Academia.edu no longer supports Internet Explorer.
To browse Academia.edu and the wider internet faster and more securely, please take a few seconds to upgrade your browser.
Acta Neuropathologica Communications
Amyloid-beta (Aβ) and tau protein are both involved in the pathogenesis of Alzheimer’s disease. Aβ produces synaptic deficits in wild-type mice that are not seen in Mapt−/− mice, suggesting that tau protein is required for these effects of Aβ. However, whether some synapses are more selectively affected and what factors may determine synaptic vulnerability to Aβ are poorly understood. Here we first observed that burst timing-dependent long-term potentiation (b-LTP) in hippocampal CA3-CA1 synapses, which requires GluN2B subunit-containing NMDA receptors (NMDARs), was inhibited by human Aβ1–42 (hAβ) in wild-type (WT) mice, but not in tau-knockout (Mapt−/−) mice. We then tested whether NMDAR currents were affected by hAβ; we found that hAβ reduced the postsynaptic NMDAR current in WT mice but not in Mapt−/− mice, while the NMDAR current was reduced to a similar extent by the GluN2B-selective NMDAR antagonist Ro 25–6981. To further investigate a possible difference in GluN2B-containing ...
Brain Pathology
N-methyl-D-aspartate receptors (NMDARs) are pivotal players in the synaptic transmission and synaptic plasticity underlying learning and memory. Accordingly, dysfunction of NMDARs has been implicated in the pathophysiology of Alzheimer disease (AD). Here, we used histoblot and sodium dodecylsulphatedigested freeze-fracture replica labelling (SDS-FRL) techniques to investigate the expression and subcellular localisation of GluN1, the obligatory subunit of NMDARs, in the hippocampus of P301S mice. Histoblots showed that GluN1 expression was significantly reduced in the hippocampus of P301S mice in a laminar-specific manner at 10 months of age but was unaltered at 3 months. Using the SDS-FRL technique, excitatory synapses and extrasynaptic sites on spines of pyramidal cells and interneuron dendrites were analysed throughout all dendritic layers in the CA1 field. Our ultrastructural approach revealed a high density of GluN1 in synaptic sites and a substantially lower density at extrasynaptic sites. Labelling density for GluN1 in excitatory synapses established on spines was significantly reduced in P301S mice, compared with agematched wild-type mice, in the stratum oriens (so), stratum radiatum (sr) and stratum lacunosum-moleculare (slm). Density for synaptic GluN1 on interneuron dendrites was significantly reduced in P301S mice in the so and sr but unaltered in the slm. Labelling density for GluN1 at extrasynaptic sites showed no significant differences in pyramidal cells, and only increased density in the interneuron dendrites of the sr. This differential alteration of synaptic versus extrasynaptic NMDARs supports the notion that the progressive accumulation of phospho-tau is associated with changes in NMDARs, in the absence of amyloid-β pathology, and may be involved in the mechanisms causing abnormal network activity of the hippocampal circuit.
The Journal of Physiology, 2013
• N -Methyl-D-aspartate receptor (NMDAR)-dependent potentiation of synaptic transmission is widely accepted as a cellular model of learning and memory. • It is most often studied in the CA1 area of rat hippocampal slices where it comprises a decremental and a sustained phase, which are commonly referred to as short-term potentiation (STP) and long-term potentiation (LTP), respectively. • In this study we show for the first time that STP and LTP are triggered by the activation of different classes of NMDARs and that STP itself comprises two pharmacologically and kinetically distinct components. • We suggest that the mechanistic separation of STP and LTP is likely to have important functional implications in that these two forms of synaptic plasticity can subserve unique physiological functions in a behaving animal.
