NMDA receptor-dependent signaling pathways that underlie amyloid beta-protein disruption of LTP in the hippocampus

Ketogenic diet and BHB rescue the fall of long-term potentiation in an Alzheimer's mouse model and stimulates synaptic plasticity pathway enzymes

The Ketogenic Diet (KD) improves memory and longevity in aged C57BL/6 mice. We tested 7 months KD vs. control diet (CD) in the mouse Alzheimer's Disease (AD) model APP/PS1. KD significantly rescued Long-Term-Potentiation (LTP) to wild-type levels, not by changing Amyloid-β (Aβ) levels. KD's 'main actor' is thought to be Beta-Hydroxy-butyrate (BHB) whose levels rose significantly in KD vs. CD mice, and BHB itself significantly rescued LTP in APP/PS1 hippocampi. KD's 6 most significant pathways induced in brains by RNAseq all related to Synaptic Plasticity. KD induced significant increases in synaptic plasticity enzymes p-ERK and p-CREB in both sexes, and of brain-derived neurotrophic factor (BDNF) in APP/PS1 females. We suggest KD rescues LTP through BHB's enhancement of synaptic plasticity. LTP falls in Mild-Cognitive Impairment (MCI) of human AD. KD and BHB, because they are an approved diet and supplement respectively, may be most therapeutically and translationally relevant to the MCI phase of Alzheimer's Disease.

Molecular insights into the structure destabilization effects of ECG and EC on the Aβ protofilament: An all-atom molecular dynamics simulation study

The formation of Aβ into amyloid fibrils was closely connected to AD, therefore, the Aβ aggregates were the primary therapeutic targets against AD. Previous studies demonstrated that epicatechin-3-gallate (ECG), which possessed a gallate moiety, exhibited a greater ability to disrupt the preformed Aβ amyloid fibrils than epicatechin (EC), indicating that the gallate moiety was crucial. In the present study, the molecular mechanisms were investigated. Our results demonstrated that ECG had more potent disruptive impacts on the β-sheet structure and K28-A42 salt bridges than EC. We found that ECG significantly interfered the interactions between Peptide-4 and Peptide-5. However, EC could not. The disruption of K28-A42 salt bridges by ECG was mainly due to the interactions between ECG and the hydrophobic residues located at C-terminus. Interestingly, EC disrupted the K28-A42 salt bridges by the interactions with C-terminal hydrophobic residues and the cation-π interactions with K28. Moreover, our results indicated that hydrophobic interactions, H-bonds, π-π interactions and cation-π interactions between ECG and the bend of L-shaped region caused the disaggregation of interactions between Peptide-4 and Peptide-5. Significantly, gallate moiety in ECG had contributed tremendously to the disaggregation. We believed that our findings could be useful for designing prospective drug candidates targeting AD.

Putative pathological mechanisms of late-life depression and Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder that is characterized by progressive impairment in cognition and memory. AD is accompanied by several neuropsychiatric symptoms, with depression being the most prominent. Although depression has long been known to be associated with AD, controversial findings from preclinical and clinical studies have obscured the precise nature of this association. However recent evidence suggests that depression could be a prodrome or harbinger of AD. Evidence indicates that the major central serotonergic nucleus-the dorsal raphe nucleus (DRN)-shows very early AD pathology: neurofibrillary tangles made of hyperphosphorylated tau protein and degenerated neurites. AD and depression share common pathophysiologies, including functional deficits of the serotonin (5-HT) system. 5-HT receptors have modulatory effects on the progression of AD pathology i.e., reduction in Aβ load, increased hyper-phosphorylation of tau, decreased oxidative stress etc. Moreover, preclinical models show a role for specific channelopathies that result in abnormal regional activational and neuroplasticity patterns. One of these concerns the pathological upregulation of the small conductance calcium-activated potassium (SK) channel in corticolimbic structure. This has also been observed in the DRN in both diseases. The SKC is a key regulator of cell excitability and long-term potentiation (LTP). SKC over-expression is positively correlated with aging and cognitive decline, and is evident in AD. Pharmacological blockade of SKCs has been reported to reverse symptoms of depression and AD. Thus, aberrant SKC functioning could be related to depression pathophysiology and diverts its late-life progression towards the development of AD. We summarize findings from preclinical and clinical studies suggesting a molecular linkage between depression and AD pathology. We also provide a rationale for considering SKCs as a novel pharmacological target for the treatment of AD-associated symptoms.

New Insights into Alzheimer’s Disease: Novel Pathogenesis, Drug Target and Delivery

Alzheimer’s disease (AD), the most common type of dementia, is characterized by senile plaques composed of amyloid β protein (Aβ) and neurofilament tangles derived from the hyperphosphorylation of tau protein. However, the developed medicines targeting Aβ and tau have not obtained ideal clinical efficacy, which raises a challenge to the hypothesis that AD is Aβ cascade-induced. A critical problem of AD pathogenesis is which endogenous factor induces Aβ aggregation and tau phosphorylation. Recently, age-associated endogenous formaldehyde has been suggested to be a direct trigger for Aβ- and tau-related pathology. Another key issue is whether or not AD drugs are successfully delivered to the damaged neurons. Both the blood–brain barrier (BBB) and extracellular space (ECS) are the barriers for drug delivery. Unexpectedly, Aβ-related SP deposition in ECS slows down or stops interstitial fluid drainage in AD, which is the direct reason for drug delivery failure. Here, we propose a new pathogenesis and perspectives on the direction of AD drug development and drug delivery: (1) aging-related formaldehyde is a direct trigger for Aβ assembly and tau hyperphosphorylation, and the new target for AD therapy is formaldehyde; (2) nano-packaging and physical therapy may be the promising strategy for increasing BBB permeability and accelerating interstitial fluid drainage.

Phospholipase D1 Attenuation Therapeutics Promotes Resilience against Synaptotoxicity in 12-Month-Old 3xTg-AD Mouse Model of Progressive Neurodegeneration

Abrogating synaptotoxicity in age-related neurodegenerative disorders is an extremely promising area of research with significant neurotherapeutic implications in tauopathies including Alzheimer's disease (AD). Our studies using human clinical samples and mouse models demonstrated that aberrantly elevated phospholipase D1 (PLD1) is associated with amyloid beta (Aβ) and tau-driven synaptic dysfunction and underlying memory deficits. While knocking out the lipolytic PLD1 gene is not detrimental to survival across species, elevated expression is implicated in cancer, cardiovascular conditions and neuropathologies, leading to the successful development of well-tolerated mammalian PLD isoform-specific small molecule inhibitors. Here, we address the importance of PLD1 attenuation, achieved using repeated 1 mg/kg of VU0155069 (VU01) intraperitoneally every alternate day for a month in 3xTg-AD mice beginning only from ~11 months of age (with greater influence of tau-driven insults) compared to age-matched vehicle (0.9% saline)-injected siblings. A multimodal approach involving behavior, electrophysiology and biochemistry corroborate the impact of this pre-clinical therapeutic intervention. VU01 proved efficacious in preventing in later stage AD-like cognitive decline affecting perirhinal cortex-, hippocampal- and amygdala-dependent behaviors. Glutamate-dependent HFS-LTP and LFS-LTD improved. Dendritic spine morphology showed the preservation of mushroom and filamentous spine characteristics. Differential PLD1 immunofluorescence and co-localization with Aβ were noted.

