenetetrazole (PTZ), to improve the cognitive deficits found in TS mice. The drugs were administered p.o. to TS and CO mice for 8 weeks and a behavioral characterization was performed. Sensorimotor abilities, including vision, hearing, strength and motor coordination, as well as locomotor activity in the home cage, were not modified by any chronic treatment in TS and CO mice. TS mice showed altered equilibrium in the aluminium rod, and this effect was larger under PTZ treatment. This result may indicate a potential adverse effect of PTZ in Ts65Dn mice. Learning and memory were evaluated in TS and CO mice after both treatments in the Morris water maze. Donepezil administration did not modify learning and memory in animals of any genotype. On the other hand, PTZ administration rescued TS performance in the Morris water maze. [Copyright &y& Elsevier]

Abstract: Down syndrome (DS) is a chromosomal disorder whereby genes on chromosome 21 are present in three copies. This gene copy imbalance is thought to be responsible for a number of debilitating conditions experienced by individuals with DS. Amongst these is a reduced cerebellar volume, or cerebellar hypoplasia, which is believed to contribute to the perturbation of fine motor control. Mouse models of DS (such as Ts65Dn, Ts1Cje, Tc1) exhibit a cerebellar phenotype similar to that of individuals with DS and which primarily manifests as a disruption of the density of the granule cell layer. Dissecting which of the three-copy genes are responsible for this phenotype (the primary gene dosage effect) has been a task undertaken by researchers working with various segmental trisomies and transgenic mice. It is generally agreed that, when expressed, three-copy genes of trisomic mice are expressed at around 1.5 times that of the same genes in euploid (wild-type) mice. However, amongst these studies there does not appear to be a consensus on the nature and extent of differential expression of two-copy genes in trisomic mice—the secondary dosage effect. Much of this variation may have to do with the stage of development investigated and the nature and complexity of the tissue (i.e. whole brain versus the cerebellum). The recent discovery that trisomic granule cell precursors are less sensitive to sonic hedgehog-induced proliferation has opened up another avenue for the identification of three-copy genes responsible for the cerebellar phenotype. It is hoped that further investigation of this phenomenon, together with new mouse segmental trisomies and transgenics, will reveal the cause of the proliferation deficit and allow for potential treatment. [Copyright &y& Elsevier]

Abstract: This study used a matching-to-position schedule of reinforcement to examine working memory in Ts65Dn and littermate control mice. Initially there appeared to be a memory deficit in the Ts65Dn mice, which disappeared with extended practice. Thus, what appeared as a memory deficit may actually be the result of a delay in learning the concept of matching. These results suggest that delayed learning may be an important factor in other procedures examining working memory in Ts65Dn mice and have important implications for clinical treatment of Down syndrome patients. [Copyright &y& Elsevier]

Abstract: Due to the homology between human chromosome 21 and mouse chromosome 16, trisomy 16 mice are considered animal models of Down syndrome (DS). Abnormal hippocampal synaptic plasticity and behavior have been reported in the segmental trisomy 16 Ts65Dn mouse. In the Ts1Cje DS mouse model, which has a shorter triplicated chromosomal segment than Ts65Dn, more subtle hippocampal behavioral deficits have been reported. In this study, we investigated CA1 hippocampal synaptic plasticity, long-term potentiation (LTP) and depression (LTD) in the Ts1Cje mouse. Field excitatory postsynaptic potentials (fEPSPs) were recorded from the CA1 area of in vitro hippocampal slices from the Ts1Cje mouse and diploid controls, LTP was induced by a single tetanizing train pulse (1s) at 100Hz and LTD by a 900-pulse train at 1Hz. We report for the first time that compared to diploid controls, the hippocampus from the Ts1Cje mouse had a smaller LTP and an increased LTD. The changes are less dramatic than had been reported previously for the Ts65Dn mouse. Furthermore, in the Ts1Cje mouse trains of pulses at both 20Hz and 100Hz produced a decrease in the evoked fEPSPs over the length of the train in comparison to diploid fEPSPs. These findings suggest that genes from Ts1Cje chromosome, including GIRK2 potassium channel, contribute to abnormal short- and long-term plasticity. [Copyright &y& Elsevier]

