Selective cholinergic denervation, independent from oxidative stress, in a mouse model of Alzheimer’s disease

Past, present, and future of serotonin-targeting therapeutics for Alzheimer's disease: Perspectives from DNA methylation

With population aging, Alzheimer's disease (AD) is becoming increasingly prevalent, causing great health and economic burdens worldwide. Despite decades of research, there are still no effective disease-modifying treatments for AD, highlighting the urgent need for more in-depth understanding of the disease-causing mechanisms. The brain serotonin (5-HT) neurotransmission system undergoes structural and functional changes in aging and AD, which contributes to cognitive decline and comorbid mood disturbances. This review discusses the critical involvement of the brain 5-HT system in aging and AD. Existing findings on the changes in projection fiber innervation and receptor/transporter expression in AD are reviewed. Preclinical and clinical progress on the development of 5-HT-modulating drugs for AD and the obstacles faced by these development efforts are discussed. Epigenetic control of the brain 5-HT system and the potential of modulating 5-HT transmission via DNA methylation are also examined.

Rodent Models of Alzheimer's Disease: Past Misconceptions and Future Prospects

Alzheimer's disease (AD) is a progressive neurodegenerative disease with no effective treatments, not least due to the lack of authentic animal models. Typically, rodent models recapitulate the effects but not causes of AD, such as cholinergic neuron loss: lesioning of cholinergic neurons mimics the cognitive decline reminiscent of AD but not its neuropathology. Alternative models rely on the overexpression of genes associated with familial AD, such as amyloid precursor protein, or have genetically amplified expression of mutant tau. Yet transgenic rodent models poorly replicate the neuropathogenesis and protein overexpression patterns of sporadic AD. Seeding rodents with amyloid or tau facilitates the formation of these pathologies but cannot account for their initial accumulation. Intracerebral infusion of proinflammatory agents offer an alternative model, but these fail to replicate the cause of AD. A novel model is therefore needed, perhaps similar to those used for Parkinson's disease, namely adult wildtype rodents with neuron-specific (dopaminergic) lesions within the same vulnerable brainstem nuclei, 'the isodendritic core', which are the first to degenerate in AD. Site-selective targeting of these nuclei in adult rodents may recapitulate the initial neurodegenerative processes in AD to faithfully mimic its pathogenesis and progression, ultimately leading to presymptomatic biomarkers and preventative therapies.

Progressive Mechanical and Structural Changes in Anterior Cerebral Arteries with Alzheimer's Disease

Alzheimer disease (AD) is a neurodegenerative disease and the main cause for dementia. The irreversible neurodegeneration leads to a gradual loss of brain function characterized predominantly by memory loss. Cerebrovascular changes are common neuropathologic findings in aged subjects with dementia. Cerebrovascular integrity is critical for proper metabolism and perfusion of the brain, as cerebrovascular remodeling may render the brain more susceptible to pulse pressure and may be associated with poorer cognitive performance and greater risk of cerebrovascular events. The objective of this study is to provide understanding of cerebrovascular remodeling with AD progression. A total of 28 brain donor participants with human anterior cerebral artery (ACA) from controls and pathologically diagnosed AD groups (early - Braak stages I-II; intermediate - Braak stages III-IV; and advanced - Braak stages V-VI) were included in this study. Mechanical testing, histology, advanced optical imaging, and mass spectrometry were performed to study the progressive structural and functional changes of ACAs with AD progression. Biaxial extension-inflation tests showed that ACAs became progressively less compliant, and the longitudinal stress in the intermediate& advanced AD groups was significantly higher than that from the control group. With pathological AD development, the inner and outer diameter of ACA remained almost unchanged; however, histology study revealed progressive smooth muscle cell atrophy and loss of elastic fibers which led to compromised structural integrity of the arterial wall. Multiphoton imaging demonstrated elastin degradation at the media-adventitia interface, which led to the formation of an empty band of 21.0 ± 15.4 μm and 32.8 ± 9.24 μm in width for the intermediate& advanced AD groups, respectively. Furthermore, quantitative birefringence microscopy showed disorganized adventitial collagen with AD development. Mass spectrometry analysis provided further evidence of altered collagen content and other extracellular matrix (ECM) molecule and smooth muscle cell changes that were consistent with the mechanical and structural alterations. Collectively, our study provides understanding of the mechanical and structural cerebrovascular deterioration in cerebral arteries with AD, which may be related to neurodegenration and pathology in the brain.

Monascus purpureus Fermented Product Ameliorates Learning and Memory Impairment in the Amyloid Precursor Protein Transgenic J20 Mouse Model of Alzheimer’s Disease

Evidence suggests that various hallmarks such as amyloid overproduction, tau dysfunction, insulin resistance/diabetic mechanisms, and neuroinflammation are associated with Alzheimer’s disease (AD). This study investigated the bioactive functions of ankaflavin (AK) and monascin (MS) in the fermented product of Monascus purpureus and found their abilities to ameliorate AD by modifying several important pathogenic factors including improved cognitive function, reversed behavioral deficits, reduced hippocampal β-amyloid peptide (Aβ) burden, decreased tau hyper-phosphorylation, and reduced neuroinflammation in the J20 mouse model of AD compared to wild type. Monascus purpureus fermented product (MPFP) was suggested to act as a peroxisome proliferator-activated receptor (PPAR)-γ agonist and it was compared against the action of a well-known anti-diabetic PPAR-γ agonist rosiglitazone. MPFP could be a promising therapeutic strategy for disease modification in AD.

Simvastatin rescues memory and granule cell maturation through the Wnt/β-catenin signaling pathway in a mouse model of Alzheimer's disease

We previously showed that simvastatin (SV) restored memory in a mouse model of Alzheimer disease (AD) concomitantly with normalization in protein levels of memory-related immediate early genes in hippocampal CA1 neurons. Here, we investigated age-related changes in the hippocampal memory pathway, and whether the beneficial effects of SV could be related to enhanced neurogenesis and signaling in the Wnt/β-catenin pathway. APP mice and wild-type (WT) littermate controls showed comparable number of proliferating (Ki67-positive nuclei) and immature (doublecortin (DCX)-positive) granule cells in the dentate gyrus until 3 months of age. At 4 months, Ki67 or DCX positive cells decreased sharply and remained less numerous until the endpoint (6 months) in both SV-treated and untreated APP mice. In 6 month-old APP mice, dendritic extensions of DCX immature neurons in the molecular layer were shorter, a deficit fully normalized by SV. Similarly, whereas mature granule cells (calbindin-immunopositive) were decreased in APP mice and not restored by SV, their dendritic arborizations were normalized to control levels by SV treatment. SV increased Prox1 protein levels (↑67.7%, p < 0.01), a Wnt/β-catenin signaling target, while significantly decreasing (↓61.2%, p < 0.05) the upregulated levels of the β-catenin-dependent Wnt pathway inhibitor DKK1 seen in APP mice. In APP mice, SV benefits were recapitulated by treatment with the Wnt/β-catenin specific agonist WAY-262611, whereas they were fully abolished in mice that received the Wnt/β-catenin pathway inhibitor XAV939 during the last month of SV treatment. Our results indicate that activation of the Wnt-β-catenin pathway through downregulation of DKK1 underlies SV neuronal and cognitive benefits.

From Neurodevelopmental to Neurodegenerative Disorders: The Vascular Continuum

Structural and functional integrity of the cerebral vasculature ensures proper brain development and function, as well as healthy aging. The inability of the brain to store energy makes it exceptionally dependent on an adequate supply of oxygen and nutrients from the blood stream for matching colossal demands of neural and glial cells. Key vascular features including a dense vasculature, a tightly controlled environment, and the regulation of cerebral blood flow (CBF) all take part in brain health throughout life. As such, healthy brain development and aging are both ensured by the anatomical and functional interaction between the vascular and nervous systems that are established during brain development and maintained throughout the lifespan. During critical periods of brain development, vascular networks remodel until they can actively respond to increases in neural activity through neurovascular coupling, which makes the brain particularly vulnerable to neurovascular alterations. The brain vasculature has been strongly associated with the onset and/or progression of conditions associated with aging, and more recently with neurodevelopmental disorders. Our understanding of cerebrovascular contributions to neurological disorders is rapidly evolving, and increasing evidence shows that deficits in angiogenesis, CBF and the blood-brain barrier (BBB) are causally linked to cognitive impairment. Moreover, it is of utmost curiosity that although neurodevelopmental and neurodegenerative disorders express different clinical features at different stages of life, they share similar vascular abnormalities. In this review, we present an overview of vascular dysfunctions associated with neurodevelopmental (autism spectrum disorders, schizophrenia, Down Syndrome) and neurodegenerative (multiple sclerosis, Huntington's, Parkinson's, and Alzheimer's diseases) disorders, with a focus on impairments in angiogenesis, CBF and the BBB. Finally, we discuss the impact of early vascular impairments on the expression of neurodegenerative diseases.