Philosophical Transactions of the Royal Society B: Biological Sciences, 2013
Many endogenous factors influence the time course and extent of the detrimental effects of amyloid β-protein (Aβ) on synaptic function. Here, we assessed the impact of varying endogenous glutamatergic and cholinergic transmission by pharmacological means on the disruption of plasticity at hippocampal CA3-to-CA1 synapses in the anaesthetized rat. NMDA receptors (NMDARs) are considered critical in mediating Aβ-induced inhibition of long-term potentiation (LTP). However, intracerebroventricular injection of Aβ 1–42 inhibited not only NMDAR-dependent LTP but also voltage-activated Ca 2+ -dependent LTP induced by strong conditioning stimulation during NMDAR blockade. On the other hand, another form of NMDAR-independent synaptic plasticity, endogenous acetylcholine-induced muscarinic receptor-dependent long-term enhancement, was not hindered by Aβ 1–42 . Interestingly, augmenting endogenous acetylcholine activation of nicotinic receptors prior to the injection of Aβ 1–42 prevented the inh...
The Journal of Neuroscience, 2011
Amyloid β (Aβ) and tau protein are both implicated in memory impairment, mild cognitive impairment (MCI), and early Alzheimer's disease (AD), but whether and how they interact is unknown. Consequently, we asked whether tau protein is required for the robust phenomenon of Aβ-induced impairment of hippocampal long-term potentiation (LTP), a widely accepted cellular model of memory. We used wild-type mice and mice with a genetic knock-out of tau protein and recorded field potentials in an acute slice preparation. We demonstrate that the absence of tau protein prevents Aβ-induced impairment of LTP. Moreover, we show that Aβ increases tau phosphorylation and that a specific inhibitor of the tau kinase glycogen synthase kinase 3 blocks the increased tau phosphorylation induced by Aβ and prevents Aβ-induced impairment of LTP in wild-type mice. Together, these findings show that tau protein is required for Aβ to impair synaptic plasticity in the hippocampus and suggest that the Aβ-induc...
Acta neuropathologica communications, 2014
Hypersynchronicity of neuronal brain circuits is a feature of Alzheimer¿s disease (AD). Mouse models of AD expressing mutated forms of the amyloid-ß precursor protein (APP), a central protein involved in AD pathology, show cortical hypersynchronicity. We studied hippocampal circuitry in APP23 transgenic mice using telemetric electroencephalography (EEG), at the age of onset of memory deficits. APP23 mice display spontaneous hypersynchronicity in the hippocampus including epileptiform spike trains. Furthermore, spectral contributions of hippocampal theta and gamma oscillations are compromised in APP23 mice, compared to non-transgenic controls. Using cross-frequency coupling analysis, we show that hippocampal gamma amplitude modulation by theta phase is markedly impaired in APP23 mice. Hippocampal hypersynchronicity and waveforms are differentially modulated by injection of riluzole and the non-competitive N-methyl-D-aspartate (NMDA) receptor inhibitor MK801, suggesting specific invol...
Journal of Alzheimer's disease : JAD, 2015
Alzheimer's disease (AD) and aging result in impaired ability to store memories, but the cellular mechanisms responsible for these defects are poorly understood. Presenilin 1 (PS1) mutations are responsible for many early-onset familial AD (FAD) cases. The phenomenon of hippocampal long-term potentiation (LTP) is widely used in studies of memory formation and storage. Recent data revealed long-term LTP maintenance (L-LTP) is impaired in PS1-M146V knock-in (KI) FAD mice. To understand the basis for this phenomenon, in the present study we analyzed structural synaptic plasticity in hippocampal cultures from wild type (WT) and KI mice. We discovered that exposure to picrotoxin induces formation of mushroom spines in both WT and KI cultures, but the maintenance of mushroom spines is impaired in KI neurons. This maintenance defect can be explained by an abnormal firing pattern during the consolidation phase of structural plasticity in KI neurons. Reduced frequency of neuronal firing ...