Abstract: Reduced number of neurons is a common feature in Down''s syndrome (DS) brains. Since reduced neuronal number also occurs in the dentate gyrus of Ts65Dn mice (TS), a model for DS, hippocampal cell proliferation and survival were analyzed in young and old TS mice. For evaluating proliferation and survival, half of the mice were sacrificed 1 day, and the other half 30 days after the last bromodeoxyuridine injection, respectively. No difference was found in the number of proliferating or surviving cells of young TS and control mice. An age-associated decline in total cell number and density has been found in both genotypes, this decline being more pronounced in TS animals. Thus, aged TS mice showed reduced cell proliferation and density of surviving cells compared to CO mice. Due to the putative involvement of newborn cells in the dentate gyrus in learning processes, the reduced proliferative capacity found in TS mice could be involved in the cognitive problems found in this model of Down syndrome. [Copyright &y& Elsevier]

With an incidence of approximately 1 in 700 live births, Down syndrome (DS) remains the most common genetic cause of mental retardation. The phenotype is assumed to be due to overexpression of some number of the >300 genes encoded by human chromosome 21. Mouse models, in particular the chromosome 16 segmental trisomies, Ts65Dn and Ts1Cje, are indispensable for DS-related studies of gene–phenotype correlations. Here we compare the updated gene content of the finished sequence of human chromosome 21 (364 genes and putative genes) with the gene content of the homologous mouse genomic regions (291 genes and putative genes) obtained from annotation of the public sector C57Bl/6 draft sequence. Annotated genes fall into one of three classes. First, there are 170 highly conserved, human/mouse orthologues. Second, there are 83 minimally conserved, possible orthologues. Included among the conserved and minimally conserved genes are 31 antisense transcripts. Third, there are species-specific genes: 111 spliced human transcripts show no orthologues in the syntenic mouse regions although 13 have homologous sequences elsewhere in the mouse genomic sequence, and 38 spliced mouse transcripts show no identifiable human orthologues. While these species-specific genes are largely based solely on spliced EST data, a majority can be verified in RNA expression experiments. In addition, preliminary data suggest that many human-specific transcripts may represent a novel class of primate-specific genes. Lastly, updated functional annotation of orthologous genes indicates genes encoding components of several cellular pathways are dispersed throughout the orthologous mouse chromosomal regions and are not completely represented in the Down syndrome segmental mouse models. Together, these data point out the potential for existing mouse models to produce extraneous phenotypes and to fail to produce DS-relevant phenotypes. [Copyright &y& Elsevier]

Individuals with Down''s syndrome (DS) develop the pathological hallmarks of Alzheimer''s (AD) disease at an early age, subsequently followed by memory decline and dementia. We have utilized an animal model for DS, mice with segmental trisomy of chromosome 16 (Ts65Dn), to study biological events linked to memory loss. Previous studies demonstrated a cognitive decline and loss of cholinergic markers after 6–8 months of age. In the current study, we found increased levels of amyloid precursor protein (APP) in the striatum by 6–8 months of age, and in the hippocampus and parietal cortex by 13–16 months of age in Ts65Dn but not in normosomic mice. Additionally, Ts65Dn mice exhibited alterations in nerve growth factor (NGF) levels in the basal forebrain and hippocampus. Ts65Dn mice demonstrated a significant decline in NGF levels in the basal forebrain with age, as well as a reduction in hippocampal NGF by 13–16 months of age. These findings demonstrate that elevated APP and decreased NGF levels in limbic areas correlate with the progressive memory decline and cholinergic degeneration seen in middle-aged trisomic mice. [Copyright &y& Elsevier]

