Mouse Model Of Cerebral Amyloidosis Research Articles

Reduction of β-amyloid and γ-secretase by calorie restriction in female Tg2576 mice

Research indicates that female risk of developing Alzheimer's disease (AD) is greater than that of males. Moderate reduction of calorie intake, known as calorie restriction (CR), reduces pathology in AD mouse models and is a potentially translatable prevention measure for individuals at-risk for AD, as well as an important tool for understanding how the brain endogenously attenuates age-related pathology. Whether sex influences the response to CR remains unknown. In this study, we assessed the effect of CR on beta-amyloid peptide (Aβ) pathology and hippocampal CA1 neuron specific gene expression in the Tg2576 mouse model of cerebral amyloidosis. Relative to ad libitum (AL) feeding, CR feeding significantly reduced hippocampal Aβ burden in 15-month-old female, but not age-matched male, Tg2576 mice. Sustained CR also significantly reduced expression of presenilin enhancer 2 (Psenen) and presenilin 1, components of the γ-secretase complex, in Tg2576 females. These results indicate that long-term CR significantly reduces age-dependent female Tg2576 Aβ pathology, which is likely to involve CR-mediated reductions in γ-secretase–dependent amyloid precursor protein (APP) metabolism.

Early Alterations in Functional Connectivity and White Matter Structure in a Transgenic Mouse Model of Cerebral Amyloidosis

Impairment of brain functional connectivity (FC) is thought to be an early event occurring in diseases with cerebral amyloidosis, such as Alzheimer's disease. Regions sustaining altered functional networks have been shown to colocalize with regions marked with amyloid plaques burden suggesting a strong link between FC and amyloidosis. Whether the decline in FC precedes amyloid plaque deposition or is a consequence thereof is currently unknown. The sequence of events during early stages of the disease is difficult to capture in humans due to the difficulties in providing an early diagnosis and also in view of the heterogeneity among patients. Transgenic mouse lines overexpressing amyloid precursor proteins develop cerebral amyloidosis and constitute an attractive model system for studying the relationship between plaque and functional changes. In this study, ArcAβ transgenic and wild-type mice were imaged using resting-state fMRI methods across their life-span in a cross-sectional design to analyze changes in FC in relation to the pathology. Transgenic mice show compromised development of FC during the first months of postnatal life compared with wild-type animals, resulting in functional impairments that affect in particular the sensory-motor cortex already in preplaque stage. These functional alterations were accompanied by structural changes as reflected by reduced fractional anisotropy values, as derived from diffusion tensor imaging. Our results suggest cerebral amyloidosis in mice is preceded by impairment of neuronal networks and white matter structures. FC analysis in mice is an attractive tool for studying the implications of impaired neuronal networks in models of cerebral amyloid pathology.

Methylene Blue Modulates β-Secretase, Reverses Cerebral Amyloidosis, and Improves Cognition in Transgenic Mice

Amyloid precursor protein (APP) proteolysis is required for production of amyloid-β (Aβ) peptides that comprise β-amyloid plaques in the brains of patients with Alzheimer disease (AD). Here, we tested whether the experimental agent methylene blue (MB), used for treatment of methemoglobinemia, might improve AD-like pathology and behavioral deficits. We orally administered MB to the aged transgenic PSAPP mouse model of cerebral amyloidosis and evaluated cognitive function and cerebral amyloid pathology. Beginning at 15 months of age, animals were gavaged with MB (3 mg/kg) or vehicle once daily for 3 months. MB treatment significantly prevented transgene-associated behavioral impairment, including hyperactivity, decreased object recognition, and defective spatial working and reference memory, but it did not alter nontransgenic mouse behavior. Moreover, brain parenchymal and cerebral vascular β-amyloid deposits as well as levels of various Aβ species, including oligomers, were mitigated in MB-treated PSAPP mice. These effects occurred with inhibition of amyloidogenic APP proteolysis. Specifically, β-carboxyl-terminal APP fragment and β-site APP cleaving enzyme 1 protein expression and activity were attenuated. Additionally, treatment of Chinese hamster ovary cells overexpressing human wild-type APP with MB significantly decreased Aβ production and amyloidogenic APP proteolysis. These results underscore the potential for oral MB treatment against AD-related cerebral amyloidosis by modulating the amyloidogenic pathway.

