Memantine protects rat cortical cultured neurons against β‐amyloid‐induced toxicity by attenuating tau phosphorylation

It has been suggested that accumulation of beta‐amyloid (Aβ) peptide triggers neurodegeneration, at least in part, via glutamate‐mediated excitotoxicity in Alzheimer’s disease (AD) brain. This is supported by observations that toxicity induced by Aβ peptide in cultured neurons and in adult rat brain is known to be mediated by activation of glutamatergic N‐methyl‐d ‐aspartate (NMDA) receptors. Additionally, recent clinical studies have shown that memantine, a noncompetitive NMDA receptor antagonist, can significantly improve cognitive functions in some AD patients. However, very little is currently known about the potential role of memantine against Aβ‐induced toxicity. In the present study, we have shown that Aβ_1–42‐induced toxicity in rat primary cortical cultured neurons is accompanied by increased extracellular and decreased intracellular glutamate levels. We subsequently demonstrated that Aβ toxicity is induced by increased phosphorylation of tau protein and activation of tau kinases, i.e. glycogen synthase kinase‐3β and extracellular signal‐related kinase 1/2. Additionally, Aβ treatment induced cleavage of caspase‐3 and decreased phosphorylation of cyclic AMP response element binding protein, which are critical in determining survival of neurons. Memantine treatment significantly protected cultured neurons against Aβ‐induced toxicity by attenuating tau‐phosphorylation and its associated signaling mechanisms. However, this drug did not alter either conformation or internalization of Aβ_1–42 and it was unable to attenuate Aβ‐induced potentiation of extracellular glutamate levels. These results, taken together, provide new insights into the possible neuroprotective action of memantine in AD pathology.     

β‐amyloid cortical deposits are accompanied by the loss of serotonergic neurons in the dog

Dogs may naturally suffer an age‐related cognitive impairment that has aroused a great deal of interest, even beyond the field of the veterinary clinic. This canine senile dementia reproduces several key aspects of Alzheimer's disease (AD), including the presence of β‐amyloid (Aβ) deposits in the cerebral cortex, neurodegeneration, and learning and memory impairments. In the present study, we have used unbiased stereological procedures to estimate the number of the dorsal and median raphe nuclei (DRN and MRN, respectively) serotonergic neurons immunolabeled with an anti‐tryptophan hydroxylase (TrH) monoclonal antibody in young and aged dogs without Aβ cortical deposits and in aged dogs with Aβ cortical deposits. The estimated total number of TrH‐labeled neurons (mean ± SD) was 94,790 ± 26,341 for the DRN and 40,404 ± 8,692 for the MRN. The statistical analyses revealed that aged dogs with Aβ cortical pathology had 33% fewer serotonergic neurons in the DRN and MRN than aged dogs without Aβ cortical deposits (108,043 ± 18,800 vs. 162,242 ± 39,942, respectively; P = 0.01). In contrast, no significant variations were found between young and aged dogs without Aβ cortical deposits. These results suggest that degeneration of the serotonergic neurons could be involved in the cognitive damage that accompanies Aβ cortical pathology in the dog and reinforce the use of the canine model for exploring the potential mechanisms linking the cortical Aβ pathology and serotonergic neurodegeneration that occurs during the course of AD. J. Comp. Neurol. 513:417–429, 2009. © 2009 Wiley‐Liss, Inc.     

Pathology of Parkinson’s disease

In Parkinson’s disease (PD), in addition to degeneration of the nigrostriatal dopaminergic pathway, a variety of neuronal systems are involved, causing multiple neuromediator dysfunctions that account for the complex patterns of functional deficits. Degeneration affects the dopaminergic mesocorticolimbic system, the noradrenergic locus ceruleus (oral parts) and motor vagal nucleus, the serotonergic raphe nuclei, the cholinergic nucleus basalis of Meynert, pedunculopontine nucleus pars compacta, Westphal-Edinger nucleus, and many peptidergic brainstem nuclei. Cell losses in subcortical projection nuclei range from 30 to 90% of controls; they are more severe in depressed and demented PD patients. Most of the lesions are region-specific, affecting not all neurons containing a specific transmitter or harboring Lewy bodies. In contrast to Alzheimer’s disease (AD), subcortical system lesions in Parkinson’s disease appear not to be related to cortical pathology, suggesting independent or concomitant degeneration. The pathogenesis of multiple-system changes contributing to chemical pathology and clinical course of Parkinson’s disease are unknown.     

