Overexpression of hAPPswe impairs rewarded alternation and contextual fear conditioning in a transgenic mouse model of Alzheimer's disease

The Tao Hong Si Wu Decoction ameliorates diabetes-associated cognitive dysfunction by inhibiting the formation of amyloid plaques

OBJECTIVES

The herbs in Tao Hong Si Wu Decoction (THSWD) are beneficial in the treatment of cognitive impairment. However, the underlying mechanisms of THSWD in treating diabetes-associated cognitive dysfunction (DACD) are not entirely explored. This study is aimed to investigate the therapeutic effects of THSWD in DACD model rats and the underlying mechanism.

METHODS

Ultra-high-phase liquid chromatography was employed to identify the main compounds contained in the THSWD extract. DACD rat model was induced by feeding with a high-sugar and high-fat diet and injecting streptozotocin (35 mg/kg). DACD rats were gavaged with THSWD for 1 week. The learning and memory abilities of the rats were measured by using the Morris water maze. Western blotting was used to detect the changes in DACD rat targets. Statistical methods were used to evaluate the correlation between proteins.

RESULTS

The results show that THSWD effectively reduced the escape latency, hippocampal neuron damage, glycosylated hemoglobin, type A1C, and blood lipid levels in DACD rats. Furthermore, DACD rats showed significantly increased amyloid precursor protein, β-secretase, Aβ1-40 , Aβ1-42 , Tau phosphorylation, and advanced glycation end products (AGEs) expression. However, THSWD treatment can reverse this phenomenon.

CONCLUSIONS

THSWD can improve the learning and memory abilities of DACD rats by inhibiting the expression of AEGs-AGE receptors pathway, which provides an experimental basis for the clinical application of THSWD. In addition, the experiment combines pharmacological and statistical methods, which offers a new perspective for the study of Chinese herbal medicine.

Sex differences in socioemotional behavior and changes in ventral hippocampal transcription across aging in C57Bl/6J mice

Socioemotional health is positively correlated with improved cognitive and physical aging. Despite known sex differences in socioemotional behaviors and the trajectory of aging, the interactive effects between sex and aging on socioemotional outcomes are poorly understood. We performed the most comprehensive assessment of sex differences in socioemotional behaviors in C57Bl/6J mice across aging to date. Compared to males, females exhibited decreased anxiety-like behavior and social preference but increased social recognition. With age, anxiety-like behavior, cued threat memory generalization, and social preference increased in both sexes. To investigate potential neural mechanisms underlying these behavioral changes, we analyzed transcriptional neuropathology markers in the ventral hippocampus and found age-related changes in genes related to activated microglia, angiogenesis, and cytokines. Sex differences emerged in the timing, direction, and magnitude of these changes, independent of reproductive senescence in aged females. Interestingly, female-specific upregulation of autophagy-related genes correlated with age-related behavioral changes selectively in females. These novel findings reveal critical sex differences in trajectories of ventral hippocampal aging that may contribute to sex- and age-related differences in socioemotional outcomes.

Novel Uracil-Based Inhibitors of Acetylcholinesterase with Potency for Treating Memory Impairment in an Animal Model of Alzheimer's Disease

Novel derivatives based on 6-methyluracil and condensed uracil, 2,4-quinazoline-2,4-dione, were synthesized with terminal meta- and para-benzoate moieties in polymethylene chains at the N atoms of the pyrimidine ring. In the synthesized compounds, the polymethylene chains were varied from having tris- to hexamethylene chains and quaternary ammonium groups; varying substituents (ester, salt, acid) at benzene ring were introduced into the chains and benzoate moieties. In vivo biological experiments demonstrated the potency of these compounds in decreasing the number of β-amyloid plaques and their suitability for the treatment of memory impairment in a transgenic model of Alzheimer's disease.

Rac1 and Akt Exhibit Distinct Roles in Mediating Aβ-Induced Memory Damage and Learning Impairment

Accumulated beta-amyloid (Aβ) in the brain is the hallmark of Alzheimer's disease (AD). Despite Aβ accumulation is known to trigger cellular dysfunctions and learning and memory damage, the detailed molecular mechanism remains elusive. Recent studies have shown that the onset of memory impairment and learning damage in the AD animal is different, suggesting that the underlying mechanism of the development of memory impairment and learning damage may not be the same. In the current study, with the use of Aβ42 transgenic flies as models, we found that Aβ induces memory damage and learning impairment via differential molecular signaling pathways. In early stage, Aβ activates both Ras and PI3K to regulate Rac1 activity, which affects mostly on memory performance. In later stage, PI3K-Akt is strongly activated by Aβ, which leads to learning damage. Moreover, reduced Akt, but not Rac1, activity promotes cell viability in the Aβ42 transgenic flies, indicating that Akt and Rac1 exhibit differential roles in Aβ regulating toxicity. Taken together, different molecular and cellular mechanisms are involved in Aβ-induced learning damage and memory decline; thus, caution should be taken during the development of therapeutic intervention in the future.

Alzheimer's Disease Animal Models: Elucidation of Biomarkers and Therapeutic Approaches for Cognitive Impairment

Alzheimer’s disease (AD) is an age-related and progressive neurodegenerative disorder. It is widely accepted that AD is mainly caused by the accumulation of extracellular amyloid β (Aβ) and intracellular neurofibrillary tau tangles. Aβ begins to accumulate years before the onset of cognitive impairment, suggesting that the benefit of currently available interventions would be greater if they were initiated in the early phases of AD. To understand the mechanisms of AD pathogenesis, various transgenic mouse models with an accelerated accumulation of Aβ and tau tangles have been developed. However, none of these models exhibit all pathologies present in human AD. To overcome these undesirable phenotypes, APP knock-in mice, which were presented with touchscreen-based tasks, were developed to better evaluate the efficacy of candidate therapeutics in mouse models of early-stage AD. This review assesses several AD mouse models from the aspect of biomarkers and cognitive impairment and discusses their potential as tools to provide novel AD therapeutic approaches.

Modeling human age-associated increase in Gadd45γ expression leads to spatial recognition memory impairments in young adult mice

Aging is associated with the progressive decay of cognitive function. Hippocampus-dependent processes, such as the formation of spatial memory, are particularly vulnerable to aging. Currently, the molecular mechanisms responsible for age-dependent cognitive decline are largely unknown. Here, we investigated the expression and function of the growth arrest DNA damage gamma (Gadd45γ) during aging and cognition. We report that Gadd45γ expression is increased in the hippocampus of aged humans and that Gadd45γ overexpression in the young adult mouse hippocampus compromises cognition. Moreover, Gadd45γ overexpression in hippocampal neurons disrupted cAMP response element-binding protein signaling and the expression of well-established activity-regulated genes. This work shows that Gadd45γ expression is tightly controlled in the hippocampus and its disruption may be a mechanism contributing to age-related cognitive impairments observed in humans.

Novel Acetylcholinesterase Inhibitors Based on Uracil Moiety for Possible Treatment of Alzheimer Disease

In this study, novel derivatives based on 6-methyluracil and condensed uracil were synthesized, namely, 2,4-quinazoline-2,4-dione with ω-(ortho-nitrilebenzylethylamino) alkyl chains at the N atoms of the pyrimidine ring. In this series of synthesized compounds, the polymethylene chains were varied from having tetra- to hexamethylene chains, and secondary NH, tertiary ethylamino, and quaternary ammonium groups were introduced into the chains. The molecular modeling of the compounds indicated that they could function as dual binding site acetylcholinesterase inhibitors, binding to both the peripheral anionic site and active site. The data from in vitro experiments show that the most active compounds exhibit affinity toward acetylcholinesterase within a nanomolar range, with selectivity for acetylcholinesterase over butyrylcholinesterase reaching four orders of magnitude. In vivo biological assays demonstrated the potency of these compounds in the treatment of memory impairment using an animal model of Alzheimer disease.

