Intact spatial learning in adult Tg2576 mice

Tg2576 mice, a transgenic model of amyloid pathology associated with Alzheimer's disease (AD), develop measurable levels of soluble amyloid beta1-40 and 1-42 by 6 months of age and amyloid plaque deposition in cortex, hippocampus and amygdala by 10 months of age. To investigate whether non-hippocampal learning strategies would predominate coincident with the age-related increase in Abeta load in the hippocampal region, we measured learning strategies in the T-maze and a redundant cued version of the water maze. Each of these tasks can be solved using either hippocampal or non-hippocampal learning strategies and has proved sensitive to hippocampal disruption in other settings. The results revealed subtle differences in T-maze and water maze performance in Tg2576 mice compared to controls. Surprisingly, however, Tg2576 mice were not impaired relative to non-transgenic littermates on any measures of hippocampal dependent behavior assessed in these tasks. These data suggest that the medial temporal lobe retains considerable function in 15-month-old Tg2576 mice despite significant Abeta pathology.     

Corticosterone and related receptor expression are associated with increased beta-amyloid plaques in isolated Tg2576 mice

Previously, we reported that the stress associated with chronic isolation was associated with increased beta-amyloid (Abeta) plaque deposition and memory deficits in the Tg2576 transgenic animal model of Alzheimer's disease (AD) [Dong H, Goico B, Martin M, Csernansky CA, Bertchume A, Csernansky JG (2004) Effects of isolation stress on hippocampal neurogenesis, memory, and amyloid plaque deposition in APP (Tg2576) mutant mice. Neuroscience 127:601-609]. In this study, we investigated the potential mechanisms of stress-accelerated Abeta plaque deposition in this Tg2576 mice by examining the relationship between plasma corticosterone levels, expression of glucocorticoid receptor (GR) and corticotropin-releasing factor receptor-1 (CRFR1) in the brain, brain tissue Abeta levels and Abeta plaque deposition during isolation or group housing from weaning (i.e. 3 weeks of age) until 27 weeks of age. We found that isolation housing significantly increased plasma corticosterone levels as compared with group-housing in both Tg+ mice (which contain and overexpress human amyloid precursor protein (hAPP) gene) and Tg- mice (which do not contain hAPP gene as control). Also, isolated, but not group-housed animals showed increases in the expression of GR in the cortex. Furthermore, the expression of CRFR1 was increased in isolated Tg+ mice, but decreased in isolated Tg- mice in both cortex and hippocampus. Changes in the components of hypothalamic-pituitary-adrenal (HPA) axis were accompanied by increases in brain tissue Abeta levels and Abeta plaque deposition in the hippocampus and overlying cortex in isolated Tg+ mice. These results suggest that isolation stress increases corticosterone levels and GR and CRFR1 expression in conjunction with increases in brain tissue Abeta levels and Abeta plaque deposition in the Tg2576 mouse model of AD.     

Cell proliferation and total granule cell number in dentate gyrus of transgenic Tg2576 mouse

This report provides in vivo evidence of adult neurogenesis and the total granule cell count in the dentate gyrus of the Tg2576 mouse model of Alzheimer's disease. Mice were deeply anaesthetized and perfused with 4 percent buffered paraformaldehyde. Brains were removed and post-fixed in the same fixative overnight. Following equilibration in 30 percent sucrose, 30 micrometer sections were cut in sagittal plane in freezing microtome for immunohistochemistry and 20 micrometer from plastic embedded brains. Thioflavin-S confirmed the presence of amyloid plaques in the Tg2576 mice. Cell proliferation in the subventricular zone and dentate gyrus of hippocampus were observed with Ki-67 and doublecortin markers. Using optical fractionator, total granule number was estimated to be 445,280 per hemisphere in the 18-month-old Tg2576 mouse. Cell proliferation tends to end in the dentate gyrus but continues in the SVZ and the total granule cell number was less compared to normal laboratory and wild rodents.     

