Altered morphology and 3D architecture of brain vasculature in a mouse model for Alzheimer's disease

Monitoring blood flow alterations in the Tg2576 mouse model of Alzheimer's disease by in vivo magnetic resonance angiography at 17.6 T

Many neurodegenerative diseases including Alzheimer's disease are linked to abnormalities in the vascular system. In AD, the deposition of amyloid β (Aβ) peptide in the cerebral vessel walls, known as cerebral amyloid angiopathy (CAA) is frequently observed, leading to blood flow abnormalities. Visualization of the changes in vascular structure is important for early diagnosis and treatment. Blood vessels can be imaged non-invasively by magnetic resonance angiography (MRA). In this study we optimized high resolution MRA at 17.6 T to longitudinally monitor morphological changes in cerebral arteries in a Tg2576 mouse model, a widely used model of AD. Our results at 17.6 T show that MRA significantly benefits from the ultra-high magnetic field strength especially to visualize smaller vessels. Visual and quantitative analysis of MRA results revealed severe blood flow defects in large and medium sized arteries in Tg2576 mice. In particular blood flow defects were observed in the middle cerebral artery (MCA) and in the anterior communicating artery (AComA) in Tg2576 mice. Histological data show that Aβ levels in the vessel wall may be responsible for impaired cerebral blood flow, thereby contributing to the early progression of AD. To our knowledge this is the first ultra-high field MRA study monitoring blood flow alterations longitudinally in living Tg2576 mice, consequently providing a powerful tool to test new therapeutic intervention related to CAA in a mouse model of AD.

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.

Vascular β-amyloid and early astrocyte alterations impair cerebrovascular function and cerebral metabolism in transgenic arcAβ mice

Cerebrovascular lesions related to congophilic amyloid angiopathy (CAA) often accompany deposition of β-amyloid (Aβ) in Alzheimer's disease (AD), leading to disturbed cerebral blood flow and cognitive dysfunction, posing the question how cerebrovascular pathology contributes to the pathology of AD. To address this question, we characterised the morphology, biochemistry and functionality of brain blood vessels in transgenic arctic β-amyloid (arcAβ) mice expressing human amyloid precursor protein (APP) with both the familial AD-causing Swedish and Arctic mutations; these mice are characterised by strong CAA pathology. Mice were analysed at early, mid and late-stage pathology. Expression of the glucose transporter GLUT1 at the blood-brain barrier (BBB) was significantly decreased and paralleled by impaired in vivo blood-to-brain glucose transport and reduced cerebral lactate release during neuronal activation from mid-stage pathology onwards. Reductions in astrocytic GLUT1 and lactate transporters, as well as retraction of astrocyte endfeet and swelling consistent with neurovascular uncoupling, preceded wide-spread β-amyloid plaque pathology. We show that CAA at later disease stages is accompanied by severe morphological alterations of brain blood vessels including stenoses, BBB leakages and the loss of vascular smooth muscle cells (SMCs). Together, our data establish that cerebrovascular and astrocytic pathology are paralleled by impaired cerebral metabolism in arcAβ mice, and that astrocyte alterations occur already at premature stages of pathology, suggesting that astrocyte dysfunction can contribute to early behavioural and cognitive impairments seen in these mice.

Cerebral autoregulation in Alzheimer's disease

Cerebral autoregulation aims to stabilize blood flow to the brain during variations in perfusion pressure, thus protecting the brain against the risks of low or high systemic blood pressure. This vital mechanism is severely impaired in the transgenic mouse model of Alzheimer's disease (AD) that abundantly produces amyloid-β peptide β(1-42). These observations have been extrapolated to human AD, wherein impairment of autoregulation could have important implications for the clinical management and prevention of AD. Research on cerebral autoregulation in human AD, however, has only recently become available. Contrary to the animal models, preliminary studies suggest that cerebral autoregulation is preserved in patients with AD. Further research is urgently needed to elucidate this discrepancy in the current literature, given the accumulating evidence that implicates cerebrovascular pathology in AD.

