N-methyl-D-aspartate receptor subunit NR2A and NR2B messenger RNA levels are altered in the hippocampus and entorhinal cortex in Alzheimer's disease

Selective disruption of synaptic NMDA receptors of the hippocampal trisynaptic circuit in Aβ pathology

Synaptic dysfunction is an early feature in Alzheimer's disease (AD) pathogenesis and a major morphological correlate of memory deficits. Given the main synaptic location of N-methyl-D-aspartate receptors (NMDARs), their dysregulation has been implicated in these pathological effects. Here, to detect possible alterations in the expression and synaptic localisation of the GluN1 subunit in the brain of amyloidogenic APP/PS1 mice, we employed histoblot and SDS-digested freeze-fracture replica labelling (SDS-FRL) techniques. Histoblots showed that GluN1 expression was significantly reduced in the hippocampus in a layer-dependent manner, in the cortex and the caudate putamen of APP/PS1 transgenic mice at 12 months of age but was unaltered at 1 and 6 months. Using quantitative SDS-FRL, we unravelled the molecular organisation of GluN1 in seven excitatory synapse populations at a high spatial resolution in the CA1 and CA3 fields and the DG of the hippocampus in 12-month-old APP/PS1 mice. In the CA1 field, the labelling density for GluN1 in the excitatory synapses established on spines and interneurons, was significantly reduced in APP/PS1 mice compared to age-matched wild-type mice in the stratum lacunosum-moleculare but unaltered in the stratum radiatum. In the CA3 field, synaptic GluN1 was reduced in mossy fibre-CA3 pyramidal cell synapses but unaltered in the A/C-CA3 pyramidal cell synapses. In the DG, the density of GluN1 in granule cell-perforant pathway synapses was reduced in APP/PS1 mice. Altogether, our findings provide evidence of specific alterations of synaptic GluN1 in the trisynaptic circuit of the hippocampus in Aβ pathology. This differential vulnerability in the disruption of NMDARs may be involved in the mechanisms causing abnormal network activity of the hippocampal circuit and cognitive impairment characteristic of APP/PS1 mice.

Targeting N-Methyl-d-Aspartate Receptors in Neurodegenerative Diseases

N-methyl-d-aspartate receptors (NMDARs) are the main class of ionotropic receptors for the excitatory neurotransmitter glutamate. They play a crucial role in the permeability of Ca2+ ions and excitatory neurotransmission in the brain. Being heteromeric receptors, they are composed of several subunits, including two obligatory GluN1 subunits (eight splice variants) and regulatory GluN2 (GluN2A~D) or GluN3 (GluN3A~B) subunits. Widely distributed in the brain, they regulate other neurotransmission systems and are therefore involved in essential functions such as synaptic transmission, learning and memory, plasticity, and excitotoxicity. The present review will detail the structure, composition, and localization of NMDARs, their role and regulation at the glutamatergic synapse, and their impact on cognitive processes and in neurodegenerative diseases (Alzheimer's, Huntington's, and Parkinson's disease). The pharmacology of different NMDAR antagonists and their therapeutic potentialities will be presented. In particular, a focus will be given on fluoroethylnormemantine (FENM), an investigational drug with very promising development as a neuroprotective agent in Alzheimer's disease, in complement to its reported efficacy as a tomography radiotracer for NMDARs and an anxiolytic drug in post-traumatic stress disorder.

The glutamatergic system in Alzheimer's disease: a systematic review with meta-analysis

Glutamatergic neurotransmission system dysregulation may play an important role in the pathophysiology of Alzheimer's disease (AD). However, reported results on glutamatergic components across brain regions are contradictory. Here, we conducted a systematic review with meta-analysis to examine whether there are consistent glutamatergic abnormalities in the human AD brain. We searched PubMed and Web of Science (database origin-October 2023) reports evaluating glutamate, glutamine, glutaminase, glutamine synthetase, glutamate reuptake, aspartate, excitatory amino acid transporters, vesicular glutamate transporters, glycine, D-serine, metabotropic and ionotropic glutamate receptors in the AD human brain (PROSPERO #CDRD42022299518). The studies were synthesized by outcome and brain region. We included cortical regions, the whole brain (cortical and subcortical regions combined), the entorhinal cortex and the hippocampus. Pooled effect sizes were determined with standardized mean differences (SMD), random effects adjusted by false discovery rate, and heterogeneity was examined by I2 statistics. The search retrieved 6 936 articles, 63 meeting the inclusion criteria (N = 709CN/786AD; mean age 75/79). We showed that the brain of AD individuals presents decreased glutamate (SMD = -0.82; I2 = 74.54%; P < 0.001) and aspartate levels (SMD = -0.64; I2 = 89.71%; P = 0.006), and reuptake (SMD = -0.75; I2 = 83.04%; P < 0.001. We also found reduced α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPAR)-GluA2/3 levels (SMD = -0.63; I2 = 95.55%; P = 0.046), hypofunctional N-methyl-D-aspartate receptor (NMDAR) (SMD = -0.60; I2 = 91.47%; P < 0.001) and selective reduction of NMDAR-GluN2B subunit levels (SMD = -1.07; I2 = 41.81%; P < 0.001). Regional differences include lower glutamate levels in cortical areas and aspartate levels in cortical areas and in the hippocampus, reduced glutamate reuptake, reduced AMPAR-GluA2/3 in the entorhinal cortex, hypofunction of NMDAR in cortical areas, and a decrease in NMDAR-GluN2B subunit levels in the entorhinal cortex and hippocampus. Other parameters studied were not altered. Our findings show depletion of the glutamatergic system and emphasize the importance of understanding glutamate-mediated neurotoxicity in AD. This study has implications for the development of therapies and biomarkers in AD.

Reduced biophotonic activities and spectral blueshift in Alzheimer's disease and vascular dementia models with cognitive impairment

Background

Although clinically, Alzheimer's disease (AD) and vascular dementia (VaD) are the two major types of dementia, it is unclear whether the biophotonic activities associated with cognitive impairments in these diseases share common pathological features.

Methods

We used the ultraweak biophoton imaging system (UBIS) and synaptosomes prepared by modified percoll method to directly evaluate the functional changes in synapses and neural circuits in AD and VaD model animals.

Results

We found that biophotonic activities induced by glutamate were significantly reduced and spectral blueshifted in synaptosomes and brain slices. These changes could be partially reversed by pre-perfusion of the ifenprodil, a specific antagonist of the GluN2B subunit of N-methyl-D-aspartate receptors (NMDARs).

Conclusion

Our findings suggest that AD and VaD pathology present similar but complex changes in biophotonic activities and transmission at synapses and neural circuits, implying that communications and information processing of biophotonic signals in the brain are crucial for advanced cognitive functions.

Alzheimer's disease as a synaptopathy: Evidence for dysfunction of synapses during disease progression

The synapse has consistently been considered a vulnerable and critical target within Alzheimer's disease, and synapse loss is, to date, one of the main biological correlates of cognitive decline within Alzheimer's disease. This occurs prior to neuronal loss with ample evidence that synaptic dysfunction precedes this, in support of the idea that synaptic failure is a crucial stage within disease pathogenesis. The two main pathological hallmarks of Alzheimer's disease, abnormal aggregates of amyloid or tau proteins, have had demonstrable effects on synaptic physiology in animal and cellular models of Alzheimer's disease. There is also growing evidence that these two proteins may have a synergistic effect on neurophysiological dysfunction. Here, we review some of the main findings of synaptic alterations in Alzheimer's disease, and what we know from Alzheimer's disease animal and cellular models. First, we briefly summarize some of the human evidence to suggest that synapses are altered, including how this relates to network activity. Subsequently, animal and cellular models of Alzheimer's disease are considered, highlighting mouse models of amyloid and tau pathology and the role these proteins may play in synaptic dysfunction, either in isolation or examining how the two pathologies may interact in dysfunction. This specifically focuses on neurophysiological function and dysfunction observed within these animal models, typically measured using electrophysiology or calcium imaging. Following synaptic dysfunction and loss, it would be impossible to imagine that this would not alter oscillatory activity within the brain. Therefore, this review also discusses how this may underpin some of the aberrant oscillatory patterns seen in animal models of Alzheimer's disease and human patients. Finally, an overview of some key directions and considerations in the field of synaptic dysfunction in Alzheimer's disease is covered. This includes current therapeutics that are targeted specifically at synaptic dysfunction, but also methods that modulate activity to rescue aberrant oscillatory patterns. Other important future avenues of note in this field include the role of non-neuronal cell types such as astrocytes and microglia, and mechanisms of dysfunction independent of amyloid and tau in Alzheimer's disease. The synapse will certainly continue to be an important target within Alzheimer's disease for the foreseeable future.

