Increased auditory startle response and reduced prepulse inhibition of startle in transgenic mice expressing a double mutant form of amyloid precursor protein

Sensory processing deficits and related cortical pathological changes in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder primarily affecting cognitive functions. However, sensory deficits in AD start to draw attention due to their high prevalence and early onsets which suggest that they could potentially serve as diagnostic biomarkers and even contribute to the disease progression. This literature review examines the sensory deficits and cortical pathological changes observed in visual, auditory, olfactory, and somatosensory systems in AD patients, as well as in various AD animal models. Sensory deficits may emerge at the early stages of AD, or even precede the cognitive decline, which is accompanied by cortical pathological changes including amyloid-beta deposition, tauopathy, gliosis, and alterations in neuronal excitability, synaptic inputs, and functional plasticity. Notably, these changes are more pronounced in sensory association areas and superficial cortical layers, which may explain the relative preservation of basic sensory functions but early display of deficits of higher sensory functions. We propose that sensory impairment and the progression of AD may establish a cyclical relationship that mutually perpetuates each condition. This review highlights the significance of sensory deficits with or without cortical pathological changes in AD and emphasizes the need for further research to develop reliable early detection and intervention through sensory systems.

Impaired astrocytic Ca2+ signaling in awake-behaving Alzheimer's disease transgenic mice

Increased astrocytic Ca²⁺ signaling has been shown in Alzheimer’s disease mouse models, but to date no reports have characterized behaviorally induced astrocytic Ca²⁺ signaling in such mice. Here, we employ an event-based algorithm to assess astrocytic Ca²⁺ signals in the neocortex of awake-behaving tg-ArcSwe mice and non-transgenic wildtype littermates while monitoring pupil responses and behavior. We demonstrate an attenuated astrocytic Ca²⁺ response to locomotion and an uncoupling of pupil responses and astrocytic Ca²⁺ signaling in 15-month-old plaque-bearing mice. Using the genetically encoded fluorescent norepinephrine sensor GRAB_NE, we demonstrate a reduced norepinephrine signaling during spontaneous running and startle responses in the transgenic mice, providing a possible mechanistic underpinning of the observed reduced astrocytic Ca²⁺ responses. Our data points to a dysfunction in the norepinephrine–astrocyte Ca²⁺ activity axis, which may account for some of the cognitive deficits observed in Alzheimer’s disease.

Neurodegenerative conditions such as Parkinson’s or Alzheimer’s disease are characterized by neurons dying and being damaged. Yet neurons are only one type of brain actors; astrocytes, for example, are star-shaped ‘companion’ cells that have recently emerged as being able to fine-tune neuronal communication. In particular, they can respond to norepinephrine, a signaling molecule that acts to prepare the brain and body for action. This activation results, for instance, in astrocytes releasing chemicals that can act on neurons.

Certain cognitive symptoms associated with Alzheimer’s disease could be due to a lack of norepinephrine. In parallel, studies in anaesthetized mice have shown perturbed astrocyte signaling in a model of the condition. Disrupted norepinephrine-triggered astrocyte signaling could therefore be implicated in the symptoms of the disease. Experiments in awake mice are needed to investigate this link, especially as anesthesia is known to disrupt the activity of astrocytes.

To explore this question, Åbjørsbråten, Skaaraas et al. conducted experiments in naturally behaving mice expressing mutations found in patients with early-onset Alzheimer’s disease. These mice develop hallmarks of the disorder. Compared to their healthy counterparts, these animals had reduced astrocyte signaling when running or being startled. Similarly, a fluorescent molecular marker for norepinephrine demonstrated less signaling in the modified mice compared to healthy ones.

Over 55 million individuals currently live with Alzheimer’s disease. The results by Åbjørsbråten, Skaaraas et al. suggest that astrocyte–norepinephrine communication may be implicated in the condition, an avenue of research that could potentially lead to developing new treatments.