The Journal of Neuroscience, 1996
The physiological role of taurine, one of the most abundant free amino acids in the mammalian brain, is still poorly understood. We have found that bath application of the amino acid taurine induces two opposite actions on field excitatory synaptic potentials (fEPSP) recorded in the CA1 area of hippocampal slices: a decrease in fEPSP slope prevented by GABAA antagonists, and a long-lasting potentiation of fEPSP independent of GABAA or NMDA receptor activation. Two long-lasting processes account for this taurine-induced potentiation: (1) an increase in synaptic efficacy that is accompanied neither by modifications in the basic postsynaptic membrane electrical properties nor by those presynaptic changes involved in fEPSP paired-pulse facilitation; and (2) an increase in the axon excitability revealed by a reduction on the threshold for antidromic action potential activation. In addition, taurine perfusion also induces a long-lasting increase in intracellularly recorded EPSPs and monos...
Neural Plasticity, 2020
For more than five decades, the field of Alzheimer’s disease (AD) has focused on two main hypotheses positing amyloid-beta (Aβ) and Tau phosphorylation (pTau) as key pathogenic mediators. In line with these canonical hypotheses, several groups around the world have shown that the synaptotoxicity in AD depends mainly on the increase in pTau levels. Confronting this leading hypothesis, a few years ago, we reported that the increase in phosphorylation levels of dendritic Tau, at its microtubule domain (MD), acts as a neuroprotective mechanism that prevents N-methyl-D-aspartate receptor (NMDAr) overexcitation, which allowed us to propose that Tau protein phosphorylated near MD sites is involved in neuroprotection, rather than in neurodegeneration. Further supporting this alternative role of pTau, we have recently shown that early increases in pTau close to MD sites prevent hippocampal circuit overexcitation in a transgenic AD mouse model. Here, we will synthesize this new evidence that ...
Journal of Alzheimer's disease : JAD, 2014
Alzheimer's disease (AD) is the most prevalent form of neurodegenerative disorders characterized by neuritic plaques containing amyloid-β peptide (Aβ) and neurofibrillary tangles. Evidence has been reported that Aβ1-42 plays an essential pathogenic role in decreased spine density, impairment of synaptic plasticity, and neuronal loss with disruption of memory-related synapse function, all associated with AD. Experimentally, Aβ1-42 oligomers perturb hippocampal long-term potentiation (LTP), an electrophysiological correlate of learning and memory. Aβ was also reported to perturb synaptic glutamate (Glu)-recycling by inhibiting excitatory-amino-acid-transporters. Elevated level of extracellular Glu leads to activation of perisynaptic receptors, including NR2B subunit containing NMDARs. These receptors were shown to induce impaired LTP and enhanced long-term depression and proapoptotic pathways, all central features of AD. In the present study, we investigated the role of Glu-recycl...
Neuropharmacology, 2012
Hippocampal long-term potentiation (LTP) is believed to be important for learning and memory. Experimentally, the pairing of precisely timed pre-and postsynaptic spikes within a time window of w10 ms can induce timing-dependent LTP (tLTP), but the requirements for induction of tLTP change with development: in young rodents single postsynaptic spikes are sufficient to induce tLTP, whereas postsynaptic burst firing appears to be required in the adult. However, hippocampal neurons in vivo show theta-modulated single spike activities also in older hippocampus. Here we investigated the conditions for single spike pairing to induce tLTP at older CA3eCA1 synapses. We found that the pairing of single pre-and postsynaptic spikes could induce tLTP in older hippocampus when the postsynaptic neuronal membrane was depolarized and the pairing frequency exceeded w4 Hz. The spike frequency requirement is postsynaptic, as tLTP could still be induced with presynaptic stimulation at 1 Hz as long as the postsynaptic spike frequency exceeded w4 Hz, suggesting that postsynaptic theta-frequency activity is required for the successful induction of tLTP at older CA3eCA1 synapses. The induction of tLTP was blocked by an NMDA receptor antagonist and by the selective mGluR5 blockers, MPEP and MTEP, whereas activation of mGluR1 and mGluR5 by DHPG relieved the postsynaptic spike frequency requirement for tLTP induction. These results suggest that activation of mGluR5 during single-spike pairing at older CA3eCA1 synapses gates NMDA receptor-dependent tLTP.
