dizocilpine-maleate and Alzheimer-Disease

Memantine is agreed officially as a therapeutic drug for moderate-to-severe Alzheimer's disease (AD) in EU and USA. Memantine is a similar uncompetitive NMDA-receptor antagonist to MK-801 and phencyclidine (PCP), and it prevents nerve cell death induced by the ischemia which induces as excessive release of glutamate. These medicines act on an ion channel binding site similar to the magnesium ion binding site. However, MK-801 and PCP cause schizophrenic symptoms, so they are not being used as a therapeutic drug for AD. Memantine does not have those toxicities and does not stimulate acetylcholine release in the cerebral cortex. Although the mechanism of the difference from memantine and MK-801 has not been made clear yet, it seems that memantine is combined and released with the ion channel depending on electric potential in the same way as the magnesium ion. Basic and clinical research will clarify the control mechanism of memantine.

Topics: Alzheimer Disease; Binding Sites; Controlled Clinical Trials as Topic; Dizocilpine Maleate; Drug Design; Excitatory Amino Acid Antagonists; Glutamates; Humans; Ion Channels; Magnesium; Memantine; Receptors, N-Methyl-D-Aspartate; Severity of Illness Index

Magnesium ion blocks the ion channel of the NMDA receptor at a stable condition. The ion channel competes with the binding site of the noncompetitive antagonists phencyclidine (PCP) and MK-801, which prevent a brain impairment due to the ischemia and so on. The binding ability of these antagonists is strong, an exchange with the magnesium ion is not easy, then the side effect of the schizophrenia-like behavior is caused. Recently, memantine can be used as a therapeutic drug of the moderate-to-severe Alzheimer's disease. Memantine is the noncompetitive antagonist, too, then those development details and a difference from MK-801 were explained.

Topics: Alzheimer Disease; Binding Sites; Brain Ischemia; Dizocilpine Maleate; Humans; Magnesium; Memantine; Phencyclidine; Receptors, N-Methyl-D-Aspartate; Schizophrenia

Alzheimer's disease is a biological process that involves the disruption of multiple neurochemical pathways. Current treatments for Alzheimer's disease focus on deficits in the cholinergic neurochemical pathway. While newer generation cholinergic agents have a more favorable side effect profile, only a limited, but consistent, degree of efficacy is seen. Treatments are emerging that focus on other areas of neurochemical activity such as oxidative damage, inflammation, glutamatergic neurotransmissions, and serotonergic and dopaminergic pathways. These treatments, supplemented with current cholinergic therapies, may help to ease patients' suffering and caregiver distress.

Topics: Alzheimer Disease; Anti-Inflammatory Agents, Non-Steroidal; Antipsychotic Agents; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Humans; Memantine; Phencyclidine; Receptors, N-Methyl-D-Aspartate; Selective Serotonin Reuptake Inhibitors

Topics: Alzheimer Disease; Amnesia; Animals; Cognition; Dizocilpine Maleate; Glycogen Synthase Kinase 3 beta; Histamine H3 Antagonists; Mice; Mice, Inbred C57BL; Phosphatidylinositol 3-Kinase; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; Signal Transduction; TOR Serine-Threonine Kinases

Nitric oxide is a small gaseous molecule that plays important roles in the majority of biological functions. Impairments of NO-related pathways contribute to the majority of neurological disorders, such as Alzheimer's disease (AD), and mental disorders, such as schizophrenia. Cognitive decline is one of the most serious impairments accompanying both AD and schizophrenia. In the present study, the activities of NO donors, slow (spermine NONOate) or fast (DETANONOate) releasers, and selective inhibitor of neuronal nitric oxide synthase N(ω)-propyl-l-arginine (NPLA) were investigated in pharmacological models of schizophrenia and AD. Cognitive impairments were induced by administration of MK-801 or scopolamine and were measured in novel object recognition (NOR) and Y-maze tests. The compounds were investigated at doses of 0.05-0.5 mg/kg. The dose-dependent effectiveness of all the compounds was observed in the NOR test, while only the highest doses of spermine NONOate and NPLA were active in the Y-maze test. DETANONOate was not active in the Y-maze test. The impact of the investigated compounds on motor coordination was tested at doses of 0.5 and 1 mg/kg. Only NPLA at a dose of 1 mg/kg slightly disturbed motor coordination in animals.