The Interplay Between Cholesterol and Amyloid-β on HT22 Cell Viability, Morphology, and Receptor Tyrosine Kinase Signaling

BACKGROUND

There is a lack of understanding in the molecular and cellular mechanisms of Alzheimer's disease that has hindered progress on therapeutic development. The focus has been on targeting toxic amyloid-β (Aβ) pathology, but these therapeutics have generally failed in clinical trials. Aβ is an aggregation-prone protein that has been shown to disrupt cell membrane structure in molecular biophysics studies and interfere with membrane receptor signaling in cell and animal studies. Whether the lipid membrane or specific receptors are the primary target of attack has not been determined.

OBJECTIVE

This work elucidates some of the interplay between membrane cholesterol and Aβ42 on HT22 neuronal cell viability, morphology, and platelet-derived growth factor (PDGF) signaling pathways.

METHODS

The effects of cholesterol depletion by methyl-β-cyclodextrin followed by treatment with Aβ and/or PDGF-AA were assessed by MTT cell viability assays, western blot, optical and AFM microscopy.

RESULTS

Cell viability studies show that cholesterol depletion was mildly protective against Aβ toxicity. Together cholesterol reduction and Aβ42 treatment compounded the disruption of the PDGFα receptor activation. Phase contrast optical microscopy and live cell atomic force microscopy imaging revealed that cytotoxic levels of Aβ42 caused morphological changes including cell membrane damage, cytoskeletal disruption, and impaired cell adhesion; cell damage was ameliorated by cellular cholesterol depletion.

CONCLUSIONS

Cholesterol depletion impacted the effects of Aβ42 on HT22 cell viability, morphology, and receptor tyrosine kinase signaling.

Inflammation-Mediated Responses in the Development of Neurodegenerative Diseases

Since its first description over a century ago, neurodegenerative diseases (NDDs) have impaired the lives of millions of people worldwide. As one of the major threats to human health, NDDs are characterized by progressive loss of neuronal structure and function, leading to the impaired function of the CNS. While the precise mechanisms underlying the emergence of NDDs remains elusive, association of neuroinflammation with the emergence of NDDs has been suggested. The immune system is tightly controlled to maintain homeostatic milieu and failure in doing so has been shown catastrophic. Here, we review current concepts on the cellular and molecular drivers responsible in the induction of neuroinflammation and how such event further promotes neuronal damage leading to neurodegeneration. Experimental data generated from cell culture and animal studies, gross and molecular pathologies of human CNS samples, and genome-wide association study are discussed to provide deeper insights into the mechanistic details of neuroinflammation and its roles in the emergence of NDDs.

Is non-invasive brain stimulation effective for cognitive enhancement in Alzheimer's disease? An updated meta-analysis

OBJECTIVE

Alzheimer's disease dementia (AD) and its preclinical stage, mild cognitive impairment (MCI), are critical issues confronting the aging society. Non-invasive brain stimulation (NIBS) techniques have the potential to be effective tools for enhancing cognitive functioning. The main objective of our meta-analysis was to quantify and update the status of the efficacy of repetitive Transcranial Magnetic Stimulation (rTMS) and Transcranial Direct Current Stimulation (tDCS) when applied in AD and MCI.

METHODS

The systematic literature search was conducted in PubMed and Web of Science according to PRISMA statement.

RESULTS

Pooled effect sizes (Hedges' g) from 32 studies were analyzed using random effect models. We found both, rTMS and tDCS to have significant immediate cognition-enhancing effect in AD with rTMS inducing also beneficial long-term effects. We found no evidence for synergistic effect of cognitive training with NIBS.

CONCLUSIONS

In AD a clinical recommendation can be made for NEURO-AD^TM system and for high-frequency rTMS over the left dorsolateral prefrontal cortex (DLPFC) as probably effective protocols (B-level of evidence) and for anodal tDCS over the left DLPFC as a possibly effective.

SIGNIFICANCE

According to scientific literature, NIBS may be an effective method for improving cognition in AD and possibly in MCI.

Heat shock proteins and the calcineurin-crz1 signaling regulate stress responses in fungi

The heat shock proteins (Hsps) act as a molecular chaperone to stabilize client proteins involved in various cell functions in fungi. Hsps are classified into different families such as HSP90, HSP70, HSP60, HSP40, and small HSPs (sHsps). Hsp90, a well-studied member of the Hsp family proteins, plays a role in growth, cell survival, and pathogenicity in fungi. Hsp70 and sHsps are involved in the development, tolerance to stress conditions, and drug resistance in fungi. Hsp60 is a mitochondrial chaperone, and Hsp40 regulates fungal ATPase machinery. In this review, we describe the cell functions, regulation, and the molecular link of the Hsps with the calcineurin-crz1 calcium signaling pathway for their role in cell survival, growth, virulence, and drug resistance in fungi and related organisms.

Memory related molecular signatures: The pivots for memory consolidation and Alzheimer's related memory decline

Age-related cognitive decline is the major cause of concern due to its 70% more incidence than dementia cases worldwide. Moreover, aging is also the major risk factor of Alzheimer's disease (AD), associated with progressive memory loss. Approx. 13 million people will have Alzheimer-related memory decline by 2050. Learning and memory is the fundamental process of brain functions. However, the mechanism for the same is still under investigation. Thus, it is critical to understand the process of memory consolidation in the brain and extrapolate its understanding to the memory decline mechanism. Research on learning and memory has identified several molecular signatures such as Protein kinase M zeta (PKMζ), Calcium/calmodulin-dependent protein kinase II (CaMKII), Brain-derived neurotrophic factor (BDNF), cAMP-response element binding protein (CREB) and Activity-regulated cytoskeleton-associated protein (Arc) crucial for the maintenance and stabilization of long-term memory in the brain. Interestingly, memory decline in AD has also been linked to the abnormality in expressing these memory-related molecular signatures. Hence, in the present consolidated review, we explored the role of these memory-related molecular signatures in long-term memory consolidation. Additionally, the effect of amyloid-beta toxicity on these molecular signatures is discussed in detail.