Neural Plasticity, 2010
Physiological activation of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors has been proposed to play a key role in both neuronal cell function and dysfunction. In the present study, we used selective NMDA receptor antagonists to investigate the involvement of NR2A and NR2B subunits in the modulatory effect of basal NMDA receptor activity on the phosphorylation of Tau proteins. We observed, in acute hippocampal slice preparations, that blockade of NR2A-containing NMDA receptors by the NR2A antagonist NVP-AAM077 provoked the hyperphosphorylation of a residue located in the proline-rich domain of Tau (i.e., Ser199). This effect seemed to be Ser199 specific as there was no increase in phosphorylation at Ser262 and Ser409 residues located in the microtubule-binding and C-terminal domains of Tau proteins, respectively. From a mechanistic perspective, our study revealed that blockade of NR2A-containing receptors influences Tau phosphorylation probably by increasing calcium influx into neurons, which seems to rely on accumulation of new NR1/NR2B receptors in neuronal membranes and could involve the cyclin-dependent kinase 5 pathway.
Aging Cell, 2013
While the spatiotemporal development of Tau pathology has been correlated with occurrence of cognitive deficits in Alzheimer's patients, mechanisms underlying these deficits remain unclear. Both brain-derived neurotrophic factor (BDNF) and its tyrosine kinase receptor TrkB play a critical role in hippocampusdependent synaptic plasticity and memory. When applied on hippocampal slices, BDNF is able to enhance AMPA receptordependent hippocampal basal synaptic transmission through a mechanism involving TrkB and N-methyl-D-Aspartate receptors (NMDAR). Using THY-Tau22 transgenic mice, we demonstrated that hippocampal Tau pathology is associated with loss of synaptic enhancement normally induced by exogenous BDNF. This defective response was concomitant to significant memory impairments. We show here that loss of BDNF response was due to impaired NMDAR function. Indeed, we observed a significant reduction of NMDA-induced field excitatory postsynaptic potential depression in the hippocampus of Tau mice together with a reduced phosphorylation of NR2B at the Y1472, known to be critical for NMDAR function. Interestingly, we found that both NR2B and Src, one of the NR2B main kinases, interact with Tau and are mislocalized to the insoluble protein fraction rich in pathological Tau species. Defective response to BDNF was thus likely related to abnormal interaction of Src and NR2B with Tau in THY-Tau22 animals. These are the first data demonstrating a relationship between Tau pathology and synaptic effects of BDNF and supporting a contribution of defective BDNF response and impaired NMDAR function to the cognitive deficits associated with Tauopathies.
Acta Neuropathologica Communications
Many mouse models of Alzheimer’s disease (AD) exhibit impairments in hippocampal long-term-potentiation (LTP), seemingly corroborating the strong correlation between synaptic loss and cognitive decline reported in human studies. In other AD mouse models LTP is unaffected, but other defects in synaptic plasticity may still be present. We recently reported that THY-Tau22 transgenic mice, that overexpress human Tau protein carrying P301S and G272 V mutations and show normal LTP upon high-frequency-stimulation (HFS), develop severe changes in NMDAR mediated long-term-depression (LTD), the physiological counterpart of LTP. In the present study, we focused on putative effects of AD-related pathologies on depotentiation (DP), another form of synaptic plasticity. Using a novel protocol to induce DP in the CA1-region, we found in 11–15 months old male THY-Tau22 and APPPS1–21 transgenic mice that DP was not deteriorated by Aß pathology while significantly compromised by Tau pathology. Our fin...
