Exploratory activity and spatial learning in 12-month-old APP695SWE/co+PS1/ΔE9 mice with amyloid plaques

Herbal Extracts Combination (WNK) Prevents Decline in Spatial Learning and Memory in APP/PS1 Mice through Improvement of Hippocampal Aβ Plaque Formation, Histopathology, and Ultrastructure

To investigate the cognitive enhancement effect of WNK, an extracts combination of P. ginseng,  G. biloba, and C. sativus L. and possible mechanisms, 5-month-old APP/PS1 transgenic mice were used in this study. After 3 months of administration, all mice received Morris water maze (MWM) training and a probe test. Mouse brain sections were detected by immunohistochemistry, HE staining, and transmission electron microscopy. MWM results showed significant difference between transgenic mice and nontransgenic littermates (P < 0.05, P < 0.01). WNK-treated mice exhibited enhanced maze performance over the training progression, especially better spatial memory retention in probe test compared to transgenic mice (P < 0.05, P < 0.01) and better spatial learning and memory at the fourth day of MWM test compared to EGB761- (G. biloba extract-) treated ones (P < 0.05). Hippocampal Aβ plaque burden significantly differed between APP/PS1 and littermate mice (P < 0.001), while decreased Aβ plaque appeared in WNK- or EGB761-treated transgenic brains (P < 0.05). Neurodegenerative changes were evident from light microscopic and ultrastructural observations in transgenic brains, which were improved by WNK or EGB761 treatment. These data indicate WNK can reduce the decline in spatial cognition, which might be due to its effects on reducing Aβ plaque formation and ameliorating histopathology and ultrastructure in hippocampus of APP/PS1 mouse brain.

APP transgenic mice for modelling behavioural and psychological symptoms of dementia (BPSD)

The discovery of gene mutations responsible for autosomal dominant Alzheimer's disease has enabled researchers to reproduce in transgenic mice several hallmarks of this disorder, notably Aβ accumulation, though in most cases without neurofibrillary tangles. Mice expressing mutated and wild-type APP as well as C-terminal fragments of APP exhibit variations in exploratory activity reminiscent of behavioural and psychological symptoms of Alzheimer dementia (BPSD). In particular, open-field, spontaneous alternation, and elevated plus-maze tasks as well as aggression are modified in several APP transgenic mice relative to non-transgenic controls. However, depending on the precise murine models, changes in open-field and elevated plus-maze exploration occur in either direction, either increased or decreased relative to controls. It remains to be determined which neurotransmitter changes are responsible for this variability, in particular with respect to GABA, 5HT, and dopamine.

17α-estradiol attenuates neuron loss in ovariectomized Dtg AβPP/PS1 mice

Quantitative microanalysis of brains from patients with Alzheimer's disease (AD) find neuronal loss and neuroinflammation in structures that control cognitive function. Though historically difficult to recapitulate in experimental models, several groups have recently reported that by middle-age, transgenic mice that co-express high levels of two AD-associated mutations, amyloid-β protein precursor (AβPP(swe)) and presenilin 1 (PS1(ΔE9)), undergo significant AD-type neuron loss in sub-cortical nuclei with heavy catecholaminergic projections to the hippocampal formation. Here we report that by 13 months of age these dtg AβPP(swe)/PS1(ΔE9) mice also show significant loss of pyramidal neuron in a critical region for learning and memory, the CA1 subregion of hippocampus, as a direct function of amyloid-β (Aβ) aggregation. We used these mice to test whether 17α-estradiol (17αE2), a less feminizing and non-carcinogenic enantiomer of 17β-estradiol, protects against this CA1 neuron loss. Female dtg AβPP(swe)/PS1(ΔE9) mice were ovariectomized at 8-9 months of age and treated for 60 days with either 17αE2 or placebo via subcutaneous pellets. Computerized stereology revealed that 17αE2 ameliorated the loss of neurons in CA1 and reduced microglial activation in the hippocampus. These findings support the view that 17αE2, which may act through non-genomic mechanisms independent of traditional estrogen receptors, could prevent or delay the progression of AD in older men and women.