Estimating neural signal dynamics in the human brain

Although brain imaging methods are highly effective for localizing the effects of neural activation throughout the human brain in terms of the blood oxygenation level dependent (BOLD) response, there is currently no way to estimate the underlying neural signal dynamics in generating the BOLD response in each local activation region (except for processes slower than the BOLD time course). Knowledge of the neural signal is critical if spatial mapping is to progress to the analysis of dynamic information flow through the cortical networks as the brain performs its tasks. We introduce an analytic approach that provides a new level of conceptualization and specificity in the study of brain processing by non-invasive methods. This technique allows us to use brain imaging methods to determine the dynamics of local neural population responses to their native temporal resolution throughout the human brain, with relatively narrow confidence intervals on many response properties. The ability to characterize local neural dynamics in the human brain represents a significant enhancement of brain imaging capabilities, with potential applications ranging from general cognitive studies to assessment of neuropathologies.

Analysis of time reduction methods for magnetic resonance elastography of the brain

Magnetic resonance elastography (MRE) uses a phase-contrast MRI technique to image shear wave propagation in tissue followed by the mathematical inversion of the equations of motion governing tissue mechanics to noninvasively image tissue stiffness. This work investigates the impact of various MR sampling strategies designed to reduce acquisition times on the accuracy of MRE inversions. The results indicate that brain MRE data can be significantly truncated while maintaining a mean global stiffness error less than 10%. The results also indicate that brain MRE data can be collected in as few as eight lines of k-space. This degree of data truncation is possible due to the relatively low spatial frequency content and low amplitude of the shear waves observed during brain MRE exams and will facilitate the design of rapid brain MRE protocols for future clinical investigations.

Neurovascular dysfunction, inflammation and endothelial activation: implications for the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is an age-related disorder characterized by progressive cognitive decline and dementia. Alzheimer's disease is an increasingly prevalent disease with 5.3 million people in the United States currently affected. This number is a 10 percent increase from previous estimates and is projected to sharply increase to 8 million by 2030; it is the sixth-leading cause of death. In the United States the direct and indirect costs of Alzheimer's and other dementias to Medicare, Medicaid and businesses amount to more than $172 billion each year. Despite intense research efforts, effective disease-modifying therapies for this devastating disease remain elusive. At present, the few agents that are FDA-approved for the treatment of AD have demonstrated only modest effects in modifying clinical symptoms for relatively short periods and none has shown a clear effect on disease progression. New therapeutic approaches are desperately needed. Although the idea that vascular defects are present in AD and may be important in disease pathogenesis was suggested over 25 years ago, little work has focused on an active role for cerebrovascular mechanisms in the pathogenesis of AD. Nevertheless, increasing literature supports a vascular-neuronal axis in AD as shared risk factors for both AD and atherosclerotic cardiovascular disease implicate vascular mechanisms in the development and/or progression of AD. Also, chronic inflammation is closely associated with cardiovascular disease, as well as a broad spectrum of neurodegenerative diseases of aging including AD. In this review we summarize data regarding, cardiovascular risk factors and vascular abnormalities, neuro- and vascular-inflammation, and brain endothelial dysfunction in AD. We conclude that the endothelial interface, a highly synthetic bioreactor that produces a large number of soluble factors, is functionally altered in AD and contributes to a noxious CNS milieu by releasing inflammatory and neurotoxic species.

Brain nitric oxide inactivation is governed by the vasculature

The mechanisms underlying nitric oxide ((•)NO) synthesis and inactivation in the brain are essential determinants of (•)NO neuroactivity. Although (•)NO production is well characterized, the pathways of inactivation in vivo remain largely unknown. Here, we characterize the kinetics and the major mechanism of (•)NO inactivation in the rat brain cortex and hippocampus in vivo by measuring locally applied (•)NO with carbon-fiber microelectrodes (CFMs) and ceramic-based microelectrode arrays (MEAs). An apparent first-order clearance was observed in both brain regions, with decay rate constants (k) of (•)NO signals of 0.67 to 0.84 per second, significantly higher than the k obtained in agarose gel (0.099 per second), used as a (•)NO diffusion-control medium. (•)NO half-life in vivo, estimated by mathematical modeling, was 0.42 to 0.75 s. Experiments using MEAs support that the (•)NO diffusion radius is heterogeneous and related to local metabolic activity and vascular density. After global ischemia, k decreased to control values of diffusion in gel, but during anoxia, k decreased only 21%. Additionally, k in brain slices was threefold to fivefold lower than that in vivo, and hemorrhagic shock induced a 53% decrease in k. Overall, the results support that (•)NO scavenging by circulating erythrocytes constitutes the major (•)NO-inactivation pathway in the brain.