Aberrant protein S-nitrosylation contributes to hyperexcitability-induced synaptic damage in Alzheimer's disease: Mechanistic insights and potential therapies

Alzheimer's disease (AD) is arguably the most common cause of dementia in the elderly and is marked by progressive synaptic degeneration, which in turn leads to cognitive decline. Studies in patients and in various AD models have shown that one of the early signatures of AD is neuronal hyperactivity. This excessive electrical activity contributes to dysregulated neural network function and synaptic damage. Mechanistically, evidence suggests that hyperexcitability accelerates production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) that contribute to neural network impairment and synapse loss. This review focuses on the pathways and molecular changes that cause hyperexcitability and how RNS-dependent posttranslational modifications, represented predominantly by protein S-nitrosylation, mediate, at least in part, the deleterious effects of hyperexcitability on single neurons and the neural network, resulting in synaptic loss in AD.

Amyloid-β (25-35) induces the morphological alteration of dendritic spines and decreases NR2B and PSD-95 expression in the hippocampus

Research on the memory impairment caused by the Amyloid-β 25-35 (Aβ25-35) peptide in animal models has provided an understanding of the causes that occurs in Alzheimer's disease. However, it is uncertain whether this cognitive impairment occurs due to disruption of information encoding and consolidation or impaired retrieval of stored memory. The aim of this study was to determine the effect of the Aβ25-35 peptide on the morphology of dendritic spines and the changes in the expression of NR2B and PSD-95 in the hippocampus associated with learning and memory deficit. Vehicle or Aβ25-35 peptide (0.1 µg/µL) was bilaterally administered into the CA1 subfield of the rat hippocampus, then tested for spatial learning and memory in the Morris Water Maze. On Day 39, the morphological changes in the CA1 of the hippocampus and dentate gyrus were examined via Golgi-Cox stain. It was observed that the Aβ25-35 peptide administered in the CA1 region of the rat hippocampus induced changes to the morphology of dendritic spines and the expression of the NR2B subunit of the NMDA receptor co-localized with both the spatial memory and PSD-95 protein in the hippocampus of learning rats. We conclude that, in soluble form, the Aβ25-35 peptide perturbs synaptic plasticity, specifically in the formation of new synapses, thus promoting the progression of memory impairment.

Tissue Plasminogen Activator in Central Nervous System Physiology and Pathology: From Synaptic Plasticity to Alzheimer's Disease

Tissue plasminogen activator's (tPA) fibrinolytic function in the vasculature is well-established. This specific role for tPA in the vasculature, however, contrasts with its pleiotropic activities in the central nervous system. Numerous physiological and pathological functions have been attributed to tPA in the central nervous system, including neurite outgrowth and regeneration; synaptic and spine plasticity; neurovascular coupling; neurodegeneration; microglial activation; and blood–brain barrier permeability. In addition, multiple substrates, both plasminogen-dependent and -independent, have been proposed to be responsible for tPA's action(s) in the central nervous system. This review aims to dissect a subset of these different functions and the different molecular mechanisms attributed to tPA in the context of learning and memory. We start from the original research that identified tPA as an immediate-early gene with a putative role in synaptic plasticity to what is currently known about tPA's role in a learning and memory disorder, Alzheimer's disease. We specifically focus on studies demonstrating tPA's involvement in the clearance of amyloid-β and neurovascular coupling. In addition, given that tPA has been shown to regulate blood–brain barrier permeability, which is perturbed in Alzheimer's disease, this review also discusses tPA-mediated vascular dysfunction and possible alternative mechanisms of action for tPA in Alzheimer's disease pathology.

Morin attenuates memory deficits in a rat model of Alzheimer's disease by ameliorating oxidative stress and neuroinflammation

This study aimed to investigate the effect of flavonoid morin on oxidative/nitrosative stress, neuroinflammation, and histological, molecular, and behavioral changes caused by amyloid-beta (Aβ)_1-42 in male Wistar rats (Alzheimer's disease model). Rats received morin (20 mg/kg, oral gavage) for 14 consecutive days after intrahippocampal injection of Aβ_1-42. Morin decreased the levels of malondialdehyde and nitric oxide, increased glutathione content, and enhanced catalase activity in the hippocampus of animals receiving Aβ_1-42. It also reduced the expression of tumor necrosis factor-α, interleukin-1β, interleukin-6, nuclear factor-kappa B, and N-methyl-D-aspartate receptor subunits 2A and 2B and increased the expression of brain-derived neurotrophic factor and α7 nicotinic acetylcholine receptor in the hippocampus of Aβ_1-42-injected rats. Besides, morin modified neuronal loss and histological changes in the CA1 region of the hippocampus. Morin allowed Aβ_1-42-infused rats to swim more time in the target quadrant in the Morris water maze test. It is concluded that morin may be suitable for the prevention and treatment of Alzheimer's disease by strengthening the antioxidant system, inhibiting neuroinflammation, preventing neuronal death, and enhancing memory function.

Increased P2×2 receptors induced by amyloid-β peptide participates in the neurotoxicity in alzheimer's disease

Amyloid beta peptide (Aβ) is tightly associated with the physiopathology of Alzheimer's Disease (AD) as one of the most important factors in the evolution of the pathology. In this context, we previously reported that Aβ increases the expression of ionotropic purinergic receptor 2 (P2×2R). However, its role on the cellular and molecular Aβ toxicity is unknown, especially in human brain of AD patients. Using cellular and molecular approaches in hippocampal neurons, PC12 cells, and human brain samples of patients with AD, we evaluated the participation of P2×2R in the physiopathology of AD. Here, we reported that Aβ oligomers (Aβo) increased P2×2 levels in mice hippocampal neurons, and that this receptor increases at late Braak stages of AD patients. Aβo also increases the colocalization of APP with Rab5, an early endosomes marker, and decreased the nuclear/cytoplasmic ratio of Fe65 and PGC-1α immunoreactivity. The overexpression in PC12 cells of P2×2a, but not P2×2b, replicated these changes in Fe65 and PGC-1α; however, both overexpressed isoforms increased levels of Aβ. Taken together, these data suggest that P2×2 is upregulated in AD and it could be a key potentiator of the physiopathology of Aβ. Our results point to a possible participation in a toxic cycle that increases Aβ production, Ca²⁺ overload, and a decrease of PGC-1α. These novel findings put the P2×2R as a key novel pharmacological target to develop new therapeutic strategies to treat Alzheimer's Disease.

Glutamatergic receptor expression changes in the Alzheimer's disease hippocampus and entorhinal cortex

Alzheimer's Disease (AD) is the leading form of dementia worldwide. Currently, the pathological mechanisms underlying AD are not well understood. Although the glutamatergic system is extensively implicated in its pathophysiology, there is a gap in knowledge regarding the expression of glutamate receptors in the AD brain. This study aimed to characterize the expression of specific glutamate receptor subunits in post‐mortem human brain tissue using immunohistochemistry and confocal microscopy. Free‐floating immunohistochemistry and confocal laser scanning microscopy were used to quantify the density of glutamate receptor subunits GluA2, GluN1, and GluN2A in specific cell layers of the hippocampal sub‐regions, subiculum, entorhinal cortex, and superior temporal gyrus. Quantification of GluA2 expression in human post‐mortem hippocampus revealed a significant increase in the stratum (str.) moleculare of the dentate gyrus (DG) in AD compared with control. Increased GluN1 receptor expression was found in the str. moleculare and hilus of the DG, str. oriens of the CA2 and CA3, str. pyramidale of the CA2, and str. radiatum of the CA1, CA2, and CA3 subregions and the entorhinal cortex. GluN2A expression was significantly increased in AD compared with control in the str. oriens, str. pyramidale, and str. radiatum of the CA1 subregion. These findings indicate that the expression of glutamatergic receptor subunits shows brain region‐specific changes in AD, suggesting possible pathological receptor functioning. These results provide evidence of specific glutamatergic receptor subunit changes in the AD hippocampus and entorhinal cortex, indicating the requirement for further research to elucidate the pathophysiological mechanisms it entails, and further highlight the potential of glutamatergic receptor subunits as therapeutic targets.