GlyCEST: Magnetic Resonance Imaging of Glycine—Distribution in the Normal Murine Brain and Alterations in 5xFAD Mice

The glycine level in the brain is known to be altered in neuropsychiatric disorders, such as schizophrenia and Alzheimer's disease (AD). Several studies have reported the in vivo measurement of glycine concentrations in the brain using proton magnetic resonance spectroscopy (¹H-MRS), but ¹H-MRS is not capable of imaging the distribution of glycine concentration with high spatial resolution. Chemical exchange saturation transfer magnetic resonance imaging (CEST-MRI) is a new technology that can detect specific molecules, including amino acids, in tissues. To validate the measurements of glycine concentrations in living tissues using CEST from glycine to water (GlyCEST), we extracted the brain tissues from mice and performed biochemical tests. In wild-type C57BL/6 mice, GlyCEST effects were found to be higher in the thalamus than in the cerebral cortex (P < 0.0001, paired t-test), and this result was in good agreement with the biochemical results. In 5xFAD mice, an animal model of AD, GlyCEST measurements demonstrated that glycine concentrations in the cerebral cortex (P < 0.05, unpaired t-test) and thalamus (P < 0.0001, unpaired t-test), but not in the hippocampus, were decreased compared to those in wild-type mice. These findings suggest that we have successfully applied the CEST-MRI technique to map the distribution of glycine concentrations in the murine brain. The present method also captured the changes in cerebral glycine concentrations in mice with AD. Imaging the distribution of glycine concentrations in the brain can be useful in investigating and elucidating the pathological mechanisms of neuropsychiatric disorders.

Past, present and future of therapeutic strategies against amyloid-β peptides in Alzheimer's disease: a systematic review

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease in ageing, affecting around 46 million people worldwide but few treatments are currently available. The etiology of AD is still puzzling, and new drugs development and clinical trials have high failure rates. Urgent outline of an integral (multi-target) and effective treatment of AD is needed. Accumulation of amyloid-β (Aβ) peptides is considered one of the fundamental neuropathological pillars of the disease, and its dyshomeostasis has shown a crucial role in AD onset. Therefore, many amyloid-targeted therapies have been investigated. Here, we will systematically review recent (from 2014) investigational, follow-up and review studies focused on anti-amyloid strategies to summarize and analyze their current clinical potential. Combination of anti-Aβ therapies with new developing early detection biomarkers and other therapeutic agents acting on early functional AD changes will be highlighted in this review. Near-term approval seems likely for several drugs acting against Aβ, with recent FDA approval of a monoclonal anti-Aβ oligomers antibody -aducanumab- raising hopes and controversies. We conclude that, development of oligomer-epitope specific Aβ treatment and implementation of multiple improved biomarkers and risk prediction methods allowing early detection, together with therapies acting on other factors such as hyperexcitability in early AD, could be the key to slowing this global pandemic.

A potential biomarker of preclinical Alzheimer's disease: The olfactory dysfunction and its pathogenesis-based neural circuitry impairments

The olfactory dysfunction can signal and act as a potential biomarker of preclinical AD. However, the precise regulatory mechanism of olfactory function on the neural pathogenesis of AD is still unclear. The impairment of neural networks in olfaction system has been shown to be tightly associated with AD. As key brain regions of the olfactory system, the olfactory bulb (OB) and the piriform cortex (PCx) have a profound influence on the olfactory function. Therefore, this review will explore the mechanism of olfactory dysfunction in preclinical AD in the perspective of abnormal neural networks in the OB and PCx and their associated brain regions, especially from two aspects of aberrant oscillations and synaptic plasticity damages, which help better understand the underlying mechanism of olfactory neural network damages related to AD.

The role of amyloids in Alzheimer's and Parkinson's diseases

With varying clinical symptoms, most neurodegenerative diseases are associated with abnormal loss of neurons. They share the same common pathogenic mechanisms involving misfolding and aggregation, and these visible aggregates of proteins are deposited in the central nervous system. Amyloid formation is thought to arise from partial unfolding of misfolded proteins leading to the exposure of hydrophobic surfaces, which interact with other similar structures and give rise to form dimers, oligomers, protofibrils, and eventually mature fibril aggregates. Accumulating evidence indicates that amyloid oligomers, not amyloid fibrils, are the most toxic species that causes Alzheimer's disease (AD) and Parkinson's disease (PD). AD has recently been recognized as the 'twenty-first century plague', with an incident rate of 1% at 60 years of age, which then doubles every fifth year. Currently, 5.3 million people in the US are afflicted with this disease, and the number of cases is expected to rise to 13.5 million by 2050. PD, a disorder of the brain, is the second most common form of dementia, characterized by difficulty in walking and movement. Keeping the above views in mind, in this review we have focused on the roles of amyloid in neurodegenerative diseases including AD and PD, the involvement of amyloid in mitochondrial dysfunction leading to neurodegeneration, are also considered in the review.

Beta Amyloid, Tau Protein, and Neuroinflammation: An Attempt to Integrate Different Hypotheses of Alzheimer’s Disease Pathogenesis

Abstract

Alzheimer’s disease (AD) is a neurodegenerative disease that inevitably results in dementia and death. Currently, there are no pathogenetically grounded methods for the prevention and treatment of AD, and all current treatment regimens are symptomatic and unable to significantly delay the development of dementia. The accumulation of β-amyloid peptide (Aβ), which is a spontaneous, aggregation-prone, and neurotoxic product of the processing of signaling protein APP (Amyloid Precursor Protein), in brain tissues, primarily in the hippocampus and the frontal cortex, was for a long time considered the main cause of neurodegenerative changes in AD. However, attempts to treat AD based on decreasing Aβ production and aggregation did not bring significant clinical results. More and more arguments are arising in favor of the fact that the overproduction of Aβ in most cases of AD is not the initial cause, but a concomitant event of pathological processes in the course of the development of sporadic AD. The concept of neuroinflammation has come to the fore, suggesting that inflammatory responses play the leading role in the initiation and development of AD, both in brain tissue and in the periphery. The hypothesis about the key role of neuroinflammation in the pathogenesis of AD opens up new opportunities in the search for ways to treat and prevent this socially significant disease.

β-Amyloid disruption of LTP/LTD balance is mediated by AKAP150-anchored PKA and Calcineurin regulation of Ca2+-permeable AMPA receptors

Regulated insertion and removal of postsynaptic AMPA glutamate receptors (AMPARs) mediates hippocampal long-term potentiation (LTP) and long-term depression (LTD) synaptic plasticity underlying learning and memory. In Alzheimer’s disease β-amyloid (Aβ) oligomers may impair learning and memory by altering AMPAR trafficking and LTP/LTD balance. Importantly, Ca²⁺-permeable AMPARs (CP-AMPARs) assembled from GluA1 subunits are excluded from hippocampal synapses basally but can be recruited rapidly during LTP and LTD to modify synaptic strength and signaling. By employing mouse knockin mutations that disrupt anchoring of the kinase PKA or phosphatase Calcineurin (CaN) to the postsynaptic scaffold protein AKAP150, we find that local AKAP-PKA signaling is required for CP-AMPAR recruitment, which can facilitate LTP but also, paradoxically, prime synapses for Aβ impairment of LTP mediated by local AKAP-CaN LTD signaling that promotes subsequent CP-AMPAR removal. These findings highlight the importance of PKA/CaN signaling balance and CP-AMPARs in normal plasticity and aberrant plasticity linked to disease.