Chronic dietary alpha-lipoic acid reduces deficits in hippocampal memory of aged Tg2576 mice

Oxidative stress may play a key role in Alzheimer's disease (AD) neuropathology. Here, the effects of the antioxidant, alpha-lipoic acid (ALA) were tested on the Tg2576 mouse, a transgenic model of cerebral amyloidosis associated with AD. Ten-month old Tg2576 and wild type mice were fed an ALA-containing diet (0.1%) or control diet for 6 months and then assessed for the influence of diet on memory and neuropathology. ALA-treated Tg2576 mice exhibited significantly improved learning, and memory retention in the Morris water maze task compared to untreated Tg2576 mice. Twenty-four hours after contextual fear conditioning, untreated Tg2576 mice exhibited significantly impaired context-dependent freezing. ALA-treated Tg2576 mice exhibited significantly more context freezing than the untreated Tg2576 mice. Assessment of brain soluble and insoluble beta-amyloid levels revealed no differences between ALA-treated and untreated Tg2576 mice. Brain levels of nitrotyrosine, a marker of nitrative stress, were elevated in Tg2576 mice, while F2 isoprostanes and neuroprostanes, oxidative stress markers, were not elevated in the Tg2576 mice relative to wild type. These data indicate that chronic dietary ALA can reduce hippocampal-dependent memory deficits of Tg2576 mice without affecting beta-amyloid levels or plaque deposition.     

Decreased phosphatidylethanolamine binding protein expression correlates with Abeta accumulation in the Tg2576 mouse model of Alzheimer's disease

Phosphatidylethanolamine binding protein (PEBP) is a multifunctional protein, with proposed roles as the precursor protein of hippocampal cholinergic neurostimulating peptide (HCNP), and as the Raf kinase inhibitor protein (RKIP). Previous studies have demonstrated a decrease in PEBP mRNA in CA1 region of AD hippocampus. The current study demonstrates that PEBP is decreased in the hippocampus of 11 month Tg2576 mice, in the absence of change in mRNA levels compared to non-transgenic littermates. The level of PEBP in transgenic mouse hippocampus significantly decreases at 11 months (a time point when Abeta begins accumulating) and 15 months (when Abeta plaques have formed). There was a significant correlation between decreased PEBP expression and accumulation of Abeta. Immunohistochemical studies on Tg2576 and AD brain sections demonstrate that PEBP immunoreactivities are present at the periphery of dense multicore Abeta plaques, and in selective astrocytes, primarily surrounding plaques. These findings suggest that PEBP expression may be influenced by accumulation of Abeta. Down-regulation of PEBP may result in lower levels of HCNP or altered coordination of signal transduction pathways that may contribute to neuronal dysfunction and pathogenesis in AD.     

Impaired rapid eye movement sleep in the Tg2576 APP murine model of Alzheimer's disease with injury to pedunculopontine cholinergic neurons

Impaired rapid eye movement sleep (REMS) is commonly observed in Alzheimer's disease, suggesting injury to mesopontine cholinergic neurons. We sought to determine whether abnormal beta-amyloid peptides impair REMS and injure mesopontine cholinergic neurons in transgenic (hAPP695.SWE) mice (Tg2576) that model brain amyloid pathologies. Tg2576 mice and wild-type littermates were studied at 2, 6, and 12 months by using sleep recordings, contextual fear conditioning, and immunohistochemistry. At 2 months of age, REMS was indistinguishable by genotype but was reduced in Tg2576 mice at 6 and 12 months. Choline acetyltransferase-positive neurons in the pedunculopontine tegmentum of Tg2576 mice at 2 months evidenced activated caspase-3 immunoreactivity, and at 6 and 12 months the numbers of pedunculopontine tegmentum choline acetyltransferase-positive neurons were reduced in the Tg2576 mice. Other cholinergic groups involved in REMS were unperturbed. At 12 months, Tg2576 mice demonstrated increased 3-nitrotyrosine immunoreactivity in cholinergic projection sites but not in cholinergic soma. We have identified a population of selectively compromised cholinergic neurons in young Tg2576 mice that manifest early onset REMS impairment. The differential vulnerability of these cholinergic neurons to Abeta injury provides an invaluable tool with which to understand mechanisms of sleep/wake perturbations in Alzheimer's disease.     