Tripchlorolide protects neuronal cells from microglia‐mediated β‐amyloid neurotoxicity through inhibiting NF‐κB and JNK signaling

Recent research has focused on soluble oligomeric assemblies of β‐amyloid peptides (Aβ) as the proximate cause of neuroinflammation, synaptic loss, and the eventual dementia associated with Alzheimer's disease (AD). In this study, tripchlorolide (T₄), an extract of Tripterygium wilfordii Hook. F (TWHF), was studied as a novel agent to suppress neuroinflammatory process in microglial cells and to protect neuronal cells against microglia‐mediated oligomeric Aβ toxicity. T₄ significantly attenuated oligomeric Aβ(1‐42)‐induced release of inflammatory productions such as tumor necrosis factor‐α, interleukin‐1β, nitric oxide (NO), and prostaglandin E₂. It also downregulated the protein levels of inducible nitric oxide synthase (iNOS) and cyclooxygenase‐2 (COX‐2) in microglial cells. Further molecular mechanism study demonstrated that T₄ inhibited the nuclear translocation of nuclear factor‐κB (NF‐κB) without affecting I‐κBα phosphorylation. It repressed Aβ‐induced JNK phosphorylation but not ERK or p38 MAPK. The inhibition of NF‐κB and JNK by T₄ is correlated with the suppression of inflammatory mediators in Aβ‐stimulated microglial cells. These results suggest that T₄ protects neuronal cells by blocking inflammatory responses of microglial cells to oligomeric Aβ(1‐42) and that T₄ acts on the signaling of NF‐κB and JNK, which are involved in the modulation of inflammatory response. Therefore, T₄ may be an effective agent in modulating neuroinflammatory process in AD. © 2009 Wiley‐Liss, Inc.     

Amyloid β‐protein suppressed nicotinic acetylcholine receptor‐mediated currents in acutely isolated rat hippocampal CA1 pyramidal neurons

Amyloid β protein (Aβ) is responsible for the deficits of learning and memory in Alzheimer's disease (AD). The high affinity between Aβ and nicotinic acetylcholine receptors (nAChRs) suggests that the impairment of cognitive function in AD might be involved in the Aβ‐induced damage of nAChRs. This study investigated the effects of Aβ fragments on nAChR‐mediated membrane currents in acutely isolated rat hippocampal pyramidal neurons by using whole‐cell patch clamp technique. The results showed that: (1) nonspecific nAChR agonist nicotine, selective α7 nAChR agonist choline, and α4β2 nAChR agonist epibatidine all effectively evoked inward currents in CA1 neurons at normal resting membrane potential, with different desensitization characteristics; (2) acute application of different concentrations (pM–μM) of Aβ25‐35, Aβ31‐35, or Aβ35‐31 alone did not trigger any membrane current, but pretreatment with 1 μM Aβ25‐35 and Aβ31‐35 similarly and reversibly suppressed the nicotine‐induced currents; (3) further, choline‐ and epibatidine‐induced currents were also reversibly suppressed by the Aβ pretreatment, but more prominent for the choline‐induced response. These results demonstrate that the functional activity of both α7 and α4β2 nAChRs in the membrane of acutely isolated hippocampal neurons was significantly downregulated by Aβ treatment, suggesting that nAChRs, especially α7 nAChRs, in the brain may be the important biological targets of neurotoxic Aβ in AD. In addition, the similar suppression of nAChR currents by Aβ25‐35 and Aβ31‐35 suggests that the sequence 31‐35 in Aβ molecule may be a shorter active center responsible for the neurotoxicity of Aβ in AD. Synapse, 2013. © 2012 Wiley Periodicals, Inc.     