In Alzheimer’s disease, Aβ oligomers disrupt hippocampal neuronal plasticity and cognition. Sanderson et al. show how the postsynaptic scaffold protein AKAP150 coordinates PKA and Calcineurin regulation of Ca²⁺-permeable AMPA-type glutamate receptors to mediate disruption of synaptic plasticity by Aβ oligomers.

An Unbalanced Synaptic Transmission: Cause or Consequence of the Amyloid Oligomers Neurotoxicity?

Amyloid-β (Aβ) 1-40 and 1-42 peptides are key mediators of synaptic and cognitive dysfunction in Alzheimer's disease (AD). Whereas in AD, Aβ is found to act as a pro-epileptogenic factor even before plaque formation, amyloid pathology has been detected among patients with epilepsy with increased risk of developing AD. Among Aβ aggregated species, soluble oligomers are suggested to be responsible for most of Aβ's toxic effects. Aβ oligomers exert extracellular and intracellular toxicity through different mechanisms, including interaction with membrane receptors and the formation of ion-permeable channels in cellular membranes. These damages, linked to an unbalance between excitatory and inhibitory neurotransmission, often result in neuronal hyperexcitability and neural circuit dysfunction, which in turn increase Aβ deposition and facilitate neurodegeneration, resulting in an Aβ-driven vicious loop. In this review, we summarize the most representative literature on the effects that oligomeric Aβ induces on synaptic dysfunction and network disorganization.

Elevating the Levels of Calcium Ions Exacerbate Alzheimer's Disease via Inducing the Production and Aggregation of β-Amyloid Protein and Phosphorylated Tau

Alzheimer’s disease (AD) is a neurodegenerative disease with a high incidence rate. The main pathological features of AD are β-amyloid plaques (APs), which are formed by β-amyloid protein (Aβ) deposition, and neurofibrillary tangles (NFTs), which are formed by the excessive phosphorylation of the tau protein. Although a series of studies have shown that the accumulation of metal ions, including calcium ions (Ca²⁺), can promote the formation of APs and NFTs, there is no systematic review of the mechanisms by which Ca²⁺ affects the development and progression of AD. In view of this, the current review summarizes the mechanisms by which Ca²⁺ is transported into and out of cells and organelles, such as the cell, endoplasmic reticulum, mitochondrial and lysosomal membranes to affect the balance of intracellular Ca²⁺ levels. In addition, dyshomeostasis of Ca²⁺ plays an important role in modulating the pathogenesis of AD by influencing the production and aggregation of Aβ peptides and tau protein phosphorylation and the ways that disrupting the metabolic balance of Ca²⁺ can affect the learning ability and memory of people with AD. In addition, the effects of these mechanisms on the synaptic plasticity are also discussed. Finally, the molecular network through which Ca²⁺ regulates the pathogenesis of AD is introduced, providing a theoretical basis for improving the clinical treatment of AD.

Chronic administration of Tat-GluR23Y ameliorates cognitive dysfunction targeting CREB signaling in rats with amyloid beta neurotoxicity

Alzheimer's disease (AD) is behaviorally characterized by memory impairments, and pathologically by amyloid β1-42 (Aβ1-42) plaques and tangles. Aβ binds to excitatory synapses and disrupts their transmission due to dysregulation of the glutamate receptors. Here we hypothesized that chronic inhibition of the endocytosis of AMPA receptors together with GluN2B subunit of NMDA receptors might improve cognition deficit induced by Aβ(1-42) neurotoxicity. Forty male Wistar rats were used in this study and divided into 5 groups: Saline + Saline, Aβ+Saline, Aβ+Ifen (Ifenprodil, 3 nmol /2 weeks), Aβ+GluR23Y (Tat-GluR23Y 3 μmol/kg/2 weeks) and Aβ+Ifen+GluR23Y (same doses and durations). Aβ(1-42) neurotoxicity was induced by intracerebroventricular (ICV) injection of Aβ1-42 (2 μg/μl/side), and then animals received the related treatments for 14 days. Cognitive performance of rats and hippocampal level of cAMP-response element-binding (CREB) were evaluated using Morris Water Maze (MWM), and western blotting respectively. Obtained data from the acquisition trials were analyzed by two way Anova and Student T test. Also one way Analysis of variance (ANOVA) with post hoc Tuckey were used to clarify between groups differences in probe test. The Group receiving Aβ, showed significant cognition deficit (long latency to platform and short total time spent in target quadrant (TTS), parallel with lower level of hippocampal CREB, versus vehicle group. While, Aβ+ GluR23Y exhibited the shortest latency to platform and the longest TTS during the probe test, parallel with the higher hippocampal level of CREB compared with other groups. The present study provides evidence that chronic administration of Tat-GluR23Y; an inhibitor of GluA2-AMPARs endocytosis, successfully restores spatial memory impaired by amyloid beta neurotoxicity targeting CREB signaling pathway.

Akt and calcium-permeable AMPA receptor are involved in the effect of pinoresinol on amyloid β-induced synaptic plasticity and memory deficits

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative disorders characterized by memory deficits. Although no drug has given promising results, synaptic dysfunction-modulating agents might be considered potential candidates for alleviating this disorder. Pinoresinol, a lignan found in Forsythia suspensa, is a memory-enhancing agent with excitatory synaptic activation. In the present study, we tested whether pinoresinol reduces learning and memory and excitatory synaptic deficits in an amyloid β (Aβ)-induced AD-like mouse model. Pinoresinol enhanced hippocampal long-term potentiation (LTP) through calcium-permeable AMPA receptor, which was mediated by Akt activation. Moreover, pinoresinol ameliorated LTP deficits in amyloid β (Aβ)-treated hippocampal slices via Akt signaling. Oral administration of pinoresinol ameliorated Aβ-induced memory deficits without sensory dysfunction. Moreover, AD-like pathology, including neuroinflammation and synaptic deficit, were ameliorated by pinoresinol administration. Collectively, pinoresinol may be a good candidate for AD therapy by modulating synaptic functions.

An Overview of the Involvement of D-Serine in Cognitive Impairment in Normal Aging and Dementia

Dementia, of which Alzheimer's disease (AD) is the most common form, is characterized by progressive cognitive deterioration, including profound memory loss, which affects functioning in many aspects of life. Although cognitive deterioration is relatively common in aging and aging is a risk factor for AD, the condition is not necessarily a part of the aging process. The N-methyl-D-aspartate glutamate receptor (NMDAR) and its co-agonist D-serine are currently of great interest as potential important contributors to cognitive function in normal aging and dementia. D-Serine is necessary for activation of the NMDAR and in maintenance of long-term potentiation (LTP) and is involved in brain development, neuronal connectivity, synaptic plasticity and regulation of learning and memory. In this paper, we review evidence, from both preclinical and human studies, on the involvement of D-serine (and the enzymes involved in its metabolism) in regulation of cognition. Potential mechanisms of action of D-serine are discussed in the context of normal aging and in dementia, as is the potential for using D-serine as a potential biomarker and/or therapeutic agent in dementia. Although there is some controversy in the literature, it has been proposed that in normal aging there is decreased expression of serine racemase and decreased levels of D-serine and down-regulation of NMDARs, resulting in impaired synaptic plasticity and deficits in learning and memory. In contrast, in AD there appears to be activation of serine racemase, increased levels of D-serine and overstimulation of NMDARs, resulting in cytotoxicity, synaptic deficits, and dementia.