Age-related changes in visual acuity, learning and memory in the APPswe/PS1dE9 mouse model of Alzheimer's disease

Mouse models of Alzheimer's disease (AD) are often tested for learning and memory deficits using visuo-spatial tasks such as the Morris water maze. Performance on these tasks is dependent on vision and the APPswe/PS1dE9 mouse model has amyloid beta plaques in their retinas which might influence their performance in these tasks. In a visual learning task, old (20-26 months) transgenic mice and their wildtype littermates of both sexes had poorer visual ability than young (5-8 months) mice and old transgenic mice had poorer visual acuity than old wildtype mice. Old transgenic mice also had deficits in visuo-spatial learning and memory on the Morris water maze. The transgenic mice had no deficits in the conditioned odour preference or conditioned taste aversion memory tests at any age. These results indicate that the old APPswe/PS1dE9 mice and their wildtype littermates both have a deficit in their visual ability and that visually dependent measures alone should not be used to assess learning and memory in this strain.

The effect of ageing on neurogenesis and oxidative stress in the APP(swe)/PS1(deltaE9) mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterised by memory loss and impaired cognitive function. One of the hallmarks of AD is the formation of beta amyloid (Aβ) plaques. Aβ has neurodegenerative properties and aggregates in the brain, causing inflammation, oxidative stress and eventually neuronal loss. In AD, adult neurogenesis in the dentate gyrus (DG) of the hippocampus is known to be impaired. We tested how ageing affects neurogenesis and oxidative stress in the commonly used APP(SWE)/PS1(ΔE9) mouse model of AD and their wild type (wt) littermate controls aged 3, 5, 10 and 15months. Progenitor cell proliferation in the DG of APP/PS1 was lower at 3, 5 and 10months compared to controls, while oxidative stress in APP/PS1 mice was increased in the cortex at 3 and 5months of age compared to controls. The numbers of new neurons in the DG were decreased in APP/PS1 mice at 10 and 15months. In APP/PS1 mice, Aβ plaques were evident in the cortex from 3months onward; however these were small and few. Plaque size and number consistently increased with age in APP/PS1 mice. These results show that the damage to the brain occurs already very early in the brain, and although neurogenesis is impaired, it is still active even in late stage AD. Therefore, therapies would have the best effects if started early, but promoting neurogenesis may act in a protective and reconstructive way even in later stages of AD.

A novel neurotrophic drug for cognitive enhancement and Alzheimer's disease

Currently, the major drug discovery paradigm for neurodegenerative diseases is based upon high affinity ligands for single disease-specific targets. For Alzheimer's disease (AD), the focus is the amyloid beta peptide (Aß) that mediates familial Alzheimer's disease pathology. However, given that age is the greatest risk factor for AD, we explored an alternative drug discovery scheme that is based upon efficacy in multiple cell culture models of age-associated pathologies rather than exclusively amyloid metabolism. Using this approach, we identified an exceptionally potent, orally active, neurotrophic molecule that facilitates memory in normal rodents, and prevents the loss of synaptic proteins and cognitive decline in a transgenic AD mouse model.

The effects of MyD88 deficiency on exploratory activity, anxiety, motor coordination, and spatial learning in C57BL/6 and APPswe/PS1dE9 mice

Toll-like receptors (TLRs) are a family of pattern-recognition receptors in innate immunity and provide a first line defense against pathogens and tissue injuries. In addition to important roles in infection, inflammation, and immune diseases, recent studies show that TLR signaling is involved in modulation of learning, memory, mood, and neurogenesis. Because MyD88 is essential for the downstream signaling of all TLRs, except TLR3, we investigated the effects of MyD88 deficiency (MyD88-/-) on behavioral functions in mice. Additionally, we recently demonstrated that a mouse model of Alzheimer's disease (AD) deficient for MyD88 had decreases in Aβ deposits and soluble Aβ in the brain as compared with MyD88 sufficient AD mouse models. Because accumulation of Aβ in the brain is postulated to be a causal event leading to cognitive deficits in AD, we investigated the effects of MyD88 deficiency on behavioral functions in the AD mouse model at 10 months of age. MyD88 deficient mice showed more anxiety in the elevated plus-maze. In the motor coordination tests, MyD88 deficient mice remained on a beam and a bar for a longer time, but with slower initial movement on the bar. In the Morris water maze test, MyD88 deficiency appeared to improve spatial learning irrespective of the transgene. Our findings suggest that the MyD88-dependent pathway contributes to behavioral functions in an AD mouse model and its control group.