Brain Research, 2009
Aβ42 oligomers as central in the etiology of the learning and memory deficits that are hallmarks of Alzheimer Disease. These effects are thought to occur by an interaction between Aβ42 and certain cellular effectors that induce LTP, however, the precise identity of the Aβ42-interactive signaling molecules is unknown. Identification of such effectors is made more difficult because LTP induced by different stimulation protocols can be expressed through heterogeneous signaling pathways. The aim of this study was to compare differences in the Aβ42-dependent levels of inhibition of LTPs that were induced using high frequency stimulation (HFS), versus theta burst stimulation (TBS). Our results show that untreated control brain slices tetanized with either HFS or TBS gave similar levels of LTP and post tetanic stimulation (PTP), suggesting that the response induced by either protocol was comparable. However, Aβ42 peptide significantly blocked LTP and PTP induced by HFS, but not when TBS was used. NMDA receptor antagonists, D-AP5 and ifenprodil, both blocked LTPs that were induced by HFS or TBS. We propose that unknown signaling effectors, other than the NMDA receptor, which are differentially involved in the induction of LTP by TBS, as compared to HFS, may be responsible for this resistance of TBS-induced LTP to Aβ42 dependent inhibition. (J.P. Smith). Abbreviations: AD, Alzheimer's Disease; Aβ42, amyloid beta 1-42; ACSF, artificial cerebral spinal fluid; fEPSP, field excitatory post synaptic potentiation; HFIP, hexafluoroisopropanol; HFS, high frequency stimulation; Hz, hertz; LTP, long term potentiation; PTP, post tetanic potentiation; s, second; sem, standard error of the mean; TBS, theta burst stimulation 0006-8993/$see front matter a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m w w w. e l s e v i e r. c o m / l o c a t e / b r a i n r e s
2013 20th Iranian Conference on Biomedical Engineering (ICBME), 2013
In this work we propose a model to describe impairment of Long-Term Potentiation (LTP) due to Amyloid Beta (Aβ) accumulation during Alzheimer's Disease (AD) in hippocampus. The model embeds astrocyte-neuron interactions and Spike Timing-Dependent Plasticity (STDP) in CA3-CA1 synapses. In our proposed model, considering physiological facts, each astrocyte has a bidirectional signaling with four neurons, consisting of two pre-synaptic and two post-synaptic neurons. Sustained elevation in strength of each synapse leads to an increase in strength of other adjacent synapse, and finally to coupling between those synapses; this is known as LTP. We increased probability of pre-synaptic glutamate release to the level of reported experimental data on AD. As expected, increase of pre-synaptic glutamate release elevates astrocytic calcium. Due to excessive elevation of astrocytic calcium loss of calcium homeostatic, depression in synaptic strength, disruption of slow inward NMDA currents and finally impairment of LTP occur. Our results confirm the hypothesis that although calcium endocytosis is vital to induce LTP, fast and excessive increase of astrocytic calcium makes major problems and impairments for the LTP.
PLoS ONE, 2013
Alzheimer disease is characterized by a gradual decrease of synaptic function and, ultimately, by neuronal loss. There is considerable evidence supporting the involvement of oligomeric amyloid-beta (Ab) in the etiology of Alzheimer's disease. Historically, AD research has mainly focused on the long-term changes caused by Ab rather than analyzing its immediate effects. Here we show that acute perfusion of hippocampal slice cultures with oligomeric Ab depresses synaptic transmission within 20 minutes. This depression is dependent on synaptic stimulation and the activation of NMDAreceptors, but not on NMDA-receptor mediated ion flux. It, therefore, appears that Ab dependent synaptic depression is mediated through a use-dependent metabotropic-like mechanism of the NMDA-receptor, but does not involve NMDAreceptor mediated synaptic transmission, i.e. it is independent of calcium flux through the NMDA-receptor.