Amyloid Beta-Related Alterations to Glutamate Signaling Dynamics During Alzheimer's Disease Progression

Alzheimer’s disease (AD) ranks sixth on the Centers for Disease Control and Prevention Top 10 Leading Causes of Death list for 2016, and the Alzheimer’s Association attributes 60% to 80% of dementia cases as AD related. AD pathology hallmarks include accumulation of senile plaques and neurofibrillary tangles; however, evidence supports that soluble amyloid beta (Aβ), rather than insoluble plaques, may instigate synaptic failure. Soluble Aβ accumulation results in depression of long-term potentiation leading to cognitive deficits commonly characterized in AD. The mechanisms through which Aβ incites cognitive decline have been extensively explored, with a growing body of evidence pointing to modulation of the glutamatergic system. The period of glutamatergic hypoactivation observed alongside long-term potentiation depression and cognitive deficits in later disease stages may be the consequence of a preceding period of increased glutamatergic activity. This review will explore the Aβ-related changes to the tripartite glutamate synapse resulting in altered cell signaling throughout disease progression, ultimately culminating in oxidative stress, synaptic dysfunction, and neuronal loss.

Molecular insights into the inhibitory mechanisms of gallate moiety on the Aβ1-40 amyloid aggregation: A molecular dynamics simulation study

Alzheimer's disease is the most common form of neurodegenerative disease and the formation of Aβ amyloid aggregates has been widely demonstrated to be the principal cause of Alzheimer's disease. Our previous study and other studies suggested that the gallate moiety played an obligatory role in the inhibition process of naturally occurring polyphenols on Aβ amyloid fibrils formation. However, the detailed mechanisms were still unknown. Thus, in the present study, the gallic acid (GA) was specially selected and the molecular recognition mechanisms between GA molecules and Aβ_1-40 monomer were examined and analyzed by molecular dynamics simulation. The in silico experiments revealed that GA significantly prevented the conformational changes of Aβ_1-40 monomer with no β-sheet structure during the whole 100 ns. By analyzing the binding sites of GA molecules to Aβ_1-40 monomer, we found that both hydrophilic and hydrophobic amino acid residues were participated in the binding of GA molecules to Aβ_1-40 monomer. Moreover, results from the binding free energy analysis further demonstrated that the strength of polar interactions was significantly stronger than that of nonpolar interactions. We believed that our results could help to elucidate the underlying mechanisms of gallate moiety on the anti-amyloidogenic effects of polyphenols at the atomic level.

Intra- and extracellular β-amyloid overexpression via adeno-associated virus-mediated gene transfer impairs memory and synaptic plasticity in the hippocampus

Alzheimer's disease (AD), the most common age-related neurodegenerative disorder, is currently conceptualized as a disease of synaptic failure. Synaptic impairments are robust within the AD brain and better correlate with dementia severity when compared with other pathological features of the disease. Nevertheless, the series of events that promote synaptic failure still remain under debate, as potential triggers such as β-amyloid (Aβ) can vary in size, configuration and cellular location, challenging data interpretation in causation studies. Here we present data obtained using adeno-associated viral (AAV) constructs that drive the expression of oligomeric Aβ either intra or extracellularly. We observed that expression of Aβ in both cellular compartments affect learning and memory, reduce the number of synapses and the expression of synaptic-related proteins, and disrupt chemical long-term potentiation (cLTP). Together, these findings indicate that during the progression AD the early accumulation of Aβ inside neurons is sufficient to promote morphological and functional cellular toxicity, a phenomenon that can be exacerbated by the buildup of Aβ in the brain parenchyma. Moreover, our AAV constructs represent a valuable tool in the investigation of the pathological properties of Aβ oligomers both in vivo and in vitro.

Probiotic treatment improves the impaired spatial cognitive performance and restores synaptic plasticity in an animal model of Alzheimer's disease

Studies demonstrate that damage to gut microbiota is associated with some brain disorders including neurodegenerative diseases such as Alzheimer's disease (AD). Accordingly, supporting gut microbiota has been considered as a possible strategy for AD treatment. We evaluated behavioral and electrophysiological aspects of the brain function in an animal model of AD made by intracerebroventricular injection of β-amyloid. Two groups of control rats recieved either water as vehicle (Con) or probitics (Pro + Con). Also two groups of Alzheimeric animals were treated by either vehicle (Alz) or probiotics (Pro + Alz). Sham group was only subjected to surgical procedure and received the vehicle. Spatial learning and memory was assessed in Morris water maze. Also, basic synaptic transmission and long-term potentiation (LTP) were assessed by recording field excitatory postsynaptic potentials (fEPSPs) in hippocampus. Change in anti-oxidant/oxidant factors was assessed via measuring plasma level of total anti-oxidant capacity (TAC) and malondealdehyde (MDA). Brain staining was done to confirm β-amyloid accumulation. Fecal bacteria quantification was accomplished to find how probiotic supplement affected gut microbiota. We found that while the Alz animals displayed a weak spatial performance, probiotic treatment improved the maze navigation in the Pro + Alz rats. Whereas basic synaptic transmission remained unchanged in the Alz rats, LTP was suppressed in this group. Probiotic treatment significantly restored LTP in the Pro + Alz group and further enhanced it in the Pro + Con rats. The intervention also showed a favorable effect on balance of the anti-oxidant/oxidant biomarkers in the Pro + Alz rats. This study provides the first proof on positive effect of probiotics on synaptic plasticity in an animal model of AD.

Doxycycline for Alzheimer's Disease: Fighting β-Amyloid Oligomers and Neuroinflammation

Alzheimer's disease (AD) is the most widespread form of dementia, affecting about 45 million people worldwide. Although the β-amyloid peptide (Aβ) remains the most acknowledged culprit of AD, the multiple failures of Aβ-centric therapies call for alternative therapeutic approaches. Conceivably, the complexity of the AD neuropathological scenario cannot be solved with single-target therapies, so multiple-target approaches are needed. Core targets of AD to date are soluble oligomeric Aβ species and neuroinflammation, in an intimate detrimental dialogue. Aβ oligomers, the most neurotoxic species, appear to induce synaptic and cognitive dysfunction through the activation of glial cells. Anti-inflammatory drugs can prevent the action of Aβ oligomers. Neuroinflammation is a chronic event whose perpetuation leads to the continuous release of pro-inflammatory cytokines, promoting neuronal cell death and gross brain atrophy. Among the possible multi-target therapeutic alternatives, this review highlights the antibiotic tetracyclines, which besides antimicrobial activity also have pleiotropic action against amyloidosis, neuroinflammation, and oxidative stress. A particular focus will be on doxycycline (Doxy), a second-generation tetracycline that crosses the blood-brain barrier more easily and has a safer clinical profile. Doxy emerged as a promising preventive strategy in prion diseases and gave compelling pre-clinical results in mouse models of AD against Aβ oligomers and neuroinflammation. This strongly supports its therapeutic potential and calls for deciphering its exact mechanisms of action so as to maximize its effects in the clinic.