Individuals with Down syndrome (DS) develop most neuropathological hallmarks of Alzheimer''s disease early in life, including loss of cholinergic markers in the basal forebrain. Ts65Dn mice, an animal model of DS, perform poorly on tasks requiring spatial memory and also exhibit basal forebrain pathology beginning around 6 months of age. We evaluated memory as well as brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) protein levels in basal forebrain, frontal cortex, hippocampus, and striatum in Ts65Dn mice at the age when cholinergic degeneration is first observed, and compared values to normosomic controls. Six-month-old Ts65Dn mice exhibited impairments in working and reference memory as assessed on a water radial-arm maze. The working memory deficit was related to the inability of Ts65Dn mice to successfully sustain performance as the working memory load increased. Coupled with cognitive performance deficiencies, Ts65Dn mice also exhibited lower frontal cortex BDNF protein levels than controls. Further, BDNF levels were negatively correlated with working memory errors during the latter portion of testing in Ts65Dn mice, thereby suggesting that lower BDNF protein levels in the frontal cortex may be associated with the observed working memory impairment. [Copyright &y& Elsevier]

Ts65Dn mice are partially trisomic for a segment of murine chromosome 16 similar to the gene segment on human chromosome 21 affected in Down''s syndrome (DS). These animals display cognitive deficits, neurochemical imbalances, and cholinergic degeneration resembling alterations in DS and early onset Alzheimer''s disease. The loss of basal forebrain cholinergic phenotype in Ts65Dn mice begins at approximately 6 months of age and may be due to an improperly functioning neurotrophic system. We compared 4 and 6 month-old Ts65Dn mice in a water-escape radial-arm maze task to investigate working and reference memory before and after the reported onset of cholinergic decline. Both 4 and 6 month-old Ts65Dn mice exhibited impaired performance compared to age-matched controls. However, the younger Ts65Dn mice displayed the capability to learn all working and reference memory measures, while the older Ts65Dn mice did not. Ts65Dn mice failed to maintain performance as working memory load increased, and the ability to handle an increasing working memory load also diminished with age. Collectively, these data suggest that major alterations in cognitive function occur in Ts65Dn mice between the ages of 4 and 6 months. [Copyright &y& Elsevier]

Piracetam is a nootropic agent that has been shown to improve cognitive performance in a number of animal model systems. Piracetam is reported to be used widely as a means of improving cognitive function in children with Down''s syndrome (DS). In order to provide a preclinical assessment of the potential efficacy of piracetam, we examined the effects of a dose range of piracetam in the Ts65Dn mouse model of DS. Ts65Dn mice are trisomic for a region of mouse chromosome 16 with homology to human chromosome 21. Daily piracetam treatment at doses of 0, 75, 150, and 300 mg/kg ip was initiated in 6-week-old male Ts65Dn and euploid control mice. Following 4 weeks of treatment, mice were tested in the visible and hidden-platform components of the Morris water maze and were placed overnight in computerized activity chambers to assess effects on overall activity. Piracetam treatment was continued through the 4 weeks of testing. In control mice, 75 and 150 mg/kg/day piracetam improved performance in both the visible- and hidden-platform tasks. Although low doses of piracetam reduced search time in the visible-platform component in Ts65Dn mice, all piracetam doses prevented trial-related improvements in performance in Ts65Dn mice. The 300-mg/kg/day-piracetam dose was associated with a reversal of the nocturnal spontaneous hyperactivity in Ts65Dn. These data do not provide support for piracetam treatment for individuals with DS. [Copyright &y& Elsevier]