Early discrimination reversal learning impairment and preserved spatial learning in a longitudinal study of Tg2576 APPsw mice

To understand the relationship between amyloid-beta and cognitive decline in Alzheimer's disease, we evaluated cortical and hippocampal function in a transgenic mouse model of amyloid over-expression in Alzheimer's disease, the Tg2576 mouse. Tg2576 mice and their non-transgenic littermates were assessed at both 6 and 14 months of age in a battery of cognitive tests: attentional set-shifting, water maze spatial reference memory and T-maze working memory. Spatial reference memory was not affected by Tg status at either age. Working memory was only affected by age, with 6-month-old mice performing better than 14-month-old ones. Older mice were also significantly impaired on reversal learning and on the intra- and extra-dimensional shift in attentional set-shifting. A significant transgene effect was apparent in reversal learning, with Tg2576 mice requiring more trials to reach criterion at 6 months old. These data indicate that the effects of normal aging in C57B6xSJL F1 mice are most pronounced on putative frontal cortex-dependent tasks and that increasing Abeta load only affects discrimination reversal learning in our study.     

Augmented senile plaque load in aged female beta-amyloid precursor protein-transgenic mice

Transgenic mice (Tg2576) overexpressing human beta-amyloid precursor protein with the Swedish mutation (APP695SWE) develop Alzheimer's disease-like amyloid beta protein (Abeta) deposits by 8 to 10 months of age. These mice show elevated levels of Abeta40 and Abeta42, as well as an age-related increase in diffuse and compact senile plaques in the brain. Senile plaque load was quantitated in the hippocampus and neocortex of 8- to 19-month-old male and female Tg2576 mice. In all mice, plaque burden increased markedly after the age of 12 months. At 15 and 19 months of age, senile plaque load was significantly greater in females than in males; in 91 mice studied at 15 months of age, the area occupied by plaques in female Tg2576 mice was nearly three times that of males. By enzyme-linked immunosorbent assay, female mice also had more Abeta40 and Abeta42 in the brain than did males, although this difference was less pronounced than the difference in histological plaque load. These data show that senescent female Tg2576 mice deposit more amyloid in the brain than do male mice, and may provide an animal model in which the influence of sex differences on cerebral amyloid pathology can be evaluated.     

Lovastatin enhances Abeta production and senile plaque deposition in female Tg2576 mice

A recent clinical study showed that statins, which are inhibitors of cholesterol biosynthesis pathway, reduced the prevalence of Alzheimer's disease (AD). Animal studies that have employed high cholesterol diet indicate significant relationship between cholesterol level and senile plaque deposition. Here, we investigated the effects of lovastatin on beta-amyloid production and senile plaque deposition in an animal model of AD (Tg2576 mice). As expected, lovastatin treatment reduced plasma cholesterol level in both male and female mice. However, lovastatin enhanced the amounts of beta-amyloid and other beta-secretase derived peptides in females, but not in males. Likewise, lovastatin increased the number of plaques in the hippocampus and cortex of females, but not in males. Lovastatin did not change the amounts of full-length or alpha-secretase processed amyloid precursor protein (APP), or presenilin 1 (PS1) in either sex. Thus, lovastatin lowers cholesterol level in both genders, but enhances beta-amyloid production and senile plaque deposition only in brains of female Tg2576 mice. Our results suggest that low plasma cholesterol levels might be a risk factor for AD in females.     

Association of aortic atherosclerosis with cerebral beta-amyloidosis and learning deficits in a mouse model of Alzheimer's disease

High fat/high cholesterol diets exacerbate beta-amyloidosis in mouse models of Alzheimer's disease (AD). It has been impossible, however, to study the relationship between atherosclerosis and beta-amyloidosis in those models because such mice were on atherosclerosis-resistant genetic backgrounds. Here we report the establishment of AD model mice, B6Tg2576, that are prone to atherosclerosis. B6Tg2576 mice were produced by back-crossing Tg2576 mice, an AD mouse model overexpressing human amyloid beta-protein precursor with the Swedish double mutation, to C57BL/6 mice, a strain susceptible to diet-induced atherosclerosis. An atherogenic diet induced aortic atherosclerosis and exacerbated cerebral beta-amyloidosis in B6Tg2576 mice. Compared with age-matched non-transgenic littermates, B6Tg2576 mice developed significantly more diet-induced aortic atherosclerosis. Unexpectedly, normal diet-fed B6Tg2576 mice also developed fatty streak lesions (early atherosclerosis) in the aorta. The aortic atherosclerotic lesion area positively correlated with cerebral beta-amyloid deposits in B6Tg2576 mice on both atherogenic and normal diets. Furthermore, behavioral assessments demonstrated that B6Tg2576 mice fed an atherogenic diet had more spatial learning impairment than those fed a normal diet. Our results suggest that synergistic mechanisms may be involved in the pathogenesis of atherosclerosis and AD. These findings may have important implications in the prevention and treatment of cardiovascular diseases as well as AD.     