[Neurobiological effects of theanine and its possible use in neurology and psychiatry]

Theanine is an analog of glutamate and the major aminoacid in green tea. It has received growing attention in recent years because of its beneficial effects on the central nervous system. Theanine was shown to increase levels of brain-derived neurotrophic factor and to stimulate neurogenesis. Anti-stress and calming effects of theanine are the most apparent and well-studied. A number of studies showed neuroprotective effects of theanine after an ischemic cerebral injury or the exposure to toxic chemicals. It also improved cognitive function including attention, memory and learning. Recent studies demonstrated a promising role of theanine in augmentation therapy for major depressive disorder and schizophrenia. Theoretical grounds for using theanine in treatment of bipolar disorder, anxiety disorder and some neurodegenerative disorders are discussed.

The Role of N-Methyl-D-Aspartate Receptor Neurotransmission and Precision Medicine in Behavioral and Psychological Symptoms of Dementia

While the world’s population is aging, the prevalence of dementia and the associated behavioral and psychological symptoms of dementia (BPSD) rises rapidly. BPSD are associated with worsening of cognitive function and poorer prognosis. No pharmacological treatment has been approved to be beneficial for BPSD to date. Dysfunction of the N-methyl-D-aspartate receptor (NMDAR)-related neurotransmission leads to cognitive impairment and behavioral changes, both of which are core symptoms of BPSD. Memantine, an NMDAR partial antagonist, is used to treat moderate to severe Alzheimer’s disease (AD). On the other hand, a D-amino acid oxidase inhibitor improved early-phase AD. Whether to enhance or to attenuate the NMDAR may depend on the phases of dementia. It will be valuable to develop biomarkers indicating the activity of NMDAR, particularly in BPSD. In addition, recent reports suggest that gender difference exists in the treatment of dementia. Selecting subpopulations of patients with BPSD who are prone to improvement with treatment would be important. We reviewed literatures regarding the treatment of BPSD, focusing on the NMDAR-related modulation and precision medicine. Future studies examining the NMDAR modulators with the aid of potential biomarkers to tailor the treatment for individualized patients with BPSD are warranted.

The anaesthetic xenon partially restores an amyloid beta-induced impairment in murine hippocampal synaptic plasticity

BACKGROUND

It is controversially discussed whether general anaesthesia increases the risk of Alzheimer's disease (AD) or accelerates its progression. One important factor in AD pathogenesis is the accumulation of soluble amyloid beta (Aβ) oligomers which affect N-methyl-d-aspartate (NMDA) receptor function and abolish hippocampal long-term potentiation (LTP). NMDA receptor antagonists, at concentrations allowing physiological activation, can prevent Aβ-induced deficits in LTP. The anaesthetics xenon and S-ketamine both act as NMDA receptor antagonists and have been reported to be neuroprotective. In this study, we investigated the effects of subanaesthetic concentrations of these drugs on LTP deficits induced by different Aβ oligomers and compared them to the effects of radiprodil, a NMDA subunit 2B (GluN2B)-selective antagonist.

METHODS

We applied different Aβ oligomers to murine brain slices and recorded excitatory postsynaptic field potentials before and after high-frequency stimulation in the CA1 region of hippocampus. Radiprodil, xenon and S-ketamine were added and recordings evoked from a second input were measured.

RESULTS

Xenon and radiprodil, applied at low concentrations, partially restored the LTP deficit induced by pre-incubated Aβ_1-42. S-ketamine showed no effect. None of the drugs tested were able to ameliorate Aβ_1-40-induced LTP-deficits.

CONCLUSIONS

Xenon administered at subanaesthetic concentrations partially restored Aβ_1-42-induced impairment of LTP, presumably via its weak NMDA receptor antagonism. The effects were in a similar range than those obtained with the NMDA-GluN2B antagonist radiprodil. Our results point to protective properties of xenon in the context of pathological distorted synaptic physiology which might be a meaningful alternative for anaesthesia in AD patients.

Cellular Receptors of Amyloid β Oligomers (AβOs) in Alzheimer's Disease

It is estimated that Alzheimer’s disease (AD) affects tens of millions of people, comprising not only suffering patients, but also their relatives and caregivers. AD is one of age-related neurodegenerative diseases (NDs) characterized by progressive synaptic damage and neuronal loss, which result in gradual cognitive impairment leading to dementia. The cause of AD remains still unresolved, despite being studied for more than a century. The hallmark pathological features of this disease are senile plaques within patients’ brain composed of amyloid beta (Aβ) and neurofibrillary tangles (NFTs) of Tau protein. However, the roles of Aβ and Tau in AD pathology are being questioned and other causes of AD are postulated. One of the most interesting theories proposed is the causative role of amyloid β oligomers (AβOs) aggregation in the pathogenesis of AD. Moreover, binding of AβOs to cell membranes is probably mediated by certain proteins on the neuronal cell surface acting as AβO receptors. The aim of our paper is to describe alternative hypotheses of AD etiology, including genetic alterations and the role of misfolded proteins, especially Aβ oligomers, in Alzheimer’s disease. Furthermore, in this review we present various putative cellular AβO receptors related to toxic activity of oligomers.

Functional human GRIN2B promoter polymorphism and variation of mental processing speed in older adults

We investigated the role of a single nucleotide polymorphism rs3764030 (G>A) within the human GRIN2B promoter in mental processing speed in healthy, cognitively intact, older adults. In vitro DNA-binding and reporter gene assays of different allele combinations in transfected cells showed that the A allele was a gain-of-function variant associated with increasing GRIN2B mRNA levels. We tested the hypothesis that individuals with A allele will have better memory performance (i.e. faster reaction times) in older age. Twenty-eight older adults (ages 65-86) from a well-characterized longitudinal cohort were recruited and performed a modified delayed match-to-sample task. The rs3764030 polymorphism was genotyped and participants were grouped based on the presence of the A allele into GG and AA/AG. Carriers of the A allele maintained their speed of memory retrieval over age compared to GG carriers (p = 0.026 slope of the regression line between AA and AG versus GG groups). To validate the results, 12 older adults from the same cohort participated in a different version of the short-term memory task. Reaction times were significantly slower with age in older adults with G allele (p < 0.001). These findings support a role for rs3764030 in maintaining faster mental processing speed over aging.