Chronic cannabidiol (CBD) treatment did not exhibit beneficial effects in 4-month-old male TAU58/2 transgenic mice

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive cognitive decline, motor impairments, and accumulation of hallmark proteins, amyloid-beta (Aβ) and tau. Traditionally, transgenic mouse models for AD have focused on Aβ pathology, however, recently a number of tauopathy transgenic models have been developed, including the TAU58/2 transgenic model. Cannabidiol (CBD), a non-toxic constituent of the Cannabis sativa plant, has been shown to prevent and reverse cognitive deficits in Aβ transgenic mouse models of AD. Importantly, the therapeutic properties of CBD on the behavioural phenotype of tauopathy mouse models have not been investigated. We assessed the impact of chronic CBD treatment (i.e. 50 mg/kg CBD i.p. administration starting 3 weeks prior to behavioural assessments) on disease-relevant behaviours of 4-month-old TAU58/2 transgenic males in paradigms for anxiety, motor functions, and cognition. TAU58/2 transgenic males demonstrated reduced body weight, anxiety and impaired motor functions. Furthermore, they demonstrated increased freezing in fear conditioning compared to wild type-like animals. Interestingly, both sociability and social recognition memory were intact in AD transgenic mice. Chronic CBD treatment did not affect behavioural changes in transgenic males. In summary, 4-month-old TAU58/2 transgenic males exhibited no deficits in social recognition memory, suggesting that motor deficits and changes in anxiety at this age do not impact on social domains. The moderate increase in fear-associated memory needs further investigation but could be related to differences in fear extinction. Future investigations will need to clarify CBD's therapeutic potential for reversing motor deficits in TAU58/2 transgenic mice by considering alternative CBD treatment designs including changed CBD dosing.

ApoE mimetic improves pathology and memory in a model of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia and is characterized pathologically by Aβ plaques. Current treatments are purely symptomatic despite decades of intensive research interest. Notably, patients with the APOE4 allele are at increased risk for developing AD. One hypothesis regarding the mechanism by which the APOE4 allele might increase AD risk is loss of adaptive function, raising the possibility that the exogenous administration of apoE mimetics would have therapeutic effects. In this study, we utilized a previously characterized murine model of AD containing human APP, PS1 and APOE4TR, the APP/PS1/APOETR mouse. We treated male APP/PS1/APOETR mice with the apoE mimetic CN-105 or vehicle for 40d, beginning either at 14-18 or 25-28 weeks of age. After termination of treatment we tested animals in both Morris water maze and contextual fear conditioning, and examined soluble Aβ by biochemistery and Aβ deposition in cortex by unbiased stereology. We found that transient treatment with CN-105 for 40d beginning at 14-18 weeks reduced Aβ pathology and rescued memory deficits in male APP/PS1/APOETR mice. Notably, delaying treatment onset to 25-28 weeks did not produce as robust an effect. These results suggest CN-105 treatment in a mouse model of AD results in a reduction in AD pathology and improved behavioral outcomes when administered early in the course of disease. As CN-105 has an excellent safety profile and is already in clinical trials, these findings raise the possibility that CN-105 represents a novel and translatable therapeutic strategy for AD.

Age-Related Changes of the Neurovascular Unit in the Cerebral Cortex of Alzheimer Disease Mouse Models: A Neuroanatomical and Molecular Study

We describe age-related histological structure and molecular changes of the neurovascular unit (NVU) in the cerebral cortex of Tg2576 and age-matched wild-type (WT) mice. Major results can be summarized as follows: (i) β-amyloid (6E10)-immunoreactivity progressively increases in neurons and astrocytes of Tg2576 mice, reaching the highest concentration at 5 months and then decreasing as soon as extracellular plaque deposition begins; (ii) the synaptic puncta density of glutamatergic and GABAergic neurons in Tg2576 mice is unbalanced versus WT at all investigated ages, with a decrease in synaptophysin and VGLUT1; density of VGAT contacts is higher in 27-month-old Tg2576 versus WT mice; (iii) capillary density is higher in 5-month-old Tg2576 versus WT mice, then decreases to a lower density at 27 months, when the capillary-astrocyte interface is lower; and (iv) mRNA expression of genes involved in microvessel dynamics indicates age- and genotype-dependent changes in the expression levels of hypoxia-related genes, i.e. the highest level is in 5-month-old animals and there is impaired regulation in Tg2576. We conclude that at 5 months, when learning and memory impairment is already present in the absence of extracellular amyloid plaque deposition, Tg2576 mice display alterations in the structure and molecular regulation of the NVU.

Fear acquisition and extinction deficits in amnestic mild cognitive impairment and early Alzheimer's disease

Impaired learning and memory functioning are prime markers for Alzheimer's disease (AD). Although initial evidence points to impaired fear acquisition in later AD, no study has investigated fear conditioning in early stages and amnestic mild cognitive impairment (aMCI), a condition often preceding AD. The present study examined if fear conditioning gradually decays from healthy elderly to patients with aMCI, to patients with AD. Patients with AD (n = 43), patients with aMCI (n = 43), and matched healthy controls (n = 40) underwent a classical fear conditioning paradigm. During acquisition, a neutral face (conditioned stimulus, CS+) was paired with an electrical stimulus, whereas another face (unconditioned stimulus, CS-) was unpaired. Conditioned responses were measured by unconditioned stimulus expectancy, valence, and skin conductance. Compared to healthy controls, both patient groups showed less differential (CS+ vs. CS-) fear acquisition across all measures. Patients further displayed slowed extinction indexed by higher unconditioned stimulus expectancy and reduced positive valence for CS+, declining from aMCI to AD. Groups did not differ in responses during a preconditioning habituation phase and in unconditioned responding. Diminished differential fear acquisition and slowed extinction could represent prognostic markers for AD onset.

Automated Behavioral Experiments in Mice Reveal Periodic Cycles of Task Engagement within Circadian Rhythms

High-throughput automated experiments accelerate discovery in neuroscience research and reduce bias. To enable high-throughput behavioral experiments, we developed a user-friendly and scalable automated system that can simultaneously train hundreds of mice on behavioral tasks, with time-stamped behavioral information recorded continuously for weeks. We trained 12 cages of C57BL/6J mice (24 mice, 2 mice/cage) to perform auditory behavioral tasks. We found that circadian rhythms modulated overall behavioral activity as expected for nocturnal animals. However, auditory detection and discrimination accuracy remained consistently high in both light and dark cycles. We also found a periodic modulation of behavioral response rates only during the discrimination task, suggesting that the mice periodically reduce task engagement (i.e., take “breaks”) when task difficulty increases due to the more complex stimulus–response paradigm for discrimination versus detection. Our results highlight how automated systems for continuous high-throughput behavioral experiments enable both efficient data collection and new observations on animal behavior.

Quantitative study of the capillaries within the white matter of the Tg2576 mouse model of Alzheimer's disease

INTRODUCTION

To quantitatively investigate the capillaries within the white matter of Tg2576 Alzheimer's disease (AD) transgenic mice during the early stage.

METHODS

In the current study, 10-month-old male Tg2576 AD mice were used as the early-stage AD group and age-matched nontransgenic littermate mice were used as the wild-type group. Then, the Morris water maze was used to examine the spatial learning and memory abilities of the mice in both groups, and unbiased stereological methods were used to accurately quantify the volume of white matter and the parameters of the capillaries within the white matter, such as the total length, total volume, and total surface area of capillaries.