Acetylcholinesterase promotes beta-amyloid plaques in cerebral cortex

Studies in vitro have suggested that acetylcholinesterase (AChE) may interact with beta-amyloid to promote deposition of amyloid plaques in the brain of patients with Alzheimer's disease. To test that hypothesis in vivo, we crossed Tg2576 mice, which express human amyloid precursor protein and develop plaques at 9 months, with transgenic mice expressing human AChE. The resulting F1 hybrids (FVB/N x [C57B6 x SJL/J]) expressed both transgenes in brain. By 6 months of age, their cerebral cortex showed authentic plaques that stained both by thioflavin S and by beta-amyloid 1-40 and 1-42 immunohistochemistry. The plaques also stained positively for other components including Cd11b, GFAP, and AChE. Plaque onset in the hybrids occurred 30-50% sooner than in the parental lines. Plaque numbers increased with age and plaques remained more numerous in the doubly transgenic animals at 9 and 12 months. Quantitative immunoassay via ELISA also showed an increase of total amyloid content in brain at 9-12 months. These histological and biochemical results support the conclusion that AChE may play a role in pathogenesis of Alzheimer's disease     

Transgenic mice overexpressing human acetylcholinesterase and the Swedish amyloid precursor protein mutation: effect of nicotine treatment

Acetylcholinesterase (AChE) is shown to promote deposition of beta-amyloid (Abeta) peptides and to enhance Abeta toxicity. Tg2576 (transgenic mice carrying the Swedish mutation of amyloid precursor protein, APPswe) mice and mice overexpressing human synaptic acetylcholinesterase (AChE-S) were crossed (hAChE-Tg//APPswe), to study the effects of brain Abeta, from 1 to 10 months of age, under the constant influence of AChE-S. The effect of nicotine treatment was also evaluated in these mice since we have previously shown that nicotine dramatically decreases Abeta levels in single transgenic APPswe mice. Already at 1 and 3 months, hAChE-Tg// APPswe mice showed increased levels of cortical insoluble Abeta1-40 and Abeta1-42 compared with APPswe mice, whereas APPswe mice displayed increased soluble Abeta1-40. Abeta plaques were detected at 7 months, thus before onset of plaque formation in APPswe mice. No differences were found in [125I]alpha-bungarotoxin binding sites or hippocampal glial fibrillary acidic protein (GFAP) immunoreactivity between hAChE-Tg//APPswe, and APPswe mice at either 1 or 10 months of age. L(-)-Nicotine (final dose 0.45 mg/kg) treatment twice daily for 10 days to 14-month-old hAChE-Tg// APPswe mice increased cortical insoluble Abeta1-40 levels, while both L(-)- and D(+)-nicotine (final dose 0.45 mg/kg) increased soluble Abeta1-42. L(-)-Nicotine reduced hippocampal GFAP immunoreactivity both in hAChE-Tg//APPswe mice and non-transgenic controls, while D(+)-nicotine caused a decrease only in hAChE-Tg//APPswe mice. Moreover, D(+)-nicotine increased the [125I]alpha-bungarotoxin binding sites in the hippocampus, and cortex of the hAChE-Tg//APPswe mice. In conclusion, already at a very young age, hAChE-Tg// APPswe mice exhibit increased levels of aggregated Abeta compared with APPswe mice, due to the possible interaction between Abeta and AChE-S, whereas APPswe mice exhibit increased soluble Abeta. The interaction between Abeta and AChE-S may also explain the different effect of nicotine on Abeta pathology in the hAChE-Tg//APPswe mice. The results in this study emphasize the importance of using different transgenic mouse models for evaluating the effect of new drug candidates for the treatment of Alzheimer's disease.     