Noninvasive magnetic resonance imaging detection of cerebral amyloid angiopathy-related microvascular alterations using superparamagnetic iron oxide particles in APP transgenic mouse models of Alzheimer's disease: application to passive Abeta immunotherapy

Cerebral amyloid angiopathy (CAA) is a common feature of Alzheimer's disease (AD). More advanced stages are accompanied by microhemorrhages and vasculitis. Peripheral blood-borne macrophages are intimately linked to cerebrovascular pathology coincident with AD. Magnetic resonance imaging (MRI) was used to noninvasively study microvascular lesions in amyloid precursor protein transgenic mouse AD models. Foci of signal attenuation were detected in cortical and thalamic brain regions of aged APP23 mice. Their strength and number was considerably enhanced by intravenous administration of iron oxide nanoparticles, which are taken up by macrophages through absorptive endocytosis, 24 h before image acquisition. The number of cortical sites displaying signal attenuation increased with age. Histology at these sites demonstrated the presence of iron-containing macrophages in the vicinity of CAA-affected blood vessels. A fraction of the sites additionally showed thickened vessel walls and vasculitis. Consistent with the visualization of CAA-associated lesions, MRI detected a much smaller number of attenuated signal sites in APP23xPS45 mice, for which a strong presenilin mutation caused a shift toward amyloid β(42), thus reducing vascular amyloid. Similar results were obtained with APP24 and APP51 mice, which develop significantly less CAA and microvascular pathology than APP23. In a longitudinal study, we noninvasively demonstrated the reinforced formation of microvascular pathology during passive amyloid β immunotherapy of APP23 mice. Histology confirmed that foci of signal attenuation reflected an increase in CAA-related lesions. Our data demonstrate that MRI has the sensitivity to noninvasively monitor the development of vascular pathology and its possible enhancement by amyloid β immunotherapy in transgenic mice modeling AD.

Spatial frequency domain imaging of intrinsic optical property contrast in a mouse model of Alzheimer's disease

Extensive changes in neural tissue structure and function accompanying Alzheimer's disease (AD) suggest that intrinsic signal optical imaging can provide new contrast mechanisms and insight for assessing AD appearance and progression. In this work, we report the development of a wide-field spatial frequency domain imaging (SFDI) method for non-contact, quantitative in vivo optical imaging of brain tissue composition and function in a triple transgenic mouse AD model (3xTg). SFDI was used to generate optical absorption and scattering maps at up to 17 wavelengths from 650 to 970 nm in 20-month-old 3xTg mice (n = 4) and age-matched controls (n = 6). Wavelength-dependent optical properties were used to form images of tissue hemoglobin (oxy-, deoxy-, and total), oxygen saturation, and water. Significant baseline contrast was observed with 13-26% higher average scattering values and elevated water content (52 ± 2% vs. 31 ± 1%); reduced total tissue hemoglobin content (127 ± 9 μM vs. 174 ± 6 μM); and lower tissue oxygen saturation (57 ± 2% vs. 69 ± 3%) in AD vs. control mice. Oxygen inhalation challenges (100% oxygen) resulted in increased levels of tissue oxy-hemoglobin (ctO(2)Hb) and commensurate reductions in deoxy-hemoglobin (ctHHb), with ~60-70% slower response times and ~7 μM vs. ~14 μM overall changes for 3xTg vs. controls, respectively. Our results show that SFDI is capable of revealing quantitative functional contrast in an AD model and may be a useful method for studying dynamic alterations in AD neural tissue composition and physiology.