RESULTS

The Morris water maze performance of the Tg2576 group was worse than that of the wild-type group, while the white matter volume did not significantly differ between the wild-type group and the Tg2576 group. The total length, total volume, and total surface area of the capillaries within the white matter of the Tg2576 group were significantly decreased compared to those of the wild-type group.

CONCLUSIONS

The current study provide structural basis for understanding the pathological changes of the early stage of AD and cognitive decline in AD might be associated with changes in the white matter capillaries. Capillaries within the white matter might, thus, serve as a valid target for the prevention and treatment of early-stage AD.

Cholinergic Modification of Neurogenesis and Gliosis Improves the Memory of AβPPswe/PSEN1dE9 Alzheimer's Disease Model Mice Fed a High-Fat Diet

We previously reported that neuroinflammation contributes to the amnesia of AβPPswe/PSEN1dE9 Alzheimer's disease model mice fed a high-fat diet to induce type-2 diabetes (T2DM-AD mice), but the underlying mechanism for the memory decline remained unclear. Recent studies have suggested that cholinergic modulation is involved in neuroinflammatory cellular reactions including neurogenesis and gliosis, and in memory improvement. In this study, we administered a broad-spectrum cholinesterase inhibitor, rivastigmine (2 mg/kg/day, s.c.), into T2DM-AD mice for 6 weeks, and evaluated their memory performance, neurogenesis, and neuroinflammatory reactions. By two hippocampal-dependent memory tests, the Morris water maze and contextual fear conditioning, rivastigmine improved the memory deterioration of the T2DM-AD mice (n = 8, p < 0.01). The number of newborn neurons in the hippocampal dentate gyrus was 1138±324 (Ave±SEM) in wild-type littermates, 2573±442 in T2DM-AD-Vehicle, and 2165±300 in T2DM-AD-Rivastigmine mice, indicating that neurogenesis was accelerated in the two T2DM-AD groups (n = 5, p < 0.05). The dendritic maturation of new neurons in T2DM-AD-Vehicle mice was severely abrogated, and rivastigmine treatment reversed this retarded maturation. In addition, the hippocampus of T2DM-AD-Vehicle mice showed increased proinflammatory cytokines IL-1β and TNF-α and gliosis, and rivastigmine treatment blocked these inflammatory reactions. Rivastigmine did not change the insulin abnormality or amyloid pathology in these mice. Thus, cholinergic modulation by rivastigmine treatment led to enhanced neurogenesis and the suppression of gliosis, which together ameliorated the memory decline in T2DM-AD model mice.

Adult hippocampal MeCP2 preserves the genomic responsiveness to learning required for long-term memory formation

MeCP2 is required both during postnatal neurodevelopment and throughout the adult life for brain function. Although it is well accepted that MeCP2 in the maturing nervous system is critical for establishing normal development, the functions of MeCP2 during adulthood are poorly understood. Particularly, the requirement of hippocampal MeCP2 for cognitive abilities in the adult is not studied. To characterize the role of MeCP2 in adult neuronal function and cognition, we used a temporal and region-specific disruption of MeCP2 expression in the hippocampus of adult male mice. We found that MeCP2 is required for long-term memory formation and that it controls the learning-induced transcriptional response of hippocampal neurons required for memory consolidation. Furthermore, we uncovered MeCP2 functions in the adult hippocampus that may underlie cognitive integrity. We showed that MeCP2 maintains the developmentally established chromatin configuration and epigenetic landscape of CA1 neurons throughout the adulthood, and that it regulates the expression of neuronal and immune-related genes in the adult hippocampus. Overall, our findings identify MeCP2 as a maintenance factor in the adult hippocampus that preserves signal responsiveness of the genome and allows for integrity of cognitive functions. This study provides new insight into how MeCP2 maintains adult brain functions, but also into the mechanisms underlying the cognitive impairments observed in RTT patients and highlights the understudied role of DNA methylation interpretation in adult cognitive processes.

Enhancing mitochondrial proteostasis reduces amyloid-β proteotoxicity

Alzheimer's disease is a common and devastating disease characterized by aggregation of the amyloid-β peptide. However, we know relatively little about the underlying molecular mechanisms or how to treat patients with Alzheimer's disease. Here we provide bioinformatic and experimental evidence of a conserved mitochondrial stress response signature present in diseases involving amyloid-β proteotoxicity in human, mouse and Caenorhabditis elegans that involves the mitochondrial unfolded protein response and mitophagy pathways. Using a worm model of amyloid-β proteotoxicity, GMC101, we recapitulated mitochondrial features and confirmed that the induction of this mitochondrial stress response was essential for the maintenance of mitochondrial proteostasis and health. Notably, increasing mitochondrial proteostasis by pharmacologically and genetically targeting mitochondrial translation and mitophagy increases the fitness and lifespan of GMC101 worms and reduces amyloid aggregation in cells, worms and in transgenic mouse models of Alzheimer's disease. Our data support the relevance of enhancing mitochondrial proteostasis to delay amyloid-β proteotoxic diseases, such as Alzheimer's disease.

Early Contextual Fear Memory Deficits in a Double-Transgenic Amyloid-β Precursor Protein/Presenilin 2 Mouse Model of Alzheimer's Disease

Presenilin 1 and presenilin 2 (PS1 and PS2) play a critical role in γ-secretase-mediated cleavage of amyloid-β precursor protein (APP) and the subsequent generation of β-amyloid peptides. The purpose of the present study was to test whether PS2 mutation accelerates the onset of contextual fear memory deficits in a mouse model of AD that expresses a mutation (K670N/M671L) of the human APP with the Swedish mutation (Tg2576 mice). In the present study, an APP/PS2 double-transgenic mouse model (PS2Tg2576) was generated by crossbreeding transgenic mice carrying the human mutant PS2 (N141I) with Tg2576 mice. Contextual fear conditioning was tested in PS2Tg2576 mice aged 3, 4, 6, and 10-12 months. PS2Tg2576 mice showed a tendency of lower freezing behavior as early as 3 months of age, but significant memory impairment was observed from the age of 4 months. The cognitive impairment was more prominent at ages of 6 and 10-12 months. In contrast, Tg2576 mice aged 3 and 4 months exhibited successful acquisition of contextual fear learning, but Tg2576 mice aged 6 months or older showed significantly impaired fear memory. These results show that PS2 mutation significantly accelerates the onset of fear memory deficits in the APP AD model mice.

Elevated emotional contagion in a mouse model of Alzheimer's disease is associated with increased synchronization in the insula and amygdala

Emotional contagion, a primitive form of empathy, is heightened in patients with Alzheimer’s disease (AD); however, the mechanism underlying this attribute has not been thoroughly elucidated. In this study, observational fear conditioning was performed to measure emotional contagion levels in a mouse model of AD. Simultaneous recording of local field potentials in the bilateral anterior insula, basolateral amygdala, anterior cingulate cortex, and retrosplenial cortex was also conducted to investigate related brain network changes. Consistent with the results obtained with AD patients, 11-month-old AD model mice exhibited significantly higher freezing levels in observational fear conditioning, indicating elevated emotional contagion compared to age-matched wild-type mice. Furthermore, the left anterior insula and right basolateral amygdala of 11-months-old AD model mice indicated sustained increases in synchronization when they observed the suffering of conspecifics. These changes did not appear in other age groups or wild-type controls. Additionally, the amyloid plaque burden within the anterior insula was significantly correlated with the freezing levels in observational fear conditioning. Taken together, this study reveals increased and sustained network synchrony between the anterior insula and basolateral amygdala, which comprise a salience network in humans, as a potential mechanism for elevated emotional contagion in a mouse model of AD.