Impaired Hippocampal Neurovascular Coupling in a Mouse Model of Alzheimer's Disease

Alzheimer’s disease (AD), the most common form of dementia, is characterized by neuronal degeneration and cerebrovascular dysfunction. Increasing evidence indicates that cerebrovascular dysfunction may be a key or an aggravating pathogenic factor in AD. This emphasizes the importance to investigate the tight coupling between neuronal activity and cerebral blood flow (CBF) termed neurovascular coupling (NVC). NVC depends on all cell types of the neurovascular unit within which astrocytes are important players in the progression of AD. Hence, the objective of this study was to characterize the hippocampal NVC in a mouse model of AD. Hippocampal NVC was studied in 6-month-old amyloid-beta precursor protein (APP) transgenic mice and their corresponding wild-type littermates using in vivo laser Doppler flowmetry to measure CBF in area CA1 of the hippocampus in response to Schaffer collaterals stimulation. Ex vivo two-photon microscopy experiments were performed to determine astrocytic Ca²⁺ and vascular responses to electrical field stimulation (EFS) or caged Ca²⁺ photolysis in hippocampal slices. Neuronal synaptic transmission, astrocytic endfeet Ca²⁺ in correlation with reactive oxygen species (ROS), and vascular reactivity in the presence or absence of Tempol, a mimetic of superoxide dismutase, were further investigated using electrophysiological, caged Ca²⁺ photolysis or pharmacological approaches. Whisker stimulation evoked-CBF increases and ex vivo vascular responses to EFS were impaired in APP mice compared with their age-matched controls. APP mice were also characterized by decreased basal synaptic transmission, a shorter astrocytic Ca²⁺ increase, and altered vascular response to elevated perivascular K⁺. However, long-term potentiation, astrocytic Ca²⁺ amplitude in response to EFS, together with vascular responses to nitric oxide remained unchanged. Importantly, we found a significantly increased Ca²⁺ uncaging-induced ROS production in APP mice. Tempol prevented the vascular response impairment while normalizing astrocytic Ca²⁺ in APP mice. These findings suggest that NVC is altered at many levels in APP mice, at least in part through oxidative stress. This points out that therapies against AD should include an antioxidative component to protect the neurovascular unit.

Brain angiotensin II and angiotensin IV receptors as potential Alzheimer's disease therapeutic targets

Alzheimer's disease (AD) is a neurodegenerative disorder that is multifactorial in nature. Yet, despite being the most common form of dementia in the elderly, AD's primary cause remains unknown. As such, there is currently little to offer AD patients as the vast majority of recently tested therapies have either failed in well-controlled clinical trials or inadequately treat AD. Recently, emerging preclinical and clinical evidence has associated the brain renin angiotensin system (RAS) to AD pathology. Accordingly, various components of the brain RAS were shown to be altered in AD patients and mouse models, including the angiotensin II type 1 (AT1R), angiotensin IV receptor (AT4R), and Mas receptors. Collectively, the changes observed within the RAS have been proposed to contribute to many of the neuropathological hallmarks of AD, including the neuronal, cognitive, and vascular dysfunctions. Accumulating evidence has additionally identified antihypertensive medications targeting the RAS, particularly angiotensin receptor blockers (ARBs) and angiotensin-converting enzyme inhibitors (ACEIs), to delay AD onset and progression. In this review, we will discuss the emergence of the RAS's involvement in AD and highlight putative mechanisms of action underlying ARB's beneficial effects that may explain their ability to modify the risk of developing AD or AD progression. The RAS may provide novel molecular targets for recovering memory pathways, cerebrovascular function, and other pathological landmarks of AD.

Centella Asiatica Improves Memory and Promotes Antioxidative Signaling in 5XFAD Mice

Centella asiatica (CA) herb is a traditional medicine, long reputed to provide cognitive benefits. We have reported that CA water extract (CAW) treatment improves cognitive function of aged Alzheimer’s disease (AD) model Tg2576 and wild-type (WT) mice, and induces an NRF2-regulated antioxidant response in aged WT mice. Here, CAW was administered to AD model 5XFAD female and male mice and WT littermates (age: 7.6 +/− 0.6 months), and object recall and contextual fear memory were tested after three weeks treatment. CAW’s impact on amyloid-β plaque burden, and markers of neuronal oxidative stress and synaptic density, was assessed after five weeks treatment. CAW antioxidant activity was evaluated via nuclear transcription factor (erythroid-derived 2)-like 2 (NRF2) and NRF2-regulated antioxidant response element gene expression. Memory improvement in both genders and genotypes was associated with dose-dependent CAW treatment without affecting plaque burden, and marginally increased synaptic density markers in the hippocampus and prefrontal cortex. CAW treatment increased Nrf2 in hippocampus and other NRF2 targets (heme oxygenase-1, NAD(P)H quinone dehydrogenase 1, glutamate-cysteine ligase catalytic subunit). Reduced plaque-associated SOD1, an indicator of oxidative stress, was observed in the hippocampi and cortices of CAW-treated 5XFAD mice. We postulate that CAW treatment leads to reduced oxidative stress, contributing to improved neuronal health and cognition.

The Effects of a Combination of Ion Channel Inhibitors in Female Rats Following Repeated Mild Traumatic Brain Injury

Following mild traumatic brain injury (mTBI), the ionic homeostasis of the central nervous system (CNS) becomes imbalanced. Excess Ca²⁺ influx into cells triggers molecular cascades, which result in detrimental effects. The authors assessed the effects of a combination of ion channel inhibitors (ICI) following repeated mTBI (rmTBI). Adult female rats were subjected to two rmTBI weight-drop injuries 24 h apart, sham procedures (sham), or no procedures (normal). Lomerizine, which inhibits voltage-gated calcium channels, was administered orally twice daily, whereas YM872 and Brilliant Blue G, inhibiting α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and P2X₇ receptors, respectively, were delivered intraperitoneally every 48 h post-injury. Vehicle treatment controls were included for rmTBI, sham, and normal groups. At 11 days following rmTBI, there was a significant increase in the time taken to cross the 3 cm beam, as a sub-analysis of neurological severity score (NSS) assessments, compared with the normal control (p < 0.05), and a significant decrease in learning-associated improvement in rmTBI in Morris water maze (MWM) trials relative to the sham (p < 0.05). ICI-treated rmTBI animals were not different to sham, normal controls, or rmTBI treated with vehicle in all neurological severity score and Morris water maze assessments (p > 0.05). rmTBI resulted in increases in microglial cell density, antioxidant responses (manganese-dependent superoxide dismutase (MnSOD) immunoreactivity), and alterations to node of Ranvier structure. ICI treatment decreased microglial density, MnSOD immunoreactivity, and abnormalities of the node of Ranvier compared with vehicle controls (p < 0.01). The authors' findings demonstrate the beneficial effects of the combinatorial ICI treatment on day 11 post-rmTBI, suggesting an attractive therapeutic strategy against the damage induced by excess Ca²⁺ following rmTBI.

PGC-1α sparks the fire of neuroprotection against neurodegenerative disorders

Recently, growing evidence has demonstrated that peroxisome proliferator activated receptor γ (PPARγ) coactivator-1α (PGC-1α) is a superior transcriptional regulator that acts via controlling the expression of anti-oxidant enzymes and uncoupling proteins and inducing mitochondrial biogenesis, which plays a beneficial part in the central nervous system (CNS). Given the significance of PGC-1α, we summarize the current literature on the molecular mechanisms and roles of PGC-1α in the CNS. Thus, in this review, we first briefly introduce the basic characteristics regarding PGC-1α. We then depict some of its important cerebral functions and discuss upstream modulators, partners, and downstream effectors of the PGC-1α signaling pathway. Finally, we highlight recent progress in research on the involvement of PGC-1α in certain major neurodegenerative disorders (NDDs), including Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Collectively, the data presented here may be useful for supporting the future potential of PGC-1α as a therapeutic target.