Reproducibility and variance of a stimulation-induced hemodynamic response in barrel cortex of awake behaving mice

The present work evaluated the reproducibility and variance of the cerebral blood flow (CBF) response to natural whisker stimulation in the barrel cortex of awake behaving mice. The animal was placed on an air float ball that allowed the animal to walk, while the head of the animal was fixed in a custom-made stereotactic apparatus. Dynamic CBF changes in the barrel cortex and animal locomotion were simultaneously monitored with laser-Doppler flowmetry (LDF) and an optical motion sensor that detected the rotation distance of the ball, respectively. Whisker stimulation-induced CBF measured under daytime and nighttime conditions showed consistent responses (24% and 23% of the pre-stimulus baseline, respectively), whereas the amount of locomotion was 1.4 times higher during nighttime relative to daytime. Repeated longitudinal experiments over 7 days showed a reproducible, evoked CBF (13-26% relative to the baseline among 7 animals). The mean of the variance coefficient (i.e., standard deviation divided by mean) across multiple days was 0.11 and 0.75 for evoked CBF and locomotion, respectively. These results showed reproducible and reliable measurements of longitudinal CBF response in behaving mice regardless of day-to-day variations in locomotion. Furthermore, we confirmed that the CBF response to whisker stimulation was well localized and reproducible, measured with laser speckle imaging under awake condition. The results further show the capability of long-term hemodynamic imaging in normal and disease-model mice, which is of particular importance for understanding the longitudinal changes and plasticity of neurovascular coupling and behavioral performances such as during growth, development and aging.

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.

Morphological study on microvasculature of left ventricular wall in infant and adult yaks

Observations on the microvasculature in the left ventricular wall of infant and adult yaks under light and scanning electron microscope (SEM) were presented. Moreover, the diameter of different microvasculature and the density of the capillaries in three layers of the ventricular myocardium were measured using Image Pro-Plus 5.0. The results showed that the average luminal diameter of arterioles and precapillary arterioles in adult yak's hearts were, in most cases, larger than those in infant yaks. On the contrary, the diameters of the capillary in infant yak's hearts were larger than those in adult yaks. The density of capillary in the myocardium of adult yak's heart had significantly higher values (P<0.01) than those in infant yaks. Arterioles of yak's hearts were characterized by the bark-like structure and the impressions of endothelial cell nuclei, and it always gave rise to capillary after three to four grades of embranchment. The outer surface of capillaries cast in infant yak's hearts was smooth, and no constrictions were found. This was different from adult yak that always had some constrictions. The capillary anastomosis of "H" and "Y" usually existed in the myocardium of both adult and infant yaks; however, those in infant yaks were not typical as in adult yaks in their shape. The peculiar arrangement of the venules in infant yak was a "baggy" or "bulgy" arrangement, while in the adult yak, they had a root-like pattern. Our findings suggest that the patterns of microvasculature in yak's heart could be propitious to adapt better in their environment following their increase of age.

Impaired orthotopic glioma growth and vascularization in transgenic mouse models of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia among the aging population and is characterized pathologically by the progressive intracerebral accumulation of beta-amyloid (Abeta) peptides and neurofibrillary tangles. The level of proangiogenic growth factors and inflammatory mediators with proangiogenic activity is known to be elevated in AD brains which has led to the supposition that the cerebrovasculature of AD patients is in a proangiogenic state. However, angiogenesis depends on the balance between proangiogenic and antiangiogenic factors and the brains of AD patients also show an accumulation of endostatin and Abeta peptides which have been shown to be antiangiogenic. To determine whether angiogenesis is compromised in the brains of two transgenic mouse models of AD overproducing Abeta peptides (Tg APPsw and Tg PS1/APPsw mice), we assessed the growth and vascularization of orthotopically implanted murine gliomas since they require a high degree of angiogenesis to sustain their growth. Our data reveal that intracranial tumor growth and angiogenesis is significantly reduced in Tg APPsw and Tg PS1/APPsw mice compared with their wild-type littermates. In addition, we show that Abeta inhibits the angiogenesis stimulated by glioma cells when cocultured with human brain microvascular cells on a Matrigel layer. Altogether our data suggest that the brain of transgenic mouse models of AD does not constitute a favorable environment to support neoangiogenesis and may explain why vascular insults synergistically precipitate the cognitive presentation of AD.