Topics: Alzheimer Disease; Animals; Arginine; Cognitive Dysfunction; Dizocilpine Maleate; Enzyme Inhibitors; Male; Mice; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase Type I; Nitroso Compounds; Nootropic Agents; Open Field Test; Rotarod Performance Test; Schizophrenia; Scopolamine; Spermine

Olfactory dysfunction is an early symptom of neurodegenerative disease. Amyloid-beta oligomers (AβOs), the pathologic protein of Alzheimer's disease (AD), have been confirmed to be firstly deposited in olfactory bulb (OB), causing smell to malfunction. However, the detailed mechanisms underlying pathogenic nature of AβOs-induced olfactory neuronal degeneration in AD are not completely realized. Here, an early-stage olfactory dysfunction pathological model of AD in vitro based on biomimetic OB neuronal network chip was established for dynamic multi-site detection of neuronal electrical activity and network connection. We found both spike firing and correlation of overall neuronal network change regularly displayed gradually active state and then rapidly decay state after AβOs induction. Moreover, MK-801 and memantine were administrated at early-stage to detect alteration of OB neurons simulating nasal administration for AD treatment, which showed an almost recovery through the intermittent firing pattern. Together, this neuronal network-on-chip has revealed synaptic impairment and network neurodegeneration of olfactory dysfunction in AD, providing potential mechanisms information for early-stage progressive olfactory amyloidogenic pathology.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Biomimetics; Biosensing Techniques; Dizocilpine Maleate; Humans; Memantine; Neurodegenerative Diseases; Neurons; Olfaction Disorders; Olfactory Bulb; Smell

Topics: Alzheimer Disease; Amyloid beta-Peptides; Benzothiazoles; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Fluorescent Dyes; Humans; In Vitro Techniques; Memantine; Nuclear Magnetic Resonance, Biomolecular; Peptide Fragments; Protein Conformation, beta-Strand; Spectrometry, Fluorescence

Many patients with sporadic Alzheimer's disease (AD) suffer from memory impairment, anxiety- and depression. The systemic utility of N-Methyl-d-Aspartate (NMDA) receptor antagonists has been shown to be potential therapeutic target for memory loss in AD. However, there is no evidence that shows whether NMDA receptor antagonists have the same effects when these blockers are directly used within the brain regions including hippocampus. It might be an urgent to further explore the therapeutic role of NMDA receptor antagonists in behavioral abnormalities such as anxiety and depression in AD. The aim of this study was to determine whether blockade of the hippocampal NMDA receptors could attenuate neurobehavioral abnormalities in rats with sporadic AD. Twelve days after AD induction by streptozotocin (STZ), animals received either vehicle or MK-801 (NMDA receptor antagonist) in the hippocampus for 10 days. Two or five days after the last MK-801 treatment, spatial memory, anxiety- and depression-related behaviors, and inflammatory cytokines (interleukin-(IL)-6, IL-1β and tumor necrosis factor (TNF)-α) were evaluated. Our findings indicated that STZ treatment significantly elevated hippocampal inflammation, impaired spatial memory, and increased anxiety- and depression-related symptoms in rats. Interestingly, the hippocampal NMDA receptor blockade improved these neurobehavioral phenotypes and decreased inflammatory cytokines in the hippocampus of STZ-treated rats. Hippocampal NMDA receptors might be involved in neurobehavioral abnormalities via inflammation in sporadic AD.

Topics: Alzheimer Disease; Animals; Anxiety; Cytokines; Depression; Disease Models, Animal; Dizocilpine Maleate; Hippocampus; Interleukin-1beta; Interleukin-6; Male; Maze Learning; Phenotype; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Tumor Necrosis Factor-alpha

The NMDA (N-methyl-D-aspartate) receptor transduces the binding of glutamate and glycine, coupling it to the opening of a calcium-permeable ion channel

Topics: Alzheimer Disease; Animals; Binding Sites; Crystallography, X-Ray; Dizocilpine Maleate; Ion Channel Gating; Memantine; Molecular Dynamics Simulation; Protein Domains; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Substrate Specificity; Xenopus

