Reduced corpus callosum, fornix and hippocampus in PDAPP transgenic mouse model of Alzheimer's disease

Diffusion MRI detects basal forebrain cholinergic abnormalities in the 3xTg-AD mouse model of Alzheimer's disease

Degeneration of the basal forebrain (BF) is detected early in the course of Alzheimer's disease (AD). Reduction in the number of BF cholinergic (ChAT) neurons associated with age-related hippocampal cholinergic neuritic dystrophy is described in the 3xTg-AD mouse model; however, no prior diffusion MRI (dMRI) study has explored the presence of BF alterations in this model. Here we investigated the ability of diffusion MRI (dMRI) to detect abnormalities in BF microstructure for the 3xTg-AD mouse model, along with related pathology in the hippocampus (HP) and white matter (WM) tracks comprising the septo-hippocampal pathway. 3xTg-AD and normal control (NC) mice were imaged in vivo using the specific dMRI technique known as diffusional kurtosis imaging (DKI) at 2, 8, and 15 months of age, and 8 dMRI parameters were measured at each time point. Our results revealed significant lower dMRI values in the BF of 2 months-old 3xTg-AD mice compared with NC mice, most likely related to the increased number of ChAT neurons seen in this AD mouse model at this age. They also showed significant age-related dMRI changes in the BF of both groups between 2 and 8 months of age, mainly a decrease in fractional anisotropy and axial diffusivity, and an increase in radial kurtosis. These dMRI changes in the BF may be reflecting the complex aging and pathological microstructural changes described in this region. Group differences and age-related changes were also observed in the HP, fimbria (Fi) and fornix (Fx). In the HP, diffusivity values were significantly higher in the 2 months-old 3xTg-AD mice, and the HP of NC mice showed a significant increase in axial kurtosis after 8 months, reflecting a normal pattern of increased fiber density complexity, which was not seen in the 3xTg-AD mice. In the Fi, mean and radial diffusivity values were significantly higher, and fractional anisotropy, radial kurtosis and kurtosis fractional anisotropy were significantly lower in the 2 months-old 3xTg-AD mice. The age trajectories for both NC and TG mice in the Fi and Fx were similar between 2 and 8 months, but after 8 months there was a significant decrease in diffusivity metrics associated with an increase in kurtosis metrics in the 3xTg-AD mice. These later HP, Fi and Fx dMRI changes probably reflect the growing number of dystrophic neurites and AD pathology progression in the HP, accompanied by WM disruption in the septo-hippocampal pathway. Our results demonstrate that dMRI can detect early cytoarchitectural abnormalities in the BF, as well as related aging and neurodegenerative changes in the HP, Fi and Fx of the 3xTg-AD mice. Since DKI is widely available on clinical scanners, these results also support the potential of the considered dMRI parameters as in vivo biomarkers for AD disease progression.

Cholinergic neurodegeneration in Alzheimer disease mouse models

Cholinergic signaling is critical for cognitive function. The basal forebrain is the major cholinergic output of the central nervous system. Degeneration of basal forebrain cholinergic neurons is a hallmark of Alzheimer's disease (AD). Mouse models are invaluable tools in disease research and have been used to study AD for over 25 years. However, animal models of AD vary greatly with respect to the degree of cholinergic degeneration observed. The following review will outline the most influential animal models of AD with an emphasis on the basal forebrain cholinergic system.

The Erythrocytic Hypothesis of Brain Energy Crisis in Sporadic Alzheimer Disease: Possible Consequences and Supporting Evidence

Alzheimer’s disease (AD) is a fatal form of dementia of unknown etiology. Although amyloid plaque accumulation in the brain has been the subject of intensive research in disease pathogenesis and anti-amyloid drug development; the continued failures of the clinical trials suggest that amyloids are not a key cause of AD and new approaches to AD investigation and treatment are needed. We propose a new hypothesis of AD development based on metabolic abnormalities in circulating red blood cells (RBCs) that slow down oxygen release from RBCs into brain tissue which in turn leads to hypoxia-induced brain energy crisis; loss of neurons; and progressive atrophy preceding cognitive dysfunction. This review summarizes current evidence for the erythrocytic hypothesis of AD development and provides new insights into the causes of neurodegeneration offering an innovative way to diagnose and treat this systemic disease.

Diffusion MRI detects longitudinal white matter changes in the 3xTg-AD mouse model of Alzheimer's disease

The sensitivity of multiple diffusion MRI (dMRI) parameters to longitudinal changes in white matter microstructure was investigated for the 3xTg-AD transgenic mouse model of Alzheimer's disease, which manifests both amyloid beta plaques and neurofibrillary tangles. By employing a specific dMRI method known as diffusional kurtosis imaging, eight different diffusion parameters were quantified to characterize distinct aspects of water diffusion. Four female 3xTg-AD mice were imaged at five time points, ranging from 4.5 to 18 months of age, and the diffusion parameters were investigated in four white matter regions (fimbria, external capsule, internal capsule and corpus callosum). Significant changes were observed in several diffusion parameters, particularly in the fimbria and in the external capsule, with a statistically significant decrease in diffusivity and a statistically significant increase in kurtosis. Our preliminary results demonstrate that dMRI can detect microstructural changes in white matter for the 3xTg-AD mouse model due to aging and/or progression of pathology, depending strongly on the diffusion parameter and anatomical region.

Structural Magnetic Resonance Imaging Markers of Alzheimer's Disease and Its Retranslation to Rodent Models

The importance of imaging biomarkers has been acknowledged in the diagnosis and in the follow-up of Alzheimer's disease (AD), one of the major causes of dementia. Next to the molecular biomarkers and PET imaging investigations, structural MRI approaches provide important information about the disease progression and about the pathomechanism. Furthermore,a growing body of literature retranslates these imaging biomarkers to various rodent models of the disease. The goal of this review is to provide an overview of the macro- and microstructural imaging biomarkers of AD, concentrating on atrophy measures and diffusion MRI alterations. A survey is also given of the imaging approaches used in rodent models of dementias that can promote drug development.