Effect of Acetamiprid on spatial memory and hippocampal glutamatergic system

Acetamiprid (ACE) is one of the widely used neonicotinoid insecticides. In mammals, in spite of the low-affinity nAChRs, neurotoxic effects following the Acetamiprid exposure have recently been reported, which suggests some concerns regarding the impacts on the nervous system of mammals. This study aims to investigate the effect of Acetamiprid on spatial memory and possible vulnerability of hippocampal glutamatergic system following the Acetamiprid exposure. 10, 20, and 40 mg/kg doses of Acetamiprid were administered to male rats by gavage once per day for 28 days. The spatial memory was examined with the Morris water maze apparatus. The amount of Acetamiprid in the serum and hippocampus was measured. In addition, glutamate level and changes in the expression of NR1, NR2, and NR2B genes were measured in the hippocampus; also, the hippocampus tissue was histologically evaluated. A significant increase in training parameters which consist of escape latency and traveled distance was observed on the first and second day of training in Acetamiprid-treated groups (20 and 40 mg/kg) compared to the control group (p < 0.001). In the probe test, rats in all Acetamiprid-treated groups significantly spent less time in the target quadrant compared to the control group (p < 0.001). Acetamiprid concentration dose dependently increased in the serum and in the hippocampus followed by Acetamiprid exposure. In all Acetamiprid-treated groups, a significant reduction of glutamate level in the hippocampus was observed (p < 0.05). The reduction of NR1, NR2A, and NR2B gene expression in the hippocampus was observed at a dose of 20 mg/kg. The histological evaluation showed neural degeneration in the dentate gyrus area of the hippocampus at a dose of 40 mg/kg in the Acetamiprid-treated group. The results of the present study indicate that Acetamiprid impairs memory consolidation through the reduction of glutamate and the expression of NMDA receptor subunits in the hippocampus at low doses, along with the loss of neural cells in dentate gyrus at high dose.

Affected albumin endocytosis as a new neurotoxicity mechanism of amyloid beta

Senile plaques, a hallmark of Alzheimer's disease, are composed by Amyloid-Beta (Aβ). Aβ 25-35 toxicity is caused mainly by increasing reactive oxygen species (ROS), which is reversed by albumin preventing Aβ internalization. In addition, key cellular processes and basic cell functions require of endocytosis, particularly relevant in neurons. To understand the protective effect of albumin and the toxicity mechanism of Aβ, the need of albumin uptake for neurons protection as well as the possible influence of Aβ on albumin endocytosis were investigated. With this aim the influence of lectin from soybeans (LEC), which prevents albumin endocytosis, on the effects of Aβ 25-35 on cellular morphology and viability, ROS generation and Aβ uptake with and without albumin in neurons in primary culture was investigated. Influence of Aβ on albumin endocytosis was studied using FITC-labelled albumin. LEC did not modify Aβ effects with or without albumin on neuronal morphology, but increased cell viability. LEC increased ROS generation with and without Aβ in the same magnitude. Diminished Aβ internalization observed with albumin was not affected by LEC. In presence of Aβ albumin is internalized, but endosomes did not deliver their cargo to the lysosomes for degradation. It is concluded that formation of Aβ-albumin complex does not require of albumin internalization, thus is extracellular. Aβ affects albumin endocytosis preventing late endosomes and lysosomes degradation, probably caused by changes in albumin structure or deregulation in vesicular transport. Considering the consequences such as its osmotic effects, the inability to exert its antioxidant properties, its effects on neuronal plasticity and excitability albumin affected endocytosis induced by Aβ is proposed as a new physiopathology mechanism in AD. It is hypothesized that there is critical intraneuronal level above which albumin becomes toxic.

Protective Effects of Borago officinalis (Borago) on Cold Restraint Stress-Induced Gastric Ulcers in Rats: A Pilot Study

Stress is a typical body's natural defense to a generic physical or psychic change. A specific linking mechanism between ulcer onset and psycho-physical stress prolonged exposure has been reported. We decided to investigate the possible effects of Borago officinalis L. (Borago) in preventing physical (stress)-induced gastric ulcers in a rat model. Eighty male Sprague-Dawley rats were randomly divided into 16 groups, pretreated with a control solution, omeprazole (20 mg/kg), Borago methanolic extract (25, 50, 100, 250, and 500 mg/kg), Borago organic extract (50, 100, 250, and 500 mg/kg), Borago aqueous extract (5, 10, 20, 30, and 40 mg/kg), and D(-)-2-Amino-5-phosphonovaleric acid (AP5) (25 mg/kg) and kept in stressful conditions such as water immersion and restraint-induced stress ulcers. The animals were sacrificed and their stomach scored for the severity and the number of gastric ulcers. Methanolic extract (500 mg/kg) significantly reduced both ulcer parameters (^***p < 0.001 and ^**p < 0.01, respectively). Aqueous and organic extract significantly decreased severity score at 5 and 10 mg/kg (^**p < 0.01 and ^***p < 0.001, respectively), and at 250 and 500 mg/kg (^***p < 0.001), respectively, while gastric ulcers' resulted number significantly reduced only at 10 mg/kg (^*p < 0.05) and at 500 mg/kg (^**p < 0.01), respectively. On the other hand, aqueous extract significantly increased the mucosal gastric content of cAMP (^*p < 0.05) and NR2A and NR2B subunits (^*p < 0.05 and ^**p < 0.01, respectively) at 5 mg/kg. Organic extract showed also a significant cytotoxic effect at 500 and 1,000 mg/kg with a 3T3 cell viability reduction of 43.6% (^**p < 0.01) and 92.1% (^***p < 0.001), respectively. Borago aqueous extract at 10 mg/kg could be considered as a potential protective agent against stress-induced ulcers, and it is reasonable to possibly ascribe such protective activity to a modulation of the NR2A and NR2B subunit expression.

Amyloid-beta1-42 induced glutamatergic receptor and transporter expression changes in the mouse hippocampus

Alzheimer's disease (AD) is the leading type of dementia worldwide. With an increasing burden of an aging population coupled with the lack of any foreseeable cure, AD warrants the current intense research effort on the toxic effects of an increased concentration of beta-amyloid (Aβ) in the brain. Glutamate is the main excitatory brain neurotransmitter and it plays an essential role in the function and health of neurons and neuronal excitability. While previous studies have shown alterations in expression of glutamatergic signaling components in AD, the underlying mechanisms of these changes are not well understood. This is the first comprehensive anatomical study to characterize the subregion- and cell layer-specific long-term effect of Aβ_1-42 on the expression of specific glutamate receptors and transporters in the mouse hippocampus, using immunohistochemistry with confocal microscopy. Outcomes are examined 30 days after Aβ_1-42 stereotactic injection in aged male C57BL/6 mice. We report significant decreases in density of the glutamate receptor subunit GluA1 and the vesicular glutamate transporter (VGluT) 1 in the conus ammonis 1 region of the hippocampus in the Aβ_1-42 injected mice compared with artificial cerebrospinal fluid injected and naïve controls, notably in the stratum oriens and stratum radiatum. GluA1 subunit density also decreased within the dentate gyrus dorsal stratum moleculare in Aβ_1-42 injected mice compared with artificial cerebrospinal fluid injected controls. These changes are consistent with findings previously reported in the human AD hippocampus. By contrast, glutamate receptor subunits GluA2, GluN1, GluN2A, and VGluT2 showed no changes in expression. These findings indicate that Aβ_1-42 induces brain region and layer specific expression changes of the glutamatergic receptors and transporters, suggesting complex and spatial vulnerability of this pathway during development of AD neuropathology. Read the Editorial Highlight for this article on page 7. Cover Image for this issue: https://doi.org/10.1111/jnc.14763.

Alpha-synuclein differentially reduces surface expression of N-methyl-d-aspartate receptors in the aging human brain

The aging brain is associated with reduced cell surface expression of N-methyl-d-aspartate receptors (NMDARs), but the mechanism remains poorly understood. In the present study, we showed that in the striatum and hippocampus but not the cerebellum and parietal cortex, levels of α-synuclein monomers and oligomers increased with age, which correlated negatively with the expression of GluN1, and positively with the expression of total Rab5B. The oligomer-α-synuclein exhibited a stronger correlation with the expression of surface GluN1 and total Rab5B. In MES23.5 cells, the monomer- or oligomer-α-synuclein were shown to increase in a manner dependent on the concentrations of the added monomers and oligomers. Again, the oligomer-α-synuclein showed more potent effects than the monomer-α-synuclein on surface GluN1 and total Rab5B expression. Accordingly, the oligomer-treated cells showed a greater reduction in NMDA-evoked Ca²⁺ influx than the monomer-treated cells, which was largely inhibited by pistop2, a clathrin inhibitor. These results suggest that the age-dependent accumulation of α-synuclein monomers and oligomers differentially contributes to the reduction in surface NMDAR expression in selective brain regions.