Presenilin 1 familial Alzheimer's disease mutation leads to defective associative learning and impaired adult neurogenesis

Alzheimer's disease is a learning and memory disorder pathologically characterized by the deposition of beta-amyloid plaques and loss of neurons and synapses in affected areas of the brain. Mutations in presenilin 1 (PS1) lead to the most aggressive form of familial Alzheimer's disease (FAD), and are associated with accelerated plaque deposition. However, since the function of PS1 is pleiotropic, we reasoned that the FAD mutations may alter multiple PS1-mediated pathways, and the combination of which may account for the early onset nature of the disease phenotype. Using the PS1M146V knockin mice in which the M146V mutation was incorporated into the endogenous mouse PS1 gene, we report here that the FAD mutation results in impaired hippocampus-dependent associative learning, as measured by a contextual fear conditioning paradigm, at 3 months of age. This is correlated with reduced adult neurogenesis in the dentate gyrus. However, short-term and long-term synaptic plasticity in both area CA1 and dentate gyrus are not affected. Our results suggest that impaired adult neurogenesis may contribute to the memory deficit associated with FAD.     

Gene expression profiles of transcripts in amyloid precursor protein transgenic mice: up-regulation of mitochondrial metabolism and apoptotic genes is an early cellular change in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerativedisease characterized by the impairment of cognitive functionsand by beta amyloid (Aß) plaques in the cerebral cortexand the hippocampus. Our objective was to determine genes thatare critical for cellular changes in AD progression, with particularemphasis on changes early in disease progression. We investigatedan established amyloid precursor protein (APP) transgenic mousemodel (the Tg2576 mouse model) for gene expression profilesat three stages of disease progression: long before (2 monthsof age), immediately before (5 months) and after (18 months)the appearance of Aß plaques. Using cDNA microarraytechniques, we measured mRNA levels in 11 283 cDNA clonesfrom the cerebral cortex of Tg2576 mice and age-matched wild-type(WT) mice at each of the three time points. This gene expressionanalysis revealed that the genes related to mitochondrial energymetabolism and apoptosis were up-regulated in 2-month-old Tg2576mice and that the same genes were up-regulated at 5 and 18 monthsof age. These microarray results were confirmed using northernblot analysis. Results from in situ hybridization of mitochondrialgenes—ATPase-6, heat-shock protein 86 and programmed celldeath gene 8—suggest that the granule cells of the hippocampaldentate gyrus and the pyramidal neurons in the hippocampus andthe cerebral cortex are up-regulated in Tg2576 mice comparedwith WT mice. Results from double-labeling in situ hybridizationsuggest that in Tg2576 mice only selective, over-expressed neuronswith the mitochondrial gene ATPase-6 undergo oxidative damage.These results, therefore, suggest that mitochondrial energymetabolism is impaired by the expression of mutant APP and/orAß, and that the up-regulation of mitochondrial genesis a compensatory response. These findings have important implicationsfor understanding the mechanism of Aß toxicity inAD and for developing therapeutic strategies for AD. ^* To whom correspondence should be addressed at: Neurogenetics Laboratory, Neurological Sciences Institute, Oregon Health and Science University, 505 NW 185th Avenue, Beaverton, OR 97006, USA. Tel: +1 5034182625; Fax: +1 5034182501; Email: reddyh{at}ohsu.edu     

Outcome-specific satiety reveals a deficit in context-outcome, but not stimulus- or action-outcome, associations in aged Tg2576 mice

The onset of Alzheimer's disease (AD) is often accompanied by changes in emotion, motivation, and goal-directed behavior. The production of beta-amyloid is thought to be a major and early contributor to the pathogenesis of AD. The present study tested the hypothesis that amyloid pathology present in the amygdala, frontal cortex, and hippocampus of Tg2576 mice would disrupt the development of instrumental- and/or Pavlovian-outcome associations. The results showed that both instrumental- and Pavlovian-conditioned behaviors were sensitive to outcome devaluation (Experiments 1 & 2) and that Pavlovian cues influenced goal-directed actions associated with the same outcome (Experiment 2) in Tg2576 mice. In contrast, context mediated Pavlovian-conditioned behaviors in aged (Experiment 3a) but not young (Experiment 3b) Tg2576 mice were insensitive to outcome devaluation. Aged Tg2576, nevertheless, successfully acquired a simple context discrimination at the same rate as control mice. We conclude that amyloid pathology in aged Tg2576 mice may specifically disrupt context-outcome associations supported by the hippocampus and/or its interaction with the amygdala.     