Luteinizing hormone as a key player in the cognitive decline of Alzheimer's disease

This article is part of a Special Issue "SBN 2014". Alzheimer's disease is one of the most prevalent and costly neurological diseases in the world. Although decades of research have focused on understanding Alzheimer's disease pathology and progression, there is still a great lack of clinical treatments for those who suffer from it. One of the factors most commonly associated with the onset of Alzheimer's disease is a decrease in levels of gonadal hormones, such as estrogens and androgens. Despite the correlational and experimental data which support the role of these hormones in the etiology of Alzheimer's disease, clinical trials involving their reintroduction through hormone therapy have had varied results and these gonadal hormones often have accompanying health risks. More recently, investigation has turned toward other hormones in the hypothalamic-pituitary-gonadal axis that are disrupted by age-related decreases in gonadal hormones. Specifically, luteinizing hormone, which is increased with age in both men and women (in response to removal of negative feedback), has surfaced as a potentially powerful player in the risk and onset of Alzheimer's disease. Mounting evidence in basic research and epidemiological studies supports the role of elevated luteinizing hormone in exacerbating age-related cognitive decline in both males and females. This review summarizes the recent developments involving luteinizing hormone in increasing the cognitive deficits and molecular pathology characteristic of Alzheimer's disease.

Alzheimer's disease and the fornix

Alzheimer’s disease (AD) is the most common form of neurodegenerative dementia. Researchers have long been focused on the cortical pathology of AD, since the most important pathologic features are the senile plaques found in the cortex, and the neurofibrillary tangles and neuronal loss that begin in the entorhinal cortex and the hippocampus. In addition to these gray matter (GM) structures, histopathological studies indicate that the white matter (WM) is also a good target for both the early diagnosis of AD and for monitoring disease progression. The fornix is a WM bundle that constitutes a core element of the limbic circuits, and is one of the most important anatomical structures related to memory. Functional and anatomical features of the fornix have naturally captured researchers’ attention as possible diagnostic and prognostic markers of AD. Indeed, neurodegeneration of the fornix has been histologically observed in AD, and growing evidence indicates that the alterations seen in the fornix are potentially a good marker to predict future conversion from mild cognitive impairment (MCI) to AD, and even from cognitively normal individuals to AD. The degree of alteration is correlated with the degree of memory impairment, indicating the potential for the use of the fornix as a functional marker. Moreover, there have been attempts to stimulate the fornix using deep brain stimulation (DBS) to augment cognitive function in AD, and ongoing research has suggested positive effects of DBS on brain glucose metabolism in AD patients. On the other hand, disease specificity for fornix degeneration, methodologies to evaluate fornix degeneration, and the clinical significance of the fornix DBS, especially for the long-term impact on the quality of life, are mostly unknown and need to be elucidated.

Comparison of manual and semi-automated segmentation methods to evaluate hippocampus volume in APP and PS1 transgenic mice obtained via in vivo magnetic resonance imaging

BACKGROUND

Magnetic resonance imaging (MRI) of transgenic mouse models of Alzheimer's disease is valuable to understand better the structural changes that occur in the brain and could provide a means to test drug treatments. A hallmark pathological feature of Alzheimer's disease is atrophy of the hippocampus, which is an early biomarker of the disease. MRI can be used to detect and monitor this biomarker.

METHOD

Repeated measurements using in vivo 3D T2-weighted imaging of mice were used to assess the methods. Each mouse was imaged twice in one week and twice the following week and no changes in volume were expected. The hippocampus was segmented both manually and semi-automatically. Registration was done to gain information on shape changes. The volumes from each mouse were compared intra-mouse, between mice and to hippocampus volume values in the literature.

RESULTS

A reliable method was developed which was able to detect difference in volumes of hippocampus between mice when performed by a single individual. The semi-automated segmentation was unable to detect the same level of differences. The semi-automated segmentation method gave larger hippocampus volumes, with 78-87% reliability between the manual and semi-automated segmentation. Although more accurate, the manual segmentation is laborious and suffers from inter- and intra-variability.

CONCLUSION

These results suggest that manual segmentation is still considered the most reliable segmentation method for small structures. However, if performing longitudinal studies, where there is at least one year between imaging sessions, the segmentation should be done all at once at the end of all the imaging sessions. If segmentation is done after each imaging session, with at least a year passing between segmentations, very small variations in volumes can be missed. This method provides a means to quantify the volume of the hippocampus in a live mouse using manual segmentation, which is the first step toward studying hippocampus atrophy in a mouse model of Alzheimer's disease.

Dynamic changes in myelin aberrations and oligodendrocyte generation in chronic amyloidosis in mice and men

Myelin loss is frequently observed in human Alzheimer's disease (AD) and may constitute to AD-related cognitive decline. A potential source to repair myelin defects are the oligodendrocyte progenitor cells (OPCs) present in an adult brain. However, until now, little is known about the reaction of these cells toward amyloid plaque deposition neither in human AD patients nor in the appropriate mouse models. Therefore, we analyzed cells of the oligodendrocyte lineage in a mouse model with chronic plaque deposition (APPPS1 mice) and samples from human patients. In APPPS1 mice defects in myelin integrity and myelin amount were prevalent at 6 months of age but normalized to control levels in 9-month-old mice. Concomitantly, we observed an increase in the proliferation and differentiation of OPCs in the APPPS1 mice at this specific time window (6-8 months) implying that improvements in myelin aberrations may result from repair mechanisms mediated by OPCs. However, while we observed a higher number of cells of the oligodendrocyte lineage (Olig2+ cells) in APPPS1 mice, OLIG2+ cells were decreased in number in postmortem human AD cortex. Our data demonstrate that oligodendrocyte progenitors specifically react to amyloid plaque deposition in an AD-related mouse model as well as in human AD pathology, although with distinct outcomes. Strikingly, possible repair mechanisms from newly generated oligodendrocytes are evident in APPPS1 mice, whereas a similar reaction of oligodendrocyte progenitors seems to be strongly limited in final stages of human AD pathology.