Automated Operant Conditioning in the Mouse Home Cage

Recent advances in neuroimaging and genetics have made mice an advantageous animal model for studying the neurophysiology of sensation, cognition, and locomotion. A key benefit of mice is that they provide a large population of test subjects for behavioral screening. Reflex-based assays of hearing in mice, such as the widely used acoustic startle response, are less accurate than operant conditioning in measuring auditory processing. To date, however, there are few cost-effective options for scalable operant conditioning systems. Here, we describe a new system for automated operant conditioning, the Psibox. It is assembled from low cost parts, designed to fit within typical commercial wire-top cages, and allows large numbers of mice to train independently in their home cages on positive reinforcement tasks. We found that groups of mice trained together learned to accurately detect sounds within 2 weeks of training. In addition, individual mice isolated from groups also showed good task performance. The Psibox facilitates high-throughput testing of sensory, motor, and cognitive skills in mice, and provides a readily available animal population for studies ranging from experience-dependent neural plasticity to rodent models of mental disorders.

Mechanisms of Alzheimer's Disease Pathogenesis and Prevention: The Brain, Neural Pathology, N-methyl-D-aspartate Receptors, Tau Protein and Other Risk Factors

The characteristic features of Alzheimer’s disease (AD) are the appearance of extracellular amyloid-beta (Aβ) plaques and neurofibrillary tangles in the intracellular environment, neuronal death and the loss of synapses, all of which contribute to cognitive decline in a progressive manner. A number of hypotheses have been advanced to explain AD. Abnormal tau phosphorylation may contribute to the formation of abnormal neurofibrillary structures. Many different structures are susceptible to AD, including the reticular formation, the nuclei in the brain stem (e.g., raphe nucleus), thalamus, hypothalamus, locus ceruleus, amygdala, substantia nigra, striatum, and claustrum. Excitotoxicity results from continuous, low-level activation of N-methyl-D-aspartate (NMDA) receptors. Premature synaptotoxicity, changes in neurotransmitter expression, neurophils loss, accumulation of amyloid β-protein deposits (amyloid/senile plaques), and neuronal loss and brain atrophy are all associated with stages of AD progression. Several recent studies have examined the relationship between Aβ and NMDA receptors. Aβ-induced spine loss is associated with a decrease in glutamate receptors and is dependent upon the calcium-dependent phosphatase calcineurin, which has also been linked to long-term depression.

REAC technology modifies pathological neuroinflammation and motor behaviour in an Alzheimer's disease mouse model

The search for new therapeutic approaches to Alzheimer disease (AD) is a major goal in medicine and society, also due to the impressive economic and social costs of this disease. In this scenario, biotechnologies play an important role. Here, it is demonstrated that the Radio Electric Asymmetric Conveyer (REAC), an innovative technology platform for neuro- and bio-modulation, used according to the neuro-regenerative protocol (RGN-N), significantly increases astroglial reaction around the amyloid plaques in an AD mouse model, as evaluated by GFAP-immunoreactivity, and reduces microglia-associated neuroinflammation markers, as evaluated by Iba1-immunoreactivity and mRNA expression level of inflammatory cytokines TREM. IL1beta, iNOS and MRC1 were not affected neither by the genotype or by REAC RGN-N treatment. Also observed was an increase in locomotion in treated animals. The study was performed in 24-month-old male Tg2576 mice and age-matching wild-type animals, tested for Y-maze, contextual fear conditioning and locomotion immediately after the end of a specific REAC treatment administered for 15 hours/day for 15 days. These results demonstrated that REAC RGN-N treatment modifies pathological neuroinflammation, and mitigates part of the complex motor behaviour alterations observed in very old Tg2576 mice.

Better Utilization of Mouse Models of Neurodegenerative Diseases in Preclinical Studies: From the Bench to the Clinic

The major symptom of Alzheimer's disease is dementia progressing with age. Its clinical diagnosis is preceded by a long prodromal period of brain pathology that encompasses both formation of extracellular amyloid and intraneuronal tau deposits in the brain and widespread neuronal death. At present, familial cases of dementia provide the most promising foundation for modeling neurodegenerative tauopathies, a group of heterogeneous disorders characterized by prominent intracellular accumulation of hyperphosphorylated tau protein. In this chapter, we describe major behavioral hallmarks of tauopathies, briefly outline the genetics underlying familial cases, and discuss the arising implications for modeling the disease in transgenic mouse systems. The selection of tests performed to evaluate the phenotype of a model should be guided by the key behavioral hallmarks that characterize human disorder and their homology to mouse cognitive systems. We attempt to provide general guidelines and establish criteria for modeling dementia in a mouse; however, interpretations of obtained results should avoid a reductionist "one gene, one disease" explanation of model characteristics. Rather, the focus should be directed to the question of how the mouse genome can cope with the over-expression of the protein coded by transgene(s). While each model is valuable within its own constraints and the experiments performed are guided by specific hypotheses, we seek to expand upon their methodology by offering guidance spanning from issues of mouse husbandry to choices of behavioral tests and routes of drug administration that might increase the external validity of studies and consequently optimize the translational aspect of preclinical research.

Rodent models for Alzheimer's disease drug discovery

INTRODUCTION

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by memory loss and personality changes, leading to dementia. Histopathological hallmarks are represented by aggregates of beta-amyloid peptide (Aβ) in senile plaques and deposition of hyperphosphorylated tau protein in neurofibrillary tangles in the brain. Rare forms of early onset familial Alzheimer's disease are due to gene mutations. This has prompted researchers to develop genetically modified animals that could recapitulate the main features of the disease. The use of these models is complemented by non-genetically modified animals.

AREAS COVERED

This review summarizes the characteristics of the most used transgenic (Tg) and non-Tg models of AD. The authors have focused on models mainly used in their laboratories including amyloid precursor protein (APP) Tg2576, APP/presenilin 1, 3xAD, single h-Tau, non-Tg mice treated with acute injections of Aβ or tau, and models of physiological aging.

EXPERT OPINION

Animal models of disease might be very useful for studying the pathophysiology of the disease and for testing new therapeutics in preclinical studies but they do not reproduce the entire clinical features of human AD. When selecting a model, researchers should consider the various factors that might influence the phenotype. They should also consider the timing of testing/treating animals since the age at which each model develops certain aspects of the AD pathology varies.

Longitudinal analysis of the behavioral phenotype in a novel transgenic rat model of early stages of Alzheimer's disease

Intraneuronal accumulation of amyloid β (iAβ) has been linked to mild cognitive impairment that may precede Alzheimer's disease (AD) onset. This neuropathological trait was recently mimicked in a novel animal model of AD, the hemizygous transgenic McGill-R-Thy1-APP (Tg^+/−) rat. The characterization of the behavioral phenotypes in this animal model could provide a baseline of efficacy for earlier therapeutic interventions. The aim of the present study was to undertake a longitudinal study of Aβ accumulation and a comprehensive behavioral evaluation of this transgenic rat model. We assessed exploratory activity, anxiety-related behaviors, recognition memory, working memory, spatial learning and reference memory at 3, 6, and 12 months of age. In parallel, we measured Aβ by ELISA, Western blots and semiquantitative immunohistochemistry in hippocampal samples. SDS-soluble Aβ peptide accumulated at low levels (~9 pg/mg) without differences among ages. However, Western blots showed SDS-resistant Aβ oligomers (~30 kDa) at 6 and 12 months, but not at 3 months. When compared to wild-type (WT), male Tg^+/− rats exhibited a spatial reference memory deficit in the Morris Water Maze (MWM) as early as 3 months of age, which persisted at 6 and 12 months. In addition, Tg^+/− rats displayed a working memory impairment in the Y-maze and higher anxiety levels in the Open Field (OF) at 6 and 12 months of age, but not at 3 months. Exploratory activity in the OF was similar to that of WT at all-time points. Spatial learning in the MWM and the recognition memory, as assessed by the Novel Object Recognition Test, were unimpaired at any time point. The data from the present study demonstrate that the hemizygous transgenic McGill-R-Thy1-APP rat has a wide array of behavioral and cognitive impairments from young adulthood to middle-age. The low Aβ burden and early emotional and cognitive deficits in this transgenic rat model supports its potential use for drug discovery purposes in early AD.