An amyloid-notch hypothesis for Alzheimer's disease

For more than 20 years, the amyloid hypothesis has provided an important framework for Alzheimer's disease (AD) research, yet after 50,000 papers, the nonpathological function of beta-amyloid (Aβ) remains enigmatic. This mystery is compounded by an absence of gross abnormalities in amyloid precursor protein (APP)-deficient mice and zebrafish even though APP has been highly conserved throughout vertebrate evolution. Here, the author hypothesizes that vertebrate cells express APP and release Aβ as part of a mechanism to optimize blood vessel density with the metabolite removal needs of local tissue neighborhoods. High-gain feedback of Aβ production at the rate-limiting γ-secretase step reduces Aβ production and Notch activation. Notch inhibition causes endothelial cells to adopt a tip cell morphology that induces more highly branched blood vessels. In vivo, γ-secretase inhibitors block Notch signaling and induce dense capillary networks that are similar to those in the brains of AD patients and mice. Notch inhibition could also contribute to synapse loss by reducing EphB2 receptor expression. EphB receptors are critical for the maintenance of dendritic spine morphology, and deficiencies result in immature spines that lack synaptic activity. This revised amyloid-Notch hypothesis may also explain the disappointing results of recent clinical trials with γ-secretase inhibitors.

Comparative gene expression analysis in mouse models for multiple sclerosis, Alzheimer's disease and stroke for identifying commonly regulated and disease-specific gene changes

The brain responds to injury and infection by activating innate defense and tissue repair mechanisms. Working upon the hypothesis that the brain defense response involves common genes and pathways across diverse pathologies, we analysed global gene expression in brain from mouse models representing three major central nervous system disorders, cerebral stroke, multiple sclerosis and Alzheimer's disease compared to normal brain using DNA microarray expression profiling. A comparison of dysregulated genes across disease models revealed common genes and pathways including key components of estrogen and TGF-beta signaling pathways that have been associated with neuroprotection as well as a neurodegeneration mediator, TRPM7. Further, for each disease model, we discovered collections of differentially expressed genes that provide novel insight into the individual pathology and its associated mechanisms. Our data provide a resource for exploring the complex molecular mechanisms that underlie brain neurodegeneration and a new approach for identifying generic and disease-specific targets for therapy.

Tenomodulin gene and obesity-related phenotypes

Different cells of adipose tissue secrete compounds which regulate various biological processes. Changes in body weight, body composition, and amount of fat mass can alter the secretory profile and function of adipose tissue. Comparison of adipose tissue mRNA expression profiles before versus after weight loss or between obese and lean subjects has promoted the identification of novel adipokines. Weight loss decreases the expression of the tenomodulin (TNMD) mRNA in the adipose tissue, and the expression level is strongly correlated with body mass index. TNMD (locus Xq22) is expressed in both adipocyte and stromal vascular fraction of adipose tissue. Tenomodulin inhibits angiogenesis, but its specific function in adipose tissue is still unknown. We have reported modest association between TNMD sequence variation and different obesity-related phenotypes, including anthropometric measurements, inflammation, glucose and lipid metabolism, and age-related macular degeneration. In this review, the potential mechanisms that could link TNMD with the pathogenesis of obesity and related disorders are discussed.

Are omega-3 fatty acids options for prevention and treatment of cognitive decline and dementia?

PURPOSE OF REVIEW

To report recent data on the potential role of omega-3 fatty acids (n-3 FA) found in oily fish, especially docosahexaenoic acid (DHA), to prevent and treat cognitive decline and Alzheimer's disease.

RECENT FINDINGS

Observational studies still provide conflicting results, in which the majority indicate beneficial effects on cognition, both when assessed as a continuous variable or as incident dementia, mainly Alzheimer's disease. Experimental studies have demonstrated potentially ameliorating effects of eicosapentaenoic acid (EPA) and DHA on amyloid fragment formation, signal transduction including upregulation of the apolipoprotein receptor SorLA, as well as on angiogenesis. The role of EPA and DHA metabolites on Alzheimer's disease pathology is under investigation. Recently, three randomized intervention studies, with duration up to 6 months have been reported. In contrast to a small study from Taiwan, no positive overall effects were reported from the Swedish OmegAD Study or from a Dutch study, although post hoc analyses indicate that selected individuals with mild forms of Alzheimer's disease or cognitive decline may respond to treatment.