Neurodegeneration Within the Amygdala Is Differentially Induced by Opioid and HIV-1 Tat Exposure

Opioid use disorder (OUD) is a critical problem that contributes to the spread of HIV and may intrinsically worsen neuroHIV. Despite the advent of combined antiretroviral therapies (cART), about half of persons infected with HIV (PWH) experience cognitive and emotional deficits that can be exacerbated by opioid abuse. HIV-1 Tat is expressed in the central nervous system (CNS) of PWH on cART and is thought to contribute to neuroHIV. The amygdala regulates emotion and memories associated with fear and stress and is important in addiction behavior. Notwithstanding its importance in emotional saliency, the effects of HIV and opioids in the amygdala are underexplored. To assess Tat- and morphine-induced neuropathology within the amygdala, male Tat transgenic mice were exposed to Tat for 8 weeks and administered saline and/or escalating doses of morphine twice daily (s.c.) during the last 2 weeks of Tat exposure. Eight weeks of Tat exposure decreased the acoustic startle response and the dendritic spine density in the basolateral amygdala, but not the central nucleus of the amygdala. In contrast, repeated exposure to morphine alone, but not Tat, increased the acoustic startle response and whole amygdalar levels of amyloid-β (Aβ) monomers and oligomers and tau phosphorylation at Ser396, but not neurofilament light chain levels. Co-exposure to Tat and morphine decreased habituation and prepulse inhibition to the acoustic startle response and potentiated the morphine-induced increase in Aβ monomers. Together, our findings indicate that sustained Tat and morphine exposure differentially promote synaptodendritic degeneration within the amygdala and alter sensorimotor processing.

A Case of Early-Onset Alzheimer's Disease Mimicking Schizophrenia in a Patient with Presenilin 1 Mutation (S170P)

Atypical psychological symptoms frequently occur in early-onset Alzheimer's disease (EOAD), which makes it difficult to differentiate it from other psychiatric disorders. We report the case of a 28-year-old woman with EOAD, carrying a presenilin-1 mutation (S170P), who was initially misdiagnosed with schizophrenia because of prominent psychiatric symptoms in the first 1-2 years of the disease. Amyloid-β positron emission tomography (PET) showed remarkably high tracer uptake in the striatum and thalamus. Tau PET showed widespread cortical uptake and relatively low uptake in the subcortical and medial temporal regions. Our case advocates for considering EOAD diagnosis for young patients with psychiatric and atypical cognitive symptoms.

Prepulse inhibition of the acoustic startle reflex and P50 gating in aging and alzheimer's disease

Inhibition plays a crucial role in many functional domains, such as cognition, emotion, and actions. Studies on cognitive aging demonstrate changes in inhibitory mechanisms are age- and pathology-related. Prepulse inhibition (PPI) is the suppression of an acoustic startle reflex (ASR) to an intense stimulus when a weak prepulse stimulus precedes the startle stimulus. A reduction of PPI is thought to reflect dysfunction of sensorimotor gating which normally suppresses excessive behavioral responses to disruptive stimuli. Both human and rodent studies show age-dependent alterations of PPI of the ASR that are further compromised in Alzheimer's disease (AD). The auditory P50 gating, an index of repetition suppression, also is characterized as a putative electrophysiological biomarker of prodromal AD. This review provides the latest evidence of age- and AD-associated impairment of sensorimotor gating based upon both human and rodent studies, as well as the AD-related disruption of P50 gating in humans. It begins with a concise review of neural networks underlying PPI regulation. Then, evidence of age- and AD-related dysfunction of both PPI and P50 gating is discussed. The attentional/ emotional aspects of sensorimotor gating and the neurotransmitter mechanisms underpinning PPI and P50 gating are also reviewed. The review ends with conclusions and research directions.