Neurotrophin receptors and selective loss of cholinergic neurons in Alzheimer disease

The most consistent neuropathological finding in Alzheimer disease (AD) is the loss of cholinergic neurons of the nucleus basalis of Meynert (NbM). Using immunohistochemistry, we have previously shown that cholinergic neurons located in the ventral striatum were affected, whereas those of the caudate nucleus, putamen, and mesencephalon were spared. Since cholinergic neurons that degenerate in AD are sensitive to NGF and those that are spared are not, it has been hypothesized that the loss of neurotrophins receptors may play a role in the death of cholinergic neuronsin AD. Using immunohistochemistry, we have detected the presence of TrkA on most cholinergic neurons from the NbM, on some from those of the striatum, but not on those of the mesencephalon in the human brain. In AD patients, the number of neurons that expressed TrkA was markedly decreased in the NbM very likely as a consequence of cholinergic neuronal loss. In the striatum, despite the loss of high-affinity NGF binding prevously reported, no loss of TrkA was observed. Taken together, these results suggest a decreased expression of NGF receptors on the striatal cholinergic neurons in AD. This loss may contribute, when it reaches a crucial threshold, to the death of cholinergic neurons occurring in AD.     

Neurotrophin receptors and selective loss of cholinergic neurons in Alzheimer disease

The most consistent neuropathological finding in Alzheimer disease (AD) is the loss of cholinergic neurons of the nucleus basalis of Meynert (NbM). Using immunohistochemistry, we have previously shown that cholinergic neurons located in the ventral striatum were affected, whereas those of the caudate nucleus, putamen, and mesencephalon were spared. Since cholinergic neurons that degenerate in AD are sensitive to NGF and those that are spared are not, it has been hypothesized that the loss of neurotrophins receptors may play a role in the death of cholinergic neuronsin AD. Using immunohistochemistry, we have detected the presence of TrkA on most cholinergic neurons from the NbM, on some from those of the striatum, but not on those of the mesencephalon in the human brain. In AD patients, the number of neurons that expressed TrkA was markedly decreased in the NbM very likely as a consequence of cholinergic neuronal loss. In the striatum, despite the loss of high-affinity NGF binding prevously reported, no loss of TrkA was observed. Taken together, these results suggest a decreased expression of NGF receptors on the striatal cholinergic neurons in AD. This loss may contribute, when it reaches a crucial threshold, to the death of cholinergic neurons occurring in AD.     

A novel antibody targeting sequence 31–35 in amyloid β protein attenuates Alzheimer's disease‐related neuronal damage

Amyloid β protein (Aβ) plays a critical role in pathogenesis of Alzheimer's disease (AD). Our previous studies indicated that the sequence 31–35 in Aβ molecule is an effective active center responsible for Aβ neurotoxicity in vivo and in vitro. In the present study, we prepared a novel antibody specifically targeting the sequence 31–35 of amyloid β protein, and investigated the neuroprotection of the anti‐Aβ_31–35 antibody against Aβ_1–42‐induced impairments in neuronal viability, spatial memory, and hippocampal synaptic plasticity in rats. The results showed that the anti‐Aβ_31–35 antibody almost equally bound to both Aβ_31–35 and Aβ_1–42, and pretreatment with the antibody dose‐dependently prevented Aβ_1–42‐induced cytotoxicity on cultured primary cortical neurons. In behavioral study, intracerebroventricular (i.c.v.) injection of anti‐Aβ_31–35 antibody efficiently attenuated Aβ_1–42‐induced impairments in spatial learning and memory of rats. In vivo electrophysiological experiments further indicated that Aβ_1–42‐induced suppression of hippocampal synaptic plasticity was effectively reversed by the antibody. These results demonstrated that the sequence 31–35 of Aβ may be a new therapeutic target, and the anti‐Aβ_31–35 antibody could be a novel immunotheraputic approach for the treatment of AD. © 2016 Wiley Periodicals, Inc.     