SUMMARY

No firm conclusions can be drawn. Based on epidemiological data, fish including oily fish could be advised as part of a balanced diet for public health purpose, although the evidence for better cognition is only fairly consistent. It is unlikely that n-3 FA will emerge as a treatment option in general for improving cognitive function in patients with Alzheimer's disease. n-3 FA, especially DHA, may turn out as an adjuvant therapy in selected cases. Further long-term intervention studies on individuals with mild cognitive reductions are awaited.

Anti-Tumoral Activity of a Short Decapeptide Fragment of the Alzheimer's Abeta Peptide

The inhibition of angiogenesis is regarded as a promising avenue for cancer treatment. Although some antiangiogenic compounds are in the process of development and testing, these often prove ineffective in vivo, therefore the search for new inhibitors is critical. We have recently identified a ten amino acid fragment of the Alzheimer Abeta peptide that is anti-angiogenic both in vitro and in vivo. In the present study, we investigated the antitumoral potential of this decapeptide using human MCF-7 breast carcinoma xenografts nude mice. We observed that this decapeptide was able to suppress MCF-7 tumor growth more potently than the antiestrogen tamoxifen. Inhibition of tumor vascularization as determined by PECAM-1 immunostaining and decreased tumor cell proliferation as determined by Ki67 immunostaining were observed following treatment with the Abeta fragment. In vitro, this peptide had no direct impact on MCF-7 tumor cell proliferation and survival suggesting that the inhibition of tumor growth and tumor cell proliferation observed in vivo is related to the antiangiogenic activity of the peptide. Taken together these data suggest that this short Abeta derivative peptide may constitute a new antitumoral agent.

Altered cerebral hemodynamics in early Alzheimer disease: a pilot study using transcranial Doppler

Cerebrovascular disease may contribute to the development and progression of Alzheimer's disease (AD). This study investigated whether impairments in cerebral hemodynamics can be detected in early-stage AD. Nine patients with mild AD and eight cognitively normal controls matched for age underwent brain magnetic resonance imaging and neuropsychological evaluation, followed by assessment of steady-state cerebral blood flow velocity (CBFV, transcranial Doppler), blood pressure (BP, Finapres), and cerebrovascular resistance index (BP/CBFV). Cerebral hemodynamics were quantified using spectral and transfer function analysis of BP and CBFV in rest, during standing up after squat, and during repeated squat-stand maneuvers. Compared to controls, AD patients had lower CBFV and higher cerebrovascular resistance index, unexplained by brain atrophy. Low-frequency variability of BP was enhanced, suggesting impaired arterial baroreflex function. However, CBFV variability was reduced despite enhanced BP variability, and dynamic cerebral autoregulation was not impaired. In conclusion, despite a distinct pattern of altered cerebral hemodynamics, AD patients may have normal autoregulation. However, the challenges for autoregulation in AD are higher, as our data show enhanced BP fluctuations. Increased cerebral vasoconstriction or reduced vasomotion also may attenuate CBFV variability.

Age effects on the regulation of adult hippocampal neurogenesis by physical activity and environmental enrichment in the APP23 mouse model of Alzheimer disease