Analogous β-Carboline Alkaloids Harmaline and Harmine Ameliorate Scopolamine-Induced Cognition Dysfunction by Attenuating Acetylcholinesterase Activity, Oxidative Stress, and Inflammation in Mice

The analogous β-carboline alkaloids, harmaline (HAL) and harmine (HAR), possess a variety of biological properties, including acetylcholinesterase (AChE) inhibitory activity, antioxidant, anti-inflammatory, and many others, and have great potential for treating Alzheimer’s disease (AD). However, studies have showed that the two compounds have similar structures and in vitro AChE inhibitory activities but with significant difference in bioavailability. The objective of this study was to comparatively investigate the effects of HAL and HAR in memory deficits of scopolamine-induced mice. In the present study, mice were pretreated with HAL (2, 5, and 10 mg/kg), HAR (10, 20, and 30 mg/kg) and donepezil (5 mg/kg) by intragastrically for 7 days, and were daily intraperitoneal injected with scopolamine (1 mg/kg) to induce memory deficits and then subjected to behavioral evaluation by Morris water maze. To further elucidate the underlying mechanisms of HAL and HAR in improving learning and memory, the levels of various biochemical factors and protein expressions related to cholinergic function, oxidative stress, and inflammation were examined. The results showed that HAL and HAR could effectively ameliorate memory deficits in scopolamine-induced mice. Both of them exhibited an enhancement in cholinergic function by inhibiting AChE and inducing choline acetyltransferase (ChAT) activities, and antioxidant defense via increasing the antioxidant enzymes activities of superoxide dismutase and glutathione peroxidase, and reducing maleic diadehyde production, and anti-inflammatory effects through suppressing myeloperoxidase, tumor necrosis factor α, and nitric oxide as well as modulation of critical neurotransmitters such as acetylcholine (ACh), choline (Ch), L-tryptophan (L-Trp), 5-hydroxytryptamine (5-HT), γ-aminobutyric acid (γ-GABA), and L-glutamic acid (L-Glu). Furthermore, the regulations of HAL on cholinergic function, inflammation, and neurotransmitters were more striking than those of HAR, and HAL manifested a comparable antioxidant capacity to HAR. Remarkably, the effective dosage of HAL (2 mg/kg) was far lower than that of HAR (20 mg/kg), which probably due to the evidently differences in the bioavailability and metabolic stability of the two analogs. Taken together, all these results revealed that HAL may be a promising candidate compound with better anti-amnesic effects and pharmacokinetic characteristics for the treatments of AD and related diseases.

Impact of Altered Cholinergic Tones on the Neurovascular Coupling Response to Whisker Stimulation

Brain imaging techniques that use vascular signals to map changes in neuronal activity rely on the coupling between electrophysiology and hemodynamics, a phenomenon referred to as "neurovascular coupling" (NVC). It is unknown whether this relationship remains reliable under altered brain states associated with acetylcholine (ACh) levels, such as attention and arousal and in pathological conditions such as Alzheimer's disease. We therefore assessed the effects of varying ACh tone on whisker-evoked NVC responses in rat barrel cortex, measured by cerebral blood flow (CBF) and neurophysiological recordings (local field potentials, LFPs). We found that acutely enhanced ACh tone significantly potentiated whisker-evoked CBF responses through muscarinic ACh receptors and concurrently facilitated neuronal responses, as illustrated by increases in the amplitude and power in high frequencies of the evoked LFPs. However, the cellular identity of the activated neuronal network within the responsive barrel was unchanged, as characterized by c-Fos upregulation in pyramidal cells and GABA interneurons coexpressing vasoactive intestinal polypeptide. In contrast, chronic ACh deprivation hindered whisker-evoked CBF responses and the amplitude and power in most frequency bands of the evoked LFPs and reduced the rostrocaudal extent and area of the activated barrel without altering its identity. Correlations between LFP power and CBF, used to estimate NVC, were enhanced under high ACh tone and disturbed significantly by ACh depletion. We conclude that ACh is not only a facilitator but also a prerequisite for the full expression of sensory-evoked NVC responses, indicating that ACh may alter the fidelity of hemodynamic signals in assessing changes in evoked neuronal activity.SIGNIFICANCE STATEMENT Neurovascular coupling, defined as the tight relationship between activated neurons and hemodynamic responses, is a fundamental brain function that underlies hemodynamic-based functional brain imaging techniques. However, the impact of altered brain states on this relationship is largely unknown. We therefore investigated how acetylcholine (ACh), known to drive brain states of attention and arousal and to be deficient in pathologies such as Alzheimer's disease, would alter neurovascular coupling responses to sensory stimulation. Whereas acutely increased ACh enhanced neuronal responses and the resulting hemodynamic signals, chronic loss of cholinergic input resulted in dramatic impairments in both types of sensory-evoked signals. We conclude that ACh is not only a potent modulator but also a requirement for the full expression of sensory-evoked neurovascular coupling responses.

Basal Forebrain and Hippocampus as Predictors of Conversion to Alzheimer's Disease in Patients with Mild Cognitive Impairment - A Multicenter DTI and Volumetry Study

BACKGROUND

Hippocampal grey matter (GM) atrophy predicts conversion from mild cognitive impairment (MCI) to Alzheimer's disease (AD). Pilot data suggests that mean diffusivity (MD) in the hippocampus, as measured with diffusion tensor imaging (DTI), may be a more accurate predictor of conversion than hippocampus volume. In addition, previous studies suggest that volume of the cholinergic basal forebrain may reach a diagnostic accuracy superior to hippocampal volume in MCI.

OBJECTIVE

The present study investigated whether increased MD and decreased volume of the hippocampus, the basal forebrain and other AD-typical regions predicted time to conversion from MCI to AD dementia.

METHODS

79 MCI patients with DTI and T1-weighted magnetic resonance imaging (MRI) were retrospectively included from the European DTI Study in Dementia (EDSD) dataset. Of these participants, 35 converted to AD dementia after 6-46 months (mean: 21 months). We used Cox regression to estimate the relative conversion risk predicted by MD values and GM volumes, controlling for age, gender, education and center.

RESULTS

Decreased GM volume in all investigated regions predicted an increased risk for conversion. Additionally, increased MD in the right basal forebrain predicted increased conversion risk. Reduced volume of the right hippocampus was the only significant predictor in a stepwise model combining all predictor variables.

CONCLUSION

Volume reduction of the hippocampus, the basal forebrain and other AD-related regions was predictive of increased risk for conversion from MCI to AD. In this study, volume was superior to MD in predicting conversion.

Neurovascular and Cognitive failure in Alzheimer's Disease: Benefits of Cardiovascular Therapy

Alzheimer's disease (AD) is a multifactorial and multifaceted disease for which we currently have very little to offer since there is no curative therapy, with only limited disease-modifying drugs. Recent studies in AD mouse models that recapitulate the amyloid-β (Aβ) pathology converge to demonstrate that it is possible to salvage cerebrovascular function with a variety of drugs and, particularly, therapies used to treat cardiovascular diseases such as hypercholesterolemia and hypertension. These drugs can reestablish dilatory function mediated by various endothelial and smooth muscle ion channels as well as nitric oxide availability, benefits that result in normalized brain perfusion. These cerebrovascular benefits would favor brain perfusion, which may help maintain neuronal function and, possibly, delay cognitive failure. However, restoring cerebrovascular function in AD mouse models was not necessarily accompanied by rescue of cognitive deficits related to spatial learning and memory. The results with cardiovascular therapies rather suggest that drugs originally designed to treat cardiovascular diseases that concurrently restore cerebrovascular and cognitive function do so through their pleiotropic effects. Specifically, recent findings suggest that these drugs act directly on brain cells and neuronal pathways involved in memory formation, hence, working simultaneously albeit independently on neuronal and vascular targets. These findings may help select medications for patients with cardiovascular diseases at risk of developing AD with increasing age. Further, they may identify molecular targets for recovering memory pathways that bear potential for new therapeutic avenues.