MyD88 Is Dispensable for Cerebral Amyloidosis and Neuroinflammation in APP/PS1 Transgenic Mice

Activated microglia are associated with amyloid plaques in transgenic mouse models of cerebral amyloidosis and in human Alzheimer disease; yet, their implication in Alzheimer disease pathogenesis remains unclear. It has been suggested that microglia play dual roles depending on the context of activation,contributing negatively to disease pathogenesis by secreting proinflammatory innate cytokines or performing a beneficial role via phagocytosis of amyloid beta (Aβ) deposits. Toll-like receptors, most of which signal through the adaptor protein myeloid differentiation factor 88 (MyD88), have been suggested as candidate Aβ innate pattern recognition receptors. It was recently reported that MyD88 deficiency reduced brain amyloid pathology and microglial activation. To assess a putative role of MyD88 in cerebral amyloidosis and glial activation in APPswe/PS1ΔE9 (APP/PS1) mice, we crossed MyD88-deficient (MyD88(-/-)) mice with APP/PS1 mice, interbred first filial offspring, and studied APP/PS1 MyD88(+/+), APP/PS1 MyD88(+/-), and APP/PS1 MyD88(-/-) cohorts. Biochemical analysis of detergent-soluble and detergent-insoluble Aβ1-40 or Aβ1-42 in brain homogenates did not reveal significant between-group differences. Furthermore, no significant differences were observed on amyloid plaque load or soluble fibrillar Aβ by quantitative immunohistochemical analysis. In addition, neither activated microglia nor astrocytes differed among the three groups. These data suggest that MyD88 signaling is dispensable for Aβ-induced glial activation and does not significantly affect the nature or extent of cerebral β-amyloidosis in APP/PS1 mice.

Oridonin ameliorates neuropathological changes and behavioural deficits in a mouse model of cerebral amyloidosis

Alzheimer’s disease (AD) is the most common form of neurodegeneration and the major cause of dementia. This multifactorial disorder is clinically defined by progressive behavioural and cognitive deficits, and neuropathologically characterized by β-amyloid aggregation, hyperphosphorylated tau and neuroinflammation. Oridonin, a diterpenoid isolated from Chinese herb Rabdosia rubescens, has multiple biological properties, especially anti-inflammatory and neuroregulatory activities. Potential therapeutic effects of Oridonin were investigated in an animal model of cerebral amyloidosis for AD, transgenic APP/PS1 mice. Oridonin was suspended in carboxymethylcellulose or loaded with a nanostructured emulsion, and was orally administrated or injected. Before, during and following the experimental treatments, behavioural tests were performed with these transgenic mice and their naive littermates. Following relatively short-term treatments of 10 days, brain tissue of mice were removed for immunohistochemical assays. The results indicate that both oral treatment and injection of Oridonin significantly attenuated β-amyloid deposition, plaque-associated APP expression and microglial activation in brain of transgenic mice. Furthermore, injection of Oridonin-nanoemulsion ameliorated deficits in nesting, an important affiliative behaviour, and in social interaction. Additional in vitro studies indicated that Oridonin effectively attenuated inflammatory reaction of macrophage and microglial cell lines. Our results suggest that Oridonin might be considered a promising therapeutic option for human AD or other neurodegenerative diseases.

Longitudinal Assessment of Amyloid Pathology in Transgenic ArcAβ Mice Using Multi-Parametric Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) can be used to monitor pathological changes in Alzheimer's disease (AD). The objective of this longitudinal study was to assess the effects of progressive amyloid-related pathology on multiple MRI parameters in transgenic arcAβ mice, a mouse model of cerebral amyloidosis. Diffusion-weighted imaging (DWI), T1-mapping and quantitative susceptibility mapping (QSM), a novel MRI based technique, were applied to monitor structural alterations and changes in tissue composition imposed by the pathology over time. Vascular function and integrity was studied by assessing blood-brain barrier integrity with dynamic contrast-enhanced MRI and cerebral microbleed (CMB) load with susceptibility weighted imaging and QSM. A linear mixed effects model was built for each MRI parameter to incorporate effects within and between groups (i.e. genotype) and to account for changes unrelated to the disease pathology. Linear mixed effects modelling revealed a strong association of all investigated MRI parameters with age. DWI and QSM in addition revealed differences between arcAβ and wt mice over time. CMBs became apparent in arcAβ mice with 9 month of age; and the CMB load reflected disease stage. This study demonstrates the benefits of linear mixed effects modelling of longitudinal imaging data. Moreover, the diagnostic utility of QSM and assessment of CMB load should be exploited further in studies of AD.