An active lifestyle is to some degree protective against Alzheimer's disease (AD), but the biological basis for this benefit is still far from clear. We hypothesize that physical and cognitive activity increase a reserve for plasticity by increasing adult neurogenesis in the hippocampal dentate gyrus (DG). We thus assessed how age affects the response to activity in the murine APP23 model of AD compared with wild type (WT) controls and studied the effects of physical exercise (RUN) and environmental enrichment (ENR) in comparison with standard housing (CTR) at two different ages (6 months and 18 months) and in both genotypes. At 18 months, both activity paradigms reduced the hippocampal human Abeta1-42/Abeta1-40 ratio when compared with CTR, despite a stable plaque load in the hippocampus. At this age, both RUN and ENR increased the number of newborn granule cells in the DG of APP23 mice when compared with CTR, whereas the levels of regulation were equivalent to those in WT mice under the same housing conditions. At 6 months, however, neurogenesis in ENR but not RUN mice responded like the WT. Quantifying the number of cells at the doublecortin-positive stage in relation to the number of cells on postmitotic stages we found that ENR overproportionally increased the number of the DCX-positive "late" progenitor cells, indicative of an increased potential to recruit even more new neurons. In summary, the biological substrates for activity-dependent regulation of adult hippocampal neurogenesis were preserved in the APP23 mice. We thus propose that in this model, ENR even more than RUN might contribute to a "neurogenic reserve" despite a stable plaque load and that age affects the outcome of an interaction based on "activity."

Branching patterns for arterioles and venules of the human cerebral cortex

Branching patterns of microvascular networks influence vascular resistance and allow control of peripheral flow distribution. The aim of this paper was to analyze these branching patterns in human cerebral cortex. Digital three-dimensional images of the microvascular network were obtained from thick sections of India ink-injected human brain by confocal laser microscopy covering a large zone of secondary cortex. A novel segmentation method was used to extract the skeletons of 228 vascular trees (152 arterioles and 76 venules) and measure the diameter at every vertex. The branching patterns (area ratios and angles of bifurcations) of nearly 10,000 bifurcations of cortical vascular trees were analyzed, establishing their statistical properties and structural variations as a function of the vessel nature (arterioles versus venules), the parent vessel topological order or the bifurcation type. We also describe their connectivity and discuss the relevance of the assumed optimal design of vascular branching to account for the complex nature of microvascular architecture. The functional implications of some of these structural variations are considered. The branching patterns established from a large database of a human organ contributes to a better understanding of the bifurcation design and provides an essential reference both for diagnosis and for a future large reconstruction of cerebral microvascular network.

Beta-amyloid, blood vessels, and brain function

Cerebrovascular disease and Alzheimer disease are common diseases of aging and frequently coexist in the same brain. Accumulating evidence suggests that the presence of brain infarction, including silent infarction, influences the course of Alzheimer disease. Conversely, there is evidence that beta-amyloid can impair blood vessel function. Vascular beta-amyloid deposition, also known as cerebral amyloid angiopathy, is associated with vascular dysfunction in animal and human studies. Alzheimer disease is associated with morphological changes in capillary networks, and soluble beta-amyloid produces abnormal vascular responses to physiological and pharmacological stimuli. In this review, we discuss current evidence linking beta-amyloid metabolism with vascular function and morphological changes in animals and humans.

Evidence of angiogenic vessels in Alzheimer's disease

Alterations in the blood brain barrier and brain vasculature may be involved in neurodegeneration and neuroinflammation. We sought to determine if vascular remodeling characterized by angiogenic vessels or increased vascular density, occurred in pathologically confirmed Alzheimer's disease (AD) postmortem human brain tissues. We examined brains of deceased, older catholic clergy from the Religious Order Study, a longitudinal clinical-pathological study of aging and AD. The hippocampus, midfrontal cortex, substantia nigra, globus pallidus and locus ceruleus were examined for integrin alphavbeta3 immunoreactivity, a marker of angiogenesis, and vascular densities. Activated microglia cell counts were also performed. All areas except the globus pallidus exhibited elevated alphavbeta3 immunoreactivity in AD cases compared with controls. Only in the hippocampus did the ongoing angiogenesis result in increased vascular density compared with controls. Vascular density was correlated with Abeta load in the hippocampus and alphavbeta3 reactivity was correlated with neurofibrillary tangles in the midfrontal cortex and in the substantia nigra. These data indicate that ongoing angiogenesis is present in brain regions affected by AD pathology and may be related to tissue injury.