Elevated plasma total homocysteine (Hcy) level is associated with an increased risk of Alzheimer's disease (AD). During transsulfuration pathways, Hcy is metabolized into hydrogen sulfide (H2S), which is a synaptic modulator, as well as a neuro-protective agent. However, the role of hydrogen sulfide, as well as N-methyl-D-aspartate receptor (NMDAR) activation, in hyperhomocysteinemia (HHcy) induced blood-brain barrier (BBB) disruption and synaptic dysfunction, leading to AD pathology is not clear. Therefore, we hypothesized that the inhibition of neuronal NMDA-R by H2S and MK801 mitigate the Hcy-induced BBB disruption and synapse dysfunction, in part by decreasing neuronal matrix degradation. Hcy intracerebral (IC) treatment significantly impaired cerebral blood flow (CBF), and cerebral circulation and memory function. Hcy treatment also decreases the expression of cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) in the brain along with increased expression of NMDA-R (NR1) and synaptosomal Ca(2+) indicating excitotoxicity. Additionally, we found that Hcy treatment increased protein and mRNA expression of intracellular adhesion molecule 1 (ICAM-1), matrix metalloproteinase (MMP)-2, and MMP-9 and also increased MMP-2 and MMP-9 activity in the brain. The increased expression of ICAM-1, glial fibrillary acidic protein (GFAP), and the decreased expression of vascular endothelial (VE)-cadherin and claudin-5 indicates BBB disruption and vascular inflammation. Moreover, we also found decreased expression of microtubule-associated protein 2 (MAP-2), postsynaptic density protein 95 (PSD-95), synapse-associated protein 97 (SAP-97), synaptosomal-associated protein 25 (SNAP-25), synaptophysin, and brain-derived neurotrophic factor (BDNF) showing synapse dysfunction in the hippocampus. Furthermore, NaHS and MK801 treatment ameliorates BBB disruption, CBF, and synapse functions in the mice brain. These results demonstrate a neuro-protective effect of H2S over Hcy-induced cerebrovascular pathology through the NMDA receptor. Our present study clearly signifies the therapeutic ramifications of H2S for cerebrovascular diseases such as Alzheimer's disease. Graphical Abstract ᅟ.

Topics: Alzheimer Disease; Animals; Antigens, CD; Avoidance Learning; Blood-Brain Barrier; Cadherins; Cerebrovascular Circulation; Claudin-5; Cystathionine beta-Synthase; Dizocilpine Maleate; Gene Expression Regulation; Glial Fibrillary Acidic Protein; Homocysteine; Hydrogen Sulfide; Intercellular Adhesion Molecule-1; Male; Matrix Metalloproteinase 2; Matrix Metalloproteinase 9; Memory; Mice, Inbred C57BL; Microtubule-Associated Proteins; Microvessels; Nerve Tissue Proteins; Permeability; RNA, Messenger; Synapses

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

Topics: Aging; Alzheimer Disease; Amyloid beta-Protein Precursor; Animals; Biophysics; Disease Models, Animal; Dizocilpine Maleate; Electric Stimulation; Excitatory Amino Acid Antagonists; Female; Hippocampus; Humans; In Vitro Techniques; Long-Term Potentiation; Mice; Mice, Inbred C57BL; Mice, Transgenic; Mutation; Presenilin-1; Synapses; Synaptic Transmission

Synaptic loss is one of the major features of Alzheimer's disease (AD) and correlates with the degree of dementia. N-methyl-D-aspartate receptors (NMDARs) have been shown to mediate downstream effects of the β-amyloid peptide (Aβ) in AD models. NMDARs can trigger intracellular cascades via Ca(2+) entry, however, also Ca(2+)-independent (metabotropic) functions of NMDARs have been described. We aimed to determine whether ionotropic or metabotropic NMDAR signaling is required for the induction of synaptic loss by Aβ. We show that endogenous Aβ as well as exogenously added synthetic Aβ oligomers induced dendritic spine loss and reductions in pre- and postsynaptic protein levels in hippocampal slice cultures. Synaptic alterations were mitigated by blocking glutamate binding to NMDARs using NMDAR antagonist APV, but not by preventing ion flux with Ca(2+) chelator BAPTA or open-channel blockers MK-801 or memantine. Aβ increased the activity of p38 MAPK, a kinase involved in long-term depression and inhibition of p38 MAPK abolished the loss of dendritic spines. Aβ-induced increase of p38 MAPK activity was prevented by APV but not by BAPTA, MK-801 or memantine treatment highlighting the role of glutamate binding to NMDARs but not Ca(2+) flux for synaptic degeneration by Aβ. We further show that treatment with the G protein inhibitor pertussis toxin (PTX) did not prevent dendritic spine loss in the presence of Aβ oligomers. Our data suggest that Aβ induces the activation of p38 MAPK and subsequent synaptic loss through Ca(2+) flux- and G protein-independent mechanisms.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Calcium; Dendritic Spines; Dizocilpine Maleate; Egtazic Acid; Glutamic Acid; GTP-Binding Proteins; Hippocampus; Memantine; Mice; Mice, Inbred C57BL; Mice, Transgenic; Neuroprotective Agents; p38 Mitogen-Activated Protein Kinases; Pertussis Toxin; Receptors, N-Methyl-D-Aspartate; Signal Transduction; Valine