Angiotensin II type 1 receptor blocker losartan prevents and rescues cerebrovascular, neuropathological and cognitive deficits in an Alzheimer's disease model

Angiotensin II (AngII) receptor blockers that bind selectively AngII type 1 (AT1) receptors may protect from Alzheimer's disease (AD). We studied the ability of the AT1 receptor antagonist losartan to cure or prevent AD hallmarks in aged (~18months at endpoint, 3months treatment) or adult (~12months at endpoint, 10months treatment) human amyloid precursor protein (APP) transgenic mice. We tested learning and memory with the Morris water maze, and evaluated neurometabolic and neurovascular coupling using [(18)F]fluoro-2-deoxy-D-glucose-PET and laser Doppler flowmetry responses to whisker stimulation. Cerebrovascular reactivity was assessed with on-line videomicroscopy. We measured protein levels of oxidative stress enzymes (superoxide dismutases SOD1, SOD2 and NADPH oxidase subunit p67phox), and quantified soluble and deposited amyloid-β (Aβ) peptide, glial fibrillary acidic protein (GFAP), AngII receptors AT1 and AT2, angiotensin IV receptor AT4, and cortical cholinergic innervation. In aged APP mice, losartan did not improve learning but it consolidated memory acquisition and recall, and rescued neurovascular and neurometabolic coupling and cerebrovascular dilatory capacity. Losartan normalized cerebrovascular p67phox and SOD2 protein levels and up-regulated those of SOD1. Losartan attenuated astrogliosis, normalized AT1 and AT4 receptor levels, but failed to rescue the cholinergic deficit and the Aβ pathology. Given preventively, losartan protected cognitive function, cerebrovascular reactivity, and AT4 receptor levels. Like in aged APP mice, these benefits occurred without a decrease in soluble Aβ species or plaque load. We conclude that losartan exerts potent preventive and restorative effects on AD hallmarks, possibly by mitigating AT1-initiated oxidative stress and normalizing memory-related AT4 receptors.

Electroacupuncture decreases cognitive impairment and promotes neurogenesis in the APP/PS1 transgenic mice

BACKGROUND

Alzheimer's disease (AD) is a severe neurodegenerative disease for which there is currently no effective treatment. The purpose of this study was to investigate whether repeated electroacupuncture (EA) stimulation would improve cognitive function and the pathological features of AD in amyloid precursor protein (APP)/presenilin 1 (PS1) double transgenic mice.

METHODS

Cognitive function of APP/PS1 double transgenic mice was assessed using the Morris water maze test before and after EA treatment. Levels of amyloid β-peptide (Aβ) deposits in the hippocampus and cortex were evaluated by immunofluorescence, western blot and enzyme-linked immunosorbent assay. Expression of brain-derived neurotrophic factor (BDNF) was also examined by immunofluorescence and western blot. The neurogenesis was labeled by the DNA marker bromodeoxyuridine.

RESULTS

EA stimulation significantly ameliorated the learning and memory deficits of AD mice by shortening escape latency and increasing the time spent in the target zone during the probe test. Additionally, decreased Aβ deposits and increased BDNF expression and neurogenesis in the hippocampus and cortex of EA-treated AD mice were detected. The same change was detected in wild-type mice after EA treatment compared with wild-type mice without EA treatment.

CONCLUSIONS

Repeated EA stimulation may improve cognitive function, attenuate Aβ deposits, up-regulate the expression of BDNF and promote neurogenesis in the APP/PS1 double transgenic mice. This suggests that EA may be a promising treatment for AD.

Early endosomal abnormalities and cholinergic neuron degeneration in amyloid-β protein precursor transgenic mice

Early endosomal changes, a prominent pathology in neurons early in Alzheimer's disease, also occur in neurons and peripheral tissues in Down syndrome. While in Down syndrome models increased amyloid-β protein precursor (AβPP) expression is known to be a necessary contributor on the trisomic background to this early endosomal pathology, increased AβPP alone has yet to be shown to be sufficient to drive early endosomal alterations in neurons. Comparing two AβPP transgenic mouse models, one that contains the AβPP Swedish K670N/M671L double mutation at the β-cleavage site (APP23) and one that has the AβPP London V717I mutation near the γ-cleavage site (APPLd2), we show significantly altered early endosome morphology in fronto-parietal neurons as well as enlargement of early endosomes in basal forebrain cholinergic neurons of the medial septal nucleus in the APP23 model, which has the higher levels of AβPP β-C-terminal fragment (βCTF) accumulation. Early endosomal changes correlate with a marked loss of the cholinergic population, which is consistent with the known dependence of the large projection cholinergic cells on endosome-mediated retrograde neurotrophic transport. Our findings support the idea that increased expression of AβPP and AβPP metabolites in neurons is sufficient to drive early endosomal abnormalities in vivo, and that disruption of the endocytic system is likely to contribute to basal forebrain cholinergic vulnerability.

Cholinergic basal forebrain atrophy predicts amyloid burden in Alzheimer's disease

We compared accuracy of hippocampus and basal forebrain cholinergic system (BFCS) atrophy to predict cortical amyloid burden in 179 cognitively normal subjects (CN), 269 subjects with early stages of mild cognitive impairment (MCI), 136 subjects with late stages of MCI, and 86 subjects with Alzheimer's disease (AD) dementia retrieved from the Alzheimer's Disease Neuroimaging Initiative database. Hippocampus and BFCS volumes were determined from structural magnetic resonance imaging scans at 3 Tesla, and cortical amyloid load from AV45 (florbetapir) positron emission tomography scans. In receiver operating characteristics analyses, BFCS volume provided significantly more accurate classification into amyloid-negative and -positive categories than hippocampus volume. In contrast, hippocampus volume more accurately identified the diagnostic categories of AD, late and early MCI, and CN compared with whole and anterior BFCS volume, whereas posterior BFCS and hippocampus volumes yielded similar diagnostic accuracy. In logistic regression analysis, hippocampus and posterior BFCS volumes contributed significantly to discriminate MCI and AD from CN, but only BFCS volume predicted amyloid status. Our findings suggest that BFCS atrophy is more closely associated with cortical amyloid burden than hippocampus atrophy in predementia AD.

Alzheimer’s disease, cerebrovascular disease, and the β-amyloid cascade

Alzheimer’s disease (AD), considered the commonest neurodegenerative cause of dementia, is associated with hallmark pathologies including extracellular amyloid-β protein (Aβ) deposition in extracellular senile plaques and vessels, and intraneuronal tau deposition as neurofibrillary tangles. Although AD is usually categorized as neurodegeneration distinct from cerebrovascular disease (CVD), studies have shown strong links between AD and CVD. There is evidence that vascular risk factors and CVD may accelerate Aβ 40-42 production/ aggregation/deposition and contribute to the pathology and symptomatology of AD. Aβ deposited along vessels also causes cerebral amyloid angiopathy. Amyloid imaging allows in vivo detection of AD pathology, opening the way for prevention and early treatment, if disease-modifying therapies in the pipeline show safety and efficacy. In this review, we review the role of vascular factors and Aβ, underlining that vascular risk factor management may be important for AD prevention and treatment.

Therapeutic approach to neurodegenerative diseases by medical gases: focusing on redox signaling and related antioxidant enzymes

Oxidative stress in the central nervous system is strongly associated with neuronal cell death in the pathogenesis of several neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. In order to overcome the oxidative damage, there are some protective signaling pathways related to transcriptional upregulation of antioxidant enzymes, such as heme oxygenase-1 (HO-1) and superoxide dismutase (SOD)-1/-2. Their expression is regulated by several transcription factors and/or cofactors like nuclear factor-erythroid 2 (NF-E2) related factor 2 (Nrf2) and peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α). These antioxidant enzymes are associated with, and in some cases, prevent neuronal death in animal models of neurodegenerative diseases. They are activated by endogenous mediators and phytochemicals, and also by several gases such as carbon monoxide (CO), hydrogen sulphide (H₂S), and hydrogen (H₂). These might thereby protect the brain from severe oxidative damage and resultant neurodegenerative diseases. In this paper, we discuss how the expression levels of these antioxidant enzymes are regulated. We also introduce recent advances in the therapeutic uses of medical gases against neurodegenerative diseases.

Age-dependent rescue by simvastatin of Alzheimer's disease cerebrovascular and memory deficits

Alzheimer's disease (AD) is now established as a progressive compromise not only of the neurons but also of the cerebral vasculature. Increasing evidence also indicates that cerebrovascular dysfunction may be a key or an aggravating pathogenic factor in AD, emphasizing the importance to properly control this deficit when aiming for effective therapy. Here, we report that simvastatin (3-6 months, 40 mg/kg/d) completely rescued cerebrovascular reactivity, basal endothelial nitric oxide synthesis, and activity-induced neurometabolic and neurovascular coupling in adult (6 months) and aged (12 months) transgenic mice overexpressing the Swedish and Indiana mutations of the human amyloid precursor protein (AD mice). Remarkably, simvastatin fully restored short- and long-term memory in adult, but not in aged AD mice. These beneficial effects occurred without any decreasing effect of simvastatin on brain amyloid-β (Aβ) levels or plaque load. However, in AD mice with recovered memory, protein levels of the learning- and memory-related immediate early genes c-Fos and Egr-1 were normalized or upregulated in hippocampal CA1 neurons, indicative of restored neuronal function. In contrast, the levels of phospholipase A2, enkephalin, PSD-95, synaptophysin, or glutamate NMDA receptor subunit type 2B were either unaltered in AD mice or unaffected by treatment. These findings disclose new sites of action for statins against Aβ-induced neuronal and cerebrovascular deficits that could be predictive of therapeutic benefit in AD patients. They further indicate that simvastatin and, possibly, other brain penetrant statins bear high therapeutic promise in early AD and in patients with vascular diseases who are at risk of developing AD.