Amyloid-β Homeostasis Bridges Inflammation, Synaptic Plasticity Deficits and Cognitive Dysfunction in Multiple Sclerosis

Cognitive deficits are frequently observed in multiple sclerosis (MS), mainly involving processing speed and episodic memory. Both demyelination and gray matter atrophy can contribute to cognitive deficits in MS. In recent years, neuroinflammation is emerging as a new factor influencing clinical course in MS. Inflammatory cytokines induce synaptic dysfunction in MS. Synaptic plasticity occurring within hippocampal structures is considered as one of the basic physiological mechanisms of learning and memory. In experimental models of MS, hippocampal plasticity is profoundly altered by proinflammatory cytokines. Although mechanisms of inflammation-induced hippocampal pathology in MS are not completely understood, alteration of Amyloid-β (Aβ) metabolism is emerging as a key factor linking together inflammation, synaptic plasticity and neurodegeneration in different neurological diseases. We explored the correlation between concentrations of Aβ_1–42 and the levels of some proinflammatory and anti-inflammatory cytokines (interleukin-1β (IL-1β), IL1-ra, IL-8, IL-10, IL-12, tumor necrosis factor α (TNFα), interferon γ (IFNγ)) in the cerebrospinal fluid (CSF) of 103 remitting MS patients. CSF levels of Aβ_1–42 were negatively correlated with the proinflammatory cytokine IL-8 and positively correlated with the anti-inflammatory molecules IL-10 and interleukin-1 receptor antagonist (IL-1ra). Other correlations, although noticeable, were either borderline or not significant. Our data show that an imbalance between proinflammatory and anti-inflammatory cytokines may lead to altered Aβ homeostasis, representing a key factor linking together inflammation, synaptic plasticity and cognitive dysfunction in MS. This could be relevant to identify novel therapeutic approaches to hinder the progression of cognitive dysfunction in MS.

Mechanisms of Alzheimer's Disease Pathogenesis and Prevention: The Brain, Neural Pathology, N-methyl-D-aspartate Receptors, Tau Protein and Other Risk Factors

The characteristic features of Alzheimer’s disease (AD) are the appearance of extracellular amyloid-beta (Aβ) plaques and neurofibrillary tangles in the intracellular environment, neuronal death and the loss of synapses, all of which contribute to cognitive decline in a progressive manner. A number of hypotheses have been advanced to explain AD. Abnormal tau phosphorylation may contribute to the formation of abnormal neurofibrillary structures. Many different structures are susceptible to AD, including the reticular formation, the nuclei in the brain stem (e.g., raphe nucleus), thalamus, hypothalamus, locus ceruleus, amygdala, substantia nigra, striatum, and claustrum. Excitotoxicity results from continuous, low-level activation of N-methyl-D-aspartate (NMDA) receptors. Premature synaptotoxicity, changes in neurotransmitter expression, neurophils loss, accumulation of amyloid β-protein deposits (amyloid/senile plaques), and neuronal loss and brain atrophy are all associated with stages of AD progression. Several recent studies have examined the relationship between Aβ and NMDA receptors. Aβ-induced spine loss is associated with a decrease in glutamate receptors and is dependent upon the calcium-dependent phosphatase calcineurin, which has also been linked to long-term depression.

Toxin-Induced Experimental Models of Learning and Memory Impairment

Animal models for learning and memory have significantly contributed to novel strategies for drug development and hence are an imperative part in the assessment of therapeutics. Learning and memory involve different stages including acquisition, consolidation, and retrieval and each stage can be characterized using specific toxin. Recent studies have postulated the molecular basis of these processes and have also demonstrated many signaling molecules that are involved in several stages of memory. Most insights into learning and memory impairment and to develop a novel compound stems from the investigations performed in experimental models, especially those produced by neurotoxins models. Several toxins have been utilized based on their mechanism of action for learning and memory impairment such as scopolamine, streptozotocin, quinolinic acid, and domoic acid. Further, some toxins like 6-hydroxy dopamine (6-OHDA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and amyloid-β are known to cause specific learning and memory impairment which imitate the disease pathology of Parkinson's disease dementia and Alzheimer's disease dementia. Apart from these toxins, several other toxins come under a miscellaneous category like an environmental pollutant, snake venoms, botulinum, and lipopolysaccharide. This review will focus on the various classes of neurotoxin models for learning and memory impairment with their specific mechanism of action that could assist the process of drug discovery and development for dementia and cognitive disorders.

Herbal formula GAPT prevents beta amyloid deposition induced Ca(2+)/Calmodulin-dependent protein kinase II and Ca(2+)/Calmodulin-dependent protein phosphatase 2B imbalance in APPV717I mice

Background

Synaptic dysfunction is one of the pathological characteristics of Alzheimer's disease (AD), which is directly related to the progressive decline of cognitive function. CaMKII and CaN have been found to play important roles in memory processes and synaptic transmission. So present study aimed to elucidate relationships between CaMKII, CaN and cognitive decline in APPV717I mice, and to reveal whether the cognitive improving effects of GAPT is conducted through rebalance CaMKII and CaN.

Methods

Three-month-old-male APPV717I mice were randomly divided into ten groups (n = 12 per group) and received intragastrically administrated vehicle, donepezil or different doses of herbal formula GAPT for 8 or 4 months. Three-month-old male C57BL/6 J mice was set as vehicle control.

Results

Immunohistochemistry analysis showed that there were CaMKII expression decrease in the CA1 region of APPV717I transgenic mice, while the CaMKII expression of donepezil or GAPT treated transgenic mice were all increased. And there were CaN expression increase in the brain cortex of APPV717I transgenic mice, while there were decrease of CaN expression in donepezil or GAPT treated transgenic group. Western blot analysis showed the similar expression pattern without significant difference.

Conclusion

GAPT extract have showed effectiveness in activating the expression of CaMKII and inhibiting the expression of CaN either before or after the formation of amyloid plaques in the brain of APPV717I transgenic mice, which may in certain way alleviated neuron synaptic dysfunction in AD.

Neurogranin restores amyloid β-mediated synaptic transmission and long-term potentiation deficits

Amyloid β (Aβ) is widely considered one of the early causes of cognitive deficits observed in Alzheimer's disease. Many of the deficits caused by Aβ are attributed to its disruption of synaptic function represented by its blockade of long-term potentiation (LTP) and its induction of synaptic depression. Identifying pathways that reverse these synaptic deficits may open the door to new therapeutic targets. In this study, we explored the possibility that Neurogranin (Ng)-a postsynaptic calmodulin (CaM) targeting protein that enhances synaptic function-may rescue Aβ-mediated deficits in synaptic function. Our results show that Ng is able to reverse synaptic depression and LTP deficits induced by Aβ. Furthermore, Ng's restoration of synaptic transmission is through the insertion of GluA1-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid glutamate receptors (AMPARs). These restorative effects of Ng are dependent on the interaction of Ng and CaM and CaM-dependent activation of CaMKII. Overall, this study identifies a novel mechanism to rescue synaptic deficits induced by Aβ oligomers. It also suggests Ng and CaM signaling as potential therapeutic targets for Alzheimer's disease as well as important tools to further explore the pathophysiology underlying the disease.