Cerebral blood volume in Alzheimer's disease and correlation with tissue structural integrity

A vascular component is increasingly recognized as important in Alzheimer's disease (AD). We measured cerebral blood volume (CBV) in patients with probable AD or Mild Cognitive Impairment (MCI) and in elderly non-demented subjects using a recently developed Vascular-Space-Occupancy (VASO) MRI technique. While both gray and white matters were examined, significant CBV deficit regions were primarily located in white matter, specifically in frontal and parietal lobes, in which CBV was reduced by 20% in the AD/MCI group. The regions with CBV deficit also showed reduced tissue structural integrity as indicated by increased apparent diffusion coefficients, whereas in regions without CBV deficits no such correlation was found. Subjects with lower CBV tended to have more white matter lesions in FLAIR MRI images and showed slower psychomotor speed. These data suggest that the vascular contribution in AD is primarily localized to frontal/parietal white matter and is associated with brain tissue integrity.

Soluble amyloid-beta peptides potently disrupt hippocampal synaptic plasticity in the absence of cerebrovascular dysfunction in vivo

Long before the onset of clinical Alzheimer's disease non-fibrillar, soluble assembly states of amyloid-beta (Abeta) peptides are believed to cause cognitive problems by disrupting synaptic function in the absence of significant neurodegeneration. Since many of the risk factors for Alzheimer's disease are vascular, impairment of cerebral blood flow by soluble Abeta has been proposed to be critical in triggering these early changes. However, it is not known if soluble Abeta can affect cerebrovascular function at the concentrations required to cause inhibition of synaptic plasticity mechanisms believed to underlie the early cognitive deficits of Alzheimer's disease. Here we developed a new method to simultaneously assess the ability of soluble Abeta to impair plasticity at synapses and to affect resting and activity-dependent local blood flow in the rat hippocampus in vivo. Intracerebroventricular injection of soluble synthetic Abeta(40) dimers rapidly inhibited plasticity of excitatory synaptic transmission at doses (10-42 pmol) comparable to natural Abeta, but failed to affect vascular function measured using laser-Doppler flowmetry (LDF). Like wild-type Abeta(40), the more vasculotropic Abeta produced by people with familial hemorrhagic stroke of the Dutch type (Abeta(40)E22Q), impaired hippocampal plasticity without causing a significant change in local blood flow. Furthermore, neither resting nor activation-evoked hippocampal perfusion was affected by soluble Abeta(42), even at a concentration that markedly (25%) reduced baseline synaptic transmission. These findings demonstrate that the putative synaptotoxic soluble Abeta species of early Alzheimer's disease cause synaptic dysfunction in the absence of detectible changes in local blood flow. This strongly indicates that early cognitive deficits can be caused by soluble Abeta independently of deleterious effects on cerebrovascular dynamics.

Alzheimer's disease, cerebrovascular dysfunction and the benefits of exercise: from vessels to neurons

Exercise training promotes extensive cardiovascular changes and adaptive mechanisms in both the peripheral and cerebral vasculature, such as improved organ blood flow, induction of antioxidant pathways, and enhanced angiogenesis and vascular regeneration. Clinical studies have demonstrated a reduction of morbidity and mortality from cardiovascular disease among exercising individuals. However, evidence from recent large clinical trials also suggests a substantial reduction of dementia risk - particularly regarding Alzheimer's disease (AD) - with regular exercise. Enhanced neurogenesis and improved synaptic plasticity have been implicated in this beneficial effect. However, recent research has revealed that vascular and specifically endothelial dysfunction is essentially involved in the disease process and profoundly aggravates underlying neurodegeneration. Moreover, vascular risk factors (VRFs) are probably determinants of incidence and course of AD. In this review, we emphasize the interconnection between AD and VRFs and the impact of cerebrovascular and endothelial dysfunction on AD pathophysiology. Furthermore, we describe the molecular mechanisms of the beneficial effects of exercise on the vasculature such as activation of the vascular nitric oxide (NO)/endothelial NO synthase (eNOS) pathway, upregulation of antioxidant enzymes, and angiogenesis. Finally, recent prospective clinical studies dealing with the effect of exercise on the risk of incident AD are briefly reviewed. We conclude that, next to upholding neuronal plasticity, regular exercise may counteract AD pathophysiology by building a vascular reserve.