Animal Models of Psychosis in Alzheimer Disease

Psychosis in Alzheimer Disease (AD) represents a distinct clinicopathologic variant associated with increased cognitive and functional morbidity and an accelerated disease course. To date, extant treatments offer modest benefits with significant risks. The development of new pharmacologic treatments for psychosis in AD would be facilitated by validated preclinical models with which to test candidate interventions. The current review provides a brief summary of the process of validating animal models of human disease together with a critical analysis of the challenges posed in attempting to apply those standards to AD-related behavioral models. An overview of phenotypic analogues of human cognitive and behavioral impairments, with an emphasis on those relevant to psychosis, in AD-related mouse models is provided, followed by an update on recent progress in efforts to translate findings in the pathophysiology of psychotic AD into novel models. Finally, some future directions are suggested to expand the catalogue of psychosis-relevant phenotypes that may provide a sturdier framework for model development and targets for preclinical treatment outcomes.

Hearing loss is an early biomarker in APP/PS1 Alzheimer's disease mice

Alzheimer's disease (AD) is a neurodegenerative disease characterized by a progressive loss of memory and cognitive decline. Over the last decade, it has been found that defects in sensory systems could be highly associated with AD. Hearing is an important neural sense. However, little is known about hearing functional changes in AD. In this study, APP/PS1 AD mice (Jackson Lab: Stack No. 004462) were used. Hearing function was assessed by auditory brainstem response (ABR), distortion product otoacoustic emission (DPOAE), and cochlear microphonics (CM) recordings. Wild-type (WT) littermates served as control. We found that APP/PS1 AD mice measured as ABR threshold had hearing loss. The hearing loss appeared at high frequency as early as 2 months old, prior to the reported occurrence of spatial learning deficit at 6-7 months of age in this AD mouse model. The hearing loss was progressive and extended from high frequency to low frequency. At 3-4 months old, the hearing loss appeared in the whole-frequency range. Moreover, the wave IV and V in the super-threshold ABR were eliminated, indicating substantial impairment in inferior colliculus, nuclei of lateral lemniscus, and medial geniculate body in the upper brainstem. DPOAE in APP/PS1 AD mice was also reduced. However, there was no reduction in CM in APP/PS1 mice. These data demonstrate that unlike age-related hearing loss APP/PS1 AD mice have early onset of hearing loss. These data also suggest that hearing function testing could provide a simple, sensitive, non-invasive screen-tool for early detecting AD and localizing lesion.

Big Data Analysis of Genes Associated With Neuropsychiatric Disorders in an Alzheimer's Disease Animal Model

Alzheimer's disease is a neurodegenerative disease characterized by the impairment of cognitive function and loss of memory, affecting millions of individuals worldwide. With the dramatic increase in the prevalence of Alzheimer's disease, it is expected to impose extensive public health and economic burden. However, this burden is particularly heavy on the caregivers of Alzheimer's disease patients eliciting neuropsychiatric symptoms that include mood swings, hallucinations, and depression. Interestingly, these neuropsychiatric symptoms are shared across symptoms of bipolar disorder, schizophrenia, and major depression disorder. Despite the similarities in symptomatology, comorbidities of Alzheimer's disease and these neuropsychiatric disorders have not been studied in the Alzheimer's disease model. Here, we explore the comprehensive changes in gene expression of genes that are associated with bipolar disorder, schizophrenia, and major depression disorder through the microarray of an Alzheimer's disease animal model, the forebrain specific PSEN double knockout mouse. To analyze the genes related with these three neuropsychiatric disorders within the scope of our microarray data, we used selected 1207 of a total of 45,037 genes that satisfied our selection criteria. These genes were selected on the basis of 14 Gene Ontology terms significantly relevant with the three disorders which were identified by previous research conducted by the Psychiatric Genomics Consortium. Our study revealed that the forebrain specific deletion of Alzheimer's disease genes can significantly alter neuropsychiatric disorder associated genes. Most importantly, most of these significantly altered genes were found to be involved with schizophrenia. Taken together, we suggest that the synaptic dysfunction by mutation of Alzheimer's disease genes can lead to the manifestation of not only memory loss and impairments in cognition, but also neuropsychiatric symptoms.