Microglial response to amyloid plaques in APPsw transgenic mice.

Microglial activation is central to the inflammatory response in Alzheimer's Disease (AD). A recently described mouse line, Tg(HuAPP695.K670N/M671L)2576, expressing human amyloid precursor protein with a familial AD gene mutation, age-related amyloid deposits, and memory deficits, was found to develop a significant microglial response using Griffonia simplicifolia lectin or phosphotyrosine probe to identify microglia Both Griffonia simplicifolia lectin and phosphotyrosine staining showed increased numbers of intensely labeled, often enlarged microglia clustered in and around plaques, consistent with microglial activation related to beta-amyloid formation. Using quantitative image analysis of coronal phosphotyrosine-immunostained sections, transgene-positive 10- to 16-month-old, hemizygous, hybrid Tg2576 (APPsw) animals showed significantly increased microglial density and size in plaque-forming areas of hippocampus and frontal, entorhinal, and occipital cortex. Quantitative analysis of microglia as a function of distance from the center of plaques (double labeled for A beta peptide and microglia) revealed highly significant, two- to fivefold elevations in microglial number and area within plaques compared with neighboring regions. Tg2576 beta-amyloid-plaque-forming mice should be a useful system for assessing the consequences of the microglial-mediated inflammatory response to beta-amyloid and developing anti-inflammatory therapeutic strategies for Alzheimer's disease. These results provide the first quantitative link between beta-amyloid plaque formation and microglial activation in an animal model with neuritic plaques and memory deficits.     

Metallothionein-I and -III expression in animal models of Alzheimer disease

Previous studies have described altered expression of metallothioneins (MTs) in neurodegenerative diseases like multiple sclerosis (MS), Down syndrome, and Alzheimer's disease (AD). In order to gain insight into the possible role of MTs in neurodegenerative processes and especially in human diseases, the use of animal models is a valuable tool. Several transgenic mouse models of AD amyloid deposits are currently available. These models express human beta-amyloid precursor protein (AbetaPP) carrying different mutations that subsequently result in a varied pattern of beta-amyloid (Abeta) deposition within the brain. We have evaluated the expression of MT-I and MT-III mRNA by in situ hybridization in three different transgenic mice models of AD: Tg2576 (carrying AbetaPP harboring the Swedish K670N/M671L mutations), TgCRND8 (Swedish and the Indiana V717F mutations), and Tg-SwDI (Swedish and Dutch/Iowa E693Q/D694N mutations). MT-I mRNA levels were induced in all transgenic lines studied, although the pattern of induction differed between the models. In the Tg2576 mice MT-I was weakly upregulated in cells surrounding Congo Red-positive plaques in the cortex and hippocampus. A more potent induction of MT-I was observed in the cortex and hippocampus of the TgCRND8 mice, likely reflecting their higher amyloid plaques content. MT-I upregulation was also more significant in Tg-SwDI mice, especially in the subiculum and hippocampus CA1 area. Immunofluorescence stainings demonstrate that astrocytes and microglia/macrophages surrounding the plaques express MT-I&II. In general, MT-I regulation follows a similar but less potent response than glial fibrillary acidic protein (GFAP) expression. In contrast to MT-I, MT-III mRNA expression was not significantly altered in any of the models examined suggesting that the various MT isoforms may have different roles in these experimental systems, and perhaps also in human AD.     

Seizure susceptibility and mortality in mice that over-express amyloid precursor protein

Alzheimer's disease and Fragile X syndrome both display synaptic phenotypes, and based on recent studies, likely share dendritic over expression of amyloid precursor protein (APP) and beta-amyloid (Abeta). In order to create a mouse model to specifically study the effects of APP and Abeta at synapses, we crossed Tg2576, which over-express human APP with the Swedish mutation (hAPPsw), with fmr-1 KO mice. The progeny, named FRAXAD, displayed increased mortality (23% by 30 days of age) compared to Tg2576 (3%) and WT and fmr-1 KO littermate controls (0%) consistent with a developmental defect. By 60 days of age, both the Tg2576 and FRAXAD mice approached a 40% mortality rate compared to 0% for WT and fmr-1 KO littermates. To understand the mechanism underlying increased mortality in APP over-expressing mice, we assessed seizure thresholds in response to pentylenetetrazol (PTZ). Both the Tg2576 and FRAXAD mice had a lower threshold to PTZ-induced seizures (average seizure score of >/=4.0) in comparison to nontransgenic littermates (average seizure score 1.9-2.9). Seizures are a major phenotype of AD, FXS, Down syndrome, autism and epilepsy, and these data suggested that developmental over-expression of dendritic APP or Abeta increased seizure susceptibility.     