• We examined which connectivity deficits are present at birth in Ts65Dn mice. • Corpus callosum volume is not changed in early postnatal Ts65Dn mice. • Hippocampal commissure volume is reduced in early postnatal Ts65Dn mice. • Early postnatal Ts65Dn mice have an in vitro stunting of hippocampal axon length. • Hippocampal commissure deficits may arise during development in Down syndrome. Down syndrome is the most common genetic cause of intellectual disability and occurs due to the trisomy of human chromosome 21. Adolescent and adult brains from humans with Down syndrome exhibit various neurological phenotypes including a reduction in the size of the corpus callosum, hippocampal commissure and anterior commissure. However, it is unclear when and how these interhemispheric connectivity defects arise. Using the Ts65Dn mouse model of Down syndrome, we examined interhemispheric connectivity in postnatal day 0 (P0) Ts65Dn mouse brains. We find that there is no change in the volume of the corpus callosum or anterior commissure in P0 Ts65Dn mice. However, the volume of the hippocampal commissure is significantly reduced in P0 Ts65Dn mice, and this may contribute to the impaired learning and memory phenotype of this disorder. Interhemispheric connectivity defects that arise during development may be due to disrupted axon growth. In line with this, we find that developing hippocampal neurons display reduced axon length in vitro , as compared to neurons from their euploid littermates. This study is the first to report the presence of defective interhemispheric connectivity at the time of birth in Ts65Dn mice, providing evidence that early therapeutic intervention may be an effective time window for the treatment of Down syndrome. [ABSTRACT FROM AUTHOR]

Objective: Down syndrome (DS) affects 1/800 infants. Prenatal NAPVSIPQ (NAP) and SALLRSIPA (SAL) (NAP+SAL) prevent developmental delay in Ts65Dn mice, a mouse model of DS. We investigated whether this finding involves N-methyl-D-aspartic acid and γ-aminobutyric acid (GABA) receptor subunits. Study Design: Pregnant Ts65Dn mice were treated with placebo or NAP+SAL on gestational days 8-12. After developmental delay prevention was shown, 4 trisomic (Ts), 4 control, and 3 Ts+NAP+SAL adult offspring brains (from 3 litters) were collected. Calibrator-normalized real-time polymerase chain reaction was performed using primers for N-methyl-D-aspartic acid subunits NR2A and NR2B, and for GABA subunits GABAAα5 and GABAAβ3 with glyceraldehyde-3-phosphate dehydrogenase standardization. Statistics included analysis of variance and Fisher PLSD with P < .05 as significant. Results: NR2A, NR2B, and GABAAβ3 levels were decreased in Ts vs control (all P < .05). Prenatal NAP+SAL increased NR2A, NR2B, and GABAAβ3 to levels similar to control (all P < .05). A significant difference in GABAAα5 levels was not found. Conclusion: Prenatal NAP+SAL increases NR2A, NR2B, and GABAAβ3 expression in adult DS mice to levels similar to controls. This may explain how NAP+SAL improve developmental milestone achievement. [Copyright &y& Elsevier]

Objective: Down syndrome (DS), a major cause of mental retardation, affects 1 of 800 newborns. Mouse models for Down syndrome have been studied and found to have developmental and learning deficits, including the Ts65Dn (DS) mouse model. N-methyl-d-aspartate receptor NR2B subunit enhances synaptic plasticity. The up-regulation of KIF17, a motor protein that transports NR2B to the synaptic region parallels up-regulation of synaptic NR2B. Down regulation of KIF17 reflects up-regulation of less plastic NR2A subunit. We evaluated NR2B, NR2A, and KIF17 in Ts65Dn and control mice. Study Design: Ts65Dn (4) and control (4) adult brains were collected; NR2A, NR2B, and KIF17 were measured by Western blot and quantified using National Institutes of Health Image software. Comparisons were made using analysis of variance, < .05 was considered significant. Results: There was a significant decrease in KIF17 (P = .04) level in Ts65Dn mice as compared with the control animals, but there were no significant differences in the levels of NR2A (P = .79) and NR2B (P = .96). Conclusion: The significant decrease of KIF17 inTs65Dn animals may in part mediate cognitive defects in DS. [Copyright &y& Elsevier]