Kalirin reduction rescues psychosis-associated behavioral deficits in APPswe/PSEN1dE9 transgenic mice

Psychosis in Alzheimer's disease (AD+P) represents a distinct clinical and neurobiological AD phenotype and is associated with more rapid cognitive decline, higher rates of abnormal behaviors, and increased caregiver burden compared with AD without psychosis. On a molecular level, AD+P is associated with greater reductions in the protein kalirin, a guanine exchange factor which has also been linked to the psychotic disease, schizophrenia. In this study, we sought to determine the molecular and behavioral consequences of kalirin reduction in APPswe/PSEN1dE9 mice. We evaluated mice with and without kalirin reduction during tasks measuring psychosis-associated behaviors and spatial memory. We found that kalirin reduction in APPswe/PSEN1dE9 mice significantly attenuated psychosis-associated behavior at 12 months of age without changing spatial memory performance. The 12-month-old APPswe/PSEN1dE9 mice with reduced kalirin levels also had increased levels of the active, phosphorylated forms of p21 protein (Cdc42/Rac)-activated kinases (PAKs), which function in signaling pathways for maintenance of dendritic spine density, morphology, and function.

Pathogenic tau species drive a psychosis-like phenotype in a mouse model of Alzheimer's disease

Psychotic Alzheimer's disease (AD+P) is a rapidly progressive variant of AD associated with an increased burden of frontal tau pathology that affects up to 50% of those with AD, and is observed more commonly in females. To date, there are no safe and effective medication interventions with an indication for treatment in this condition, and there has been only very limited exploration of potential animal models for pre-clinical drug development. Pathogenic tau is over represented in the frontal cortex in AD+P, especially in females. In order to develop a candidate animal model of AD+P, we employed a tau mouse model with a heavy burden of frontal tau pathology, the rTg(tauP301L)4510 mouse, hereafter termed rTg4510. We explored deficits of prepulse inhibition of acoustic startle (PPI), a model of psychosis in rodents, and the correlation between pathogenic phospho-tau species associated with AD+P and PPI deficits in female mice. We found that female rTg4510 mice exhibit increasing PPI deficits relative to littermate controls from 4.5 to 5.5 months of age, and that these deficits are driven by insoluble fractions of the phospho-tau species pSer396/404, pSer202, and pThr231 found to be associated with human AD+P. This preliminary data suggests the utility of the rTg4510 mouse as a candidate disease model of human female AD+P. Further work expanded to include both genders and other behavioral outcome measures relevant to AD+P is necessary.

Modeling Alzheimer's disease: from past to future

Alzheimer’s disease (AD) is emerging as the most prevalent and socially disruptive illness of aging populations, as more people live long enough to become affected. Although AD is placing a considerable and increasing burden on society, it represents the largest unmet medical need in neurology, because current drugs improve symptoms, but do not have profound disease-modifying effects. Although AD pathogenesis is multifaceted and difficult to pinpoint, genetic and cell biological studies led to the amyloid hypothesis, which posits that amyloid β (Aβ) plays a pivotal role in AD pathogenesis. Amyloid precursor protein (APP), as well as β- and γ-secretases are the principal players involved in Aβ production, while α-secretase cleavage on APP prevents Aβ deposition. The association of early onset familial AD with mutations in the APP and γ-secretase components provided a potential tool of generating animal models of the disease. However, a model that recapitulates all the aspects of AD has not yet been produced. Here, we face the problem of modeling AD pathology describing several models, which have played a major role in defining critical disease-related mechanisms and in exploring novel potential therapeutic approaches. In particular, we will provide an extensive overview on the distinct features and pros and contras of different AD models, ranging from invertebrate to rodent models and finally dealing with computational models and induced pluripotent stem cells.