Increased hippocampal CA1 density of serotonergic terminals in a triple transgenic mouse model of Alzheimer's disease: an ultrastructural study

Alzheimer's disease (AD) is a neurodegenerative pathology that deteriorates mnesic functions and associated brain regions including the hippocampus. Serotonin (5-HT) has an important role in cognition. We recently demonstrated an increase in 5-HT transporter (SERT) fibre density in the hippocampal CA1 in an AD triple transgenic mouse model (3xTg-AD). Here, we analyse the ultrastructural localisation, distribution and numerical density (N_v) of hippocampal SERT axons (SERT-Ax) and terminals (SERT-Te) and their relationship with SERT fibre sprouting and altered synaptic N_v in 3xTg-AD compared with non-transgenic control mice. 3xTg-AD animals showed a significant increase in SERT-Te N_v in CA1 at both, 3 (95%) and 18 months of age (144%), being restricted to the CA1 stratum moleculare (S. Mol; 227% at 3 and 180% at 18 months). 3xTg-AD animals also exhibit reduced N_v of perforated axospinous synapses (PS) in CA1 S. Mol (56% at 3 and 52% at 18 months). No changes were observed in the N_v of symmetric and asymmetrical synapses or SERT-Ax. Our results suggest that concomitant SERT-Te N_v increase and PS reduction in 3xTg-AD mice may act as a compensatory mechanism maintaining synaptic efficacy as a response to the AD cognitive impairment.

Ligand-dependent TrkA activity in brain differentially affects spatial learning and long-term memory

In the central nervous system, the nerve growth factor (NGF) receptor TrkA is expressed primarily in cholinergic neurons that are implicated in spatial learning and memory, whereas the NGF receptor p75(NTR) is expressed in many neuronal populations and glia. We asked whether selective TrkA activation may have a different impact on learning, short-term memory, and long-term memory. We also asked whether TrkA activation might affect cognition differently in wild-type mice versus mice with cognitive deficits due to transgenic overexpression of mutant amyloid-precursor protein (APP mice). Mice were treated with wild-type NGF (a ligand of TrkA and p75(NTR)) or with selective pharmacological agonists of TrkA that do not bind to p75(NTR). In APP mice, the selective TrkA agonists significantly improved learning and short-term memory. These improvements are associated with a reduction of soluble Aβ levels in the cortex and AKT activation in the cortex and hippocampus. However, this improved phenotype did not translate into improved long-term memory. In normal wild-type mice, none of the treatments affected learning or short-term memory, but a TrkA-selective agonist caused persistent deficits in long-term memory. The deficit in wild-type mice was associated temporally, in the hippocampus, with increased AKT activity, increased brain-derived neurotrophic factor precursor, increased neurotrophin receptor homolog-2 (p75-related protein), and long-term depression. Together, these data indicate that selective TrkA activation affects cognition but does so differently in impaired APP mice versus normal wild-type mice. Understanding mechanisms that govern learning and memory is important for better treatment of cognitive disorders.

Neurovascular function in Alzheimer's disease patients and experimental models

The ability of the brain to locally augment glucose delivery and blood flow during neuronal activation, termed neurometabolic and neurovascular coupling, respectively, is compromised in Alzheimer's disease (AD). Since perfusion deficits may hasten clinical deterioration and have been correlated with negative treatment outcome, strategies to improve the cerebral circulation should form an integral element of AD therapeutic efforts. These efforts have yielded several experimental models, some of which constitute AD models proper, others which specifically recapture the AD cerebrovascular pathology, characterized by anatomical alterations in brain vessel structure, as well as molecular changes within vascular smooth muscle cells and endothelial cells forming the blood-brain barrier. The following paper will present the elements of AD neurovascular dysfunction and review the in vitro and in vivo model systems that have served to deepen our understanding of it. It will also critically evaluate selected groups of compounds, the FDA-approved cholinesterase inhibitors and thiazolidinediones, for their ability to correct neurovascular dysfunction in AD patients and models. These and several others are emerging as compounds with pleiotropic actions that may positively impact dysfunctional cerebrovascular, glial, and neuronal networks in AD.

Near infrared light reduces oxidative stress and preserves function in CNS tissue vulnerable to secondary degeneration following partial transection of the optic nerve

Traumatic injury to the central nervous system (CNS) is accompanied by the spreading damage of secondary degeneration, resulting in further loss of neurons and function. Partial transection of the optic nerve (ON) has been used as a model of secondary degeneration, in which axons of retinal ganglion cells in the ventral ON are spared from initial dorsal injury, but are vulnerable to secondary degeneration. We have recently demonstrated that early after partial ON injury, oxidative stress spreads through the ventral ON vulnerable to secondary degeneration via astrocytes, and persists in the nerve in aggregates of cellular debris. In this study, we show that diffuse transcranial irradiation of the injury site with far red to near infrared (NIR) light (WARP 10 LED array, center wavelength 670 nm, irradiance 252 W/m(-2), 30 min exposure), as opposed to perception of light at this wavelength, reduced oxidative stress in areas of the ON vulnerable to secondary degeneration following partial injury. The WARP 10 NIR light treatment also prevented increases in NG-2-immunopositive oligodendrocyte precursor cells (OPCs) that occurred in ventral ON as a result of partial ON transection. Importantly, normal visual function was restored by NIR light treatment with the WARP 10 LED array, as assessed using optokinetic nystagmus and the Y-maze pattern discrimination task. To our knowledge, this is the first demonstration that 670-nm NIR light can reduce oxidative stress and improve function in the CNS following traumatic injury in vivo.

Cholinotrophic basal forebrain system alterations in 3xTg-AD transgenic mice

The cholinotrophic system, which is dependent upon nerve growth factor and its receptors for survival, is selectively vulnerable in Alzheimer's disease (AD). But, virtually nothing is known about how this deficit develops in relation to the hallmark lesions of this disease, amyloid plaques and tau containing neurofibrillary tangles. The vast majority of transgenic models of AD used to evaluate the effect of beta amyloid (Aβ) deposition upon the cholinotrophic system over-express the amyloid precursor protein (APP). However, nothing is known about how this system is affected in triple transgenic (3xTg)-AD mice, an AD animal model displaying Aβ plaque- and tangle-like pathology in the cortex and hippocampus, which receive extensive cholinergic innervation. We performed a detailed morphological and biochemical characterization of the cholinotrophic system in young (2-4 months), middle-aged (13-15 months) and old (18-20 months) 3xTg-AD mice. Cholinergic neuritic swellings increased in number and size with age, and were more conspicuous in the hippocampal-subicular complex in aged female than in 3xTg-AD male mice. Stereological analysis revealed a reduction in choline acetyltransferase (ChAT) positive cells in the medial septum/vertical limb of the diagonal band of Broca in aged 3xTg-AD mice. ChAT enzyme activity levels decreased significantly in the hippocampus of middle-aged 3xTg-AD mice compared to age-matched non-transgenic (or wild type) mice. ProNGF protein levels increased in the cortex of aged 3xTg-AD mice, whereas TrkA protein levels were reduced in a gender-dependent manner in aged mutant mice. In contrast, p75(NTR) protein cortical levels were stable but increased in the hippocampus of aged 3xTg-AD mice. These data demonstrate that cholinotrophic alterations in 3xTg-AD mice are age- and gender-dependent and more pronounced in the hippocampus, a structure more severely affected by Aβ plaque pathology.