2011
Soluble amyloid beta (Ab) oligomers are widely accepted to be neurotoxic and lead to the memory loss and neuronal death observed in Alzheimer's disease (AD). Ample evidence suggests that impairment in glutamatergic signalling is associated with AD pathology. In particular, Ab 1e42 is thought to affect N-methyl-D-aspartate (NMDA) receptor function and abolish the induction of long-term potentiation (LTP), which is regarded to be a phenomenon relevant to memory formation. The involvement of glutamatergic signalling in the pathology of AD is underscored by the therapeutic success of memantine, an uncompetitive NMDA receptor antagonist, used to treat patients with moderate to severe AD. In this study we show that Ab 1e42 oligomers applied to acute murine hippocampal slices prevented, in a concentration-dependent manner, the development of CA1-LTP after tetanic stimulation of the Schaffer collaterals with a half maximal inhibitory concentration of around 2 nM (before oligomerization). The highest concentration of Ab 1e42 oligomers (50 nM before oligomerization) completely blocked LTP (105 AE 1% potentiation versus 141 AE 3% in control) whereas scrambled Ab 1e42 (50 nM) was without effect (144 AE 10% potentiation).
Journal of Neuroscience, 2005
NMDA receptor (NMDAR) 2A (NR2A)-and NR2B-type NMDARs coexist in synapses of CA1 pyramidal cells. Recent studies using pharmacological blockade of NMDAR subtypes proposed that the NR2A type is responsible for inducing long-term potentiation (LTP), whereas the NR2B type induces long-term depression (LTD). This contrasts with the finding in genetically modified mice that NR2B-type NMDARs induce LTP when NR2A signaling is absent or impaired, although compensatory mechanisms might have contributed to this result. We therefore assessed the contribution of the two NMDAR subtypes to LTP in mouse hippocampal slices by different induction protocols and in the presence of NMDAR antagonists, including the NR2A-type blocker NVP-AAM077, for which an optimal concentration for subtype selectivity was determined on recombinant and native NMDARs. Partial blockade of NMDA EPSCs by 40%, either by preferentially antagonizing NR2A-or NR2B-type NMDARs or by the nonselective antagonist D-AP-5, did not impair LTP, demonstrating that hippocampal LTP induction can be generated by either NMDAR subtype.
Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 2014
N-Methyl-d-aspartate receptor (NMDAR)-dependent synaptic plasticity is a strong candidate to mediate learning and memory processes that require the hippocampus. This plasticity is bidirectional, and how the same receptor can mediate opposite changes in synaptic weights remains a conundrum. It has been suggested that the NMDAR subunit composition could be involved. Specifically, one subunit composition of NMDARs would be responsible for the induction of long-term potentiation (LTP), whereas NMDARs with a different subunit composition would be engaged in the induction of long-term depression (LTD). Unfortunately, the results from studies that have investigated this hypothesis are contradictory, particularly in relation to LTD. Nevertheless, current evidence does suggest that the GluN2B subunit might be particularly important for plasticity and may make a synapse bidirectionally malleable. In particular, we conclude that the presence of GluN2B subunit-containing NMDARs at the postsynap...
Journal of Neuroscience, 2011
Amyloid  (A) and tau protein are both implicated in memory impairment, mild cognitive impairment (MCI), and early Alzheimer's disease (AD), but whether and how they interact is unknown. Consequently, we asked whether tau protein is required for the robust phenomenon of A-induced impairment of hippocampal long-term potentiation (LTP), a widely accepted cellular model of memory. We used wild-type mice and mice with a genetic knockout of tau protein and recorded field potentials in an acute slice preparation. We demonstrate that the absence of tau protein prevents A-induced impairment of LTP. Moreover, we show that A increases tau phosphorylation and that a specific inhibitor of the tau kinase glycogen synthase kinase 3 blocks the increased tau phosphorylation induced by A and prevents A-induced impairment of LTP in wild-type mice. Together, these findings show that tau protein is required for A to impair synaptic plasticity in the hippocampus and suggest that the A-induced impairment of LTP is mediated by tau phosphorylation. We conclude that preventing the interaction between A and tau could be a promising strategy for treating cognitive impairment in MCI and early AD.
Loading Preview
Sorry, preview is currently unavailable. You can download the paper by clicking the button above.