Nucleus raphe dorsalis in Alzheimer's disease: neurofibrillary tangles and loss of large neurons

Diffuse serotonergic fibers are presumed to project to the telencephalon from the nucleus raphe dorsalis (NRD) of the midbrain, in a manner similar to the cholinergic projections from the nucleus basalis of Meynert (nbM) to the cerebral cortex. Neuropathological changes in both of these nuclei have been reported in Alzheimer's disease (AD). Although many morphometric studies of the nbM in AD have been documented, only one such study of the NRD has been conducted so far; it demonstrated a sixfold increase in neurofibrillary tangles in AD but no statistically significant difference in the number of neurons in patients with AD and age-matched controls. A study of the NRD utilizing different stains and wider anatomical boundaries is detailed in this report of 5 patients with AD and 7 age-matched controls. In AD the NRD showed 39 times more neurofibrillary tangles and the number and cell density of large neurons were reduced to 23% and 28%, respectively, of those in the controls. A small number of senile plaques were found in the NRD in all patients with AD but none were found in the controls.     

Methyl 3,4‐dihydroxybenzoate protects primary cortical neurons against Aβ25–35‐induced neurotoxicity through mitochondria pathway

Amyloid‐β peptides (Aβ), which can aggregate into oligomers or fibrils in neurons, play a critical role in the pathogenesis of Alzheimer's disease (AD). Methyl 3,4‐dihydroxybenzoate (MDHB), a phenolic acid compound, has been reported to have antioxidative and neurotrophic effects. The present study investigated the neuroprotective effects of MDHB against Aβ‐induced apoptosis in rat primary cortical neutons. The primary cortical neurons were pretreated with different concentrations of MDHB for 24 hr, then incubated with 10 μM Aβ_25–35 for 24 hr. The results showed that Aβ_25–35 could induce neurotoxicity as evidenced by the decreased cell viability and the increased apoptotic rate. In parallel, Aβ_25–35 significantly increased the reactive oxygen species accumulation and decreased mitochondrial membrane potential. However, pretreatment of the primary cortical neurons with MDHB could effectively suppress these cellular events caused by Aβ_25–35 exposure. In addition, MDHB could increase the level of Bcl‐2, decrease the level of Bax, and inhibit the activation of caspase‐9 and caspase‐3 in Aβ_25–35‐treated primary cortical neurons. All these results were beneficial in their protective effect against Aβ‐induced neurotoxicity. Our results suggest that MDHB has a neuroprotective effect that provides a pharmacological basis for its clinical use in the treatment of AD. © 2013 Wiley Periodicals, Inc.     

β-amyloid binds to p75NTR and activates NFκB in human neuroblastoma cells

Amyloid β peptide (Aβ), a proteolytic fragment of the amyloid precursor protein (APP), is a major component of the plaques found in the brain of Alzheimer's disease (AD) patients. These plaques are thought to cause the observed loss of cholinergic neurons in the basal forebrain of AD patients. In these neurons, particularly those of the nucleus basalis of Meynert, an up-regulation of 75kD-neurotrophin receptor (p75^NTR), a nonselective neurotrophin receptor belonging to the death receptor family, has been reported. p75^NTR expression has been described to correlate with β-amyloid sensitivity in vivo and in vitro, suggesting a possible role for p75^NTR as a receptor for Aβ. Here we used a human neuroblastoma cell line to investigate the involvement of p75^NTR in Aβ-induced cell death. Aβ peptides were found to bind to p75^NTR resulting in activation of NFκB in a time- and dose-dependent manner. Blocking the interaction of Aβ with p75^NTR using NGF or inhibition of NFκB activation by curcumin or NFκB SN50 attenuated or abolished Aβ-induced apoptotic cell death. The present results suggest that p75^NTR might be a death receptor for Aβ, thus being a possible drug target for treatment of AD. J. Neurosci. Res. 54:798–804, 1998. © 1998 Wiley-Liss, Inc.     