S14G-humanin improves cognitive deficits and reduces amyloid pathology in the middle-aged APPswe/PS1dE9 mice

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by clinical cognitive decline and pathological deposition of amyloid-beta protein (Aβ) in the brain. So far, there has been no causative therapy for this devastating disease. S14G-Humanin (HNG), a synthetic derivative of Humanin (HN), has been shown to have strong neuroprotective ability against AD-related insults in vitro and prevent cognitive impairments in Aβ-infused animal models. In addition, a recent study has reported a beneficial effect of intranasal HNG treatment on memory deficit and Aβ accumulation in triple transgenic (3xTg-AD) mice at the early plaque-bearing stage. However, whether HNG treatment has the disease-modifying efficacy on AD with pre-existing well-established amyloid plaque pathology remains unclear. In this study, we employed 9-month-old APPswe/PS1dE9 mice with pre-existing robust amyloid plaque pathology to investigate the effects of chronic HNG treatment on the progression of cognitive dysfunction and Aβ-associated neuropathology. We found that vehicle-treated APPswe/PS1dE9 mice showed impaired spatial learning and memory compared with vehicle- and HNG-treated wild-type mice, while intraperitoneal HNG treatment for 3 months significantly improved spatial learning and memory deficits in APPswe/PS1dE9 mice compared with vehicle control treatment. Coincidental with this, HNG treatment significantly reduced cerebral Aβ plaque deposition, insoluble Aβ levels, and neuroinflammatory responses in APPswe/PS1dE9 mice compared with control treatment. Cumulatively, these findings demonstrate that chronic administration of HNG is able to attenuate cognitive deficits and reduce Aβ loads as well as neuroinflammation in the middle-aged APPswe/PS1dE9 mice even with pre-existing substantial Aβ neuropathology, indicating that HNG has potential as a pharmacotherapeutic intervention in the development of cognitive deficits and neuropathology seen in the cases of established AD.

TLR4 mutation reduces microglial activation, increases Aβ deposits and exacerbates cognitive deficits in a mouse model of Alzheimer's disease

BACKGROUND

Amyloid plaques, a pathological hallmark of Alzheimer's disease (AD), are accompanied by activated microglia. The role of activated microglia in the pathogenesis of AD remains controversial: either clearing Aβ deposits by phagocytosis or releasing proinflammatory cytokines and cytotoxic substances. Microglia can be activated via toll-like receptors (TLRs), a class of pattern-recognition receptors in the innate immune system. We previously demonstrated that an AD mouse model homozygous for a loss-of-function mutation of TLR4 had increases in Aβ deposits and buffer-soluble Aβ in the brain as compared with a TLR4 wild-type AD mouse model at 14-16 months of age. However, it is unknown if TLR4 signaling is involved in initiation of Aβ deposition as well as activation and recruitment of microglia at the early stage of AD. Here, we investigated the role of TLR4 signaling and microglial activation in early stages using 5-month-old AD mouse models when Aβ deposits start.

METHODS

Microglial activation and amyloid deposition in the brain were determined by immunohistochemistry in the AD models. Levels of cerebral soluble Aβ were determined by ELISA. mRNA levels of cytokines and chemokines in the brain and Aβ-stimulated monocytes were quantified by real-time PCR. Cognitive functions were assessed by the Morris water maze.

RESULTS

While no difference was found in cerebral Aβ load between AD mouse models at 5 months with and without TLR4 mutation, microglial activation in a TLR4 mutant AD model (TLR4M Tg) was less than that in a TLR4 wild-type AD model (TLR4W Tg). At 9 months, TLR4M Tg mice had increased Aβ deposition and soluble Aβ42 in the brain, which were associated with decrements in cognitive functions and expression levels of IL-1β, CCL3, and CCL4 in the hippocampus compared to TLR4W Tg mice. TLR4 mutation diminished Aβ-induced IL-1β, CCL3, and CCL4 expression in monocytes.