Sensorimotor gating and memory deficits in an APP/PS1 double transgenic mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder associated with cognitive deterioration and neuropsychiatric symptoms. Sensorimotor gating deficit has been identified in neuropsychiatric diseases. The aim of the present study was to evaluate the possible sensorimotor gating deficit and its correlation to memory impairment and cerebral β-amyloid (Aβ) plaque deposits in an amyloid precursor protein (APP)/presenilin-1 (PS1) double transgenic mouse model of AD. The sensorimotor gating in 3-, 7- and-22-month-old non-transgenic and transgenic mice was evaluated in a prepulse inhibition (PPI) task. Results revealed that the PPI was lower in the 7- and 22-month-old transgenic mice compared with the age-matched control, while the response to startle pulse-alone in the transgenic and non-transgenic mice was comparable. Congo red staining showed that Aβ neuropathology of transgenic mice aggravated with age, and the 3-month-old transgenic mice started to have minimum brain Aβ plaques, corresponding to the early stage of AD phenotype. Furthermore, memory impairment in the 7-month-old transgenic mice was detected in a water maze test. These results suggest that the sensorimotor gating is impaired with the progressing of AD phenotype, and its deficit may be correlated to cerebral Aβ neuropathology and memory impairment in the APP/PS1 transgenic mouse model of AD.

A novel mouse model of Niemann-Pick type C disease carrying a D1005G-Npc1 mutation comparable to commonly observed human mutations

We have identified a point mutation in Npc1 that creates a novel mouse model (Npc1(nmf164)) of Niemann-Pick type C1 (NPC) disease: a single nucleotide change (A to G at cDNA bp 3163) that results in an aspartate to glycine change at position 1005 (D1005G). This change is in the cysteine-rich luminal loop of the NPC1 protein and is highly similar to commonly occurring human mutations. Genetic and molecular biological analyses, including sequencing the Npc1(spm) allele and identifying a truncating mutation, confirm that the mutation in Npc1(nmf164) mice is distinct from those in other existing mouse models of NPC disease (Npc1(nih), Npc1(spm)). Analyses of lifespan, body and spleen weight, gait and other motor activities, as well as acoustic startle responses all reveal a more slowly developing phenotype in Npc1(nmf164) mutant mice than in mice with the null mutations (Npc1(nih), Npc1(spm)). Although Npc1 mRNA levels appear relatively normal, Npc1(nmf164) brain and liver display dramatic reductions in Npc1 protein, as well as abnormal cholesterol metabolism and altered glycolipid expression. Furthermore, histological analyses of liver, spleen, hippocampus, cortex and cerebellum reveal abnormal cholesterol accumulation, glial activation and Purkinje cell loss at a slower rate than in the Npc1(nih) mouse model. Magnetic resonance imaging studies also reveal significantly less demyelination/dysmyelination than in the null alleles. Thus, although prior mouse models may correspond to the severe infantile onset forms of NPC disease, Npc1(nmf164) mice offer many advantages as a model for the late-onset, more slowly progressing forms of NPC disease that comprise the large majority of human cases.

Spatial learning and memory impairment and increased locomotion in a transgenic amyloid precursor protein mouse model of Alzheimer's disease

This study provides an examination of spatial learning and a behavioral assessment of irritability and locomotion in TgCRND8 mice, an amyloid precursor protein transgenic model of Alzheimer's disease. Performance was assessed using the Barnes maze, the touch escape test, and an open-field test. While past research focused primarily on 2-5-month-old TgCRND8 mice, the present study used an older age cohort (9-month-old female mice), in addition to a 4-month-old cohort of both transgenic (Tg) and wildtype female mice. Both younger and older Tg mice displayed poor spatial learning in the Barnes maze task compared to their wildtype littermates, as demonstrated by significantly longer latencies and more errors both during acquisition and at a 2-week retest. No differences in irritability were found between Tg and control mice in the younger cohort; however, older Tg mice displayed significantly higher irritability compared with wildtype littermates, as measured by the touch escape test. Additionally, Tg mice of both age cohorts showed increased locomotion and slowed habituation during a 60-min open-field test over 3 days of testing. These results demonstrate that TgCRND8 mice show significant deficits in spatial and nonspatial behavioral tasks at advanced stages of amyloid pathology.