Alterations in spontaneous delta and gamma activity might provide clues to detect changes induced by amyloid‐β administration

Alzheimer's disease (AD) is the most prevalent form of dementia and has an increasing incidence. The neuropathogenesis of AD is suggested to be a result of the accumulation of amyloid‐β (Aβ) peptides in the brain. To date, Aβ‐induced cognitive and neurophysiologic impairments have not been illuminated sufficiently. Therefore, we aimed to examine how spontaneous brain activities of rats changed by injection of increasing Aβ doses into the brain hemispheres, and whether these changes could be used as a new biomarker for the early diagnosis of the AD. Rats were randomized into following groups: sham (Sham) and seven Aβ‐treated (i.c.v.) groups in increasing concentrations (from Aβ‐1 to Aβ‐7). After recovery, EEG recordings were obtained from implanted electrodes from eight electrode locations, and then, spectral and statistical analyses were performed. A significant decrement in gamma activity was observed in all Aβ groups compared with the sham group. In delta activity, we observed significant changes from Aβ‐4 to Aβ‐7 group compared with sham group. Delta coherence values were decreased from Aβ‐4 to Aβ‐7 and Aβ‐5 to Aβ‐7 groups for frontal and temporal electrode pairs, respectively. A gradual increment was observed in Aβ_1‐42 level till Aβ‐4 group. Positive correlation for global delta power and negative correlation for global gamma power between Aβ_1‐42 peptide levels were detected. Consequently, it is conceivable to suggest gamma oscillation might be used to detect early stages of AD. Moreover, changes in delta activity provide information about the onset of major pathologic changes in the progress of AD.     

In vivo labelling of hippocampal β‐amyloid in triple‐transgenic mice with a fluorescent acetylcholinesterase inhibitor released from nanoparticles

The drastic loss of cholinergic projection neurons in the basal forebrain is a hallmark of Alzheimer’s disease (AD), and drugs most frequently applied for the treatment of dementia include inhibitors of the acetylcholine‐degrading enzyme acetylcholinesterase (AChE). This protein is known to act as a ligand of β‐amyloid (Aβ) in senile plaques, a further neuropathological sign of AD. Recently, we have shown that the fluorescent, heterodimeric AChE inhibitor PE154 allows for the histochemical staining of cortical Aβ plaques in triple‐transgenic (TTG) mice with age‐dependent β‐amyloidosis and tau hyperphosphorylation, an established animal model for aspects of AD. In the present study, we have primarily demonstrated the targeting of Aβ‐immunopositive plaques with PE154 in vivo for 4 h up to 1 week after injection into the hippocampi of 13–20‐month‐old TTG mice. Numerous plaques, double‐stained for PE154 and Aβ‐immunoreactivity, were revealed by confocal laser‐scanning microscopy. Additionally, PE154 targeted hippocampal Aβ deposits in aged TTG mice after injection of carboxylated polyglycidylmethacrylate nanoparticles delivering the fluorescent marker in vivo. Furthermore, biodegradable core‐shell polystyrene/polybutylcyanoacrylate nanoparticles were found to be suitable, alternative vehicles for PE154 as a useful in vivo label of Aβ. Moreover, we were able to demonstrate that PE154 targeted Aβ, but neither phospho‐tau nor reactive astrocytes surrounding the plaques. In conclusion, nanoparticles appear as versatile carriers of AChE inhibitors and other promising drugs for the treatment of AD.     