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

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

Targeting mitochondrial bioenergetics for Alzheimer's prevention and treatment

Alzheimer's is a neurodegenerative disease with a complex and progressive pathological phenotype characterized first by hypometabolism and impaired mitochondrial bioenergetics followed by pathological burden. The progressive and multifaceted degenerative phenotype of Alzheimer's suggests that successful treatment strategies necessarily will be equally multi-faceted and disease stage specific. Traditional therapeutic strategies based on the pathological aspect of the disease have achieved success in preclinical models which has not translated into clinical therapeutic efficacy. Meanwhile, increasing evidence indicates an antecedent and potentially causal role of mitochondrial bioenergetic deficits and brain hypometabolism coupled with increased mitochondrial oxidative stress in AD pathogenesis. The essential role of mitochondrial bioenergetics and the unique trajectory of alterations in brain metabolic capacity enable a bioenergetic- centric strategy that targets disease-stage specific pattern of brain metabolism for disease prevention and treatment. A combination of nutraceutical and pharmaceutical intervention that enhances glucose-driven metabolic activity and potentiates mitochondrial bioenergetic function could prevent the antecedent decline in brain glucose metabolism, promote healthy aging and prevent AD. Alternatively, during the prodromal incipient phase of AD, sustained activation of ketogenic metabolic pathways coupled with supplement of the alternative fuel source, ketone bodies, could sustain mitochondrial bioenergetic function to prevent or delay further progression of the disease.

Increased regional cerebral glucose uptake in an APP/PS1 model of Alzheimer's disease

Alzheimer's disease (AD), the most common age-related neurodegenerative disorder, is characterized by the invariant cerebral accumulation of β-amyloid peptide. This event occurs early in the disease process. In humans, [18F]-fluoro-2-deoxy-D-glucose ([18F]-FDG) positron emission tomography (PET) is largely used to follow-up in vivo cerebral glucose utilization (CGU) and brain metabolism modifications associated with the Alzheimer's disease pathology. Here, [18F]-FDG positron emission tomography was used to study age-related changes of cerebral glucose utilization under resting conditions in 3-, 6-, and 12-month-old APP(SweLon)/PS1(M146L), a mouse model of amyloidosis. We showed an age-dependent increase of glucose uptake in several brain regions of APP/PS1 mice but not in control animals and a higher [18F]-FDG uptake in the cortex and the hippocampus of 12-month-old APP/PS1 mice as compared with age-matched control mice. We then developed a method of 3-D microscopic autoradiography to evaluate glucose uptake at the level of amyloid plaques and showed an increased glucose uptake close to the plaques rather than in amyloid-free cerebral tissues. These data suggest a macroscopic and microscopic reorganization of glucose uptake in relation to cerebral amyloidosis.

Fiber Tracts Anomalies in APPxPS1 Transgenic Mice Modeling Alzheimer's Disease

Amyloid beta (Aβ) peptides are known to accumulate in the brain of patients with Alzheimer's disease (AD). However, the link between brain amyloidosis and clinical symptoms has not been elucidated and could be mediated by secondary neuropathological alterations such as fiber tracts anomalies. In the present study, we have investigated the impact of Aβ overproduction in APPxPS1 transgenic mice on the integrity of forebrain axonal bundles (corpus callosum and anterior commissure). We found evidence of fiber tract volume reductions in APPxPS1 mice that were associated with an accelerated age-related loss of axonal neurofilaments and a myelin breakdown. The severity of these defects was neither correlated with the density of amyloid plaques nor associated with cell neurodegeneration. Our data suggest that commissural fiber tract alterations are present in Aβ-overproducing transgenic mice and that intracellular Aβ accumulation preceding extracellular deposits may act as a trigger of such morphological anomalies.

A role for noncanonical microRNAs in the mammalian brain revealed by phenotypic differences in Dgcr8 versus Dicer1 knockouts and small RNA sequencing

Noncanonical microRNAs (miRNAs) and endogenous small interfering RNAs (endo-siRNAs) are distinct subclasses of small RNAs that bypass the DGCR8/DROSHA Microprocessor but still require DICER1 for their biogenesis. What role, if any, they have in mammals remains unknown. To identify potential functional properties for these subclasses, we compared the phenotypes resulting from conditional deletion of Dgcr8 versus Dicer1 in post-mitotic neurons. The loss of Dicer1 resulted in an earlier lethality, more severe structural abnormalities, and increased apoptosis relative to that from Dgcr8 loss. Deep sequencing of small RNAs from the hippocampus and cortex of the conditional knockouts and control littermates identified multiple noncanonical microRNAs that were expressed at high levels in the brain relative to other tissues, including mirtrons and H/ACA snoRNA-derived small RNAs. In contrast, we found no evidence for endo-siRNAs in the brain. Taken together, our findings provide evidence for a diverse population of highly expressed noncanonical miRNAs that together are likely to play important functional roles in post-mitotic neurons.

Automated detection of amyloid-β-related cortical and subcortical signal changes in a transgenic model of Alzheimer's disease using high-field MRI

In vivo imaging of amyloid-β (Aβ) load as a biomarker of Alzheimer's disease (AD) would be of considerable clinical relevance for the early diagnosis and monitoring of treatment effects. Here, we investigated automated quantification of in vivo T2 relaxation time as a surrogate measure of plaque load in the brains of ten AβPP/PS1 transgenic mice (age 20 weeks) using in vivo MRI acquisitions on a 7T Bruker ClinScan magnet. AβPP/PS1 mice present with rapid-onset cerebral β-amyloidosis, and were compared with eight age-matched, wild-type control mice (C57Bl/6J) that do not develop Aβ-deposition in brain. Data were analyzed with a novel automated voxel-based analysis that allowed mapping the entire brain for significant signal changes. In AβPP/PS1 mice, we found a significant decrease in T2 relaxation times in the deeper neocortical layers, caudate-putamen, thalamus, hippocampus, and cerebellum compared to wildtype controls. These changes were in line with the histological distribution of cerebral Aβ plaques and activated microglia. Grey matter density did not differ between wild-type mice and AβPP/PS1 mice, consistent with a lack of neuronal loss in histological investigations. High-field MRI with automated mapping of T2 time changes may be a useful tool for the detection of plaque load in living transgenic animals, which may become relevant for the evaluation of amyloid lowering intervention effects in future studies.

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.

In vivo imaging biomarkers in mouse models of Alzheimer's disease: are we lost in translation or breaking through?

Identification of biomarkers of Alzheimer's Disease (AD) is a critical priority to efficiently diagnose the patients, to stage the progression of neurodegeneration in living subjects, and to assess the effects of disease-modifier treatments. This paper addresses the development and usefulness of preclinical neuroimaging biomarkers of AD. It is today possible to image in vivo the brain of small rodents at high resolution and to detect the occurrence of macroscopic/microscopic lesions in these species, as well as of functional alterations reminiscent of AD pathology. We will outline three different types of imaging biomarkers that can be used in AD mouse models: biomarkers with clear translational potential, biomarkers that can serve as in vivo readouts (in particular in the context of drug discovery) exclusively for preclinical research, and finally biomarkers that constitute new tools for fundamental research on AD physiopathogeny.