Localization of pre- and postsynaptic cholinergic markers in rodent forebrain: a brief history and comparison of rat and mouse

Rat and mouse models are widely used for studies in cognition and pathophysiology, among others. Here, we sought to determine to what extent these two model species differ for cholinergic and cholinoceptive features. For this purpose, we focused on cholinergic innervation patterns based on choline acetyltransferase (ChAT) immunostaining, and the expression of muscarinic acetylcholine receptors (mAChRs) detected immunocytochemically. In this brief review we first place cholinergic and cholinoceptive markers in a historic perspective, and then provide an overview of recent publications on cholinergic studies and techniques to provide a literature survey of current research. Next, we compare mouse (C57Bl/J6) and rat (Wistar) cholinergic and cholinoceptive systems simultaneously stained, respectively, for ChAT (analyzed qualitatively) and mAChRs (analyzed qualitatively and quantitatively). In general, the topographic cholinergic innervation patterns of both rodent species are highly comparable, with only considerable (but region specific) differences in number of detectable cholinergic interneurons, which are more numerous in rat. In contrast, immunolabeling for mAChRs, detected by the monoclonal antibody M35, differs markedly in the forebrain between the two species. In mouse brain, basal levels of activated and/or internalized mAChRs (as a consequence of cholinergic neurotransmission) are significantly higher. This suggests a higher cholinergic tone in mouse than rat, and hence the animal model of choice may have consequences for cholinergic drug testing experiments.

Transgenic mice overexpressing APP and transforming growth factor-beta1 feature cognitive and vascular hallmarks of Alzheimer's disease

High brain levels of amyloid-β (Aβ) and transforming growth factor-β1 (TGF-β1) have been implicated in the cognitive and cerebrovascular alterations of Alzheimer's disease (AD). We sought to investigate the impact of combined increases in Aβ and TGF-β1 on cerebrovascular, neuronal, and mnemonic function using transgenic mice overproducing these peptides (A/T mice). In particular, we measured cerebrovascular reactivity, evoked cerebral blood flow and glucose uptake during brain activation, cholinergic status, and spatial memory, along with cerebrovascular fibrosis, amyloidosis, and astrogliosis, and their evolution with age. An assessment of perfusion and metabolic responses was considered timely, given ongoing efforts for their validation as AD biomarkers. Relative to wild-type littermates, A/T mice displayed an early progressive decline in cerebrovascular dilatory ability, preserved contractility, and reduction in constitutive nitric oxide synthesis that establishes resting vessel tone. Altered levels of vasodilator-synthesizing enzymes and fibrotic proteins, resistance to antioxidant treatment, and unchanged levels of the antioxidant enzyme, superoxide dismutase-2, accompanied these impairments. A/T mice featured deficient neurovascular and neurometabolic coupling to whisker stimulation, cholinergic denervation, cerebral and cerebrovascular Aβ deposition, astrocyte activation, and impaired Morris water maze performance, which gained severity with age. The combined Aβ- and TGF-β1-driven pathology recapitulates salient cerebrovascular, neuronal, and cognitive AD landmarks and yields a versatile model toward highly anticipated diagnostic and therapeutic tools for patients featuring Aβ and TGF-β1 increments.

Serotonin: a regulator of neuronal morphology and circuitry

Serotonin is an important neuromodulator associated with a wide range of physiological effects in the central nervous system. The exact mechanisms whereby serotonin influences brain development are not well understood, although studies in invertebrate and vertebrate model organisms are beginning to unravel a regulatory role for serotonin in neuronal morphology and circuit formation. Recent data suggest a developmental window during which altered serotonin levels permanently influence neuronal circuitry, however, the temporal constraints and molecular mechanisms responsible are still under investigation. Growing evidence suggests that alterations in early serotonin signaling contribute to a number of neurodevelopmental and neuropsychiatric disorders. Thus, understanding how altered serotonin signaling affects neuronal morphology and plasticity, and ultimately animal physiology and pathophysiology, will be of great significance.

Early events of secondary degeneration after partial optic nerve transection: an immunohistochemical study

Secondary degeneration in the central nervous system involves indirect damage to neurons and glia away from the initial injury. Partial transection of the dorsal optic nerve (ON) results in precise spatial separation of the primary trauma from delayed degenerative events in ventrally placed axons and parent somata. Here we conduct an immunohistochemical survey of secondary cellular changes in and around axons and their parent retinal ganglion cell (RGC) somata during the first 3 days after a restricted, dorsal ON transection. This is before the secondary loss of RGCs and axons projecting through the uninjured, ventral portion of the ON. Within 5 min, manganese superoxide dismutase (MnSOD; a marker of oxidative stress) co-localizes within the astrocytic network across the entire profile of the ON. Secondary astrocyte hypertrophy of immunofluorescent labeling was evident from 3 h, with sustained increases in myelin basic protein immunoreactivity across the nerve by 24 h. Increases in NG-2-positive oligodendrocyte precursor cells, ED-1-positive activated microglia/macrophages, and Iba1-positive reactive resident microglia/macrophage numbers were only seen in ON vulnerable to secondary degeneration by 3 days. Changes within RGC somata exclusively vulnerable to secondary degeneration were detected at 24 h, as evidenced by increases in MnSOD immunoreactivity, followed by increases in c-jun immunoreactivity at 3 days. Treatment with the voltage-gated calcium channel blocker lomerizine did not alter any measured outcome. We conclude that oxidative stress spreading via the astrocytic network and from injured axons to parent RGC somata is an early event during secondary degeneration, and containment is likely to be required in order to prevent further damage to the nerve.

Amyloid-beta expression in retrosplenial cortex of triple transgenic mice: relationship to cholinergic axonal afferents from medial septum

Triple transgenic (3xTg-AD) mice harboring the presenilin 1, amyloid precursor protein, and tau transgenes (Oddo et al., 2003b) display prominent levels of amyloid-beta (Abeta) immunoreactivity in forebrain regions. The Abeta immunoreactivity is first seen intracellularly in neurons and later as extracellular plaque deposits. The present study examined Abeta immunoreactivity that occurs in layer III of the granular division of retrosplenial cortex (RSg). This pattern of Abeta immunoreactivity in layer III of RSg develops relatively late, and is seen in animals older than 14 months. The appearance of the Abeta immunoreactivity is similar to an axonal terminal field and thus may offer a unique opportunity to study the relationship between afferent projections and the formation of Abeta deposits. Axonal tract tracing techniques demonstrated that the pattern of axon terminal labeling in layer III of RSg, following placement of DiI in medial septum, is remarkably similar to the pattern of cholinergic axons in RSg, as detected by acetylcholinesterase histochemical staining, choline acetyltransferase immunoreactivity, or p75 receptor immunoreactivity; this pattern also is strikingly similar to the band of Abeta immunoreactivity. In animals sustaining early damage to the medial septal nucleus (prior to the advent of Abeta immunoreactivity), the band of Abeta in layer III of RSg does not develop; the corresponding band of cholinergic markers also is eliminated. In older animals (after the appearance of the Abeta immunoreactivity) damage to cholinergic afferents by electrolytic lesions, immunotoxin lesions, or cutting the cingulate bundle, result in a rapid loss of the cholinergic markers and a slower reduction of Abeta immunoreactivity. These results suggest that the septal cholinergic axonal projections transport Abeta or amyloid precursor protein (APP) to layer III of RSg.

Altered brain serotonin transporter and associated glucose metabolism in Alzheimer disease

Whether preclinical depression is one of the pathophysiologic features of Alzheimer disease (AD) has been under debate. In vivo molecular imaging helps clarify this kind of issue. Here, we examined in vivo changes in the brain serotoninergic system and glucose metabolism by scanning early- to moderate-stage AD patients with and without depression using PET with a radiotracer for the serotonin transporter, (11)C-3-amino-4-(2-dimethylaminomethylphenylsulfanyl) benzonitrile (DASB), and a metabolic marker, (18)F-FDG.

METHODS

Fifteen AD patients (8 nondepressed and 7 depressed) and 10 healthy subjects participated. All participants underwent 3-dimensional MRI and quantitative (11)C-DASB PET measurements, followed by (18)F-FDG PET scans in the AD group. Region-of-interest analysis was used to examine changes in (11)C-DASB binding potential estimated quantitatively by the Logan plot method in the serotonergic projection region. In addition, statistical parametric mapping was used to examine whether glucose metabolism in any brain region correlated with levels of (11)C-DASB binding in the dense serotonergic projection region (striatum) in AD.

RESULTS

Psychologic evaluation showed that general cognitive function (Mini-Mental State Examination) was similar between the 2 AD subgroups. Striatal (11)C-DASB binding was significantly lower in AD patients, irrespective of depression, than in healthy controls (P < 0.05, corrected), and (11)C-DASB binding in other dense projection areas decreased significantly in the depressive group, compared with the control group. The (11)C-DASB binding potential levels in the subcortical serotonergic projection region correlated negatively with depression score (Spearman correlation, P < 0.01) but not with dementia score. Statistical parametric mapping correlation analysis showed that glucose metabolism in the right dorsolateral prefrontal cortex was positively associated with the level of striatal (11)C-DASB binding in AD.