AZ-4217: A High Potency BACE Inhibitor Displaying Acute Central Efficacy in Different In Vivo Models and Reduced Amyloid Deposition in Tg2576 Mice

Aβ, the product of APP (amyloid precursor protein), has been implicated in the pathophysiology of Alzheimer's disease (AD). β-Site APP cleaving enzyme1 (BACE1) is the enzyme initiating the processing of the APP to Aβ peptides. Small molecule BACE1 inhibitors are expected to decrease Aβ-peptide generation and thereby reduce amyloid plaque formation in the brain, a neuropathological hallmark of AD. BACE1 inhibition thus addresses a key mechanism in AD and its potential as a therapeutic target is currently being addressed in clinical studies. Here, we report the discovery and the pharmacokinetic and pharmacodynamic properties of BACE1 inhibitor AZ-4217, a high potency compound (IC50 160 pM in human SH-SY5Y cells) with an excellent in vivo efficacy. Central efficacy of BACE1 inhibition was observed after a single dose in C57BL/6 mice, guinea pigs, and in an APP transgenic mouse model of cerebral amyloidosis (Tg2576). Furthermore, we demonstrate that in a 1 month treatment paradigm BACE1 inhibition of Aβ production does lower amyloid deposition in 12-month-old Tg2576 mice. These results strongly support BACE1 inhibition as concretely impacting amyloid deposition and therefore potentially an important approach for therapeutic intervention in AD.

Ferulic acid is a nutraceutical β-secretase modulator that improves behavioral impairment and alzheimer-like pathology in transgenic mice.

Amyloid precursor protein (APP) proteolysis is required for production of amyloid-β (Aβ) peptides that comprise β-amyloid plaques in brains of Alzheimer’s disease (AD) patients. Recent AD therapeutic interest has been directed toward a group of anti-amyloidogenic compounds extracted from plants. We orally administered the brain penetrant, small molecule phenolic compound ferulic acid (FA) to the transgenic PSAPP mouse model of cerebral amyloidosis (bearing mutant human APP and presenilin-1 transgenes) and evaluated behavioral impairment and AD-like pathology. Oral FA treatment for 6 months reversed transgene-associated behavioral deficits including defective: hyperactivity, object recognition, and spatial working and reference memory, but did not alter wild-type mouse behavior. Furthermore, brain parenchymal and cerebral vascular β-amyloid deposits as well as abundance of various Aβ species including oligomers were decreased in FA-treated PSAPP mice. These effects occurred with decreased cleavage of the β-carboxyl-terminal APP fragment, reduced β-site APP cleaving enzyme 1 protein stability and activity, attenuated neuroinflammation, and stabilized oxidative stress. As in vitro validation, we treated well-characterized mutant human APP-overexpressing murine neuron-like cells with FA and found significantly decreased Aβ production and reduced amyloidogenic APP proteolysis. Collectively, these results highlight that FA is a β-secretase modulator with therapeutic potential against AD.

Multiple Low-Dose Infusions of Human Umbilical Cord Blood Cells Improve Cognitive Impairments and Reduce Amyloid-β-Associated Neuropathology in Alzheimer Mice

Alzheimer's disease (AD) is the most common progressive age-related dementia in the elderly and the fourth major cause of disability and mortality in that population. The disease is pathologically characterized by deposition of β-amyloid plaques neurofibrillary tangles in the brain. Current strategies for the treatment of AD are symptomatic only. As such, they are less than efficacious in terms of significantly slowing or halting the underlying pathophysiological progression of the disease. Modulation by cell therapy may be new promising disease-modifying therapy. Recently, we showed reduction in amyloid-β (Aβ) levels/β-amyloid plaques and associated astrocytosis following low-dose infusions of mononuclear human umbilical cord blood cells (HUCBCs). Our current study extended our previous findings by examining cognition via (1) the rotarod test, (2) a 2-day version of the radial-arm water maze test, and (3) a subsequent observation in an open pool platform test to characterize the effects of monthly peripheral HUCBC infusion (1×10(6) cells/μL) into the transgenic PSAPP mouse model of cerebral amyloidosis (bearing mutant human APP and presenilin-1 transgenes) from 6 to 12 months of age. We show that HUCBC therapy correlates with decreased (1) cognitive impairment, (2) Aβ levels/β-amyloid plaques, (3) amyloidogenic APP processing, and (4) reactive microgliosis after a treatment of 6 or 10 months. As such, this report lays the groundwork for an HUCBC therapy as potentially novel alternative to oppose AD at the disease-modifying level.