Regional cerebral glucose uptake in the 3xTG model of Alzheimer's disease highlights common regional vulnerability across AD mouse models

We have previously used fluorodeoxyglucose (FDG) autoradiography to detect the pattern of metabolic declines in two different transgenic mouse models of fibrillar beta-amyloid pathology in Alzheimer's disease (AD), including the PDAPP mouse, which overexpresses a mutant form of human APP, and the PSAPP mouse, which overexpresses mutant forms of the human APP and PS1 genes. In this study, we used the same approach to study a triple-transgenic (3xTG) model of AD, which overexpresses human APP, PS1 and tau mutations, and progressively develops amyloid plaques, neurofibrillary tangles, and synaptic dysfunction. Densitometric measurements from 55 brain regions were characterized and compared in 2, 12, and 18 month-old 3xTG and wildtype control mice (n = 12/group). By 18 months of age, the 3xTG mice had significant reductions in FDG uptake in every measured brain region, including cortical and subcortical gray matter, cerebellar and brainstem regions. However, regional differences in normalized FDG uptake were apparent in the 2- and 12-month-old 3xTG mice, in a brain network pattern reminiscent of our previous analyses in the other mouse models. This prominently included the posterior cingulate/retrosplenial cortex, as in each previously-analyzed model. Overall, our analyses highlight consistencies in brain glucose uptake abnormalities across multiple mouse models of amyloid-associated pathophysiology. These mouse brain regional changes are homologous to alterations seen in PET scans from human AD patients and could thus be useful biomarkers for early testing of novel interventions.

A lifespan MRI evaluation of ventricular enlargement in normal aging mice

Ventricular enlargement has been proposed as a structural biomarker for the progression of Alzheimer's disease (AD). This biomarker, established in human patients, needs to be translated to animals to facilitate drug development for the disease. However, ventricular enlargement is not exclusive to AD, since the ventricle size increases during normal aging. A longitudinal characterization of ventricular enlargement in normal aging in mice is therefore crucial before further evaluations of mouse models or neurodegenerative diseases associated to brain atrophy. To this end, ventricular enlargement in normal aging mice was characterized over the lifespan (i.e., 2 years). The results showed that the overall ventricle size increased with age, with the expansion beginning during the early life stages and continuing to old age. The reported data represent a biomarker benchmark for normal aging mice under unmodified conditions. This provides a foundation for evaluating the validity of AD mouse models or the effects of potential drugs. The considerable physiological ventricular enlargement during normal aging must be considered in related experiments.

Chronic 13-cis-retinoic acid administration disrupts network interactions between the raphe nuclei and the hippocampal system in young adult mice

Previously, we showed that chronic administration of 13-cis-retinoic acid (13-cis-RA) induces depression-related behaviors in mice and that 13-cis-RA alters components of the serotonergic system in vitro. Work by others has shown that 13-cis-RA reduces hippocampal neurogenesis in mice and orbitofrontal cortex metabolism in humans. In the current study, we measured cytochrome oxidase activity, a metabolic marker that reflects steady state neuronal energy demand, in various regions of the brain to determine the effects of 13-cis-RA on neuronal metabolic activity and network interactions between the raphe nuclei and the hippocampal system. Brain cytochrome oxidase activity in young adult male mice was analyzed following 6 weeks of daily 13-cis-RA (1 mg/kg) or vehicle injection and behavioral testing. Chronic 13-cis-RA administration significantly decreased cytochrome oxidase activity only in the inferior rostral linear nucleus of the raphe. However, covariance analysis of interregional correlations in cytochrome oxidase activity revealed that 13-cis-RA treatment caused a functional uncoupling between the dorsal raphe nuclei and the hippocampus. Furthermore, a path analysis indicated that a network comprising lateral habenula to dorsal raphe to hippocampus was effectively uncoupled in 13-cis-RA treated animals. Finally, cytochrome oxidase activity in the dentate gyrus of 13-cis-RA treated mice was inversely correlated with depression-related behavior. Taken together, these data show that 13-cis-RA alters raphe metabolism and disrupts functional connectivity between the raphe nuclei and the hippocampal formation, which may contribute to the observed increase in depression-related behaviors.

Overview on rodent models of Alzheimer's disease

In Alzheimer's disease (AD), characteristic lesions develop in brain regions that subserve cognitive functions, ultimately leading to dementia. There are now several lesioned or transgenic small-animal models of the disease that model select aspects of cognitive deficits and/or recapitulate many, but not all, of the characteristic pathologic lesions observed in AD. This overview describes the most common approaches used to model AD in rodents, highlights their utility, and discusses some of their deficiencies.

Coexisting cholinergic and parahippocampal degeneration: a key to memory loss in dementia and a challenge for transgenic models?

One century after Alzheimer's initial report, a variety of animal models of Alzheimer's disease (AD) are being used to mimic one or more pathological signs viewed as critical for the evolution of cognitive decline in dementia. Among the most common are, (a) traditional lesion models aimed at reproducing the degeneration of one of two key brain regions affected in AD, namely the cholinergic basal forebrain (CBF) and the transentorhinal region, and (b) transgenic mouse models aimed at reproducing AD histopathological hallmarks, namely amyloid plaques and neurofibrillary tangles. These models have provided valuable insights into the development and consequences of the pathology, but they have not consistently reproduced the severity of memory deficits exhibited in AD. The reasons for this lack of correspondence with the severity of expected deficits may include the limited replication of multiple neuropathology in potentially key brain regions. A recent lesion model in the rat found that severe memory impairment was obtained only when the two traditional lesions were combined together (i.e. conjoint CBF and entorhinal cortex lesions), indicative of a dramatic impact on cognitive function when there is coexisting, rather than isolated, damage in these two brain regions. It is proposed that combining AD transgenic mouse models with additional experimental damage to both the CBF and entorhinal regions might provide a unique opportunity to further understand the evolution of the disease and improve treatments of severe cognitive dysfunction in neurodegenerative dementias.