Using mice to model Alzheimer's dementia: an overview of the clinical disease and the preclinical behavioral changes in 10 mouse models

The goal of this review is to discuss how behavioral tests in mice relate to the pathological and neuropsychological features seen in human Alzheimer's disease (AD), and present a comprehensive analysis of the temporal progression of behavioral impairments in commonly used AD mouse models that contain mutations in amyloid precursor protein (APP). We begin with a brief overview of the neuropathological changes seen in the AD brain and an outline of some of the clinical neuropsychological assessments used to measure cognitive deficits associated with the disease. This is followed by a critical assessment of behavioral tasks that are used in AD mice to model the cognitive changes seen in the human disease. Behavioral tests discussed include spatial memory tests [Morris water maze (MWM), radial arm water maze (RAWM), Barnes maze], associative learning tasks (passive avoidance, fear conditioning), alternation tasks (Y-Maze/T-Maze), recognition memory tasks (Novel Object Recognition), attentional tasks (3 and 5 choice serial reaction time), set-shifting tasks, and reversal learning tasks. We discuss the strengths and weaknesses of each of these behavioral tasks, and how they may correlate with clinical assessments in humans. Finally, the temporal progression of both cognitive and non-cognitive deficits in 10 AD mouse models (PDAPP, TG2576, APP23, TgCRND8, J20, APP/PS1, TG2576 + PS1 (M146L), APP/PS1 KI, 5×FAD, and 3×Tg-AD) are discussed in detail. Mouse models of AD and the behavioral tasks used in conjunction with those models are immensely important in contributing to our knowledge of disease progression and are a useful tool to study AD pathophysiology and the resulting cognitive deficits. However, investigators need to be aware of the potential weaknesses of the available preclinical models in terms of their ability to model cognitive changes observed in human AD. It is our hope that this review will assist investigators in selecting an appropriate mouse model, and accompanying behavioral paradigms to investigate different aspects of AD pathology and disease progression.

Behavioral assays with mouse models of Alzheimer's disease: practical considerations and guidelines

In Alzheimer's disease (AD) basic research and drug discovery, mouse models are essential resources for uncovering biological mechanisms, validating molecular targets and screening potential compounds. Both transgenic and non-genetically modified mouse models enable access to different types of AD-like pathology in vivo. Although there is a wealth of genetic and biochemical studies on proposed AD pathogenic pathways, as a disease that centrally features cognitive failure, the ultimate readout for any interventions should be measures of learning and memory. This is particularly important given the lack of knowledge on disease etiology - assessment by cognitive assays offers the advantage of targeting relevant memory systems without requiring assumptions about pathogenesis. A multitude of behavioral assays are available for assessing cognitive functioning in mouse models, including ones specific for hippocampal-dependent learning and memory. Here we review the basics of available transgenic and non-transgenic AD mouse models and detail three well-established behavioral tasks commonly used for testing hippocampal-dependent cognition in mice - contextual fear conditioning, radial arm water maze and Morris water maze. In particular, we discuss the practical considerations, requirements and caveats of these behavioral testing paradigms.

β-Amyloid pathology alters neural network activation during retrieval of contextual fear memories in a mouse model of Alzheimer's disease

Although episodic memory deficits are the most conspicuous cognitive change in patients with Alzheimer's disease (AD), patients also display alterations in emotional expression, including anxiety and impaired conditioned fear behaviours. The neural circuitry underlying emotional learning is known to involve the amygdala and hippocampus, although the precise impact of amyloid pathology on the interaction between these brain regions remains unclear. Recent evidence suggests that Tg2576 mice, which express a human amyloid precursor protein (APP) mutation associated with early-onset AD, demonstrate normal acquisition of conditioned freezing to auditory and contextual stimuli paired with footshock. However, examination of the expression of c-Fos revealed altered neural network activity in transgenic mice. In the present study we examined the effects of the APP mutation on the expression of c-Fos following the retrieval of emotional memories. To this end, stimulus-induced cellular activity was measured by analysing expression of the immediate-early gene c-Fos after the retrieval of auditory or contextual fear memories. To characterize regional interdependencies of c-Fos expression, structural equation modelling was used to compare patterns of neural network activity. Consistent with previous findings, Tg2576 mice displayed reduced freezing elicited by the auditory stimulus but not by the conditioning context. Interestingly, the analysis of c-Fos expression revealed that the APPswe mutation disrupted dentate gyrus and amygdala function, as well as altering the influence of these regions on the neural network dynamics activated during context memory retrieval. These results provide novel insight into the influence of excess amyloid production on neural network activity during memory retrieval.

Differences in memory development among C57BL/6NCrl, 129S2/SvPasCrl, and FVB/NCrl mice after delay and trace fear conditioning

Fear-conditioning testing paradigms have been used to study differences in memory formation between inbred mouse strains, including numerous mouse models of human diseases. In this study, we characterized the conditioned fear memory of 3 inbred strains: C57BL/6NCrl, 129S2/SvPasCrl, and FVB/NCrl, obtained from Charles River Laboratories. We used 2 training paradigms: delay conditioning, in which an unconditional stimulus coterminates with the presentation of a conditional stimulus, and trace conditioning, in which the conditional and unconditional stimuli are separated by a trace interval. In each paradigm, we evaluated the recent (3 d) and remote (25 d) memory of the mice by using a longitudinal design. Our results showed that both C57BL/6NCrl and 129S2/SvPasCrl mice developed strong and long-lasting context and tone memories in both paradigms, but FVB/NCrl mice showed a weaker but nevertheless consistent tone memory after delay training. Tone memory in the FVB strain was stronger in male than female mice. The remote tone memory of 129S2/SvPasCrl mice diminished after delay training but was stable and stronger than that of C57BL/6NCrl mice after trace training. In conclusion, both C57BL/6NCrl and 129S2/SvPasCrl mice showed reliable and long-lasting fear memory after delay or trace training, with 129 mice showing particularly strong tone memory after trace conditioning. The FVB/NCrl strain, especially male mice, showed reliable tone fear memory after delay training. Our findings confirm that both C57BL/6NCrl and 129S2/SvPasCrl mice develop strong context and tone memory in delay and trace fear-conditioning paradigms.