CONCLUSION

This is the first demonstration of TLR4-dependent activation of microglia at the early stage of β-amyloidosis. Our results indicate that TLR4 is not involved in the initiation of Aβ deposition and that, as Aβ deposits start, microglia are activated via TLR4 signaling to reduce Aβ deposits and preserve cognitive functions from Aβ-mediated neurotoxicity.

Anomalies in social behaviors and exploratory activities in an APPswe/PS1 mouse model of Alzheimer's disease

Alzheimer's disease is characterized by deficits in social communication, associated with generalized apathy or agitation, as well as social memory. To assess social behaviors in 6-month-old male APPswe/PS1 bigenics relative to non-transgenic controls, the 3-chamber test was used, together with open-field and elevated plus-maze tests of exploration. APPswe/PS1 mice were less willing to engage in social interaction than wild-type, avoiding an unfamiliar stimulus mouse, probably not due to generalized apathy because in both tests of exploratory activity the mutants were hyperactive. This study reveals reduced "sociability" combined with hyperactivity in an APPswe/PS1 mouse model of Alzheimer dementia.

Simvastatin enhances immune responses to Aβ vaccination and attenuates vaccination-induced behavioral alterations

Statins are widely used to lower cholesterol levels by inhibiting cholesterol biosynthesis. Some evidence has indicated that statins might have therapeutic and preventive benefits for Alzheimer's disease (AD). We and others also have shown the beneficial effect of statin treatment in reversing learning and memory deficits in animal models of AD. However, data from clinical trials are inconclusive. We previously documented that the adenovirus vector encoding 11 tandem repeats of Aβ1-6 fused to the receptor-binding domain (Ia) of Pseudomonas exotoxin A, AdPEDI-(Aβ1-6)(11), is effective in inducing an immune response against amyloid-β protein (Aβ) and reducing brain Aβ load in Alzheimer's mouse models. In the present study, we examined whether the administration of simvastatin can modulate immune and behavioral responses of C57BL/6 mice to vaccination. Simvastatin was given to the animals as a diet admixture for four weeks, followed by nasal vaccination with AdPEDI-(Aβ1-6)(11) once per week for four weeks. The cholesterol-lowering action of simvastatin was monitored by measuring the cholesterol levels in plasma. Simvastatin significantly increased the number of the mice responding to vaccination compared with the mice receiving only AdPEDI-(Aβ1-6)(11). Immunoglobulin isotyping revealed that the vaccination predominantly induced Th2 immune responses. Simvastatin treatment prevented Aβ-induced production of IFN-γ in splenocytes. The adenovirus vaccination altered mouse behavior in T- and elevated plus-maze tests and simvastatin counteracted such behavioral changes. Our results indicate that simvastatin clearly enhances the immune responses of C57BL/6 mice to the nasal vaccination with AdPEDI-(Aβ1-6)(11). Simvastatin may be effective in preventing behavioral changes associated with vaccination.

Impaired neurogenesis is an early event in the etiology of familial Alzheimer's disease in transgenic mice

Formation of new neurons in the adult brain takes place in the subventricular zone and in the subgranule layer of the dentate gyrus throughout life. Neurogenesis is thought to play a role in hippocampus- and olfaction-dependent learning and memory. However, whether impairments in neurogenesis take place in learning and memory disorders, such as Alzheimer's disease, is yet to be established. Importantly, it remains to be elucidated whether neurogenic impairments play a role in the course of the disease or are the result of extensive neuropathology. We now report that transgenic mice harboring familial Alzheimer's disease-linked mutant APPswe/PS1DeltaE9 exhibit severe impairments in neurogenesis that are evident as early as 2 months of age. These mice exhibit a significant reduction in the proliferation of neural progenitor cells and their neuronal differentiation. Interestingly, levels of hyperphosphorylated tau, the cytotoxic precursor of the Alzheimer's disease hallmark neurofibrillary tangles, are particularly high in the neurogenic niches. Isolation of neural progenitor cells in culture reveals that APPswe/PS1DeltaE9-expressing neurospheres exhibit impaired proliferation and tau hyperphosphorylation compared with wildtype neurospheres isolated from nontransgenic littermates. This study suggests that impaired neurogenesis is an early critical event in the course of Alzheimer's disease that may underlie memory impairments, at least in part, and exacerbate neuronal vulnerability in the hippocampal formation and olfaction circuits. Furthermore, impaired neurogenesis is the result of both intrinsic pathology in neural progenitor cells and extrinsic neuropathology in the neurogenic niches. Finally, hyperphosphorylation of the microtubule-associated protein tau, a critical player in cell proliferation, neuronal maturation, and axonal transport, is a major contributor to impaired neurogenesis in Alzheimer's disease.