Age-related synaptic dysfunction in Tg2576 mice starts as a failure in early long-term potentiation which develops into a full abolishment of late long-term potentiation

Tg2576 mice are widely used to study amyloid-dependent synaptic dysfunction related to Alzheimer's disease. However, conflicting data have been reported for these mice with regard to basal transmission as well as the in vitro correlate of memory, long-term potentiation (LTP). Some studies show clear impairments, whereas others report no deficiency. The present study uses hippocampal slices from 3-, 10-, and 15-month-old wild-type (WT) and Tg2576 mice to evaluate synaptic function in each group, including experiments to investigate basal synaptic transmission, short- and long-term plasticity by inducing paired-pulse facilitation, and both early and late LTP. We show that synaptic function remains intact in hippocampal slices from Tg2576 mice at 3 months of age. However, both early and late LTP decline progressively during aging in these mice. This deterioration of synaptic plasticity starts affecting early LTP, ultimately leading to the abolishment of both forms of LTP in 15-month-old animals. In comparison, WT littermates display normal synaptic parameters during aging. Additional pharmacological investigation into the involvement of NMDA receptors and L-type voltage-gated calcium channels in LTP suggests a distinct mechanism of induction among age groups, demonstrating that both early and late LTP are differentially affected by these channels in Tg2576 mice during aging.

Administration of NaHS Attenuates Footshock-Induced Pathologies and Emotional and Cognitive Dysfunction in Triple Transgenic Alzheimer's Mice

Alzheimer's disease (AD) is characterized by progressive cognitive decline and neuropsychiatric symptoms. Increasing evidence indicates that environmental risk factors in young adults may accelerate cognitive loss in AD and that Hydrogen Sulfide (H2S) may represent an innovative treatment to slow the progression of AD. Therefore, the aim of this study was to evaluate the effects of NaHS, an H2S donor, in a triple transgenic AD mouse model (3×Tg-AD) under footshock with situational reminders (SRs). Inescapable footshock with SRs induced anxiety and cognitive dysfunction as well as a decrease in the levels of plasma H2S and GSH and an increase in IL-6 levels in 3×Tg-AD mice. Under footshock with SR stimulus, amyloid deposition, tau protein hyperphosphorylation, and microgliosis were highly increased in the stress-responsive brain structures, including the hippocampus and amygdala, of the AD mice. Oxidative stress, inflammatory response, and β-site APP cleaving enzyme 1 (BACE1) levels were also increased, and the level of inactivated glycogen synthase kinase-3β (GSK3β) (pSer9) was decreased in the hippocampi of AD mice subjected to footshock with SRs. Furthermore, the numbers of cholinergic neurons in the medial septum/diagonal band of Broca (MS/DB) and noradrenergic neurons in the locus coeruleus (LC) were also decreased in the 3×Tg-AD mice under footshock with SRs. These biochemical hallmarks and pathological presentations were all alleviated by the semi-acute administration of NaHS in the AD mice. Together, these findings suggest that footshock with SRs induces the impairment of spatial cognition and emotion, which involve pathological changes in the peripheral and central systems, including the hippocampus, MS/DB, LC, and BLA, and that the administration of NaHS may be a candidate strategy to ameliorate the progression of neurodegeneration.

Amyloid beta modulation of neuronal network activity in vitro

In vitro assays offer a means of screening potential therapeutics and accelerating the drug development process. Here, we utilized neuronal cultures on planar microelectrode arrays (MEA) as a functional assay to assess the neurotoxicity of amyloid-β 1-42 (Aβ42), a biomolecule implicated in the Alzheimer׳s disease (AD). In this approach, neurons harvested from embryonic mice were seeded on the substrate-integrated microelectrode arrays. The cultured neurons form a spontaneously active network, and the spiking activity as a functional endpoint could be detected via the MEA. Aβ42 oligomer, but not monomer, significantly reduced network spike rate. In addition, we demonstrated that the ionotropic glutamate receptors, NMDA and AMPA/kainate, play a role in the effects of Aβ42 on neuronal activity in vitro. To examine the utility of the MEA-based assay for AD drug discovery, we tested two model therapeutics for AD, methylene blue (MB) and memantine. Our results show an almost full recovery in the activity within 24h after administration of Aβ42 in the cultures pre-treated with either MB or memantine. Our findings suggest that cultured neuronal networks may be a useful platform in screening potential therapeutics for Aβ induced changes in neurological function.

Neural Plasticity in Multiple Sclerosis: The Functional and Molecular Background

Multiple sclerosis is an autoimmune neurodegenerative disorder resulting in motor dysfunction and cognitive decline. The inflammatory and neurodegenerative changes seen in the brains of MS patients lead to progressive disability and increasing brain atrophy. The most common type of MS is characterized by episodes of clinical exacerbations and remissions. This suggests the presence of compensating mechanisms for accumulating damage. Apart from the widely known repair mechanisms like remyelination, another important phenomenon is neuronal plasticity. Initially, neuroplasticity was connected with the developmental stages of life; however, there is now growing evidence confirming that structural and functional reorganization occurs throughout our lifetime. Several functional studies, utilizing such techniques as fMRI, TBS, or MRS, have provided valuable data about the presence of neuronal plasticity in MS patients. CNS ability to compensate for neuronal damage is most evident in RR-MS; however it has been shown that brain plasticity is also preserved in patients with substantial brain damage. Regardless of the numerous studies, the molecular background of neuronal plasticity in MS is still not well understood. Several factors, like IL-1β, BDNF, PDGF, or CB1Rs, have been implicated in functional recovery from the acute phase of MS and are thus considered as potential therapeutic targets.

Conformation-specific antibodies to target amyloid β oligomers and their application to immunotherapy for Alzheimer's disease

Amyloid β-protein (Aβ) oligomers, intermediates of Aβ aggregation, cause cognitive impairment and synaptotoxicity in the pathogenesis of Alzheimer's disease (AD). Immunotherapy using anti-Aβ antibody is one of the most promising approaches for AD treatment. However, most clinical trials using conventional sequence-specific antibodies have proceeded with difficulty. This is probably due to the unintended removal of the non-pathological monomer and fibrils of Aβ as well as the pathological oligomers by these antibodies that recognize Aβ sequence, which is not involved in synaptotoxicity. Several efforts have been made recently to develop conformation-specific antibodies that target the tertiary structure of Aβ oligomers. Here, we review the recent findings of Aβ oligomers and anti-Aβ antibodies including our own, and discuss their potential as therapeutic and diagnostic tools.