Tannic Acid Is a Natural β-Secretase Inhibitor That Prevents Cognitive Impairment and Mitigates Alzheimer-like Pathology in Transgenic Mice

Amyloid precursor protein (APP) proteolysis is essential for production of amyloid-β (Aβ) peptides that form β-amyloid plaques in brains of Alzheimer disease (AD) patients. Recent focus has been directed toward a group of naturally occurring anti-amyloidogenic polyphenols known as flavonoids. We orally administered the flavonoid tannic acid (TA) to the transgenic PSAPP mouse model of cerebral amyloidosis (bearing mutant human APP and presenilin-1 transgenes) and evaluated cognitive function and AD-like pathology. Consumption of TA for 6 months prevented transgene-associated behavioral impairment including hyperactivity, decreased object recognition, and defective spatial reference memory, but did not alter nontransgenic mouse behavior. Accordingly, brain parenchymal and cerebral vascular β-amyloid deposits and abundance of various Aβ species including oligomers were mitigated in TA-treated PSAPP mice. These effects occurred with decreased cleavage of the β-carboxyl-terminal APP fragment, lowered soluble APP-β production, reduced β-site APP cleaving enzyme 1 protein stability and activity, and attenuated neuroinflammation. As in vitro validation, we treated well characterized mutant human APP-overexpressing murine neuron-like cells with TA and found significantly reduced Aβ production associated with less amyloidogenic APP proteolysis. Taken together, these results raise the possibility that dietary supplementation with TA may be prophylactic for AD by inhibiting β-secretase activity and neuroinflammation and thereby mitigating AD pathology.

Detection of Cerebral Microbleeds with Quantitative Susceptibility Mapping in the Arcabeta Mouse Model of Cerebral Amyloidosis

Cerebral microbleeds (CMBs) are findings in patients with neurological disorders such as cerebral amyloid angiopathy and Alzheimer's disease, and are indicative of an underlying vascular pathology. A diagnosis of CMBs requires an imaging method that is capable of detecting iron-containing lesions with high sensitivity and spatial accuracy in the presence of potentially confounding tissue abnormalities. In this study, we investigated the feasibility of quantitative magnetic susceptibility mapping (QSM), a novel technique based on gradient-recalled echo (GRE) phase data, for the detection of CMBs in the arcAβ mouse, a mouse model of cerebral amyloidosis. Quantitative susceptibility maps were generated from phase data acquired with a high-resolution T(2)(*)-weighted GRE sequence at 9.4 T. We examined the influence of different regularization parameters on susceptibility computation; a proper adjustment of the regularization parameter minimizes streaking artifacts and preserves fine structures. In the present study, it is shown that QSM provides increased detection sensitivity of CMBs and improved contrast when compared with GRE magnitude imaging. Furthermore, QSM corrects for the blooming effect observed in magnitude and phase images and depicts both the localization and spatial extent of CMBs with high accuracy. Therefore, QSM may become an important tool for diagnosing CMBs in neurological diseases.

The role of immune cells in mouse models of cerebral amyloidosis

The role of immune cells in mouse models of cerebral amyloidosis

Vascular response to acetazolamide decreases as a function of age in the arcAβ mouse model of cerebral amyloidosis

Deposition of β-amyloid along cerebral vessels is found in most patients suffering from Alzheimer's disease. The effects of cerebral amyloid angiopathy (CAA) on the function of cerebral blood vessels were analyzed applying cerebral blood volume (CBV)-based fMRI to transgenic arcAβ mice. In a cortical brain region of interest (ROI), displaying high CAA, arcAβ mice older than 16 months showed reduced response to the vasodilatory substance acetazolamide compared to age-matched wild-type animals, both with regard to rate (vascular reactivity) and extent of vasodilation (maximal vasodilation). In a subcortical ROI, displaying little CAA, no genotype-specific decrease was observed, but maximal vasodilation decreased with age in arcAβ and wild-types. These findings indicate that vascular β-amyloid deposits reduce the capacity of cerebral blood vessels to dilate upon demand, supporting the hypothesis that vascular β-amyloid contributes to hypoperfusion and neurological deficits observed in AD and CAA. High diagnostic accuracy of the combined readouts in detecting vascular dysfunction in arcAβ mice was found.