Cognitive dysfunction and dementia in Parkinson’s disease

Parkinson's disease (PD) is a slowly progressive neurodegenerative disorder mainly characterized by degeneration of dopaminergic neurons in the substantia nigra and the ventral tegmental area, in combination with a varying loss of central noradrenergic (locus coeruleus), cholinergic (nucleus basalis of Meynert) and serotonergic (dorsal raphe nuclei) integrity, leading to a multitude of motor and non-motor behavioral disturbances. Apart from the clinical motor hallmarks, in the early stages of disease, subtle cognitive dysfunction might be seen comprising mainly executive dysfunction, with secondary visuospatial and mnemonic disturbances. In about 20-40% of patients, these problems may eventually proceed to dementia, which constitutes an important risk factor for caregiver distress, decreased quality of life and nursing home placement. Dementia in PD is typically characterized by a progressive dysexecutive syndrome with attentional deficits and fluctuating cognition, often accompanied by psychotic symptoms. It is thought to be the result of a combination of both subcortical and cortical changes. PD-related dopaminergic deficiency in the nucleus caudatus and mesocortical areas (due to degeneration of projections from the substantia nigra and ventral tegmental area) and cholinergic deficiency in the cortex (due to degeneration of ascending projections from the nucleus basalis of Meynert), combined with additional Alzheimer-pathology and cortical Lewy bodies, may greatly contribute to dementia.Current treatment of dementia in PD is based on compensation of the profound cholinergic deficiency. Recent studies with the cholinesterase inhibitors galantamine, donepezil and rivastigmine show promising results in improving cognition and ameliorating psychotic symptoms, which must further be confirmed in randomized controlled trials.     

Tyrosine phosphatase STEP61 negatively regulates amyloid β‐mediated ERK/CREB signaling pathways via α7 nicotinic acetylcholine receptors

Striatal‐enriched phosphatase 61 (STEP₆₁) plays an essential role in synaptic plasticity and has recently been implicated in neurodegenerative disease. Here we characterized a possible role of STEP₆₁ in Alzheimer's disease (AD) pathology using a mouse model of AD (Tg‐APPswe/PSEN1dE9, APP/PS1 mice) and an in vitro model of AD [cortical neurons treated with amyloid β (Aβ)_1–42 peptides]. Our data indicate age‐related elevation of STEP₆₁ levels and the proportion of dephosphorylated STEP₆₁ (active STEP₆₁) in wild‐type mice, which was enhanced in APP/PS1 mice. Furthermore, the increased STEP₆₁ levels and active STEP₆₁ were observed in the hippocampus and cortex from 12‐month‐old APP/PS1 mice and in Aβ_1–42‐treated cortical neurons. An α7 nicotinic acetylcholine receptors (nAChRs) antagonist, α‐bungarotoxin (BTX), inhibited the Aβ_1–42‐induced increase of STEP₆₁ expression and activation. In addition, extracellular signal‐regulated kinase 1/2 (ERK1/2) and cAMP response element binding (CREB) were impaired in Aβ_1–42‐treated cortical neurons, and knockdown of STEP₆₁ enhanced the activation of ERK1/2 and CREB. Collectively, these findings indicate two alternate pathological pathways effecting STEP₆₁ regulation in AD. First, Aβ regulating STEP₆₁ activity is mediated by Aβ binding to α7 nAChRs. Second, STEP₆₁ negatively regulates Aβ‐mediated ERK/CREB pathway, an important signaling cascade involved in memory formation. © 2013 Wiley Periodicals, Inc.     

Astrocytic Aβ1‐42 uptake is determined by Aβ‐aggregation state and the presence of amyloid‐associated proteins

Intracerebral accumulation of amyloid‐β (Aβ) leading to Aβ plaque formation, is the main hallmark of Alzheimer's disease and might be caused by defective Aβ‐clearance. We previously found primary human astrocytes and microglia able to bind and ingest Aβ1‐42 in vitro, which appeared to be limited by Aβ1‐42 fibril formation. We now confirm that astrocytic Aβ‐uptake depends on size and/or composition of Aβ‐aggregates as astrocytes preferably take up oligomeric Aβ over fibrillar Aβ. Upon exposure to either fluorescence‐labelled Aβ1‐42 oligomers (Aβ_oligo) or fibrils (Aβ_fib), a larger (3.7 times more) proportion of astrocytes ingested oligomers compared to fibrils, as determined by flow cytometry. Aβ‐internalization was verified using confocal microscopy and live‐cell imaging. Neither uptake of Aβ_oligo nor Aβ_fib, triggered proinflammatory activation of the astrocytes, as judged by quantification of interleukin‐6 and monocyte‐chemoattractant protein‐1 release. Amyloid‐associated proteins, including α1‐antichymotrypsin (ACT), serum amyloid P component (SAP), C1q and apolipoproteins E (ApoE) and J (ApoJ) were earlier found to influence Aβ‐aggregation. Here, astrocytic uptake of Aβ_fib increased when added to the cells in combination with SAP and C1q (SAP/C1q), but was unchanged in the presence of ApoE, ApoJ and ACT. Interestingly, ApoJ and ApoE dramatically reduced the number of Aβ_oligo‐positive astrocytes, whereas SAP/C1q slightly reduced Aβ_oligo uptake. Thus, amyloid‐associated proteins, especially ApoJ and ApoE, can alter Aβ‐uptake in vitro and hence may influence Aβ clearance and plaque formation in vivo. © 2010 Wiley‐Liss, Inc.     