Motor deficits, neuron loss, and reduced anxiety coinciding with axonal degeneration and intraneuronal Aβ aggregation in the 5XFAD mouse model of Alzheimer's disease

In the present report, we extend previous findings in the 5XFAD mouse model and demonstrate that these mice develop an age-dependent motor phenotype in addition to working memory deficits and reduced anxiety levels as demonstrated in an elevated plus maze task. Employing a variety of N- and C-terminal specific Aβ antibodies, abundant intraneuronal and plaque-associated pathology, including accumulation of pyroglutamate Aβ, was observed as early as the age of 3 months. Using unbiased stereology, we demonstrate that the 5XFAD mice develop a significant selective neuron loss in layer 5 of the cortex, leaving the overall neuron number of the total frontal cortex and hippocampus unaffected. This observation coincides with the accumulation of intraneuronal Aβ peptides only in cortical Layer 5, but not in CA1, despite comparable APP expression levels. The motor phenotype correlates with abundant spinal cord pathology, as demonstrated by abundant intraneuronal Aβ accumulation and extracellular plaque deposition. In addition, comparable to the APP/PS1KI mouse model, 5XFAD mice develop an age-dependent axonopathy likely contributing to the behavioral deficits.

Enoxaparin treatment administered at both early and late stages of amyloid β deposition improves cognition of APPswe/PS1dE9 mice with differential effects on brain Aβ levels

Enoxaparin (Enox), a low molecular weight heparin, has been shown to lower brain amyloid beta (A beta) load in a mouse model for Alzheimer's disease. However, the effect of Enox on cognition was not studied. Therefore, we examined the effect of peripheral Enox treatment on cognition and brain A beta levels in the APPswe/PS1dE9 mouse model by giving injections at an early (starting at 5 months of age) and late (starting at 10 and 12 months of age) stage of A beta accumulation for 3 months. Although Enox had no effect on behaviour in the open field at any age, it improved spatial memory in the Morris water maze in 5-, 10- and 12-month-old mice. Furthermore, Enox treatment seemed to decrease guanidine HCl-extracted brain A beta levels at 5 months of age, but significantly increased guanidine HCl-extracted A beta 42 and A beta 40 levels in both 10- and 12-month-old mice. In vitro, Enox increased aggregation of A beta, even when A beta was pre-aggregated. In conclusion, Enox treatment, either at an early or a late stage of A beta accumulation, could improve cognition in APPswe/PS1dE9 mice. However, since Enox treatment at an early stage of A beta accumulation decreased guanidine HCl-extracted A beta levels and Enox treatment at a late stage enhanced guanidine HCl-extracted A beta levels, it seems that Enox influences A beta deposition differently at different stages of A beta pathology. In any case, our study suggests that enoxaparin treatment has potential as a therapeutic agent for Alzheimer's disease.

Antioxidants and cognitive training interact to affect oxidative stress and memory in APP/PSEN1 mice

The present study investigated the relationships among oxidative stress, beta-amyloid and cognitive abilities in the APP/PSEN1 double-transgenic mouse model of Alzheimer's disease. In two experiments, long-term dietary supplements were given to aged APP/PSEN1 mice containing vitamin C alone (1 g/kg diet; Experiment 1) or in combination with a high (750 IU/kg diet, Experiments 1 and 2) or lower (400 IU/kg diet, Experiment 2) dose of vitamin E. Oxidative stress, measured by F(4)-neuroprostanes or malondialdehyde, was elevated in cortex of control-fed APP/PSEN1 mice and reduced to wild-type levels by vitamin supplementation. High-dose vitamin E with C was less effective at reducing oxidative stress than vitamin C alone or the low vitamin E+C diet combination. The high-dose combination also impaired water maze performance in mice of both genotypes. In Experiment 2, the lower vitamin E+C treatment attenuated spatial memory deficits in APP/PSEN1 mice and improved performance in wild-type mice in the water maze. Amyloid deposition was not reduced by antioxidant supplementation in either experiment.