The hematopoietic growth factor "erythropoietin" enhances the therapeutic effect of mesenchymal stem cells in Alzheimer's disease

Alzheimer's disease is a neurodegenerative disorder clinically characterized by cognitive dysfunction and by deposition of amyloid plaques, neurofibrillary tangles in the brain. The study investigated the therapeutic effect of combined mesenchymal stem cells and erythropoietin on Alzheimer's disease. Five groups of mice were used: control group, Alzheimer's disease was induced in four groups by a single intraperitoneal injection of 0.8 mg kg(-1) lipopolysaccharide and divided as follows: Alzheimer's disease group, mesenchymal stem cells treated group by injecting mesenchymal stem cells into the tail vein (2 x 10(6) cells), erythropoietin treated group (40 microg kg(-1) b.wt.) injected intraperitoneally 3 times/week for 5 weeks and mesenchymal stem cells and erythropoietin treated group. Locomotor activity and memory were tested using open field and Y-maze. Histological, histochemical, immunohistochemical studies, morphometric measurements were examined in brain sections of all groups. Choline transferase activity, brain derived neurotrophic factor expression and mitochondrial swellings were assessed in cerebral specimens. Lipopolysaccharide decreased locomotor activity, memory, choline transferase activity and brain derived neurotrophic factor. It increased mitochondrial swelling, apoptotic index and amyloid deposition. Combined mesenchymal stem cells and erythropoietin markedly improved all these parameters. This study proved the effective role of mesenchymal stem cells in relieving Alzheimer's disease symptoms and manifestations; it highlighted the important role of erythropoietin in the treatment of Alzheimer's disease.

An update of animal models of Alzheimer disease with a reevaluation of plaque depositions

Animal models of Alzheimer disease (AD) are used to study the mechanisms underlying AD pathogenesis, genetic interactions with genes of interest, and environmental risk factors that cause sporadic AD as well as to test the therapeutic effects of AD drug-candidates on neuropathology and cognitive function. To attain a comparative view on the AD models developed, representative AD lines were selected and summarized with respect to transgenic constructs and AD-related pathology. In addition, age-dependent plaque deposition data available in the literature for six representative AD models such as Tg2576, PDAPP, TgAPP23, Tg-APPswe/PS1dE9, 3xTg-AD, and 5XFAD mice were reevaluated using a photographic plaque reference scale method that was introduced recently. Tg2576, PDAPP, and TgAPP23 mice, which carry the amyloid precursor protein (APP) transgene, produced initially slow, but progressively accelerated plaque deposition as they aged, resulting in logistic plaque deposition. In contrast, Tg-APPswe/PS1dE9 and 3xTg-AD mice, which carry both APP and PS1 transgenes, developed abruptly accelerated plaque formation from the beginning, resulting in logarithmic plaque deposition. 5XFAD mice, which also carry both the APP and PS1 transgenes, developed a logarithmic deposition beginning at 2 months. This comparative analysis suggests that AD models may be classified into two distinct plaque deposition groups, and that early plaque models such as APPswe/PS1dE9, 3xTg-AD and 5XFAD might be useful to study the biochemical aspects of APP metabolism, whereas late plaque models such as Tg2576, PDAPP, and TgAPP23 might be useful to study more physiological and environmental aspects of AD pathogenesis, which occur on a longer time scale.

Comprehensive behavioral characterization of an APP/PS-1 double knock-in mouse model of Alzheimer's disease

INTRODUCTION

Despite the extensive mechanistic and pathological characterization of the amyloid precursor protein (APP)/presenilin-1 (PS-1) knock-in mouse model of Alzheimer's disease (AD), very little is known about the AD-relevant behavioral deficits in this model. Characterization of the baseline behavioral performance in a variety of functional tasks and identification of the temporal onset of behavioral impairments are important to provide a foundation for future preclinical testing of AD therapeutics. Here we perform a comprehensive behavioral characterization of this model, discuss how the observed behavior correlates with the mechanistic and pathological observations of others, and compare this model with other commonly used AD mouse models.

METHODS

FOUR DIFFERENT GROUPS OF MICE RANGING ACROSS THE LIFESPAN OF THIS MODEL (TEST GROUPS: 7, 11, 15, and 24 months old) were run in a behavioral test battery consisting of tasks to assess motor function (grip strength, rotor rod, beam walk, open field ambulatory movement), anxiety-related behavior (open field time spent in peripheral zone vs. center zone, elevated plus maze), and cognitive function (novel object recognition, radial arm water maze).

RESULTS

There were no differences in motor function or anxiety-related behavior between APP/PS-1 knock-in mice and wild-type counterpart mice for any age group. Cognitive deficits in both recognition memory (novel object recognition) and spatial reference memory (radial arm water maze) became apparent for the knock-in animals as the disease progressed.

CONCLUSION

This is the first reported comprehensive behavioral analysis of the APP/PS1 knock-in mouse model of AD. The lack of motor/coordination deficits or abnormal anxiety levels, coupled with the age/disease-related cognitive decline and high physiological relevance of this model, make it well suited for utilization in preclinical testing of AD-relevant therapeutics.

Normal cognition in transgenic BRI2-Aβ mice

BACKGROUND

Recent research in Alzheimer's disease (AD) field has been focused on the potential role of the amyloid-β protein that is derived from the transmembrane amyloid precursor protein (APP) in directly mediating cognitive impairment in AD. Transgenic mouse models overexpressing APP develop robust AD-like amyloid pathology in the brain and show various levels of cognitive decline. In the present study, we examined the cognition of the BRI2-Aβ transgenic mouse model in which secreted extracellular Aβ1-40, Aβ1-42 or both Aβ1-40/Aβ1-42 peptides are generated from the BRI-Aβ fusion proteins encoded by the transgenes. BRI2-Aβ mice produce high levels of Aβ peptides and BRI2-Aβ1-42 mice develop amyloid pathology that is similar to the pathology observed in mutant human APP transgenic models.

RESULTS

Using established behavioral tests that reveal deficits in APP transgenic models, BRI2-Aβ1-42 mice showed completely intact cognitive performance at ages both pre and post amyloid plaque formation. BRI2-Aβ mice producing Aβ1-40 or both peptides were also cognitively intact.

CONCLUSIONS

These data indicate that high levels of Aβ1-40 or Aβ1-42, or both produced in the absence of APP overexpression do not reproduce memory deficits observed in APP transgenic mouse models. This outcome is supportive of recent data suggesting that APP processing derivatives or the overexpression of full length APP may contribute to cognitive decline in APP transgenic mouse models. Alternatively, Aβ aggregates may impact cognition by a mechanism that is not fully recapitulated in these BRI2-Aβ mouse models.

Preventing formation of reticulon 3 immunoreactive dystrophic neurites improves cognitive function in mice

Neuritic dystrophy is one of the important pathological features associated with amyloid plaques in Alzheimer's disease (AD) and age-dependent neuronal dysfunctions. We reported previously that reticulon-3 (RTN3) immunoreactive dystrophic neurites (RIDNs) are abundantly present in the hippocampus of AD patients, in AD mouse models, and in aged wild-type mice. Transgenic mice overexpressing the human RTN3 transgene spontaneously develop RIDNs in their hippocampi, and the formation of RIDNs correlates with the appearance of RTN3 aggregation. To further elucidate whether the formation of RIDNs is reversible, we generated transgenic mice expressing wild-type human RTN3 under the control of a tetracycline-responsive promoter. Treatment with doxycycline for 2 months effectively turned off expression of the human RTN3 transgene, confirming the inducible nature of the system. However, the formation of hippocampal RIDNs was dependent on whether the transgene was turned off before or after the formation of RTN3 aggregates. When transgenic human RTN3 expression was turned off at young age, formation of RIDNs was essentially eliminated compared with the vehicle-treated transgenic mice. More importantly, a fear conditioning study demonstrated that contextual associative learning and memory in inducible transgenic mice was improved if the density of RIDNs was lowered. Additional mechanistic study suggested that a reduction in BDNF levels in transgenic mice might contribute to the reduced learning and memory in transgenic mice overexpressing RTN3. Hence, we conclude that age-dependent RIDNs cannot be effectively cleared once they have formed, and we postulate that successful prevention of RIDN formation should be initiated before RTN3 aggregation.