Resveratrol derivative excited postsynaptic potentiation specifically via PKCβ-NMDA receptor mediation

Several decades have passed since resveratrol (RSV) was first identified in red wine. Researchers have reported the pleiotropic anti-oxidant, anti-inflammatory, anti-cancer, anti-aging, and neuronal protective effects of resveratrol and its glycosylated derivative. However, few studies have distinguished the minute differences in the properties between resveratrol and its glycosylated derivative in terms of synaptic plasticity. As an abundant natural product of glycosylated resveratrol, the derivative 2,3,4',5-tetrahydroxystilbene-2-O-β-d-glucoside (TSG) has been determined to be a better option for long-term potentiation (LTP) in the hippocampus under physiological and pathological conditions than resveratrol. TSG, as well as its parent molecule RSV, could elicit early-LTP and recover fast excitatory postsynaptic potentials (EPSPs) in the hippocampus. Using various modalities, including pre- and post-whole-cell patch clamping techniques in the calyx of Held, pharmacological inhibition of the N-methyl-d-aspartic acid receptor (NMDAr) and the α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor (AMPAr) as well as protein kinase C (PKC) activation, we demonstrated that TSG, unlike RSV, could merely promote NMDA-mediated EPSC via PKCβ cascade. Our results provide new knowledge that glycosylation of resveratrol could significantly improve its specificity in promoting sole NMDAr mediation of EPSPs, in addition to improving solubility and resistance against oxidation in vivo. These observations could contribute to further exploration of pharmaceutical evaluation of glycosylated stilbene in the future.

Acute and Chronic Sleep Deprivation-Related Changes in N-methyl-D-aspartate Receptor-Nitric Oxide Signalling in the Rat Cerebral Cortex with Reference to Aging and Brain Lateralization

Aging and chronic sleep deprivation (SD) are well-recognized risk factors for Alzheimer’s disease (AD), with N-methyl-D-aspartate receptor (NMDA) and downstream nitric oxide (NO) signalling implicated in the process. Herein, we investigate the impact of the age- and acute or chronic SD-dependent changes on the expression of NMDA receptor subunits (NR1, NR2A, and NR2B) and on the activities of NO synthase (NOS) isoforms in the cortex of Wistar rats, with reference to cerebral lateralization. In young adult controls, somewhat lateralized seasonal variations in neuronal and endothelial NOS have been observed. In aged rats, overall decreases in NR1, NR2A, and NR2B expression and reduction in neuronal and endothelial NOS activities were found. The age-dependent changes in NR1 and NR2B significantly correlated with neuronal NOS in both hemispheres. Changes evoked by chronic SD (dysfunction of endothelial NOS and the increasing role of NR2A) differed from those evoked by acute SD (increase in inducible NOS in the right side). Collectively, these results demonstrate age-dependent regulation of the level of NMDA receptor subunits and downstream NOS isoforms throughout the rat brain, which could be partly mimicked by SD. As described herein, age and SD alterations in the prevalence of NMDA receptors and NOS could contribute towards cognitive decline in the elderly, as well as in the pathobiology of AD and the neurodegenerative process.

The Role of NMDA Receptors in Alzheimer's Disease

In Alzheimer’s disease (AD), early synaptic dysfunction is associated with the increased oligomeric amyloid-beta peptide, which causes NMDAR-dependent synaptic depression and spine elimination. Memantine, low-affinity NMDAR channel blocker, has been used in the treatment of moderate to severe AD. However, clear evidence is still deficient in demonstrating the underlying mechanisms and a relationship between NMDARs dysfunction and AD. This review focuses on not only changes in expression of different NMDAR subunits, but also some unconventional modes of NMDAR action.

NMDA Receptor Antagonist MK801 Protects Against 1-Bromopropane-Induced Cognitive Dysfunction

Occupational exposure to 1-bromopropane (1-BP) induces learning and memory deficits. However, no therapeutic strategies are currently available. Accumulating evidence has suggested that N-methyl-D-aspartate receptors (NMDARs) and neuroinflammation are involved in the cognitive impairments in neurodegenerative diseases. In this study we aimed to investigate whether the noncompetitive NMDAR antagonist MK801 protects against 1-BP-induced cognitive dysfunction. Male Wistar rats were administered with MK801 (0.1 mg/kg) prior to 1-BP intoxication (800 mg/kg). Their cognitive performance was evaluated by the Morris water maze test. The brains of rats were dissected for biochemical, neuropathological, and immunological analyses. We found that the spatial learning and memory were significantly impaired in the 1-BP group, and this was associated with neurodegeneration in both the hippocampus (especially CA1 and CA3) and cortex. Besides, the protein levels of phosphorylated NMDARs were increased after 1-BP exposure. MK801 ameliorated the 1-BP-induced cognitive impairments and degeneration of neurons in the hippocampus and cortex. Mechanistically, MK801 abrogated the 1-BP-induced disruption of excitatory and inhibitory amino-acid balance and NMDAR abnormalities. Subsequently, MK801 inhibited the microglial activation and release of pro-inflammatory cytokines in 1-BP-treated rats. Our findings, for the first time, revealed that MK801 protected against 1-BP-induced cognitive dysfunction by ameliorating NMDAR function and blocking microglial activation, which might provide a potential target for the treatment of 1-BP poisoning.

Pretangle pathology within cholinergic nucleus basalis neurons coincides with neurotrophic and neurotransmitter receptor gene dysregulation during the progression of Alzheimer's disease

Cholinergic basal forebrain neurons of the nucleus basalis of Meynert (nbM) regulate attentional and memory function and are exquisitely prone to tau pathology and neurofibrillary tangle (NFT) formation during the progression of Alzheimer's disease (AD). nbM neurons require the neurotrophin nerve growth factor (NGF), its cognate receptor TrkA, and the pan-neurotrophin receptor p75NTR for their maintenance and survival. Additionally, nbM neuronal activity and cholinergic tone are regulated by the expression of nicotinic (nAChR) and muscarinic (mAChR) acetylcholine receptors as well as receptors modulating glutamatergic and catecholaminergic afferent signaling. To date, the molecular and cellular relationships between the evolution of tau pathology and nbM neuronal survival remain unknown. To address this knowledge gap, we profiled cholinotrophic pathway genes within nbM neurons immunostained for pS422, a pretangle phosphorylation event preceding tau C-terminal truncation at D421, or dual-labeled for pS422 and TauC3, a later stage tau neo-epitope revealed by this same C-terminal truncation event, via single-population custom microarray analysis. nbM neurons were obtained from postmortem tissues from subjects who died with an antemortem clinical diagnosis of no cognitive impairment (NCI), mild cognitive impairment (MCI), or mild/moderate AD. Quantitative analysis revealed significant downregulation of mRNAs encoding TrkA as well as TrkB, TrkC, and the Trk-mediated downstream pro-survival kinase Akt in pS422+ compared to unlabeled, pS422-negative nbM neurons. In addition, pS422+ neurons displayed a downregulation of transcripts encoding NMDA receptor subunit 2B, metabotropic glutamate receptor 2, D2 dopamine receptor, and β1 adrenoceptor. By contrast, transcripts encoding p75NTR were downregulated in dual-labeled pS422+/TauC3+ neurons. Appearance of the TauC3 epitope was also associated with an upregulation of the α7 nAChR subunit and differential downregulation of the β2 nAChR subunit. Notably, we found that gene expression patterns for each cell phenotype did not differ with clinical diagnosis. However, linear regression revealed that global cognition and Braak stage were predictors of select transcript changes within both unlabeled and pS422+/TauC3- neurons. Taken together, these cell phenotype-specific gene expression profiling data suggest that dysregulation of neurotrophic and neurotransmitter signaling is an early pathogenic mechanism associated with NFT formation in vulnerable nbM neurons and cognitive decline in AD, which may be amenable to therapeutic intervention early in the disease process.

Prion acute synaptotoxicity is largely driven by protease-resistant PrPSc species

Although misfolding of normal prion protein (PrP^C) into abnormal conformers (PrP^Sc) is critical for prion disease pathogenesis our current understanding of the underlying molecular pathophysiology is rudimentary. Exploiting an electrophysiology paradigm, herein we report that at least modestly proteinase K (PK)-resistant PrP^Sc (PrP^res) species are acutely synaptotoxic. Brief exposure to ex vivo PrP^Sc from two mouse-adapted prion strains (M1000 and MU02) prepared as crude brain homogenates (cM1000 and cMU02) and cell lysates from chronically M1000-infected RK13 cells (MoRK13-Inf) caused significant impairment of hippocampal CA1 region long-term potentiation (LTP), with the LTP disruption approximating that reported during the evolution of murine prion disease. Proof of PrP^Sc (especially PrP^res) species as the synaptotoxic agent was demonstrated by: significant rescue of LTP following selective immuno-depletion of total PrP from cM1000 (dM1000); modestly PK-treated cM1000 (PK+M1000) retaining full synaptotoxicity; and restoration of the LTP impairment when employing reconstituted, PK-eluted, immuno-precipitated M1000 preparations (PK+IP-M1000). Additional detailed electrophysiological analyses exemplified by impairment of post-tetanic potentiation (PTP) suggest possible heightened pre-synaptic vulnerability to the acute synaptotoxicity. This dysfunction correlated with cumulative insufficiency of replenishment of the readily releasable pool (RRP) of vesicles during repeated high-frequency stimulation utilised for induction of LTP. Broadly comparable results with LTP and PTP impairment were obtained utilizing hippocampal slices from PrP^C knockout (PrPo/o) mice, with cM1000 serial dilution assessments revealing similar sensitivity of PrPo/o and wild type (WT) slices. Size fractionation chromatography demonstrated that synaptotoxic PrP correlated with PK-resistant species >100kDa, consistent with multimeric PrP^Sc, with levels of these species >6 ng/ml appearing sufficient to induce synaptic dysfunction. Biochemical analyses of hippocampal slices manifesting acute synaptotoxicity demonstrated reduced levels of multiple key synaptic proteins, albeit with noteworthy differences in PrPo/o slices, while such changes were absent in hippocampi demonstrating rescued LTP through treatment with dM1000. Our findings offer important new mechanistic insights into the synaptic impairment underlying prion disease, enhancing prospects for development of targeted effective therapies.