Physical exercise has become a potentially beneficial therapy for reducing neurodegeneration symptoms in Alzheimer's disease. Previous studies have shown that cognitive deterioration, anxiety and the startle response observed in 7-month-old 3xTg-AD mice were ameliorated after 6 months of free access to a running wheel. Also, alterations in synaptic response to paired-pulse stimulation were improved. The present study further investigated some molecular mechanisms underlying the beneficial effects of 6 months of voluntary exercise on synaptic plasticity in 7-month-old 3xTg-AD mice. Changes in binding parameters of [(3)H]-flunitrazepam to GABAA receptor and of [(3)H]-MK-801 to NMDA receptor in cerebral cortex of 3xTgAD mice were restored by voluntary exercise. In addition, reduced expression levels of NMDA receptor NR2B subunit were reestablished. The synaptic proteins synaptophysin and PSD-95 and the neuroprotective proteins GDNF and SIRT1 were downregulated in 3xTgAD mice and were recovered by exercise treatment. Overall, in this paper we highlight the fact that different interrelated mechanisms are involved in the beneficial effects of exercise on synaptic plasticity alterations in the 3xTg-AD mouse model.

Topics: Alzheimer Disease; Amyloid beta-Protein Precursor; Animals; Apoptosis Regulatory Proteins; Cerebral Cortex; Disease Models, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Flunitrazepam; GABA Modulators; Gene Expression Regulation; Humans; Mice; Mice, Transgenic; Physical Conditioning, Animal; Presenilin-1; Protein Binding; Receptors, N-Methyl-D-Aspartate; Synapses; Tritium

Hypersynchronicity of neuronal brain circuits is a feature of Alzheimer's disease (AD). Mouse models of AD expressing mutated forms of the amyloid-β 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 involvement of voltage-gated sodium channels and NMDA receptors in hypersynchronicity thresholds in APP23 mice. Furthermore, APP23 mice show marked activation of p38 mitogen-activated protein (MAP) kinase in hippocampus, and injection of MK801 but not riluzole reduces activation of p38 in the hippocampus. A p38 inhibitor induces hypersynchronicity in APP23 mice to a similar extent as MK801, thus supporting suppression of hypersynchronicity involves NMDA receptors-mediated p38 activity. In summary, we characterize components of hippocampal hypersynchronicity, waveform patterns and cross-frequency coupling in the APP23 mouse model by pharmacological modulation, furthering the understanding of epileptiform brain activity in AD.

Topics: Alzheimer Disease; Animals; Disease Models, Animal; Dizocilpine Maleate; Electrodes, Implanted; Electroencephalography; Enzyme Inhibitors; Epilepsy; Excitatory Amino Acid Antagonists; Gamma Rhythm; Hippocampus; Imidazoles; Male; Mice, Inbred C57BL; Mice, Transgenic; p38 Mitogen-Activated Protein Kinases; Pyridines; Receptors, N-Methyl-D-Aspartate; Riluzole; Theta Rhythm