APP transgenic mice: their use and limitations

Alzheimer's disease is the most widespread form of dementia. Its histopathological hallmarks include vascular and extracellular β-amyloid (Aβ) deposition and intraneuronal neurofibrillary tangles (NFTs). Gradual decline of cognitive functions linked to progressive synaptic loss makes patients unable to store new information in the earlier stages of the pathology, later becoming completely dependent because they are unable to do even elementary daily life actions. Although more than a hundred years have passed since Alois Alzheimer described the first case of AD, and despite many years of intense research, there are still many crucial points to be discovered in the neuropathological pathway. The development of transgenic mouse models engineered with overexpression of the amyloid precursor protein carrying familial AD mutations has been extremely useful. Transgenic mice present the hallmarks of the pathology, and histological and behavioural examination supports the amyloid hypothesis. As in human AD, extracellular Aβ deposits surrounded by activated astrocytes and microglia are typical features, together with synaptic and cognitive defects. Although animal models have been widely used, they are still being continuously developed in order to recapitulate some missing aspects of the disease. For instance, AD therapeutic agents tested in transgenic mice gave encouraging results which, however, were very disappointing in clinical trials. Neuronal cell death and NFTs typical of AD are much harder to replicate in these mice, which thus offer a fundamental but still imperfect tool for understanding and solving dementia pathology.

Realistic expectations of prepulse inhibition in translational models for schizophrenia research

INTRODUCTION

Under specific conditions, a weak lead stimulus, or "prepulse", can inhibit the startling effects of a subsequent intense abrupt stimulus. This startle-inhibiting effect of the prepulse, termed "prepulse inhibition" (PPI), is widely used in translational models to understand the biology of brainbased inhibitory mechanisms and their deficiency in neuropsychiatric disorders. In 1981, four published reports with "prepulse inhibition" as an index term were listed on Medline; over the past 5 years, new published Medline reports with "prepulse inhibition" as an index term have appeared at a rate exceeding once every 2.7 days (n=678). Most of these reports focus on the use of PPI in translational models of impaired sensorimotor gating in schizophrenia. This rapid expansion and broad application of PPI as a tool for understanding schizophrenia has, at times, outpaced critical thinking and falsifiable hypotheses about the relative strengths vs. limitations of this measure.

OBJECTIVES

This review enumerates the realistic expectations for PPI in translational models for schizophrenia research, and provides cautionary notes for the future applications of this important research tool.

CONCLUSION

In humans, PPI is not "diagnostic"; levels of PPI do not predict clinical course, specific symptoms, or individual medication responses. In preclinical studies, PPI is valuable for evaluating models or model organisms relevant to schizophrenia, "mapping" neural substrates of deficient PPI in schizophrenia, and advancing the discovery and development of novel therapeutics. Across species, PPI is a reliable, robust quantitative phenotype that is useful for probing the neurobiology and genetics of gating deficits in schizophrenia.

One-year longitudinal evaluation of sensorimotor functions in APP751SL transgenic mice