Misfolding of the normal prion protein (PrP^C) into disease-associated conformations (PrP^Sc) is the critical initiating step for prion diseases. Similar to other neurodegenerative disorders, progressive failure of brain synapses is considered a primary deleterious event underpinning prion disease evolution. Our current understanding of the underlying mechanisms associated with synaptic failure is rudimentary contributing to difficulties in developing effective treatments. Herein we report the use of an electrophysiology paradigm that allowed us to demonstrate that at least modestly proteinase K (PK)-resistant PrP^Sc species from two mouse-adapted prion strains (M1000 and MU02) are directly synaptotoxic causing significant acute impairment of hippocampal CA1 region long-term potentiation (LTP). Of note, the LTP disruption approximated that reported in prion animal models. Additional detailed analyses provided novel pathophysiological insights suggesting possible heightened pre-synaptic vulnerability to the acute synaptotoxicity through impairment of replenishment of the readily releasable pool of neurotransmitter vesicles, while biochemical analyses demonstrated reduced levels of multiple key pre-and post-synaptic proteins. Broadly similar acute synaptic dysfunction and dose-response susceptibility were observed in slices from mice not expressing PrP^C albeit with minor but noteworthy differences in electrophysiological and biochemical findings. Our study offers important new mechanistic insights into the synaptic impairment underlying prion disease, enhancing prospects for development effective therapies.

Inhibition of NMDA Receptors Prevents the Loss of BDNF Function Induced by Amyloid β

Brain-derived neurotrophic factor (BDNF) plays important functions in cell survival and differentiation, neuronal outgrowth and plasticity. In Alzheimer’s disease (AD), BDNF signaling is known to be impaired, partially because amyloid β (Aβ) induces truncation of BDNF main receptor, TrkB-full length (TrkB-FL). We have previously shown that such truncation is mediated by calpains, results in the formation of an intracellular domain (ICD) fragment and causes BDNF loss of function. Since calpains are Ca²⁺-dependent proteases, we hypothesized that excessive intracellular Ca²⁺ build-up could be due to dysfunctional N-methyl-d-aspartate receptors (NMDARs) activation. To experimentally address this hypothesis, we investigated whether TrkB-FL truncation by calpains and consequent BDNF loss of function could be prevented by NMDAR blockade. We herein demonstrate that a NMDAR antagonist, memantine, prevented excessive calpain activation and TrkB-FL truncation induced by Aβ_25–35. When calpains were inhibited by calpastatin, BDNF was able to increase the dendritic spine density of neurons exposed to Aβ₂₅₁₃₅. Moreover, NMDAR inhibition by memantine also prevented Aβ-driven deleterious impact of BDNF loss of function on structural (spine density) and functional outcomes (synaptic potentiation). Collectively, these findings support NMDAR/Ca²⁺/calpains mechanistic involvement in Aβ-triggered BDNF signaling disruption.

Clonidine preconditioning improved cerebral ischemia-induced learning and memory deficits in rats via ERK1/2-CREB/ NF-κB-NR2B pathway

Clonidine, a classical α-2 adrenergic agonists, has been shown to antagonize brain damage caused by hypoxia, cerebral ischemia and excitotoxicity and reduce cerebral infarction volume in recent studies. We herein investigate the regulatory effect and possible underlying mechanism of clonidine on learning and memory in rats with cerebral ischemia. The cerebral ischemia rat model was established by right middle cerebral artery occlusion for 2h and reperfusion for 28 days. Drugs were administrated to the rats for consecutive 7 days intraperitoneally and once again on the day of surgery. The learning and memory in rats was assayed by Morris water maze. Moreover, protein expression levels of NMDAR2B (NR2B)/ phosphor - NR2B, ERK1/2/phosphor- ERK1/2, CREB/phosphor-CREB and NF-κB/phosphor-NF-κB in the cortex and hippocampus of the rats were assayed by western blotting. Our results demonstrated that clonidine treatment significantly abrogated the negative effect induced by cerebral ischemia on the learning and memory in the rats. In the Western blotting assay, clonidine treatment led to significant up-regulation of the expression level of NR2B and Phospho-NR2B in the hippocampus of the rats when compared with the cerebral ischemia group. Furthermore, clonidine also significantly decreased the protein expression levels of ERK1/2, Phospho-ERK1/2, CREB, Phospho-CREB and Phospho-NF-κB in the hippocampus of the rats when compared with the cerebral ischemia group. In conclusion, clonidine could improve the learning and memory ability of rats with cerebral ischemia, and NR2B, ERK1/2, CREB, NF-κB were involved in this effect.

Downregulating ANP32A rescues synapse and memory loss via chromatin remodeling in Alzheimer model

Background

The impairment of histone acetylation is causally linked to the cognitive decline in Alzheimer’s disease (AD). In addition to histone acetyltransferases (HATs) and histone deacetylases (HDACs), inhibitor of acetyltransferases (INHAT) can also regulate histone acetylation. As a key component of INHAT, level of ANP32A is selectively upregulated in the brain of AD patients. Here we investigated whether downregulating ANP32A can rescue AD-like synapse and memory deficits.

Methods

RFP-labeled lentiviral ANP32A-shRNA was infused stereotaxically into the hippocampal CA3 region of the human tau transgenic mice (termed htau). The spatial learning and memory were assessed by Morris water maze (MWM). The synaptic function was measured by electrophysiological recording and the spine density was detected by Golgi staining. RT-PCR and Western blotting were used to detect the mRNA and protein levels.

Results

Elevation of ANP32 in htau transgenic mice was correlated with learning deficits, while the hippocampal infusion of lenti-siANP32A to downregulate ANP32A in 12 m-old htau mice could rescue memory loss. Further studies demonstrated that downregulating ANP32A restored synapse morphology and the function. In the brain of htau mice, the acetylated histone decreased while knockdown ANP32A unmasked histone for a robust acetylation with reduced INHAT complex formation. Downregulating of ANP32A also attenuated AD-like tau hyperphosphorylation. Finally, several AD-associated risk factors, including tau accumulation, β-amyloid and H₂O₂ exposure, increased ANP32A by activating CCAAT/enhancer binding protein-β (C/EBPβ).

Conclusion

We conclude that downregulating ANP32A rescues synaptic plasticity and memory ability by reducing INHAT formation and unmasking histone for hyperacetylation. Our findings reveal novel mechanisms for AD memory loss and potential molecular markers for protection.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-017-0178-8) contains supplementary material, which is available to authorized users.

Generalized reduced rank latent factor regression for high dimensional tensor fields, and neuroimaging-genetic applications

We propose a generalized reduced rank latent factor regression model (GRRLF) for the analysis of tensor field responses and high dimensional covariates. The model is motivated by the need from imaging-genetic studies to identify genetic variants that are associated with brain imaging phenotypes, often in the form of high dimensional tensor fields. GRRLF identifies from the structure in the data the effective dimensionality of the data, and then jointly performs dimension reduction of the covariates, dynamic identification of latent factors, and nonparametric estimation of both covariate and latent response fields. After accounting for the latent and covariate effects, GRLLF performs a nonparametric test on the remaining factor of interest. GRRLF provides a better factorization of the signals compared with common solutions, and is less susceptible to overfitting because it exploits the effective dimensionality. The generality and the flexibility of GRRLF also allow various statistical models to be handled in a unified framework and solutions can be efficiently computed. Within the field of neuroimaging, it improves the sensitivity for weak signals and is a promising alternative to existing approaches. The operation of the framework is demonstrated with both synthetic datasets and a real-world neuroimaging example in which the effects of a set of genes on the structure of the brain at the voxel level were measured, and the results compared favorably with those from existing approaches.