The mechanisms by which β-amyloid (Aβ), a peptide fragment believed to contribute to Alzheimer's disease, leads to synaptic deficits are not known. Here we find that elevated oligomeric Aβ requires ion flux-independent function of NMDA receptors (NMDARs) to produce synaptic depression. Aβ activates this metabotropic NMDAR function on GluN2B-containing NMDARs but not on those containing GluN2A. Furthermore, oligomeric Aβ leads to a selective loss of synaptic GluN2B responses, effecting a switch in subunit composition from GluN2B to GluN2A, a process normally observed during development. Our results suggest that conformational changes of the NMDAR, and not ion flow through its channel, are required for Aβ to produce synaptic depression and a switch in NMDAR composition. This Aβ-induced signaling mediated by alterations in GluN2B conformation may be a target for therapeutic intervention of Alzheimer's disease.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; CA1 Region, Hippocampal; Calcium Signaling; Dizocilpine Maleate; Humans; Long-Term Synaptic Depression; Peptide Fragments; Protein Conformation; Protein Structure, Quaternary; Rats; Receptors, N-Methyl-D-Aspartate; Recombinant Proteins

Herein we report on a novel series of multitargeted compounds obtained by linking together galantamine and memantine. The compounds were designed by taking advantage of the crystal structures of acetylcholinesterase (AChE) in complex with galantamine derivatives. Sixteen novel derivatives were synthesized, using spacers of different lengths and chemical composition. The molecules were then tested as inhibitors of AChE and as binders of the N-methyl-d-aspartate (NMDA) receptor (NMDAR). Some of the new compounds were nanomolar inhibitors of AChE and showed micromolar affinities for NMDAR. All compounds were also tested for selectivity toward NMDAR containing the 2B subunit (NR2B). Some of the new derivatives showed a micromolar affinity for NR2B. Finally, selected compounds were tested using a cell-based assay to measure their neuroprotective activity. Three of them showed a remarkable neuroprotective profile, inhibiting the NMDA-induced neurotoxicity at subnanomolar concentrations (e.g., 5, named memagal, IC(50) = 0.28 nM).

Topics: Acetylcholinesterase; Alzheimer Disease; Animals; Cell Proliferation; Cerebral Cortex; Cholinesterase Inhibitors; Computer Simulation; Drug Combinations; Drug Design; Feasibility Studies; Galantamine; Humans; Male; Memantine; Neuroblastoma; Neuroprotective Agents; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate

Aberrant activation of signaling pathways plays a pivotal role in central nervous system disorders, such as Alzheimer's disease (AD). Using a combination of virtual screening and experimental testing, novel small molecule inhibitors of tPA-mediated extracellular signal-regulated kinase (Erk)1/2 activation were identified that provide higher levels of neuroprotection from Aβ-induced apoptosis than Memantine, the most recently FDA-approved drug for AD treatment. Subsequent target deconvolution efforts revealed that they all share low micromolar affinity for the imidazoline I(2) receptor, while being devoid of any significant affinity to a list of AD-relevant targets, including the N-methyl-d-aspartate receptor (NMDAR), acetylcholinesterase (AChE), and monoamine oxidase B (MAO-B). Targeting the imidazoline I(2) receptor emerges as a new mechanism of action to inhibit tPA-induced signaling in neurons for the treatment of AD and other neurodegenerative diseases.

Topics: Acetylcholinesterase; Alzheimer Disease; Amyloid beta-Peptides; Animals; Apoptosis; Cells, Cultured; Embryo, Mammalian; Enzyme-Linked Immunosorbent Assay; Extracellular Signal-Regulated MAP Kinases; Hippocampus; Imidazoline Receptors; In Situ Nick-End Labeling; Mice; Molecular Structure; Monoamine Oxidase; Neurons; Neuroprotective Agents; Receptors, N-Methyl-D-Aspartate; Signal Transduction; Structure-Activity Relationship