Independent Effects of Intra- and Extracellular Aβ on Learning-Related Gene Expression

Alzheimer's disease is characterized by numerous pathological abnormalities, including amyloid beta (Abeta) deposition in the brain parenchyma and vasculature. In addition, intracellular Abeta accumulation may affect neuronal viability and function. In this study, we evaluated the effects of different forms of Abeta on cognitive decline by analyzing the behavioral induction of the learning-related gene Arc/Arg3.1 in three different transgenic mouse models of cerebral amyloidosis (APPPS1, APPDutch, and APP23). Following a controlled spatial exploration paradigm, reductions in both the number of Arc-activated neurons and the levels of Arc mRNA were seen in the neocortices of depositing mice from all transgenic lines (deficits ranging from 14 to 26%), indicating an impairment in neuronal encoding and network activation. Young APPDutch and APP23 mice exhibited intracellular, granular Abeta staining that was most prominent in the large pyramidal cells of cortical layer V; these animals also had reductions in levels of Arc. In the dentate gyrus, striking reductions (up to 58% in aged APPPS1 mice) in the number of Arc-activated cells were found. Single-cell analyses revealed both the proximity to fibrillar amyloid in aged mice, and the transient presence of intracellular granular Abeta in young mice, as independent factors that contribute to reduced Arc levels. These results provide evidence that two independent Abeta pathologies converge in their impact on cognitive function in Alzheimer's disease.

Cerebral and Peripheral Amyloid Phagocytes— an Old Liaison with a New Twist

In this month's issue of Nature Medicine, Town et al. suggest that peripheral macrophages invading the brain reduce cerebral amyloidosis and thus may play a key role in the pathogenesis of Alzheimer's disease (AD). This observation intensifies the longstanding controversy of whether mononuclear cells such as macrophages and/or microglial cells are beneficial or detrimental in AD.

P1-110: Microglia ablation does not alter plaque formation and maintenance in a mouse model of cerebral amyloidosis

P1-110: Microglia ablation does not alter plaque formation and maintenance in a mouse model of cerebral amyloidosis

Neurogenesis and Alterations of Neural Stem Cells in Mouse Models of Cerebral Amyloidosis

The hippocampus in Alzheimer's disease is burdened with amyloid plaques and is one of the few locations where neurogenesis continues throughout adult life. To evaluate the impact of amyloid-beta deposition on neural stem cells, hippocampal neurogenesis was assessed using bromodeoxyuridine incorporation and doublecortin staining in two amyloid precursor protein (APP) transgenic mouse models. In 5-month-old APP23 mice prior to amyloid deposition, neurogenesis showed no robust difference relative to wild-type control mice, but 25-month-old amyloid-depositing APP23 mice showed significant increases in neurogenesis compared to controls. In contrast, 8-month-old amyloid-depositing APPPS1 mice revealed decreases in neurogenesis compared to controls. To study whether alterations in neurogenesis are the result of amyloid-induced changes at the level of neural stem cells, APPPS1 mice were crossed with mice expressing green fluorescence protein (GFP) under a central nervous system-specific nestin promoter. Eight-month-old nestin-GFP x APPPS1 mice exhibited decreases in quiescent nestin-positive astrocyte-like stem cells, while transient amplifying progenitor cells did not change in number. Strikingly, both astrocyte-like and transient-amplifying progenitor cells revealed an aberrant morphologic reaction toward congophilic amyloid-deposits. A similar reaction toward the amyloid was no longer observed in doublecortin-positive immature neurons. Results provide evidence for a disruption of neural stem cell biology in an amyloidogenic environment and support findings that neurogenesis is differently affected among various transgenic mouse models of Alzheimer's disease.