Cholinergic degeneration is associated with increased plaque deposition and cognitive impairment in APPswe/PS1dE9 mice

Cholinergic dysfunction and deposition of plaques containing amyloid β-peptides (Aβ) are two of the characteristics of Alzheimer's disease. Here, we combine APPswe/PS1dE9 (APP/PS1) mice with the cholinergic immunotoxin mu p75-saporin (SAP) to integrate partial basal forebrain cholinergic degeneration and the neuropathology of APP/PS1 mice. By 6 months of age, APP/PS1 mice and wild type littermates (Wt) received intracerebroventricular injection of 0.6 μg SAP (lesion) or PBS (sham). Two months following surgery, APP/PS1 mice treated with SAP were significantly impaired compared to sham treated APP/PS1 mice in a behavioural paradigm addressing working memory. Conversely, the performance of Wt mice was unaffected by SAP treatment. Choline acetyltransferase activity was reduced in the hippocampus and frontal cortex following SAP treatment. The selective effect of a mild SAP lesion in APP/PS1 mice was not due to a more extensive cholinergic degeneration since the reduction in choline acetyltransferase activity was similar following SAP treatment in APP/PS1 mice and Wt. Interestingly, plaque load was significantly increased in SAP treated APP/PS1 mice relative to sham lesioned APP/PS1 mice. Additionally, APP/PS1 mice treated with SAP showed a tendency towards an increased level of soluble and insoluble Aβ1-40 and Aβ1-42 measured in brain tissue homogenate. Our results suggest that the combination of cholinergic degeneration and Aβ overexpression in the APP/PS1 mouse model results in cognitive decline and accelerated plaque burden. SAP treated APP/PS1 mice might thus constitute an improved model of Alzheimer's disease-like neuropathology and cognitive deficits compared to the conventional APP/PS1 model without selective removal of basal forebrain cholinergic neurons.

Early impairment in a water-finding test in a longitudinal study of the Tg2576 mouse model of Alzheimer's disease

Behavioral assessments of mouse models of neurodegenerative disorders are useful for investigating the molecular basis of the pathologies of the diseases. Here, we investigated the utility of a water-finding test using a video tracking system as a tool for evaluating cognitive deficits in Alzheimer's disease model mice. Transgenic mice expressing mutant amyloid precursor protein that incorporated the Swedish mutation (Tg2576 mice) were tested for behavioral alterations at 3, 5, 6, or 10 months of age. Tg2576 mice, which are widely used as a model of Alzheimer's disease, exhibited significant cognitive deficits in the water-finding test as early as 5 months of age. The impairments progressively worsened at 6 and 10 months of age. In addition, we analyzed spontaneous physical activities, such as locomotor activity, in the home-cage environment with an automated video analysis system (HomeCageScan). Our longitudinal study revealed that spontaneous behavior was altered in the Tg2576 mice, starting at the age of 10 months. Impairment in the Morris water maze (MWM) task was also first observed in the Tg2576 mice at the age of 10 months. These results indicated that the ability to perform the water-finding test was more susceptible to age-related cognitive deterioration in Tg2576 mice than the MWM test. We therefore propose that the water-finding test is a rapid and sensitive method that can be used to assess cognitive and/or behavioral deficits in mouse models of Alzheimer's disease.

miR-206 regulates brain-derived neurotrophic factor in Alzheimer disease model

OBJECTIVE

Alzheimer disease (AD) brains are deficient in brain-derived neurotrophic factor (BDNF), which regulates synaptic plasticity and memory. MicroRNAs (miRNAs) are ∼22-nucleotide small noncoding RNAs that control a variety of physiological and disease processes. Here, we show that miR-206 regulates BDNF and memory function in AD mice.

METHODS

Expression of miRNAs was analyzed in Tg2576 AD transgenic mice and human AD brain samples. Regulation of BDNF by a selected miRNA was validated by in silico prediction, target gene luciferase assay, and dendritic spine responses in neurons. AM206, a neutralizing inhibitor of miR-206 (antagomir), was injected into the third ventricle of Tg2576 mice, after which memory function, synaptogenesis, neurogenesis, and target gene expression were assessed. For noninvasive delivery, antagomirs were administered intranasally.

RESULTS

The brains of Tg2576 mice and the temporal cortex of human AD brains had increased levels of miR-206. This miRNA targeted BDNF transcripts, and AM206 prevented the detrimental effects of amyloid-β42 on BDNF and dendritic spine degeneration in Tg2576 neurons. Injection of AM206 into the cerebral ventricles of AD mice increased the brain levels of BDNF and improved their memory function. In parallel, AM206 enhanced the hippocampal synaptic density and neurogenesis. Furthermore, intranasally administered AM206 also reached the brain and increased BDNF levels and memory function in AD mice.

INTERPRETATION

Our findings demonstrate a novel miRNA-dependent regulation of BDNF in AD and suggest possible therapeutic approaches, such as noninvasive intranasal delivery of AM206.

Age-related increase in amyloid plaque burden is associated with impairment in conditioned fear memory in CRND8 mouse model of amyloidosis

Introduction

The current pathological confirmation of the diagnosis of Alzheimer's disease (AD) is still based on postmortem identification of parenchymal amyloid beta (Aβ) plaques, intra-neuronal neurofibrillary tangles, and neuronal loss. The memory deficits that are present in the early stages of AD are linked to the dysfunction of structures in the entorhinal cortex and limbic system, especially the hippocampus and amygdala. Using the CRND8 transgenic mouse model of amyloidosis, which over-expresses a mutant human amyloid precursor protein (APP) gene, we evaluated hippocampus-dependent contextual and amygdala-dependent tone fear conditioned (FC) memory, and investigated the relationship between the fear memory indices and Aβ plaque burden.

Methods

Mice were tested at three, six, and 12 months of age, which corresponds to early, mild, and severe Aβ plaque deposition, following a cross-sectional experimental design. We used a delay version of the fear conditioning paradigm in which tone stimulus was co-terminated with foot-shocks during exploration of the training chamber. The Aβ plaque burden was evaluated at each age after the completion of the behavioral tests.

Results

CRDN8 mice showed context fear memory comparable to control mice at three and six months, but were significantly impaired at 12 months of age. In contrast, the tone fear memory was significantly impaired in the model at each age of testing. The Aβ plaque burden significantly increased with age, and was correlated with the overall impairment in context and tone fear memory in the CRND8 mice within the studied age.

Conclusions

Our data extend previous studies showing that other APP mouse models exhibit impairment in fear conditioned memory, by demonstrating that this impairment is progressive and correlates well with an overall increase in Aβ burden. Also, the demonstrated greater sensitivity of the tone conditioning test in the identification of age dependent differences between CRND8 and control mice suggests that this paradigm might be particularly suitable in studies evaluating potential therapeutics related to memory improvement in mouse models of amyloidosis.

Context processing in aging: older mice are impaired in renewal of extinguished fear

Fear conditioning, extinction, and renewal were evaluated in adult (6-month-old) and aging (17-month-old) male C57Bl/6 mice. Mice were subjected to five tone-shock trials and later exposed to 150 tone-alone trials. Thereafter, all mice showed little fear in the extinction context. Adult mice demonstrated return of fear in a distinct context (renewal) but aging mice did not. Aging mice showed normal shock sensitivity, tone fear learning, and extinction. Aging mice thus exhibited a very selective deficit in the contextual gating of extinguished fear. This contextual gating deficit may reflect age-related pathology in the hippocampus and prefrontal cortex.