GluN2B-containing NMDA receptors contribute to the beneficial effects of hydrogen sulfide on cognitive and synaptic plasticity deficits in APP/PS1 transgenic mice

Alzheimer's disease (AD) is the most common type of clinical dementia. Previous studies have demonstrated that hydrogen sulfide (H2S) is implicated with the pathology of AD, and exogenous H2S attenuates spatial memory impairments in AD animal models. However, the molecular mechanism by which H2S improves cognition in AD has not been fully explored. Here, we report that chronic administration of sodium hydrosulfide (NaHS, a H2S donor) elevated hippocampal H2S levels and enhanced hippocampus-dependent contextual fear memory and novel object recognition in amyloid precursor protein (APP)/presenilin-1 (PS1) transgenic mice. In parallel with these behavioral results, treating transgenic mice with NaHS reversed impaired hippocampal long-term potentiation (LTP), which is deemed as the neurobiological basis of learning and memory. At the molecular level, we found that treatment with NaHS did not affect the expression of the GluN1 and GluN2A subunits of NMDA receptor (NMDAR), but did prevent the downregulation of GluN2B subunit and restored its synaptic abundance, response and downstream signaling in the hippocampus in transgenic mice. Moreover, applying Ro 25-6981, a specific GluN2B antagonist, abolished the beneficial effects of NaHS on cognitive performance and hippocampal LTP in transgenic mice. Collectively, our results indicate that H2S can reverse cognitive and synaptic plasticity deficits in AD model mice by restoring surface GluN2B expression and the function of GluN2B-containing NMDARs.

Effects of Long-Term Environmental Enrichment on Anxiety, Memory, Hippocampal Plasticity and Overall Brain Gene Expression in C57BL6 Mice

There is ample evidence that physical activity exerts positive effects on a variety of brain functions by facilitating neuroprotective processes and influencing neuroplasticity. Accordingly, numerous studies have shown that continuous exercise can successfully diminish or prevent the pathology of neurodegenerative diseases such as Alzheimer’s disease in transgenic mouse models. However, the long-term effect of physical activity on brain health of aging wild-type (WT) mice has not yet been studied in detail. Here, we show that prolonged physical and cognitive stimulation, mediated by an enriched environment (EE) paradigm for a duration of 11 months, leads to reduced anxiety and improved spatial reference memory in C57BL6 WT mice. While the number of CA1 pyramidal neurons remained unchanged between standard housed (SH) and EE mice, the number of dentate gyrus (DG) neurons, as well as the CA1 and DG volume were significantly increased in EE mice. A whole-brain deep sequencing transcriptome analysis, carried out to better understand the molecular mechanisms underlying the observed effects, revealed an up-regulation of a variety of genes upon EE, mainly associated with synaptic plasticity and transcription regulation. The present findings corroborate the impact of continuous physical activity as a potential prospective route in the prevention of age-related cognitive decline and neurodegenerative disorders.

Adolescent Mice Demonstrate a Distinct Pattern of Injury after Repetitive Mild Traumatic Brain Injury

Recently, there has been increasing interest in outcomes after repetitive mild traumatic brain injury (rmTBI) (e.g., sports concussions). Although most of the scientific attention has focused on elite athlete populations, the sequelae of rmTBI in children and young adults have not been well studied. Prior TBI studies have suggested that developmental differences in response to injury, including differences in excitotoxicity and inflammation, could result in differences in functional and histopathological outcomes after injury. The purpose of this study is to compare outcomes in adolescent (5-week-old) versus adult (4-month-old) mice in a clinically relevant model of rmTBI. We hypothesized that functional and histopathological outcomes after rmTBI would differ in developing adolescent brains compared with mature adult brains. Male adolescent and adult (C57Bl/6) mice were subjected to a weight drop model of rmTBI (n = 10-16/group). Loss of consciousness (LOC) after each injury was measured. Functional outcomes were assessed including tests of balance (rotorod), spatial memory (Morris water maze), and impulsivity (elevated plus maze). After behavioral testing, brains were assessed for histopathological outcomes including microglial immunolabeling and N-methyl-d-aspartate (NMDA) receptor subunit expression. Injured adolescent mice had longer LOC than injured adult mice compared with their respective sham controls. Compared with sham mice, adolescent and adult mice subjected to rmTBI had impaired balance, increased impulsivity, and worse spatial memory that persisted up to 3 months after injury, and the effect of injury was worse in adolescent than in adult mice in terms of spatial memory. Three months after injury, adolescent and adult mice demonstrated increased ionized calcium binding adaptor 1 (IbA1) immunolabeling compared with sham controls. Compared with sham controls, NMDA receptor subtype 2B (NR2B) expression in the hippocampus was reduced by ∼20% in both adolescent and adult injured mice. The data suggest that injured adolescent mice may show a distinct pattern of functional deficits after injury that warrants further mechanistic studies.

New genes for focal epilepsies with speech and language disorders

The last 2 years have seen exciting advances in the genetics of Landau-Kleffner syndrome and related disorders, encompassed within the epilepsy-aphasia spectrum (EAS). The striking finding of mutations in the N-methyl-D-aspartate (NMDA) receptor subunit gene GRIN2A as the first monogenic cause in up to 20% of patients with EAS suggests that excitatory glutamate receptors play a key role in these disorders. Patients with GRIN2A mutations have a recognizable speech and language phenotype that may assist with diagnosis. Other molecules involved in RNA binding and cell adhesion have been implicated in EAS; copy number variations are also found. The emerging picture highlights the overlap between the genetic determinants of EAS with speech and language disorders, intellectual disability, autism spectrum disorders and more complex developmental phenotypes.

Calorie Restriction Suppresses Age-Dependent Hippocampal Transcriptional Signatures

Calorie restriction (CR) enhances longevity and mitigates aging phenotypes in numerous species. Physiological responses to CR are cell-type specific and variable throughout the lifespan. However, the mosaic of molecular changes responsible for CR benefits remains unclear, particularly in brain regions susceptible to deterioration during aging. We examined the influence of long-term CR on the CA1 hippocampal region, a key learning and memory brain area that is vulnerable to age-related pathologies, such as Alzheimer's disease (AD). Through mRNA sequencing and NanoString nCounter analysis, we demonstrate that one year of CR feeding suppresses age-dependent signatures of 882 genes functionally associated with synaptic transmission-related pathways, including calcium signaling, long-term potentiation (LTP), and Creb signaling in wild-type mice. By comparing the influence of CR on hippocampal CA1 region transcriptional profiles at younger-adult (5 months, 2.5 months of feeding) and older-adult (15 months, 12.5 months of feeding) timepoints, we identify conserved upregulation of proteome quality control and calcium buffering genes, including heat shock 70 kDa protein 1b (Hspa1b) and heat shock 70 kDa protein 5 (Hspa5), protein disulfide isomerase family A member 4 (Pdia4) and protein disulfide isomerase family A member 6 (Pdia6), and calreticulin (Calr). Expression levels of putative neuroprotective factors, klotho (Kl) and transthyretin (Ttr), are also elevated by CR in adulthood, although the global CR-specific expression profiles at younger and older timepoints are highly divergent. At a previously unachieved resolution, our results demonstrate conserved activation of neuroprotective gene signatures and broad CR-suppression of age-dependent hippocampal CA1 region expression changes, indicating that CR functionally maintains a more youthful transcriptional state within the hippocampal CA1 sector.

α-Synuclein-induced internalization of NMDA receptors in hippocampal neurons is associated with reduced inward current and Ca(2+) influx upon NMDA stimulation

Abnormal α-synuclein (α-syn) expression and aggregation have been implicated in the pathogenesis of Parkinson's disease (PD), dementia with Lewy bodies (DLB), and Alzheimer's disease (AD). These neurodegenerative disorders, collectively known as synucleinopathies, are usually associated with cognitive impairment that could be caused by impaired hippocampal function. Although abnormal expressions of α-syn and N-methyl-d-aspartate (NMDA) receptor are frequently observed in the hippocampus of patients with synucleinopathies, how these proteins interact with each other in hippocampal neurons remains poorly understood. In the present study, primary cultures of hippocampal neurons and α-syn transgenic mice were used to investigate the effect of α-syn on NMDA receptors. Neurons were treated either by direct addition of recombinant human α-syn (hα-syn) to the medium, or by infection with the hα-syn gene, to increase intracellular levels of α-syn. In both cases, NMDA receptor NR1 subunits on the cell surface were reduced while the total amount of NR1 was unchanged, indicating an internalization of NR1 subunits. Neurons with elevated α-syn also showed a profound increase in Rab5B, an isoform of the small GTPases essential for NMDA receptor endocytosis. Knockdown of Rab5B expression by siRNA inhibited the α-syn-induced reduction in surface NR1. The in vitro findings were confirmed in α-syn transgenic mice, showing that increased α-syn expression was accompanied by reduced levels of surface NR1 and increased expression of Rab5B. Due to the essential role of NR1 subunits for assembling a complete NMDA receptor, its reduction on the cell surface indicated impaired receptor function. This was demonstrated by observations that neurons with elevated α-syn showed profound reductions in NMDA-elicited Ca(2+) influx and inward current, which were also inhibited by knockdown of Rab5B expression. Our data suggest that increased α-syn expression may impair NMDA receptor function in the hippocampus by reducing the density of NR1 subunits on the cell surface.