Intracerebral amyloid-beta (Abeta) peptide deposition is considered to play a key role in Alzheimer's disease and is designated as a principal therapeutic target. The relationship between brain Abeta levels and clinical deficits remains, however, unclear, both in human patients and in animal models of the disease. The purpose of the present study was to investigate, in a transgenic mouse model of brain amyloidosis, the consequences of Abeta deposition on basic neurological functions using a longitudinal approach. Animals were phenotyped at different ages corresponding to graded neuropathological stages (from no extracellular Abeta deposition to high amyloid loads). Sensory functions were evaluated by assessing visual and olfactory abilities and did not show any effects of the amyloid precursor protein (APP) transgene. Motor functions were assessed using multiple experimental paradigms. Results showed that motor strength was considerably reduced in APP transgenic mice compared with control animals. No deficit was noted in a motor coordination test although APP transgenic mice displayed decreased locomotion on a stationary beam. Hypolocomotion was also observed in the standard open-field test. Measures of anxiety obtained in the elevated plus-maze show some evidence of hyperanxiety in 15-month-old transgenic mice. Some of the neurological impairments showed by APP mice had an early onset and worsened with progressive aging, in parallel to gradual accumulation of Abeta in brain parenchyma. Relationships between neuropathologically assessed amyloid loads and behavioral deficits were further explored, and it was observed that motor strength deficits were correlated with cortical amyloid burden.

Alzheimer disease models and human neuropathology: similarities and differences

Animal models aim to replicate the symptoms, the lesions or the cause(s) of Alzheimer disease. Numerous mouse transgenic lines have now succeeded in partially reproducing its lesions: the extracellular deposits of Abeta peptide and the intracellular accumulation of tau protein. Mutated human APP transgenes result in the deposition of Abeta peptide, similar but not identical to the Abeta peptide of human senile plaque. Amyloid angiopathy is common. Besides the deposition of Abeta, axon dystrophy and alteration of dendrites have been observed. All of the mutations cause an increase in Abeta 42 levels, except for the Arctic mutation, which alters the Abeta sequence itself. Overexpressing wild-type APP alone (as in the murine models of human trisomy 21) causes no Abeta deposition in most mouse lines. Doubly (APP x mutated PS1) transgenic mice develop the lesions earlier. Transgenic mice in which BACE1 has been knocked out or overexpressed have been produced, as well as lines with altered expression of neprilysin, the main degrading enzyme of Abeta. The APP transgenic mice have raised new questions concerning the mechanisms of neuronal loss, the accumulation of Abeta in the cell body of the neurons, inflammation and gliosis, and the dendritic alterations. They have allowed some insight to be gained into the kinetics of the changes. The connection between the symptoms, the lesions and the increase in Abeta oligomers has been found to be difficult to unravel. Neurofibrillary tangles are only found in mouse lines that overexpress mutated tau or human tau on a murine tau -/- background. A triply transgenic model (mutated APP, PS1 and tau) recapitulates the alterations seen in AD but its physiological relevance may be discussed. A number of modulators of Abeta or of tau accumulation have been tested. A transgenic model may be analyzed at three levels at least (symptoms, lesions, cause of the disease), and a reading key is proposed to summarize this analysis.

Abnormal processing of tau in the brain of aged TgCRND8 mice

Amyloid plaques and neurofibrillary tangles are the main histopathological hallmarks of Alzheimer's disease (AD). In the neocortex and hippocampus of aged TgCRND8 mice, tau is hyperphosphorylated at different sites recognized by PHF-1, AT100, AT8 and CP13 antibodies. Phospho-SAPK/JNK levels were increased in the tg mouse brain, where activated SAPK/JNK co-localizes with PHF-1-positive cells. Phosphorylated tau-positive cells showed Bielschowsky- and Thioflavine S-positive intraneuronal deposits. PHF-1 and nitrotyrosine immunoreactivity merged within neurons surrounding amyloid deposits in cortical and hippocampal areas and immunoprecipitation studies confirmed that tau is nitrosylated. Our findings, demonstrating the presence of hyperphosphorylated and nitrosylated tau protein as well as of insoluble aggregates after the onset of amyloid deposition in the TgCRND8 mouse brain, indicate that the abnormal processing of tau may occur subsequently to cerebral amyloidosis and that activation of SAPK/JNK and induction of nitrosative stress are the more likely connecting factors between amyloidosis and tauopathy in AD.