BACE1 gene deletion: Impact on behavioral function in a model of Alzheimer's disease

Accumulation of cerebral amyloid-beta (Abeta) has been implicated as a putative causal factor in the development of Alzheimer's disease (AD). Transgenic mice like the PDAPP line overexpress human mutant Amyloid Precursor Protein (hAPP) and recapitulate many features of AD, including amyloid neuropathology and cognitive deficits. Inhibition of the beta-site aspartyl cleaving enzyme (BACE1) enzyme responsible for the first proteolytic cleavage that ultimately generates Abeta has been proposed as a strategy for AD therapy. To assess the theoretical repercussions of beta-secretase activity reduction in an in vivo model of AD, BACE1(-/-) mice bred to the PDAPP line were examined in a series of behavioral tasks. Although BACE1 gene ablation abolished hAbeta accumulation, BACE1(-/-) mice had unexpected sensorimotor impairments, spatial memory deficits, and displayed seizures, phenotypes which were severe on the PDAPP background. These results suggest that while excess Abeta is functionally pathological, BACE1-mediated processing of APP and other substrates play a role in "normal" learning, memory and sensorimotor processes.

FDG autoradiography reveals developmental and pathological effects of mutant amyloid in PDAPP transgenic mice

Transgenic mouse models of Alzheimer's disease (AD) show some characteristic features of the disease, and we aim to further bridge the gap between studies of humans with AD, those at risk, and these murine models by providing shared markers of disease which could be used to track progression and assess future interventions. Brain imaging measurements may prove useful in this regard. We previously found that the homozygous PDAPP mouse model of AD showed significant declines in glucose uptake with age in posterior cingulate cortex (PCC), an area homologous to the human posterior cingulate, which shows significant declines in AD and in those at risk for AD. To further evaluate this potential biomarker and its correlation across age, we used fluorodeoxyglucose (FDG) autoradiography at two ages (2 and 12 months) in wildtype, heterozygous, and homozygous PDAPP mice. We found significant posterior cingulate fluorodeoxyglucose uptake declines again in homozygous PDAPP mice, but at both ages assessed. There was a strong effect of gene dose; homozygous mice showed larger and earlier effects. These results, in conjunction with our previous analyses, indicate a nonlinear progression stemming from synergistic effects of the overexpressed mutant gene, both developmental and pathological. The posterior cingulate is preferentially vulnerable to both effects of transgene in the PDAPP mouse, and both are independent of amyloid deposition.

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.

MRI of mouse models of neurological disorders

MRI has contributed to significant advances in the understanding of neurological diseases in humans. It has also been used to evaluate the spectrum of mouse models spanning from developmental abnormalities during embryogenesis, evaluation of transgenic and knockout models, through various neurological diseases such as stroke, tumors, degenerative and inflammatory diseases. The MRI techniques used clinically are technically more challenging in the mouse because of the size of the brain; however, mouse imaging provides researchers with the ability to explore cellular and molecular imaging that one day may translate into clinical practice. This article presents an overview of the use of MRI in mouse models of a variety of neurological disorders and a brief review of cellular imaging using magnetically tagged cells in the mouse central nervous system.

Linking brain imaging and genomics in the study of Alzheimer's disease and aging

My colleagues and I have been using positron emission tomography (PET) and magnetic resonance imaging (MRI) to detect and track the brain changes associated with Alzheimer's disease (AD) and normal brain aging in cognitively normal persons with two copies, one copy, and no copies of the apolipoprotein E (APOE) epsilon4 allele, a common AD susceptibility gene. In this review article, I consider how brain imaging techniques could be used to evaluate putative AD prevention therapies in cognitively normal APOE epsilon4 carriers and putative age-modifying therapies in cognitively normal APOE epsilon4 noncarriers, how they could help investigate the individual and aggregate effects of putative AD risk modifiers, and how they could help guide the investigation of a molecular mechanism associated with AD vulnerability and normal neurological aging. I suggest how high-resolution genome-wide genetic and transcriptomic studies could further help in the scientific understanding of AD, aging, and other common and genetically complex phenotypes, such as variation in normal human memory performance, and in the discovery and evaluation of promising treatments for these phenotypes. Finally, I illustrate the push-pull relationship between brain imaging, genomics research, and other neuroscientific research in the study of AD and aging.

Age- and transgene-related changes in regional cerebral metabolism in PSAPP mice

In parallel to imaging studies in humans with Alzheimer's disease (AD), we have mapped brain metabolic activity in transgenic mouse models of AD. Our aim in both is to provide new surrogate markers of progression to help clarify disease mechanisms and rapidly screen candidate therapeutics. Since previous findings of preferential reductions in posterior cingulate glucose metabolism may have been confounded by morphological abnormalities in previously studied "PDAPP" transgenic mice, we first assessed hippocampal and callosal anatomy in PSAPP (PS1xAPP) mice, another transgenic mouse model of AD, and found no major abnormalities. We then used fluorodeoxyglucose (FDG) autoradiography in older and younger PSAPP and wildtype mice to assess the functional state of 56 regions-of-interest across group, age and increasing amyloid load. Reductions in FDG uptake in aged transgenic mice, with significant interactions between group and age, were found in retrosplenial cingulate gyrus, found to be metabolically affected in persons affected by or at risk for AD, and in brain regions known to participate with retrosplenial cingulate in networks contributing to spatial learning deficits found in these animals. Like patients with AD, PSAPP mice have age-related metabolic reductions in posterior cingulate cortex, a finding that does not appear to be related to morphological abnormalities. If longitudinal studies support these progressive and preferential reductions in retrosplenial metabolism in PSAPP mice, these reductions could provide an indicator of disease progression, help bridge the gap between human and animal studies of AD, and aid in clarification of disease mechanisms and screening of promising treatments.

Nonprogressive transgene-related callosal and hippocampal changes in PDAPP mice

We have previously shown that homozygous PDAPP mice, a transgenic model of Alzheimer's-like amyloidosis, have abnormal corpus callosi and anterior hippocampi. Now, we investigated the extent to which these morphological abnormalities are correlated with mutant gene dose in a larger, independent, and substantially younger cohort. Homozygous and heterozygous PDAPP mice had significantly smaller callosal commissure length and anterior hippocampal area than controls. Reductions correlated with mutant APP gene dose, with homozygotes showing the greatest reduction, and were present at 2 months of age. These findings and previous work with APP knockouts suggest that PDAPP mice have impaired white matter development due to interference with native murine APP.