Small Aβ1–42 oligomer‐induced membrane depolarization of neuronal and microglial cells: Role of N‐methyl‐D‐aspartate receptors

Although it is well documented that soluble beta amyloid (Aβ) oligomers are critical factors in the pathogenesis of Alzheimer's disease (AD) by causing synaptic dysfunction and neuronal death, the primary mechanisms by which Aβ oligomers trigger neurodegeneration are not entirely understood. We sought to investigate whether toxic small Aβ_1–42 oligomers induce changes in plasma membrane potential of cultured neurons and glial cells in rat cerebellar granule cell cultures leading to neuronal death and whether these effects are sensitive to the N‐methyl‐D‐aspartate receptor (NMDA‐R) antagonist MK801. We found that small Aβ_1–42 oligomers induced rapid, protracted membrane depolarization of both neurons and microglia, whereas there was no change in membrane potential of astrocytes. MK801 did not modulate Aβ‐induced neuronal depolarization. In contrast, Aβ_1?42 oligomer‐induced decrease in plasma membrane potential of microglia was prevented by MK801. Small Aβ_1–42 oligomers significantly elevated extracellular glutamate and caused neuronal necrosis, and both were prevented by MK801. Also, small Aβ_1–42 oligomers decreased resistance of isolated brain mitochondria to calcium‐induced opening of mitochondrial permeability transition pore. In conclusion, the results suggest that the primary effect of toxic small Aβ oligomers on neurons is rapid, NMDA‐R‐independent plasma membrane depolarization, which leads to neuronal death. Aβ oligomers‐induced depolarization of microglial cells is NMDA‐R dependent. © 2014 Wiley Periodicals, Inc.     

Galanin immunoreactivity is increased in the nucleus basalis of Meynert in Alzheimer's disease.

A depletion of large cholinergic neurons in the nucleus basalis of Meynert is a consistent finding in Alzheimer's disease (AD). The nucleus basalis of Meynert also contains interneurons and afferents that may modulate its functioning. In the present study we examined neurochemical markers for neuropeptides, amino acid neurotransmitters, and monoaminergic neurotransmitters in postmortem samples of the nucleus basalis in 16 control subjects and 30 patients with AD. There were no significant changes in glutamate, aspartate, taurine, gamma-aminobutyric acid (GABA), and catecholamines; however, concentrations of serotonin, 5-hydroxyindoleacetic acid, and 5-hydroxytryptophol were significantly reduced. Choline acetyltransferase activity was significantly reduced, consistent with previous reports. Galanin immunoreactivity was significantly increased twofold in the patients with AD, but there were no significant changes in substance P, somatostatin, or neuropeptide Y immunoreactivity. Since galanin inhibits acetylcholine release, and produces cognitive deficits in animals, increased galanin immunoreactivity in the nucleus basalis of Meynert in AD may contribute to the cognitive deficits that characterize the illness.     