CONCLUSION

The significant reduction in (11)C-DASB binding in nondepressed AD patients suggests that presynaptic serotonergic function is altered before the development of psychiatric problems such as depression in AD. The depressive AD group showed greater and broader reductions in binding, suggesting that a greater loss of serotonergic function relates to more severe psychiatric symptoms in the disease. This serotonergic dysfunction may affect the activity of the right dorsolateral prefrontal cortex, a higher center of cognition and emotion in AD.

Secondary degeneration of the optic nerve following partial transection: the benefits of lomerizine

Secondary degeneration is a form of 'bystander' damage that can affect neural tissue both nearby and remote from an initial injury. Partial optic nerve transection is an excellent model in which to unequivocally differentiate events occurring during secondary degeneration from those resulting from primary CNS injury. We analysed the primary injury site within the optic nerve (ON) and intact areas vulnerable to secondary degeneration. Areas affected by the primary injury showed morphological disruption, loss of beta-III tubulin axonal staining, reduced myelinated axon density, greater proteoglycan expression (phosphacan), increased microglia and macrophage numbers and increased oxidative stress. Similar, but less extreme, changes were seen in areas of the optic nerve undergoing secondary degeneration. The CNS-specific L- and T-type calcium channel blocker lomerizine alleviated some of the changes in areas vulnerable to secondary degeneration. Lomerizine reduced morphological disruption, oxidative stress and phosphacan expression, and limited early increases in macrophage numbers. However, lomerizine failed to prevent progressive de-myelination of ON axons. Within the retina, secondary retinal ganglion cell (RGC) death was significant in areas vulnerable to secondary degeneration. Lomerizine protected RGCs from secondary death at 4 weeks but did not fully restore behavioural function (optokinetic nystagmus). We conclude that blockade of calcium channels is neuroprotective and limits secondary degenerative changes following CNS injury. However such an approach may need to be combined with other treatments to ensure long-term maintenance of full visual function.

Episodic memory deficits are not related to altered glutamatergic synaptic transmission and plasticity in the CA1 hippocampus of the APPswe/PS1δE9-deleted transgenic mice model of ß-amyloidosis

Alzheimer's disease (AD) is characterized by progressive memory impairment and the formation of amyloid plaques in the brain. Dysfunctional excitatory synaptic transmission and synaptic plasticity are generally accepted as primary events in the development of AD, and beta-amyloid is intimately involved. Here we describe age related differences in learning, memory, synaptic transmission and long-term potentiation (LTP) in wild type and APPswe/PS1DeltaE9 mice, which produce increasing amounts of Abeta1-42 with age. The mice have both age related and age-independent deficits in radial arm water maze performance. Blind studies of hippocampal slices from transgenic and wild type mice demonstrate that transgenic mice have impaired transient LTP and that the degree of impairment is not related to age from 3 to 12 months. The deficiencies in transient LTP may be related to the behavioral deficits that did not progress with age. The accumulation of beta-amyloid and the episodic memory deficits, both of which increased with age, were not accompanied by an alteration in synaptic transmission or sustained LTP in the in vitro hippocampal slices.

Complete rescue of cerebrovascular function in aged Alzheimer's disease transgenic mice by antioxidants and pioglitazone, a peroxisome proliferator-activated receptor gamma agonist

Accumulating evidence suggests that cerebrovascular dysfunction is an important factor in the pathogenesis of Alzheimer's disease (AD). Using aged ( approximately 16 months) amyloid precursor protein (APP) transgenic mice that exhibit increased production of the amyloid-beta (Abeta) peptide and severe cerebrovascular and memory deficits, we examined the capacity of in vivo treatments with the antioxidants N-acetyl-L-cysteine (NAC) and tempol, or the peroxisome proliferator-activated receptor gamma agonist pioglitazone to rescue cerebrovascular function and selected markers of AD neuropathology. Additionally, we tested the ability of pioglitazone to normalize the impaired increases in cerebral blood flow (CBF) and glucose uptake (CGU) induced by whisker stimulation, and to reverse spatial memory deficits in the Morris water maze. All compounds fully restored cerebrovascular reactivity of isolated cerebral arteries concomitantly with changes in proteins regulating oxidative stress, without reducing brain Abeta levels or Abeta plaque load. Pioglitazone, but not NAC, significantly attenuated astroglial activation and improved, albeit nonsignificantly, the reduced cortical cholinergic innervation. Furthermore, pioglitazone completely normalized the CBF and CGU responses to increased neuronal activity, but it failed to improve spatial memory. Our results are the first to demonstrate that late pharmacological intervention with pioglitazone not only overcomes cerebrovascular dysfunction and altered neurometabolic coupling in aged APP mice, but also counteracts cerebral oxidative stress, glial activation, and, partly, cholinergic denervation. Although early or combined therapy may be warranted to improve cognition, these findings unequivocally point to pioglitazone as a most promising strategy for restoring cerebrovascular function and counteracting several AD markers detrimental to neuronal function.

Intracellular Aß triggers neuron loss in the cholinergic system of the APP/PS1KI mouse model of Alzheimer's disease

Loss of cholinergic neurons in the Nucleus Basalis of Meynert in Alzheimer's disease (AD) patients was one of the first discoveries of neuron loss in AD. Despite an intense focus on the cholinergic system in AD, the reason for this cholinergic neuron loss is yet unknown. In the present study we examined Abeta-induced pathology and neuron loss in the cholinergic system of the bigenic APP/PS1KI mouse model. Expression of the APP transgene was found in ChAT-positive neurons of motor nuclei accompanied by robust intracellular Abeta accumulation, whereas no APP expressing neurons and thus no intracellular Abeta accumulation were found in neither the forebrain or pons complexes, nor in the caudate putamen. This expression pattern was used as a model system to study the effect of intra- and extracellular Abeta accumulation on neuron loss in the cholinergic system. Stereological quantification revealed a loss of ChAT-positive neurons in APP/PS1KI mice only in the motor nuclei Mo5 and 7N accumulating intracellular Abeta. This study supports the hypothesis of intracellular Abeta accumulation as an early pathological alteration contributing to cell death in AD.

Dystrophic serotonergic axons in neurodegenerative diseases

Neurodegenerative diseases such as Parkinson's disease (PD), frontal lobe dementia (FLD) and diffuse Lewy-body dementia (DLBD) have diverse neuropathologic features. Here we report that serotonin fibers are dystrophic in the brains of individuals with these three diseases. In neuropathologically normal (control) brains (n=3), serotonin axons immunoreactive (IR) with antibodies against the serotonin transporter (5-HTT) protein were widely distributed in cortex (entorhinal and dorsolateral prefrontal), hippocampus and rostral brainstem. 5-HTT-IR fibers-of-passage appeared thick, smooth, and unbranched in medial forebrain bundle, medial lemniscus and cortex white matter. The terminal branches were fine, highly branched and varicose in substantia nigra, hippocampus and cortical gray matter. In the diseased brains, however, 5-HTT-IR fibers in the forebrain were reduced in number and were frequently bulbous, splayed, tightly clustered and enlarged. Morphometric analysis revealed significant differences in the size distribution of the 5-HTT-IR profiles in dorsolateral prefrontal area between neurodegenerative diseases and controls. Our observations provide direct morphologic evidence for degeneration of human serotonergic axons in the brains of patients with neurodegenerative diseases despite the limited size (n=3 slices for each region (3) from each brain (4), total slices was n=36) and the lack of extensive clinical characterization of the analyzed cohort. This is the first report of dystrophic 5-HTT-IR axons in postmortem human tissue.

Longitudinal neuroanatomical changes determined by deformation-based morphometry in a mouse model of Alzheimer's disease

Magnetic resonance imaging (MRI) of transgenic mice has the potential to provide valuable insight into the complex mechanisms underlying Alzheimer's disease (AD). Quantification of pathological changes is typically performed using manual segmentation methods, and requires a priori hypotheses about anatomical structures for volumetric measurement. Alternatively, deformation-based morphometry (DBM) has been shown to be a powerful, automated technique for detecting anatomical differences between populations by examining the deformation fields used to nonlinearly warp MR images. In this multiple timepoint, in vivo study, we have applied an automated, unbiased technique for the creation of a nonlinear, population-specific reference space from which robust DBM analysis can be performed. A general, linear mixed-effects model framework was developed to follow the evolution of structural changes in mouse brain from 2.5 to 9 months of age, and to examine neuroanatomical differences between a transgenic (TG) APP/PS1 murine model of AD and wild-type (WT) littermates. Morphometric abnormalities in the TG group were localized to regions of the hippocampus, cortex, olfactory bulbs, stria terminalis, brain stem, cerebellum, and ventricles. Although volumetric reductions were detected in TG mice, no general brain atrophy was found, suggesting a developmental, rather than a degenerative, pathological process. Finally, we established a strong correlation between a DBM summary measure and manually segmented volumes for each image in the dataset. These results support the utility of DBM to study longitudinal morphological changes in mouse models of central nervous system diseases in an automated and exploratory fashion.