Differential activation of mitogen-activated protein kinase signalling pathways in the hippocampus of CRND8 transgenic mouse, a model of Alzheimer's disease

Transgenic Centre for Research in Neurodegenerative Diseases 8 (TgCRND8) mice expressing a double mutant form of human amyloid precursor protein represent a good model of Alzheimer's disease, and can be useful to clarify the involvement of mitogen-activated protein kinases (MAPK) dysregulation in the pathophysiology of this neurodegenerative disorder. Activation of extracellular regulated kinase (ERK) 1/2, jun kinase (JNK) and p38MAPK was studied in the hippocampus of 7-month-old TgCRND8 mice by immunohistochemistry and Western blot analysis using antibodies selective for the phosphorylated, and thus active, forms of the enzymes. We demonstrated that the three main MAPK pathways were differentially activated in cells of the hippocampus of TgCRND8 mice in comparison to wild type (Wt) littermates, p38MAPK and JNK being more activated, while ERK less activated. p38MAPK was significantly activated in microglia, astrocytes and neurons, around and distant from the plaques. JNK was highly activated in cells closely surrounding the plaques. No difference was observed in the activation of the two major bands of JNK, at a molecular weight of 46 kDa and 54 kDa. These data indicate the possible involvement of p38MAPK and JNK pathways dysregulation in the pathogenesis of Alzheimer's disease. The ERK2 isoform of the ERK pathway was less activated in the hippocampal dentate gyrus of Tg mice in basal conditions. Furthermore activation of the ERK pathway by ex vivo cholinergic stimulation with carbachol caused significantly higher activation of ERK in the hippocampus of Wt mice than in Tg mice. These findings may pose a molecular basis for the memory disruption of Alzheimer's disease, since proper functioning of the basal forebrain cholinergic neurons and of ERK2 is critical for memory formation.     

Amyloid cored plaques in Tg2576 transgenic mice are characterized by giant plaques,slightly activated microglia,and the lack of paired helical filament-typed,dystrophic neurites

We examined the brains of Tg2576 transgenic mice carrying human amyloid precursor protein with the Swedish mutation and Alzheimer's disease (AD) by means of immunohistochemistry and electron microscopy to clarify the characteristics of amyloid-associated pathology in the transgenic mice. In 12- to 29-month-old Tg2576 mice, congophilic cored plaques in the neocortex and hippocampus were labeled by all of the Abeta1-, Abeta40- and 42-specific antibodies, as seen in the classical plaques in AD. However, large-sized (>50 micro m in core diameter) plaques were seen more frequently in the older mice (18-29 months) than in those with AD (approximately 20% vs 2% in total cored plaques), and Tg2576 mice contained giant plaques (>75 micro m in core diameter), which were almost never seen in the brain of those with AD. Neither thread-like structures nor peripheral coronas were observed in the cored plaques of the transgenic mice in the silver impregnations. Immunohistochemically, plaque-accompanied microglia showed a slight enlargement of the cytoplasm with consistent labeling of Mac-1 and macrosialin (murine CD68), and with partial labeling of Ia antigen and macrophage-colony stimulating factor receptor. Ultrastructurally, the microglia surrounding the extracellular amyloid fibrils in the large, cored plaques showed some organella with phagocytic activity, such as secondary lysosomal, dense bodies, but intracellular amyloid fibrils were not evident. Dystrophic neurites in the plaques of the transgenic mice contained many dense multilaminar bodies, but no paired helical filaments. Our results suggest that giant cored plaques without coronas or paired helical filament-typed, dystrophic neurites are characteristic in Tg2576 mice, and that plaque-associated microglia in transgenic mice are activated to be in phagocytic function but not sufficient enough to digest extracellularly deposited amyloid fibrils.