Spines, plasticity, and cognition in Alzheimer's model mice

The pathological hallmarks of Alzheimer's disease (AD)--widespread synaptic and neuronal loss and the pathological accumulation of amyloid-beta peptide (Aβ) in senile plaques, as well as hyperphosphorylated tau in neurofibrillary tangles--have been known for many decades, but the links between AD pathology and dementia and effective therapeutic strategies remain elusive. Transgenic mice have been developed based on rare familial forms of AD and frontotemporal dementia, allowing investigators to test in detail the structural, functional, and behavioral consequences of AD-associated pathology. Here, we review work on transgenic AD models that investigate the degeneration of dendritic spine structure, synaptic function, and cognition. Together, these data support a model of AD pathogenesis in which soluble Aβ initiates synaptic dysfunction and loss, as well as pathological changes in tau, which contribute to both synaptic and neuronal loss. These changes in synapse structure and function as well as frank synapse and neuronal loss contribute to the neural system dysfunction which causes cognitive deficits. Understanding the underpinnings of dementia in AD will be essential to develop and evaluate therapeutic approaches for this widespread and devastating disease.

LMN diet, rich in polyphenols and polyunsaturated fatty acids, improves mouse cognitive decline associated with aging and Alzheimer's disease

We examined whether LMN diet, reported to induce neurogenesis in adult mice, was able to antagonize the age-related behavioural impairment and neuropathology in wild type (WT) mice and Tg2576 mice, a mouse model of Alzheimer's disease (AD). Thirteen-month-old mice (once the amyloid (Aβ) plaques were formed) were fed with the LMN diet for 5 months, and in the last 2 months of the regimen they received a battery of behavioural tests. In general, both aging and (to a higher extent) Tg2576 genotype deteriorated sensorimotor reflexes, exploratory behaviour in the hole board, activity (but not anxiety) in the elevated plus-maze, ambulation in the home cage during the dark phase, and spatial learning in the Morris water maze. LMN diet did not affect the detrimental effects observed in sensorimotor reflexes, but clearly reversed the effects of both aging and Tg2576 genotype. This behavioural amelioration was correlated with a 70% increase in cellular proliferation in subventricular zone (SVZ) of the brain, but did not correlate with a decrease of amyloid plaques. In contrast, administration of LMN diet to 10 months old mice (before the plaques are formed) strongly suggested a putative delay in the formation of plaques, as indicated by a decreasing tendency of soluble and fibrillar Aβ levels in hippocampus which correlated with a decrease in Aβ (1-40, 1-42) plasma content. Herein we describe for the first time that LMN diet rich in polyphenols, dry fruits and cocoa, was able to decrease behavioural deterioration caused by aging and Tg2576 genotype and to delay the Aβ plaque formation. These results corroborate the increasing importance of polyphenols as human dietary supplements in amelioration of the cognitive impairment during aging and neurological disorders such as AD.

Impaired long-trace eyeblink conditioning in a Tg2576 mouse model of Alzheimer's disease

Eyeblink conditioning has been used for assessing cognitive performance in cases of human neurodegenerative diseases including Alzheimer's disease (AD). Here, we tested and compared the delay and long-trace interval (TI=500ms) eyeblink conditionings in a Tg2576 mouse model of AD, at the age of 3, 6, and 12 months. Tg2576 mice exhibited significant impairment in trace conditioning at 6 months of age. In contrast, delay conditioning was not impaired in Tg2576 mice even at 12 months. These findings indicate that the long-TI eyeblink conditioning is more susceptible to age-related cognitive deterioration than delay conditioning in Tg2576 mice. The long-trace eyeblink conditioning could be a potential tool for detecting early cognitive deficits in AD mouse model.

Non-steroidal anti-inflammatory drugs and cognitive function: are prostaglandins at the heart of cognitive impairment in dementia and delirium?

Studies of non-steroidal anti-inflammatory drugs (NSAIDs) in rheumatoid arthritis imply that inflammation is important in the development of Alzheimer’s disease (AD). However, these drugs have not alleviated the symptoms of AD in those who have already developed dementia. This suggests that the primary mediator targeted by these drugs, PGE2, is not actively suppressing memory function in AD. Amyloid-β oligomers appear to be important for the mild cognitive changes seen in AD transgenic mice, yet amyloid immunotherapy has also proven unsuccessful in clinical trials. Collectively, these findings indicate that NSAIDs may target a prodromal process in mice that has already passed in those diagnosed with AD, and that synaptic and neuronal loss are key determinants of cognitive dysfunction in AD. While the role of inflammation has not yet become clear, inflammatory processes definitely have a negative impact on cognitive function during episodes of delirium during dementia. Delirium is an acute and profound impairment of cognitive function frequently occurring in aged and demented patients exposed to systemic inflammatory insults, which is now recognised to contribute to long-term cognitive decline. Recent work in animal models is beginning to shed light on the interactions between systemic inflammation and CNS pathology in these acute exacerbations of dementia. This review will assess the role of prostaglandin synthesis in the memory impairments observed in dementia and delirium and will examine the relative contribution of amyloid, synaptic and neuronal loss. We will also discuss how understanding the role of inflammatory mediators in delirious episodes will have major implications for ameliorating the rate of decline in the demented population.

A novel operant testing regimen for multi-construct cognitive characterization of a murine model of Alzheimer's amyloid-related behavioral impairment

A common method for modeling pathological and behavioral aspects of Alzheimer's disease (AD) is the transgenic mouse. While transgenic strains are often well characterized pathologically, behavioral studies of cognitive deficits often employ a limited set of aversively motivated, spatial learning and memory tests, under brief testing periods. Here we illustrate an alternative operant behavioral methodology to provide a comprehensive characterization under repetitive testing conditions, and with appetitive motivation. In this study, we employed the commonly used Tg2576 murine model of Alzheimer's disease amyloid pathology, since it has been the subject of many previous behavioral studies. In these mice, we compared the learning of simple and complex, as well as spatial and non-spatial rules. The mice were assessed on a progressively more complex and interlocking battery of operant tasks, ranging from simple rule learning to delayed recall, as well as tests of motor and sensory ability. In general, as compared to wild type control mice, within-group variability was high in the Tg2576 mice, and deficits were most apparent in more complex discrimination tasks. Furthermore, a consistent decrease in the rate at which Tg2576 mice completed testing trials was observed, pointing to a potential motivation difference or speed-accuracy tradeoffs as a defining characteristic of this strain under these test conditions. Using sensitive adjusting retention interval procedures, it was also possible to isolate a difference in retention interval and separate it from non-mnemonic processes. Overall, these experiments demonstrate the utility of this novel operant approach for characterizing the cognitive deficits of transgenic murine models of dementia.

Metallothionein and brain inflammation

Since the seminal discoveries of Bert Vallee regarding zinc and metallothioneins (MTs) more than 50 years ago, thousands of studies have been published concerning this fascinating story. One of the most active areas of research is the involvement of these proteins in the inflammatory response in general, and in neuroinflammation in particular. We describe the general aspects of the inflammatory response, highlighting the essential role of the major cytokine interleukin-6, and review briefly the expression and function of MTs in the central nervous system in the context of neuroinflammation. Particular attention is paid to the Tg2576 Alzheimer disease mouse model and the preliminary results obtained in mice into which human Zn(7)MT-2A was injected, which suggest a reversal of the behavioral deficits while enhancing amyloid plaque load and gliosis.