Vitamin C deficiency increases basal exploratory activity but decreases scopolamine-induced activity in APP/PSEN1 transgenic mice

Vitamin C is a powerful antioxidant and its levels are decreased in Alzheimer's patients. Even sub-clinical vitamin C deficiency could impact disease development. To investigate this principle we crossed APP/PSEN1 transgenic mice with Gulo knockout mice unable to synthesize their own vitamin C. Experimental mice were maintained from 6 weeks of age on standard (0.33 g/L) or reduced (0.099 g/L) levels of vitamin C and then assessed for changes in behavior and neuropathology. APP/PSEN1 mice showed impaired spatial learning in the Barnes maze and water maze that was not further impacted by vitamin C level. However, long-term decreased vitamin C levels led to hyperactivity in transgenic mice, with altered locomotor habituation and increased omission errors in the Barnes maze. Decreased vitamin C also led to increased oxidative stress. Transgenic mice were more susceptible to the activity-enhancing effects of scopolamine and low vitamin C attenuated these effects in both genotypes. These data indicate an interaction between the cholinergic system and vitamin C that could be important given the cholinergic degeneration associated with Alzheimer's disease.

Phenotypic characterization of mice heterozygous for a null mutation of glutamate carboxypeptidase II

Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system. Disturbed glutamate signaling resulting in hypofunction of N-methyl-D-aspartate receptors (NMDAR) has been implicated in the pathophysiology of schizophrenia. Glutamate Carboxypeptidase II (GCP II) hydrolyzes N-acetyl-alpha L-aspartyl-L-glutamate (NAAG) into glutamate and N-acetyl-aspartate. NAAG is a neuropeptide that is an NMDAR antagonist as well as an agonist for the metabotropic glutamate receptor-3 (mGluR3), which inhibits glutamate release. The aggregate effect of NAAG is thus to attenuate NMDAR activation. To manipulate the expression of GCP II, LoxP sites were inserted flanking exons 1 and 2, which were excised by crossing with a Cre-expressing mouse. The mice heterozygous for this deletion showed a 50% reduction in the expression level of protein and functional activity of GCP II in brain samples. Heterozygous mutant crosses did not yield any homozygous null animals at birth or as embryos (N > 200 live births and fetuses). These data are consistent with the previous report that GCP II homozygous mutant mice generated by removing exons 9 and 10 of GCP II gene were embryonically lethal and confirm our hypothesis that GCP II plays an essential role early in embryonic development. Heterozygous mice, however, developed normally to adulthood and exhibited increased locomotor activity, reduced social interaction, and a subtle cognitive deficit in working memory.

Vitamin C reduces spatial learning deficits in middle-aged and very old APP/PSEN1 transgenic and wild-type mice

Alzheimer's disease is a progressive and fatal neurodegenerative disease characterized by a build up of amyloid beta (Abeta) deposits, elevated oxidative stress, and deterioration of the cholinergic system. The present study investigated short-term cognitive-enhancing effects of acute intraperitoneal (i.p.) Vitamin C (ascorbate) treatment in APP/PSEN1 mice, a mouse model of Alzheimer's disease. Middle-aged (12 months) and very old (24 months) APP/PSEN1 bigenic and wild-type mice were treated with ascorbate (125 mg/kg i.p.) or the vehicle 1 h before testing on Y-maze spontaneous alternation and Morris water maze tasks. Very old mice performed more poorly on cognitive tasks than middle-aged mice. Ascorbate treatment improved Y-maze alternation rates and swim accuracy in the water maze in both wild-type and APP/PSEN1 mice. Abeta deposits and oxidative stress both increased with age, and acetylcholinesterase (AChE) activity was significantly reduced in APP/PSEN1 compared to wild-type mice. However, the short course of acute ascorbate treatment did not alter Alzheimer-like neuropathological features of plaque deposition, oxidative stress, or AChE activity. These data suggest that ascorbate may have noötropic functions when administered parenterally in high doses and that the mode of action is via an acute, pharmacological-like mechanism that likely modulates neurotransmitter function.