The G protein‐coupled oestrogen receptor,GPER1, mediates direct anti‐inflammatory effects of oestrogens in human cholinergic neurones from the nucleus basalis of Meynert

It has been well established, particularly in animal models, that oestrogens exert neuroprotective effects in brain areas linked to cognitive processes. A key protective role could reside in the capacity of oestrogen to modulate the inflammatory response. However, the direct neuroprotective actions of oestrogens on neurones are complex and remain to be fully clarified. In the present study, we took advantage of a previously characterised primary culture of human cholinergic neurones (hfNBM) from the foetal nucleus basalis of Meynert, which is known to regulate hippocampal and neocortical learning and memory circuits, aiming to investigate the direct effects of oestrogens under inflammatory conditions. Exposure of cells to tumour necrosis factor (TNF)α (10 ng mL^‐1) determined the activation of an inflammatory response, as demonstrated by nuclear factor‐kappa B p65 nuclear translocation and cyclooxygenase‐2 mRNA expression. These effects were inhibited by treatment with either 17β‐oestradiol (E₂) (10 nmol L^‐1) or G1 (100 nmol L^‐1), the selective agonist of the G protein‐coupled oestrogen receptor (GPER1). Interestingly, the GPER1 antagonist G15 abolished the effects of E₂ in TNFα‐treated cells, whereas the ERα/ERβ inhibitor tamoxifen did not. Electrophysiological measurements in hfNBMs revealed a depolarising effect caused by E₂ that was specifically blocked by tamoxifen and not by G15. Conversely, G1 specifically hyperpolarised the cell membrane and also increased both inward and outward currents elicited by a depolarising stimulus, suggesting a modulatory action on hfNBM excitability by GPER1 activation. Interestingly, pretreating cells with TNFα completely blocked the effects of G1 on membrane properties and also significantly reduced GPER1 mRNA expression. In addition, we found a peculiar subcellular localisation of GPER1 to focal adhesion sites that implicates new possible mechanisms of action of GPER1 in the neuronal perception of mechanical stimuli. The results obtained in the present study indicate a modulatory functional role of GPER1 with respect to mediating the oestrogen neuroprotective effect against inflammation in brain cholinergic neurones and, accordingly, may help to identify protective strategies for preventing cognitive impairments.     

A critical role of TRPM2 channel in Aβ42‐induced microglial activation and generation of tumor necrosis factor‐α

Amyloid β (Aβ)‐induced neuroinflammation plays an important part in Alzheimer's disease (AD). Emerging evidence supports a role for the transient receptor potential melastatin‐related 2 (TRPM2) channel in Aβ‐induced neuroinflammation, but how Aβ induces TRPM2 channel activation and this relates to neuroinflammation remained poorly understood. We investigated the mechanisms by which Aβ₄₂ activates the TRPM2 channel in microglial cells and the relationships to microglial activation and generation of tumor necrosis factor‐α (TNF‐α), a key cytokine implicated in AD. Exposure to 10–300 nM Aβ₄₂ induced concentration‐dependent microglial activation and generation of TNF‐α that were ablated by genetically deleting (TRPM2 knockout ;TRPM2‐KO) or pharmacologically inhibiting the TRPM2 channel, revealing a critical role of this channel in Aβ₄₂‐induced microglial activation and generation of TNF‐α. Mechanistically, Aβ₄₂ activated the TRPM2 channel via stimulating generation of reactive oxygen species (ROS) and activation of poly(ADPR) polymerase‐1 (PARP‐1). Aβ₄₂‐induced generation of ROS and activation of PARP‐1 and TRPM2 channel were suppressed by inhibiting protein kinase C (PKC) and NADPH oxidases (NOX). Aβ₄₂‐induced activation of PARP‐1 and TRPM2 channel was also reduced by inhibiting PYK2 and MEK/ERK. Aβ₄₂‐induced activation of PARP‐1 was attenuated by TRPM2‐KO and moreover, the remaining PARP‐1 activity was eliminated by inhibiting PKC and NOX, but not PYK2 and MEK/ERK. Collectively, our results suggest that PKC/NOX‐mediated generation of ROS and subsequent activation of PARP‐1 play a role in Aβ₄₂‐induced TRPM2 channel activation and TRPM2‐dependent activation of the PYK2/MEK/ERK signalling pathway acts as a positive feedback to further facilitate activation of PARP‐1 and TRPM2 channel. These findings provide novel insights into the mechanisms underlying Aβ‐induced AD‐related neuroinflammation.