Associative and motor learning in 12-month-old transgenic APP+PS1 mice

Doubly transgenic 12-month-old amyloid precursor protein and presenilins 1 (APP+PS1) mice (n=14) and littermate control mice (n=17) were tested on eyeblink classical conditioning-a task impaired in humans with Alzheimer's disease (AD). Mice were also tested on a motor learning task (rotorod) and on sensory tasks (prepulse inhibition [PPI] and acoustic startle). Transgenic mice had impaired motor performance on rotorod. Overall, APP+PS1 mice performed similarly to controls on both 500ms delay and 500ms trace eyeblink conditioning as well as on prepulse inhibition (PPI) and acoustic startle. However, within the transgenic group, cortical amyloid burden correlated significantly with decreased trace eyeblink conditioning. Moreover, cortical amyloid burden and hippocampal microglia activation correlated significantly with decreased PPI. These data suggest that only those transgenic mice with the most severe amyloid pathology exhibited deficits in hippocampus-dependent tasks. Transgenic mouse models of amyloid deposition differ from Alzheimer patients not only by the absence of major neuronal loss, but also by the general absence of severe impairments in eyeblink conditioning, except for mice with the greatest amyloid pathology.

Axonal Transport and Alzheimer's Disease

In contrast to most eukaryotic cells, neurons possess long, highly branched processes called axons and dendrites. In large mammals, such as humans, some axons reach lengths of over 1 m. These lengths pose a major challenge to the movement of proteins, vesicles, and organelles between presynaptic sites and cell bodies. To overcome this challenge axons and dendrites rely upon specialized transport machinery consisting of cytoskeletal motor proteins generating directed movements along cytoskeletal tracks. Not only are these transport systems crucial to maintain neuronal viability and differentiation, but considerable experimental evidence suggests that failure of axonal transport may play a role in the development or progression of neurological diseases such as Alzheimer's disease.

Evaluation of white matter integrity in ex vivo brains of amyloid plaque-bearing APPsw transgenic mice using magnetic resonance diffusion tensor imaging

Magnetic resonance diffusion tensor imaging (DTI) was used to examine the integrity of midline white matter tracts in APPsw (Tg2576) transgenic mice, a mouse-model of cerebral amyloid deposition. Ex vivo DTI was performed on formalin-fixed brains from APPsw and age-matched transgene-negative control mice at the ages of 12, 15, and 17 months. The characteristics of water diffusion in six midline white matter tracts were quantified using four metrics: relative anisotropy (RA), mean diffusivity, axial diffusivity, and radial diffusivity. Two-way ANOVA analyses indicated a significant main effect of transgene on RA in the corpus callosum (CC) and ventral hippocampal commissure (VHC), due to small reductions (2-6%) in RA in APPsw mice relative to age-matched control mice. However, these reductions were not significant at any specific age group and were not progressive with increasing age. The other diffusion metrics exhibited no significant differences between APPsw and control mice in the CC and VHC, nor did any of the diffusion metrics exhibit significant differences between APPsw and control mice in other midline white matter tracts (anterior commissure, posterior commissure, fornix, and dorsal fornix). Overall, these results indicate that white matter integrity, as measured by ex vivo DTI, is predominately unaltered in formalin-fixed brains from amyloid plaque-bearing APPsw mice.

In vivo MRI and histological evaluation of brain atrophy in APP/PS1 transgenic mice

Regional cerebral atrophy was evaluated in APP/PS1 mice harboring mutated transgenes linked to familial Alzheimer's disease, using complementary methods. In vivo high resolution MRI was selected for measurements of brain atrophy and associated cerebrospinal fluid dilation; histological analysis was performed to reveal localized atrophies and to evaluate amyloid burden. Young APP/PS1 mice examined at a pre-amyloid stage (10 weeks) showed disruption in development (reduced intracranial and brain volumes). Comparison of young and old (24 months) mice, indicated that both APP/PS1 and control brains endure growth during adulthood. Aged APP/PS1 animals showed a moderate although significant global brain atrophy and a dilation of CSF space in posterior brain regions. The locus of this atrophy was identified in the midbrain area and not, as expected, at isocortical/hippocampal levels. Atrophy was also detected in fiber tracts. The severity of brain atrophy in old APP/PS1 mice was not correlated with the extent of cerebral amyloidosis. The relevance of current transgenic mouse models for the study of brain atrophy related to Alzheimer's disease is discussed.

Decreased adult hippocampal neurogenesis in the PDAPP mouse model of Alzheimer's disease

Abnormal subgranular zone (SGZ) neurogenesis is proposed to contribute to Alzheimer's disease (AD)-related decreases in hippocampal function. Our goal was to examine hippocampal neurogenesis in the PDAPP mouse, a model of AD with age-dependent accumulation of amyloid-beta(42) (Abeta(42))-containing plaques that is well studied with regard to AD therapies. A secondary goal was to determine whether altered neurogenesis in the PDAPP mouse is associated with abnormal maturation or number of mature cells. A tertiary goal was to provide insight into why hippocampal neurogenesis appears to be increased in AD post-mortem tissue and decreased in most AD mouse models. We report an age-dependent decrease in SGZ proliferation in homozygous PDAPP mice. At 1 year of age, PDAPP mice also had new dentate gyrus granule neurons with abnormal maturation and fewer dying cells relative to control mice. In contrast to decreased SGZ cell birth, PDAPP mice had increased birth of immature neurons in the outer portion of the granule cell layer (oGCL), providing insight into why some studies link AD with increased neurogenesis. However, these ectopic oGCL cells were still rare compared with SGZ proliferating cells, emphasizing that the primary characteristic of PDAPP mice is decreased neurogenesis. The decrease in SGZ neurogenesis was not associated with an age-dependent loss of dentate granule neurons. The altered neurogenesis in the PDAPP mouse may contribute to the age-related cognitive deficits reported in this model of AD and may be a useful adjunct target for assessing the impact of AD therapies.