Visuo-spatial learning and memory deficits on the Barnes maze in the 16-month-old APPswe/PS1dE9 mouse model of Alzheimer's disease

The APPswe/PS1dE9 mouse is a double transgenic model of Alzheimer's disease, which harbors mutant mouse/human amyloid precursor protein (Swedish K594N/M595L) and presenilin-1 genes (PS1-dE9). These mice develop beta-amyloid plaques and exhibit visuo-spatial learning and memory impairment in the Morris water maze (MWM) at 8-12 and 16-18 months of age. To extend these findings, we tested visuo-spatial learning and memory of male and female APPswe/PS1dE9 mice at 16 months of age on the Barnes maze. APPswe/PS1dE9 mice showed impaired acquisition learning using measures of latency, distance traveled, errors and hole deviation scores, and were less likely to use the spatial search strategy to locate the escape hole than wild-type mice. APPswe/PS1dE9 mice also showed a deficit in memory in probe tests on the Barnes maze relative to wild-type mice. Learning and memory deficits, however, were not found during reversal training and reversal probe tests. Sex differences were observed, as male APPswe/PS1dE9 mice had smaller reversal effects than male wild-type mice, but females of each genotype did not differ. Overall, these results replicate previous findings using the MWM, and indicate that APPswe/PS1dE9 mice have impaired visuo-spatial learning and memory at 16 months of age.

DHA and cholesterol containing diets influence Alzheimer-like pathology, cognition and cerebral vasculature in APPswe/PS1dE9 mice

Cholesterol and docosahexenoic acid (DHA) may affect degenerative processes in Alzheimer's Disease (AD) by influencing Abeta metabolism indirectly via the vasculature. We investigated whether DHA-enriched diets or cholesterol-containing Typical Western Diets (TWD) alter behavior and cognition, cerebral hemodynamics (relative cerebral blood volume (rCBV)) and Abeta deposition in 8- and 15-month-old APP(swe)/PS1(dE9) mice. In addition we investigated whether changes in rCBV precede changes in Abeta deposition or vice versa. Mice were fed regular rodent chow, a TWD-, or a DHA-containing diet. Behavior, learning and memory were investigated, and rCBV was measured using contrast-enhanced MRI. The Abeta load was visualized immunohistochemically. We demonstrate that DHA altered rCBV in 8-month-old APP/PS1 and wild type mice[AU1]. In 15-month-old APP/PS1 mice DHA supplementation improved spatial memory, decreased Abeta deposition and slightly increased rCBV, indicating that a DHA-enriched diet can diminish AD-like pathology. In contrast, TWD diets decreased rCBV in 15-month-old mice. The present data indicate that long-term dietary interventions change AD-like pathology in APP/PS1 mice. Additionally, effects of the tested diets on vascular parameters were observed before effects on Abeta load were noted. These data underline the importance of vascular factors in the APP/PS1 mouse model of AD pathology.

GSK3 inhibitors show benefits in an Alzheimer's disease (AD) model of neurodegeneration but adverse effects in control animals

The dysregulation of glycogen synthase kinase-3 (GSK3) has been implicated in Alzheimer disease (AD) pathogenesis and in Abeta-induced neurotoxicity, leading us to investigate it as a therapeutic target in an intracerebroventricular Abeta infusion model. Infusion of a specific GSK3 inhibitor SB216763 (SB) reduced a downstream target, phospho-glycogen synthase 39%, and increased glycogen levels 44%, suggesting effective inhibition of enzyme activity. Compared to vehicle, Abeta increased GSK3 activity, and was associated with elevations in levels of ptau, caspase-3, the tau kinase phospho-c-jun N-terminal kinase (pJNK), neuronal DNA fragmentation, and gliosis. Co-infusion of SB corrected all responses to Abeta infusion except the induction of gliosis and behavioral deficits in the Morris water maze. Nevertheless, SB alone was associated with induction of neurodegenerative markers and behavioral deficits. These data support a role for GSK3 hyperactivation in AD pathogenesis, but emphasize the importance of developing inhibitors that do not suppress constitutive activity.