Local N-methyl-d-aspartate receptor antagonism in the prefrontal cortex attenuates spatial cognitive deficits induced by gonadectomy in adult male rats

Gonadectomy in adult male rats significantly impairs spatial working memory, behavioral flexibility and other functions associated with the prefrontal cortex (PFC). However, the mechanisms through which this occurs are largely unknown. In this study, intracortical drug challenge with the selective N-methyl-d-aspartate receptor (NMDAR) antagonist D(-)-2-amino-5-phosphonopentanoic acid (APV) was combined with Barnes maze testing, gonadectomy (GDX) and hormone replacement (17β-estradiol, testosterone propionate) to explore the contributions of NMDAR-mediated activity within the PFC to hormone effects on spatial cognition in adult male rats. Previous studies have shown that Barnes maze testing reveals significant estrogen-dependent, GDX-induced deficits in spatial working memory and androgen-sensitive, GDX-induced deficits in spatial search strategy. Here we found that bilateral infusion of APV into the medial PFC prior to testing significantly improved both sets of behaviors in gonadectomized rats and significantly worsened performance measures in gonadally intact controls. In hormone-replaced cohorts, we further found that behaviors that are normally similar to controls were significantly disrupted by APV, and those that are normally similar to gonadectomized rats were rescued by intracortical APV infusion. There were, however, no residual effects of APV on retention testing conducted 24h later. Together these findings suggest that hormone regulation of NMDAR-mediated activity specifically within the PFC may be fundamental to the effects of gonadal steroids on spatial cognition in males. Our findings further identify NMDAR antagonists as potentially novel, non-steroidal means of attenuating the cognitive deficits that can accompany gonadal hormone decline in human males in aging, clinical cases of hypogonadalism and in certain neurologic and psychiatric illnesses. Accordingly, it may be important to obtain in males the kind of detailed knowledge concerning hormone effects on, for example, the channel and electrophysiological properties of NMDAR that currently exists for the female brain.

PAK in Alzheimer disease, Huntington disease and X-linked mental retardation

Developmental cognitive deficits including X-linked mental retardation (XLMR) can be caused by mutations in P21-activated kinase 3 (PAK3) that disrupt actin dynamics in dendritic spines. Neurodegenerative diseases such as Alzheimer disease (AD), where both PAK1 and PAK3 are dysregulated, may share final common pathways with XLMR. Independent of familial mutation, cognitive deficits emerging with aging, notably AD, begin after decades of normal function. This prolonged prodromal period involves the buildup of amyloid-β (Aβ) extracellular plaques and intraneuronal neurofibrillary tangles (NFT). Subsequently region dependent deficits in synapses, dendritic spines and cognition coincide with dysregulation in PAK1 and PAK. Specifically proximal to decline, cytoplasmic levels of actin-regulating Rho GTPase and PAK1 kinase are decreased in moderate to severe AD, while aberrant activation and translocation of PAK1 appears around the onset of cognitive deficits. Downstream to PAK1, LIM kinase inactivates cofilin, contributing to cofilin pathology, while the activation of Rho-dependent kinase ROCK increases Aβ production. Aβ activation of fyn disrupts neuronal PAK1 and ROCK-mediated signaling, resulting in synaptic deficits. Reductions in PAK1 by the anti-amyloid compound curcumin suppress synaptotoxicity. Similarly other neurological disorders, including Huntington disease (HD) show dysregulation of PAKs. PAK1 modulates mutant huntingtin toxicity by enhancing huntingtin aggregation, and inhibition of PAK activity protects HD as well as fragile X syndrome (FXS) symptoms. Since PAK plays critical roles in learning and memory and is disrupted in many cognitive disorders, targeting PAK signaling in AD, HD and XLMR may be a novel common therapeutic target for AD, HD and XLMR.

Impaired Src signaling and post-synaptic actin polymerization in Alzheimer's disease mice hippocampus--linking NMDA receptors and the reelin pathway

Early cognitive deficits in Alzheimer's disease (AD) have been related to deregulation of N-methyl-d-aspartate receptors (NMDARs) and synaptic dysfunction in response to amyloid-beta peptide. NMDAR anchorage to post-synaptic membrane depends in part on Src kinase, which is also implicated in NMDAR activation and actin cytoskeleton stabilization, two processes relevant for normal synaptic function. In this study we analyzed the changes in GluN2B subunit phosphorylation and the levels of proteins involved in Src related signaling pathways linking the Tyr kinase to actin cytoskeleton polymerization, namely reelin, disabled-1 (Dab1) and cortactin, in hippocampal and cortical homogenates obtained from the triple transgenic mouse model of AD (3xTg-AD) that shows progression of pathology as a function of age versus age-matched wild-type mice. Moreover, we evaluated regional post-synaptic actin polymerization using phalloidin labeling in hippocampal slices. Young (3month-old) 3xTg-AD male mice hippocampus exhibited decreased GluN2B Tyr1472 phosphorylation and reduced Src activity. In the cortex, decreased Src activity correlated with reduced levels of reelin and Dab1, implicating changes in the reelin pathway. We also observed diminished phosphorylated Dab1 and cortactin protein levels in the hippocampus and cortex of young 3xTg-AD male mice. Concordantly with the recognized role of these proteins in actin stabilization, we detected a significant decrease in post-synaptic F-actin in 3month-old 3xTg-AD male CA1 and CA3 hippocampal regions. These data suggest deregulated Src-dependent signaling pathways involving GluN2B-composed NMDARs and post-synaptic actin cytoskeleton depolymerization in the hippocampus in early stages of AD.

Protective effect of spleen-yin-nourishing recipe on amyloid beta-peptide-induced damage of primarily cultured rat hippocampal neurons and its mechanism

OBJECTIVE

To observe the relationship among amyloid beta-peptide (Abeta)-induced neurotoxicity, serum-inducible kinase (SNK)-spine-associated Rap guanosine triphosphatase activating protein (SPAR) pathway and N-methyl-D-aspartate receptor (NMDAR), and to explore the mechanism of the protective effect of spleen-yin nourishing recipe (Zibu Piyin Recipe, ZBPYR) in hippocampal neurons against Abeta-induced neurotoxicity.

METHODS

The Abeta(1-40) powder was dissolved in 1 x PBS and incubated at 37 degrees centigrade, and then aggregated fibrillar Abeta(1-40) was obtained 72 h later. We used rat primary hippocampal neurons as cell model. ZBPYR-containing serum was gained by the method of serum pharmacology. ZBPYR-containing serum was added to the culture 1 h before Abeta(1-40) (5 micromol/L) exposure. Cells were harvested 2 h after Abeta(1-40) exposure for total RNA extracting. Then the mRNA expression levels of SNK, SPAR and NMDAR subunits NR1, NR2A and NR2B were detected by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

After 2-hour Abeta(1-40) exposure, we found that the expression level of SNK mRNA was up-regulated and the expression levels of SPAR, NR1, NR2A and NR2B mRNAs were down-regulated in hippocampal neurons as compared with control group (P < 0.01, P < 0.05). While with ZBPYR-containing serum pretreatment, the expression level of SNK mRNA was down-regulated and the levels of SPAR, NR1, NR2A and NR2B were up-regulated as compared with Abeta(1-40) exposure, and 2% ZBPYR-containing serum showed the best effect (P < 0.05).

CONCLUSION

Abeta-induced neurotoxicity was related to SNK-SPAR pathway and NMDAR; ZBPYR-containing serum can protect neurons from Abeta-induced neurotoxicity, and this protective effect may be performed by regulating the expression of NMDAR and blocking of the SNK-SPAR pathway.