Differences in regional brain atrophy in genetic forms of Alzheimer's disease

Multiple degenerative hallmarks characterize Alzheimer's disease: insoluble protein deposition, neuronal loss and cortical atrophy. Atrophy begins in the medial temporal lobe and becomes global by end stage. In a small proportion of cases, these tissue changes are caused by mutations in three known genes. These cases are affected earlier in life and have more abundant protein deposition, which may indicate greater tissue atrophy and degeneration. This issue remains unresolved. Grey matter atrophy in different cortical regions was determined in genetic cases of Alzheimer's disease (N = 13) and compared to sporadic cases (N = 13) and non-diseased controls (N = 23). Genetic mutations were found to influence the degree and regional pattern of atrophy. The majority of cases had greater medial temporal atrophy than sporadic disease, suggesting that abnormalities affecting Abeta metabolism selectively increase hippocampal degeneration. Cases with mutations in presenilin-1 demonstrated additional increased frontotemporal atrophy. This effect may be due to the influence of presenilin-1 on tau phosphorylation and metabolism. These differences may explain the earlier onset ages in these different forms of Alzheimer's disease.

Treatment with an amyloid-beta antibody ameliorates plaque load, learning deficits, and hippocampal long-term potentiation in a mouse model of Alzheimer's disease

PDAPP transgenic mice overexpress a mutant form of human amyloid precursor protein under control of the platelet-derived growth factor promoter in CNS neurons that causes early onset, familial Alzheimer's disease in humans. These mice, on a mixed genetic background, have been shown to have substantial learning impairments from early ages, as well as an age-dependent decline in learning ability that has been hypothesized to be caused by amyloid-beta (Abeta) accumulation. The goals of this study were to determine: (1) whether PDAPP mice on a pure C57BL/6 background develop more severe age-dependent learning deficits than wild-type mice; (2) if so, whether Abeta accumulation accounts for the excessive decline in learning ability; and (3) whether the learning deficits are reversible, even after significant Abeta deposition. At 4-6, 10-12, or 17-19 months of age, PDAPP and littermate wild-type mice on a C57BL/6 background were tested on a 5 week water maze protocol in which the location of the escape platform changed weekly, requiring the mice to repeatedly learn new information. PDAPP mice exhibited impaired spatial learning as early as 4 months (pre-Abeta deposition), and the performance of both wild-type and PDAPP mice declined with age. However, PDAPP mice exhibited significantly greater deterioration with age. Direct evidence for the role of Abeta accumulation in the age-related worsening in PDAPP mice was provided by the observation that systemic treatment over several weeks with the anti-Abeta antibody 10D5 reduced plaque deposition, increased plasma Abeta, improved hippocampal long-term potentiation, and improved behavioral performance in aged PDAPP mice with substantial Abeta burden.

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.

A Computational Positron Emission Tomography Simulation Model for Imaging ?-Amyloid in Mice

PURPOSE

We aimed to develop a computational simulation model for beta-amyloid (Abeta) positron emission tomography (PET) imaging.

PROCEDURES

Model parameters were set to reproduce levels of Abeta within the PDAPP mouse. Pharmacokinetic curves of virtual tracers were computed and a PET detector simulator was configured for a commercially available preclinical PET-imaging system.

RESULTS

We modeled the effects of Abeta therapy and tracer affinity on the ability to differentiate Abeta levels by PET. Varying affinity had a significant effect on the ability to quantitate Abeta. Further, PET tracers for Abeta monomers were more sensitive to the therapeutic reduction in Abeta levels than total brain amyloid. Following therapy, the decrease in total brain Abeta corresponded to the slow rate of change in total amyloid load as expected.

CONCLUSIONS

We have developed a first proof-of-concept Abeta-PET simulation model that will be a useful tool in the interpretation of preclinical Abeta imaging data and tracer development.

Overexpression of the human β-amyloid precursor protein downregulates cortistatin mRNA in PDAPP mice

We measured preprocortistatin mRNA expression in young and aged transgenic (Tg) mice overexpressing the human beta-amyloid precursor protein (hbetaAPP) under the platelet-derived growth factor-beta promoter. Our findings suggest that the significant increase in hippocampal cortistatin mRNA expression during normal aging is significantly attenuated in Tg mice at an age known to exhibit beta-amyloid protein (Abeta) deposition. These deficits in cortistatin expression may play a role in the deficits in hippocampal-dependent spatial learning and sleep/wake states previously demonstrated in aged Tg mice.

Regional cerebral blood volume reduction in transgenic mutant APP (V717F, K670N/M671L) mice

Recent advance in nuclear magnetic resonance (NMR) microimaging has enabled in vivo cerebral blood volume (CBV) mapping with high spatial resolution. Using an intravascular susceptibility contrast agent and T(2)-weighted magnetic resonance imaging (MRI) on a 9.4T NMR microimager, the regional CBV was measured in mice as the transverse relaxation increase induced by the contrast agent. CBV maps in an Alzheimer's disease mouse model at resting state were obtained and examined. Four-month-old male transgenic mutant APP (V717F, K670N/M671L) mice (N = 10) and littermate wild-type controls (N = 12) were used. Regional analysis of the multi-slice CBV maps revealed statistically significant CBV reductions among the APP mice in cerebral cortex (-9.29%, P = 0.0002), hippocampus (-4.22%, P = 0.02), and thalamus (-5.21%, P = 0.03), indicating an early change of microvasculature in these selected regions. No significant difference was found in olfactory bulb, pons, midbrain, superior colliculus, medulla, and cerebellum.

Regional brain cytochrome oxidase activity in beta-amyloid precursor protein transgenic mice with the Swedish mutation

Cytochrome oxidase activity was examined in a transgenic mouse model of Alzheimer's disease with overexpression of the 751 amino acid isoform of beta-amyloid precursor protein with the Swedish mutation under control of the murine thy-1 promoter. The neuritic plaques, abundantly localized in the hippocampus and anterior neocortical areas, showed a core devoid of enzymatic activity surrounded by higher cytochrome oxidase activity at the sites of the dystrophic neurites and activated glial cells. Quantitative measures, taken only in the healthy-appearing regional areas without neuritic plaques, were higher in numerous limbic and non-limbic regions of transgenic mice in comparison with controls. Enzymatic activity was higher in the dentate gyrus and CA2-CA3 region of the hippocampus, the anterior cingulate and primary visual cortex, two olfactory structures, the ventral part of the neostriatum, the parafascicularis nucleus of the thalamus, and the subthalamic nucleus. Brainstem regions anatomically related with altered forebrain regions were more heavily labeled as well, including the substantia nigra, the periaqueductal gray, the superior colliculus, the medial raphe, the locus coeruleus and the adjacent parabrachial nucleus, as well as the pontine nuclei, red nucleus, and trigeminal motor nucleus. Functional brain organization is discussed in the context of Alzheimer's disease. Although hypometabolism is generally observed in this pathology, the increased cytochrome oxidase activity obtained in these transgenic mice can be the result of a functional compensation on the surviving neurons, or of an early mitochondrial alteration related to increased oxidative damage.