Impaired angiogenesis in a transgenic mouse model of cerebral amyloidosis

Aβ peptides are naturally occurring peptides, which are thought to play a key role in the pathophysiology of Alzheimer’s disease (AD). In AD cases, levels of soluble and insoluble Aβ peptides increase in the brain as well as in the cerebrovasculature, a phenomenon that does not occur in extra-cranial vessels. There are frequently anomalies in the cerebrovasculature in AD, and despite increases in several pro-angiogenic factors in AD brain, evidence for increased vascularity is lacking; in fact there is evidence to the contrary. It has also been recently shown that Aβ peptides may have profound anti-angiogenic effects in vitro and in vivo. We therefore investigated whether there is evidence for altered angiogenesis in the vasculature in a transgenic mouse model of Aβ amyloidosis (Tg APPsw line 2576). In vitro, the formation of capillary-like structures on a reconstituted extracellular matrix by endothelial cells isolated from Tg APPsw is impaired. Ex vivo, the sprouting of new capillaries from arterial explants (over expressing Aβ) isolated from 9-month-old Tg APPsw is reduced compared to arterial explants isolated from control littermates. In addition, Tg APPsw mice show a reduction in vascular density in the cortex and hippocampus compared to control littermates. Altogether, our data suggest that the over expression of APPsw in the vasculature may oppose angiogenesis.

Novel aspects of accumulation dynamics and Aβ composition in transgenic models of AD

A homogeneous time-resolved fluorescence immunoassay for detection of β-amyloid (Aβ) peptides has been adapted for quantification of Aβ(40) and Aβ(42) accumulation in brains of APP695SWE transgenic mice. These over-express human βAPP swe, β-amyloid precursor protein (β-APP) containing the K670N/M671L ‘Swedish’ familial Alzheimer’s disease (FAD) mutation. Both peptides start to accumulate in this line from about 260 to 280 days of age. Co-expression of a human presenilin-1 (PS1) transgene containing the A246E FAD mutation accelerates deposition and also favors—at least initially—accumulation of Aβ(42) so that the Aβ(2):Aβ(40) ratio of peptides from 7- to 12-month-old APP695SWE × PS1A246E animals is significantly elevated above that observed throughout the lifetime of APP695SWE mice. These findings, supported by parallel immunohistochemical staining and surface-enhanced laser desorption/ionization time-of-flight (SELDI-TOF) mass spectrometry data, offer important longitudinal characterization of two mouse models of cerebral amyloidosis. Application of the same extraction and quantitation procedures to samples of temporal cortex from AD sufferers indicates however that Aβ(40) is only a minor component of β-amyloid in humans.

Cholinergic changes in the APP23 transgenic mouse model of cerebral amyloidosis.

Alzheimer's Disease (AD) is a neurodegenerative disorder that is characterized by extracellular deposits of amyloid-beta peptide (Abeta) and a severe depletion of the cholinergic system, although the relationship between these two events is poorly understood. In the neocortex, there is a loss of cholinergic fibers and receptors and a decrease of both choline acetyltransferase (ChAT) and acetylcholinesterase enzyme activities. The nucleus basalis of Meynert (NBM), which provides the major cholinergic input to the neocortex, undergoes profound neuron loss in AD. In the present study, we have examined the cholinergic alterations in amyloid precursor protein transgenic mice (APP23), a mouse model of cerebral beta-amyloidosis. In aged APP23 mice, our results reveal modest decreases in cortical cholinergic enzyme activity compared with age-matched wild-type mice. Total cholinergic fiber length was more severely affected, with 29 and 35% decreases in the neocortex of aged APP23 mice compared with age-matched wild-type mice and young transgenic mice, respectively. However, there was no loss of cholinergic basal forebrain neurons in these aged APP23 mice, suggesting that the cortical cholinergic deficit in APP23 mice is locally induced by the deposition of amyloid and is not caused by a loss of cholinergic basal forebrain neurons. To study the impact of cholinergic basal forebrain degeneration on cortical amyloid deposition, we performed unilateral NBM lesions in adult APP23 mice. Three to 8 months after lesioning, a 38% reduction in ChAT activity and significant cholinergic fiber loss were observed in the ipsilateral frontal cortex. There was a 19% decrease in Abeta levels of the ipsilateral compared with contralateral frontal cortex with no change in the ratio of Abeta40 to Abeta42. We conclude that the severe cholinergic deficit in AD is caused by both the loss of cholinergic basal forebrain neurons and locally by cerebral amyloidosis in the neocortex. Moreover, our results suggest that disruption of the basal cholinergic forebrain system does not promote cerebral amyloidosis in APP23 transgenic mice.