Potential involvement of GRIN2B encoding the NMDA receptor subunit NR2B in the spectrum of Alzheimer's disease

Increasing evidence links dysregulation of NR2B-containing N-methyl-D-aspartate receptor remodelling and trafficking to Alzheimer's disease (AD). This theme offers the possibility that the GRIN2B gene, encoding this selective NR2B subunit, represents a potential molecular modulating factor for this disease. Based on this hypothesis, we carried out a mutation scanning of exons and flanking regions of GRIN2B in a well-characterized cohort of AD patients, recruited from Southern Italy. A "de novo" p.K1293R mutation, affecting a highly conserved residue of the protein in the C-terminal domain, was observed for the first time in a woman with familial AD, as the only genetic alteration of relevance. Moreover, an association study between the other detected sequence variants and AD was performed. In particular, the study was focused on five identified single nucleotide polymorphisms: rs7301328, rs1805482, rs3026160, rs1806191 and rs1806201, highlighting a significant contribution from the GRIN2B rs1806201 T allele towards disease susceptibility [adjusted odds ratio (OR) = 1.92, 95% confidence interval (CI) 1.40-2.63, p < 0.001, after correction for sex, age, and APOE ε4 genotype]. This was confirmed by haplotype analysis that identified a specific haplotype, carrying the rs1806201 T allele (CCCTC), over-represented in patients versus controls (adjusted OR = 6.03; p < 0.0001). Although the pathogenic role of the GRIN2B-K1293R mutation in AD is not clear, our data advocate that genetic variability in the GRIN2B gene, involved in synaptic functioning, might provide valuable insights into disease pathogenesis, continuing to attract significant attention in biomedical research on its genetic and functional role.

Dysfunctional synapse in Alzheimer's disease - A focus on NMDA receptors

Alzheimer's disease (AD) is the most prevalent form of dementia in the elderly. Alterations capable of causing brain circuitry dysfunctions in AD may take several years to develop. Oligomeric amyloid-beta peptide (Aβ) plays a complex role in the molecular events that lead to progressive loss of function and eventually to neurodegeneration in this devastating disease. Moreover, N-methyl-D-aspartate (NMDA) receptors (NMDARs) activation has been recently implicated in AD-related synaptic dysfunction. Thus, in this review we focus on glutamatergic neurotransmission impairment and the changes in NMDAR regulation in AD, following the description on the role and location of NMDARs at pre- and post-synaptic sites under physiological conditions. In addition, considering that there is currently no effective ways to cure AD or stop its progression, we further discuss the relevance of NMDARs antagonists to prevent AD symptomatology. This review posits additional information on the role played by Aβ in AD and the importance of targeting the tripartite glutamatergic synapse in early asymptomatic and possible reversible stages of the disease through preventive and/or disease-modifying therapeutic strategies. This article is part of the Special Issue entitled 'The Synaptic Basis of Neurodegenerative Disorders'.

Tetrahydroxystilbene glucoside improves the learning and memory of amyloid-β(₁₋₄₂)-injected rats and may be connected to synaptic changes in the hippocampus

The aim of this study was to evaluate the protective effects of 2,3,5,4'-tetrahydroxystilbene-2-O-β-D-glucoside (TSG), an active component extracted from Polygonum multiflorum, on learning/memory deficits in Alzheimer's disease (AD). We randomly divided 24 male Sprague-Dawley rats among 4 groups: (i) the sham-operated group (control); (ii) sham-operated group also treated with TSG (sham+TSG); (iii) beta amyloid treated group (Aβ); and (iv) Aβ treatment group also treated with TSG (Aβ+TSG). Rats in the Aβ and Aβ+TSG groups were treated with Aβ₁₋₄₂ intracerebroventricularly, whereas the control and sham+TSG groups were given phosphate-buffered saline. Rats in the sham+TSG and Aβ+TSG groups were then treated intragastrically with TSG (50 mg·(kg body mass)⁻¹·day⁻¹) for 4 weeks, and rats in the Aβ and control groups were treated with saline. The results from Morris water maze tests, electron microscopy, real-time polymerase chain reaction, and Western blotting demonstrated that Aβ₁₋₄₂ induced impairment in learning and memory, degeneration in synaptic structures, and downregulation of Src and NR2B at the gene and protein level, respectively. These alterations were reversed by the administration of TSG, suggesting that TSG exerts anti-AD properties by protecting synaptic structure and function. TSG-induced upregulation of Src and NR2B may be responsible for this process.

Increasing power for voxel-wise genome-wide association studies: the random field theory, least square kernel machines and fast permutation procedures

Imaging traits are thought to have more direct links to genetic variation than diagnostic measures based on cognitive or clinical assessments and provide a powerful substrate to examine the influence of genetics on human brains. Although imaging genetics has attracted growing attention and interest, most brain-wide genome-wide association studies focus on voxel-wise single-locus approaches, without taking advantage of the spatial information in images or combining the effect of multiple genetic variants. In this paper we present a fast implementation of voxel- and cluster-wise inferences based on the random field theory to fully use the spatial information in images. The approach is combined with a multi-locus model based on least square kernel machines to associate the joint effect of several single nucleotide polymorphisms (SNP) with imaging traits. A fast permutation procedure is also proposed which significantly reduces the number of permutations needed relative to the standard empirical method and provides accurate small p-value estimates based on parametric tail approximation. We explored the relation between 448,294 single nucleotide polymorphisms and 18,043 genes in 31,662 voxels of the entire brain across 740 elderly subjects from the Alzheimer's disease neuroimaging initiative (ADNI). Structural MRI scans were analyzed using tensor-based morphometry (TBM) to compute 3D maps of regional brain volume differences compared to an average template image based on healthy elderly subjects. We find method to be more sensitive compared with voxel-wise single-locus approaches. A number of genes were identified as having significant associations with volumetric changes. The most associated gene was GRIN2B, which encodes the N-methyl-d-aspartate (NMDA) glutamate receptor NR2B subunit and affects both the parietal and temporal lobes in human brains. Its role in Alzheimer's disease has been widely acknowledged and studied, suggesting the validity of the approach. The various advantages over existing approaches indicate a great potential offered by this novel framework to detect genetic influences on human brains.

Genetic interactions associated with 12-month atrophy in hippocampus and entorhinal cortex in Alzheimer's Disease Neuroimaging Initiative

Missing heritability in late onset Alzheimer disease can be attributed, at least in part, to heterogeneity in disease status and to the lack of statistical analyses exploring genetic interactions. In the current study, we use quantitative intermediate phenotypes derived from magnetic resonance imaging data available from the Alzheimer's Disease Neuroimaging Initiative, and we test for association with gene-gene interactions within biological pathways. Regional brain volumes from the hippocampus (HIP) and entorhinal cortex (EC) were estimated from baseline and 12-month magnetic resonance imaging scans. Approximately 560,000 single nucleotide polymorphisms (SNPs) were available genome-wide. We tested all pairwise SNP-SNP interactions (approximately 151 million) within 212 Kyoto Encyclopedia of Genes and Genomes pathways for association with 12-month regional atrophy rates using linear regression, with sex, APOE ε4 carrier status, age, education, and clinical status as covariates. A total of 109 SNP-SNP interactions were associated with right HIP atrophy, and 125 were associated with right EC atrophy. Enrichment analysis indicated significant SNP-SNP interactions were overrepresented in the calcium signaling and axon guidance pathways for both HIP and EC atrophy and in the ErbB signaling pathway for HIP atrophy.

Neurotransmitter receptors and cognitive dysfunction in Alzheimer's disease and Parkinson's disease

Cognitive dysfunction is one of the most typical characteristics in various neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease (advanced stage). Although several mechanisms like neuronal apoptosis and inflammatory responses have been recognized to be involved in the pathogenesis of cognitive dysfunction in these diseases, recent studies on neurodegeneration and cognitive dysfunction have demonstrated a significant impact of receptor modulation on cognitive changes. The pathological alterations in various receptors appear to contribute to cognitive impairment and/or deterioration with correlation to diversified mechanisms. This article recapitulates the present understandings and concepts underlying the modulation of different receptors in human beings and various experimental models of Alzheimer's disease and Parkinson's disease as well as a conceptual update on the underlying mechanisms. Specific roles of serotonin, adrenaline, acetylcholine, dopamine receptors, and N-methyl-D-aspartate receptors in Alzheimer's disease and Parkinson's disease will be interactively discussed. Complex mechanisms involved in their signaling pathways in the cognitive dysfunction associated with the neurodegenerative diseases will also be addressed. Substantial evidence has suggested that those receptors are crucial neuroregulators contributing to cognitive pathology and complicated correlations exist between those receptors and the expression of cognitive capacities. The pathological alterations in the receptors would, therefore, contribute to cognitive impairments and/or deterioration in Alzheimer's disease and Parkinson's disease. Future research may shed light on new clues for the treatment of cognitive dysfunction in neurodegenerative diseases by targeting specific alterations in these receptors and their signal transduction pathways in the frontal-striatal, fronto-striato-thalamic, and mesolimbic circuitries.