Episodic memory deficits are not related to altered glutamatergic synaptic transmission and plasticity in the CA1 hippocampus of the APPswe/PS1δE9-deleted transgenic mice model of ß-amyloidosis

Alzheimer's disease (AD) is characterized by progressive memory impairment and the formation of amyloid plaques in the brain. Dysfunctional excitatory synaptic transmission and synaptic plasticity are generally accepted as primary events in the development of AD, and beta-amyloid is intimately involved. Here we describe age related differences in learning, memory, synaptic transmission and long-term potentiation (LTP) in wild type and APPswe/PS1DeltaE9 mice, which produce increasing amounts of Abeta1-42 with age. The mice have both age related and age-independent deficits in radial arm water maze performance. Blind studies of hippocampal slices from transgenic and wild type mice demonstrate that transgenic mice have impaired transient LTP and that the degree of impairment is not related to age from 3 to 12 months. The deficiencies in transient LTP may be related to the behavioral deficits that did not progress with age. The accumulation of beta-amyloid and the episodic memory deficits, both of which increased with age, were not accompanied by an alteration in synaptic transmission or sustained LTP in the in vitro hippocampal slices.

GABA(A) receptor-mediated acceleration of aging-associated memory decline in APP/PS1 mice and its pharmacological treatment by picrotoxin

Advanced age and mutations in the genes encoding amyloid precursor protein (APP) and presenilin (PS1) are two serious risk factors for Alzheimer's disease (AD). Finding common pathogenic changes originating from these risks may lead to a new therapeutic strategy. We observed a decline in memory performance and reduction in hippocampal long-term potentiation (LTP) in both mature adult (9-15 months) transgenic APP/PS1 mice and old (19-25 months) non-transgenic (nonTg) mice. By contrast, in the presence of bicuculline, a GABA(A) receptor antagonist, LTP in adult APP/PS1 mice and old nonTg mice was larger than that in adult nonTg mice. The increased LTP levels in bicuculline-treated slices suggested that GABA(A) receptor-mediated inhibition in adult APP/PS1 and old nonTg mice was upregulated. Assuming that enhanced inhibition of LTP mediates memory decline in APP/PS1 mice, we rescued memory deficits in adult APP/PS1 mice by treating them with another GABA(A) receptor antagonist, picrotoxin (PTX), at a non-epileptic dose for 10 days. Among the saline vehicle-treated groups, substantially higher levels of synaptic proteins such as GABA(A) receptor alpha1 subunit, PSD95, and NR2B were observed in APP/PS1 mice than in nonTg control mice. This difference was insignificant among PTX-treated groups, suggesting that memory decline in APP/PS1 mice may result from changes in synaptic protein levels through homeostatic mechanisms. Several independent studies reported previously in aged rodents both an increased level of GABA(A) receptor alpha1 subunit and improvement of cognitive functions by long term GABA(A) receptor antagonist treatment. Therefore, reduced LTP linked to enhanced GABA(A) receptor-mediated inhibition may be triggered by aging and may be accelerated by familial AD-linked gene products like Abeta and mutant PS1, leading to cognitive decline that is pharmacologically treatable at least at this stage of disease progression in mice.

Review on the APP/PS1KI mouse model: intraneuronal Abeta accumulation triggers axonopathy, neuron loss and working memory impairment

Accumulating evidence points to an important role of intraneuronal Abeta as a trigger of the pathological cascade of events leading to neurodegeneration and eventually to Alzheimer's disease (AD) with its typical clinical symptoms, like memory impairment and change in personality. As a new concept, intraneuronal accumulation of Abeta instead of extracellular Abeta deposition has been introduced to be the disease-triggering event in AD. The present review compiles current knowledge on the amyloid precursor protein (APP)/PS1KI mouse model with early and massive intraneuronal Abeta42 accumulation: (1) The APP/PS1KI mouse model exhibits early robust brain and spinal cord axonal degeneration and hippocampal CA1 neuron loss. (2) At the same time-point, a dramatic, age-dependent reduced ability to perform working memory and motor tasks is observed. (3) The APP/PS1KI mice are smaller and show development of a thoracolumbar kyphosis, together with an incremental loss of body weight. (4) Onset of the observed behavioral alterations correlates well with robust axonal degeneration in brain and spinal cord and with abundant hippocampal CA1 neuron loss.