Sensory gating in patients with Alzheimer's disease and their biological children

Research has shown that sensory gating is largely modualted by acetylcholine. Diminished levels of acetylcholine and sensory gating deficits have been reported in research involving Alzheimer's disease (AD) patients. However, there has been little investigation into those with a family history (FH+) of AD. The rationale of this study was to determine whether sensory gating impairments could distinguish those with early AD from individuals with increased risk for the disease while replicating previous findings of gating abnormalities in AD patients. Using the paried-click paradigm, evoked potentials were recorded from 4 groups of 20 subjects per group (AD, older controls, FH+, FH-). The results showed that while the AD group demonstrated sensory gating abnormalities, the FH+ group did not when compared to their peers with no family history of the disease (FH-). These results are discussed in relation to previous findings reporting P300 abnormalities in the FH+ group.

Plaques, tangles, and memory loss in mouse models of neurodegeneration

Within the past decade, our understanding of the pathogenic mechanisms in Alzheimer's disease (AD) has dramatically advanced because of the development of transgenic mouse models that recapitulate the key pathological and behavioral phenotypes of the disease. These mouse models have allowed investigators to test detailed questions about how pathology develops and to evaluate potential therapeutic approaches that could slow down the development of this disease. In this review, we discuss the status of transgenic mouse models and review the complex relationship between pathology and behavior in the development of neuropathological syndromes in AD.

Reduction in mitochondrial superoxide dismutase modulates Alzheimer's disease-like pathology and accelerates the onset of behavioral changes in human amyloid precursor protein transgenic mice

Alzheimer's disease (AD) is associated with accumulations of amyloid-beta (Abeta) peptides, oxidative damage, mitochondrial dysfunction, neurodegeneration, and dementia. The mitochondrial antioxidant manganese superoxide dismutase-2 (Sod2) might protect against these alterations. To test this hypothesis, we inactivated one Sod2 allele (Sod2(+/-)) in human amyloid precursor protein (hAPP) transgenic mice, reducing Sod2 activity to approximately 50% of that in Sod2 wild-type (Sod2(+/+)) mice. A reduction in Sod2 activity did not obviously impair mice without hAPP/Abeta expression. In hAPP mice, however, it accelerated the onset of behavioral alterations and of deficits in prepulse inhibition of acoustic startle, a measure of sensorimotor gating. In these mice, it also worsened hAPP/Abeta-dependent depletion of microtubule-associated protein 2, a marker of neuronal dendrites. Sod2 reduction decreased amyloid plaques in the brain parenchyma but promoted the development of cerebrovascular amyloidosis, gliosis, and plaque-independent neuritic dystrophy. Sod2 reduction also increased the DNA binding activity of the transcription factor nuclear factor kappaB. These results suggest that Sod2 protects the aging brain against hAPP/Abeta-induced impairments. Whereas reductions in Sod2 would be expected to trigger or exacerbate neuronal and vascular pathology in AD, increasing Sod2 activity might be of therapeutic benefit.

Behavioral phenotypes of amyloid-based genetically modified mouse models of Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative affliction of the elderly, presenting with progressive memory loss and dementia and terminating with death. There have been significant advances in understanding the biology and subsequent diagnosis of AD; however, the furious pace of research has not yet translated into a disease-modifying treatment. While scientific inquiry in AD is largely centered on identifying biological players and pathological mechanisms, the day-to-day realities of AD patients and their caregivers revolve around their steady and heartbreaking cognitive decline. In the past decade, AD research has been fundamentally transformed by the development of genetically modified animal models of amyloid-driven neurodegeneration. These important in vivo models not only replicate some of the hallmark pathology of the disease, such as plaque-like amyloid accumulations and astrocytic inflammation, but also some of the cognitive impairments relevant to AD. In this article, we will provide a detailed review of the behavioral and cognitive deficits present in several transgenic mouse models of AD and discuss their functional changes in response to experimental treatments.