A robust, efficient and flexible method for staining myelinated axons in blocks of brain tissue

Previous studies have demonstrated the utility of the gold chloride method for en bloc staining of a bisected brain in mice and rats. The present study explores several variations in the method, assesses its reliability, and extends the limits of its application. We conclude that the method is very efficient, highly robust, sufficiently accurate for most purposes, and adaptable to many morphometric measures. We obtained acceptable staining of commissures in every brain, despite a wide variety of fixation methods. One-half could be stained 24 h after the brain was extracted and the other half could be stained months later. When staining failed because of an exhausted solution, the brain could be stained successfully in fresh solution. Relatively small changes were found in the sizes of commissures several weeks after initial fixation or staining. A half brain stained to reveal the mid-sagittal section could then be sectioned coronally and stained again in either gold chloride for myelin or cresyl violet for Nissl substance. Uncertainty, arising from pixelation of digitized images was far less than errors arising from human judgments about the histological limits of major commissures. Useful data for morphometric analysis were obtained by scanning the surface of a gold chloride stained block of brain with an inexpensive flatbed scanner.

Antibody therapy for Alzheimer's disease

The economic, social and emotional impact of Alzheimer's dementia is increasing dramatically as greater numbers live to advanced ages. The dearth of effective therapies has led to innovative approaches to treat the disease. This review summarizes the rationale, progress and setbacks regarding the use of antibody-based therapies to treat Alzheimer's disease and discusses future directions for this approach in Alzheimer's and other disorders.

Impaired eyeblink conditioning and decreased hippocampal volume in PDAPP V717F mice

We examined heterozygous transgenic (Tg) mice that overexpress V717F amyloid precursor protein (APP) for delay eyeblink conditioning (EBC) and hippocampal volume with magnetic resonance imaging (MRI). Platelet-derived APP mice were significantly impaired on EBC relative to wild type (WT) litter-mate controls. T2-weighted spin echo images (62.5 x 125 x 500 microm) of the same mice were acquired under anesthesia using a 9.4T magnet. Tg mice had hippocampal to brain volume ratios that were significantly smaller than WT controls (31% smaller in the rostral dorsal hippocampus, 13-22% smaller among equal dorsal-ventral thirds of a caudal section). These results indicate that overexpression of APP or beta amyloid profoundly affects learning and memory and hippocampal volume. The results also indicate that eyeblink conditioning and quantitative MRI in mice may be useful assays to follow the progression of disease-related changes, and to test the effectiveness of potential therapeutics against Alzheimer's disease.

Loss of medial septal modulation of dentate gyrus physiology in young mice overexpressing human beta-amyloid precursor protein

Mice overexpressing the human mutant beta-amyloid precursor protein (hbetaAPP; PDAPP mice) show deficits in hippocampal-dependent spatial learning and hippocampal short- and long-term plasticity at ages preceding Abeta plaque deposition. We determined whether young PDAPP mice also exhibit alterations in septohippocampal function in vivo, which plays an important role in cognitive function. Electrical stimulation of the medial septum significantly increased neuronal excitability and reduced paired-pulse facilitation in the dentate gyrus. Medial septal-induced facilitation of dentate neuronal excitability was reduced in PDAPP mice. The inhibitory effects of medial septum stimulation on dentate paired-pulse facilitation were also attenuated in PDAPP mice. Young mice overexpressing hbetaAPP exhibit early abnormalities in neural circuits implicated in cognitive function that may play an important role in the more profound deficits observed in aged PDAPP mice.

Does my mouse have Alzheimer's disease?

Small animal models that manifest many of the characteristic neuropathological and behavioral features of Alzheimer's disease (AD) have been developed and have proven of great value for studying the pathogenesis of this disorder at the molecular, cellular and behavioral levels. The great progress made in our understanding of the genetic factors that either cause or contribute to the risk of developing AD has prompted many laboratories to create transgenic (tg) mice that overexpress specific genes which cause familial forms of the disease. Several of these tg mice display neuropathological and behavioral features of AD including amyloid beta-peptide (A beta) and amyloid deposits, neuritic plaques, gliosis, synaptic alterations and signs of neurodegeneration as well as memory impairment. Despite these similarities, important differences in neuropathology and behavior between these tg mouse models and AD have also been observed, and to date no perfect animal model has emerged. Moreover, ascertaining which elements of the neuropathological and behavioral phenotype of these various strains of tg mice are relevant to that observed in AD continues to be a challenge. Here we provide a critical review of the AD-like neuropathology and behavioral phenotypes of several well-known and utilized tg mice that express human APP transgenes.

Effects of image resolution on autoradiographic measurements of posterior cingulate activity in PDAPP mice: implications for functional brain imaging studies of transgenic mouse models of Alzheimer's Disease

Fluorodeoxyglucosepositron emission tomography (PET) studies find that persons with Alzheimer's disease have preferential reductions in posterior cingulate activity. Using fluorodeoxyglucose autoradiography, we found that transgenic mice overexpressing a mutant form of the human amyloid precursor protein have preferentially reduced activity in the same region, providing a potential brain imaging indicator of Alzheimer's disease in these animals. In this study, we considered the feasibility of using in vivo imaging techniques, such as PET, to detect this reduction despite their limitations in spatial resolution. Autoradiographic measurements of posterior cingulate activity were remeasured in the previously studied PDAPP transgenic and littermate control mice after the images were filtered to lower spatial resolutions. We continued to detect significantly lower cingulate activity in the transgenic mice when the images were blurred to 0.50 mm, failed to detect significantly abnormal activity when the images were blurred to 0.75 mm, and, indeed, found significantly higher activity when the images were blurred to 1.0 mm. Reversal in direction of the abnormality appears attributable to a previously observed truncation in the corpus callosum in PDAPP mice. With the possible exception of future in vivo imaging techniques that have a spatial resolution greater than or equal to 0.50 mm and high sensitivity, noninvasive functional brain imaging techniques like PET may not be suitable for detecting declines in regional activity in PDAPP mice. It remains possible that these imaging techniques will prove useful in transgenic mouse lines that do not exhibit the same morphological abnormalities in neighboring white matter regions.