Dietary and genetic compromise in folate availability reduces acetylcholine, cognitive performance and increases aggression: critical role of S-adenosyl methionine

Folate deficiency has been associated with age-related neurodegeneration. One direct consequence of folate deficiency is a decline in the major methyl donor, S-adenosyl methionine (SAM). We demonstrate herein that pro-oxidant stress and dietary folate deficiency decreased levels of acetylcholine and impaired cognitive performance to various degrees in normal adult mice (9-12 months of age, adult mice heterozygously lacking 5',10'-methylene tetrahydrofolate reductase, homozygously lacking apolipoprotein E, or expressing human ApoE2, E3 or E4, and aged (2-2.5 year old) normal mice. Dietary supplementation with SAM in the absence of folate restored acetylcholine levels and cognitive performance to respective levels observed in the presence of folate. Increased aggressive behavior was observed among some but not all genotypes when maintained on the deficient diet, and was eliminated in all cases supplementation with SAM. Folate deficiency decreased levels of choline and N-methyl nicotinamide, while dietary supplementation with SAM increased methylation of nicotinamide to generate N-methyl nicotinamide and restored choline levels within brain tissue. Since N-methyl nicotinamide inhibits choline transport out of the central nervous system, and choline is utilized as an alternative methyl donor, these latter findings suggest that SAM may maintain acetylcholine levels in part by maintaining availability of choline. These findings suggest that dietary supplementation with SAM represents a useful therapeutic approach for age-related neurodegeneration which may augment pharmacological approaches to maintain acetylcholine levels, in particular during dietary or genetic compromise in folate usage.

Oxidative stress and cerebrovascular dysfunction in mouse models of Alzheimer's disease

Several factors have been implicated in Alzheimer's disease (AD) but there is no definite conclusion as to the main pathogenic agents. Mutations in the amyloid precursor protein (APP) that lead to increased production of amyloid beta peptide (A beta) are associated with the early-onset, familial forms of AD. However, in addition to ageing, the most common risk factors for the sporadic, prevalent form of AD are hypertension, hypercholesterolaemia, ischaemic stroke, the ApoE4 allele and diabetes, all characterized by a vascular pathology. In AD, the vascular pathology includes accumulation of A beta in the vessel wall, vascular fibrosis, and other ultrastructural changes in constituent endothelial and smooth muscle cells. Moreover, the ensuing chronic cerebral hypoperfusion has been proposed as a determinant factor in the accompanying cognitive deficits. In transgenic mice that overexpress mutated forms of the human APP (APP mice), the increased production of A beta results in vascular oxidative stress and loss of vasodilatory function. The culprit molecule, superoxide, triggers the synthesis of other reactive oxygen species and the sequestration of nitric oxide (NO), thus impairing resting cerebrovascular tone and NO-dependent dilatations. The A beta-induced cerebrovascular dysfunction can be completely abrogated in aged APP mice with antioxidant therapy. In contrast, in mice that overproduce an active form of the cytokine transforming growth factor-beta1 and recapitulate the vascular structural changes seen in AD, antioxidants have no beneficial effect on the accompanying cerebrovascular deficits. This review discusses the beneficial role and limitations of antioxidant therapy in AD cerebrovascular pathology.

Cholinergic forebrain degeneration in the APPswe/PS1DeltaE9 transgenic mouse

The impact of Abeta deposition upon cholinergic intrinsic cortical and striatal, as well as basal forebrain long projection neuronal systems was qualitatively and quantitatively evaluated in young (2-6 months) and middle-aged (10-16 months) APPswe/PS1DeltaE9 transgenic (tg) mice. Cholinergic neuritic swellings occurred as early as 2-3 months of age in the cortex and hippocampus and 5-6 months in the striatum of tg mice. However, cholinergic neuron number or choline acetyltransferase (ChAT) optical density measurements remained unchanged in the forebrain structures with age in APPswe/PS1DeltaE9 tg mice. ChAT enzyme activity decreased significantly in the cortex and hippocampus of middle-aged tg mice. These results suggest that Abeta deposition has age-dependent effects on cortical and hippocampal ChAT fiber networks and enzyme activity, but does not impact the survival of cholinergic intrinsic or long projection forebrain neurons in APPswe/PS1DeltaE9 tg mice.

Dynamic remodelling of synapses can occur in the absence of the parent cell body

Background

Retraction of nerve terminals is a characteristic feature of development, injury and insult and may herald many neurodegenerative diseases. Although morphological events have been well characterized, we know relatively little about the nature of the underlying cellular machinery. Evidence suggests a strong local component in determining which neuronal branches and synapses are lost, but a greater understanding of this basic neurological process is required. Here we test the hypothesis that nerve terminals are semi-autonomous and able to rapidly respond to local stimuli in the absence of communication with their parent cell body.

Results

We used an isolated preparation consisting of distal peripheral nerve stumps, associated nerve terminals and post-synaptic muscle fibres, maintained in-vitro for up to 3 hrs. In this system synapses are intact but the presynaptic nerve terminal is disconnected from its cell soma. In control preparations synapses were stable for extended periods and did not undergo Wallerian degneration. In contrast, addition of purines triggers rapid changes at synapses. Using fluorescence and electron microscopy we observe ultrastructural and gross morphological events consistent with nerve terminal retraction. We find no evidence of Wallerian or Wallerian-like degeneration in these preparations. Pharmacological experiments implicate pre-synaptic P2X7 receptor subunits as key mediators of these events.

Conclusion

The data presented suggest; first that isolated nerve terminals are able to regulate connectivity independent of signals from the cell body, second that synapses exist in a dynamic state, poised to shift from stability to loss by activating intrinsic mechanisms and molecules, and third that local purines acting at purinergic receptors can trigger these events. A role for ATP receptors in this is not surprising since they are frequently activated during cellular injury, when adenosine tri-phosphate is released from damaged cells. Local control demands that the elements necessary to drive retraction are constitutively present. We hypothesize that pre-existing scaffolds of molecular motors and cytoskeletal proteins could provide the dynamism required to drive such structural changes in nerve terminals in the absence of the cell body.

The length of hippocampal cholinergic fibers is reduced in the aging brain

Cholinergic deficits occur in the aged hippocampus and they are significant in Alzheimer's disease. Using stereological and biochemical approaches, we characterized the cholinergic septohippocampal pathway in old (24 months) and young adult (3 months) rats. The total length of choline acetyltransferase (ChAT)-positive fibers in the dorsal hippocampus was significantly decreased by 32% with aging (F((1,9))=20.94, p=0.0014), along with the levels of synaptophysin, a presynaptic marker. No significant changes were detected in ChAT activity or in the amounts of ChAT protein, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), tropomyosin related kinase receptor (Trk) A, TrkB, or p75 neurotrophin receptor (p75(NTR)) in the aged dorsal hippocampus. The number and size of ChAT-positive neurons and the levels of ChAT activity, NGF and BDNF were not statistically different in the septum of aged and young adult rats. This study suggests that substantial synaptic loss and cholinergic axonal degeneration occurs during aging and reinforces the importance of therapies that can protect axons and promote their growth in order to restore cholinergic neurotransmission.

Impairment of muscarinic transmission in transgenic APPswe/PS1dE9 mice

We assessed the integrity of cholinergic neurotransmission in parietal cortex of young adult (7 months) and aged (17 months) transgenic APPswe/PS1dE9 female mice compared to littermate controls. Choline acetyltransferase and acetylcholinesterase activity declined age-dependently in both genotypes, whereas both age- and genotype-dependent decline was found in butyrylcholinesterase activity, vesicular acetylcholine transporter density, muscarinic receptors and carbachol stimulated binding of GTP gamma S in membranes as a functional indicator of muscarinic receptor coupling to G-proteins. Notably, vesicular acetylcholine transporter levels and muscarinic receptor-G-protein coupling were impaired in transgenic mice already at the age of 7 months compared to wild type littermates. Thus, brain amyloid accumulation in this mouse model is accompanied by a serious deterioration of muscarinic transmission already before the mice manifest significant cognitive deficits.

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

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