Hypofunction of brain N-methyl-d-aspartate (NMDA) receptors has been implicated in psychiatric disorders such as schizophrenia and Alzheimer's disease. Inhibition of glycine transporter-1 (GlyT1) is expected to increase glycine, a co-agonist of the NMDA receptor and, consequently, to facilitate NMDA receptor function. We have identified ASP2535 (4-[3-isopropyl-5-(6-phenyl-3-pyridyl)-4H-1,2,4-triazol-4-yl]-2,1,3-benzoxadiazole) as a novel GlyT1 inhibitor, and here describe our in vitro and in vivo characterization of this compound. ASP2535 potently inhibited rat GlyT1 (IC(50)=92 nM) with 50-fold selectivity over rat glycine transporter-2 (GlyT2). It showed minimal affinity for many other receptors except for μ-opioid receptors (IC(50)=1.83 μM). Oral administration of ASP2535 dose-dependently inhibited ex vivo [(3)H]-glycine uptake in mouse cortical homogenate, suggesting good brain permeability. This profile was confirmed by pharmacokinetic analysis. We then evaluated the effect of ASP2535 on animal models of cognitive impairment in schizophrenia and Alzheimer's disease. Working memory deficit in MK-801-treated mice and visual learning deficit in neonatally phencyclidine (PCP)-treated mice were both attenuated by ASP2535 (0.3-3mg/kg, p.o. and 0.3-1mg/kg, p.o., respectively). ASP2535 (1-3mg/kg, p.o.) also improved the PCP-induced deficit in prepulse inhibition in rats. Moreover, the working memory deficit in scopolamine-treated mice and the spatial learning deficit in aged rats were both attenuated by ASP2535 (0.1-3mg/kg, p.o. and 0.1mg/kg, p.o., respectively). These studies provide compelling evidence that ASP2535 is a novel and centrally-active GlyT1 inhibitor that can improve cognitive impairment in animal models of schizophrenia and Alzheimer's disease, suggesting that ASP2535 may satisfy currently unmet medical needs for the treatment of these diseases.

Topics: Administration, Oral; Alzheimer Disease; Animals; Brain; Cognition Disorders; Disease Models, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Female; Glycine Plasma Membrane Transport Proteins; Humans; Inhibitory Concentration 50; Male; Memory Disorders; Mice; Oxadiazoles; Permeability; Rats; Rats, Wistar; Schizophrenia; Triazoles

We previously reported that some N-methyl-D-aspartate (NMDA)-receptor antagonists enhanced histamine neuron activity in rodents. Here, we have investigated the effects of memantine, an NMDA-receptor antagonist used for the treatment of Alzheimer's disease, on histaminergic neurotransmission. In vitro, memantine antagonized native NMDA receptors with a micromolar potency but had no effect at recombinant human histamine receptors. In vivo, a single administration of memantine increased histamine neuron activity, as shown by the 60% increase of tele-methylhistamine (t-MeHA) levels observed in the brain of mice. This increase occurred with an ED(50) of 0.3 ± 0.1 mg/kg, similar to that found on inhibition of ex vivo [(3)H]dizocilpine maleate (MK-801) binding (1.8 ± 1.3 mg/kg). Two days after pretreatment of mice with memantine at 5 mg/kg twice daily for 5 days, t-MeHA levels were enhanced by 50 ± 7% (p < 0.001), indicating a long-lasting activation of histamine neurons. Quantitative polymerase chain reaction analysis was used to explore genes involved in this persistent effect. H(3) receptor mRNAs were strongly increased, but the density of H(3) receptor binding sites was increased solely in hypothalamus (by 141 ± 24%). Up-regulations of brain-derived neurotrophic factor and NMDA-receptor 1 subunit mRNAs were also found but were restricted to hippocampus. mRNA expression of α7-nicotinic receptors remained unchanged in any region. Considering the well established cognitive effects of histamine neurons, the increase in brain t-MeHA levels after single or repeated administration of therapeutic doses of memantine suggests that the drug exerts its beneficial effects on cognitive deficits of Alzheimer's disease, at least partly, by activating histamine neurons.

Topics: Alzheimer Disease; Animals; Brain; Brain-Derived Neurotrophic Factor; Calcium; Cognition; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Histamine; Humans; Male; Memantine; Methylhistamines; Mice; Pyrilamine; Rats; Rats, Wistar; Receptors, Histamine; Receptors, N-Methyl-D-Aspartate; Synaptic Transmission

Nicotinic acetylcholine receptors (nAChRs) were studied in detail in the past regarding their interaction with therapeutic and drug addiction related compounds. Using fast kinetic whole-cell recording, we have now studied effects of tacrine, an agent used clinically to treat Alzheimer's disease, on currents elicited by activation of rat α(3)β(4) nAChR heterologously expressed in KXα3β4R2 cells. Characterization of receptor activation by nicotine used as agonist revealed a K(d) of 23 ± 0.2 μM and 4.3 ± 1.3 for the channel opening equilibrium constant, Φ(-1). Experiments were performed to investigate whether tacrine is able to activate the α(3)β(4) nAChR. Tacrine did not activate whole-cell currents in KXα3β4R2 cells but inhibited receptor activity at submicromolar concentration. Dose-response curves obtained with increasing agonist or inhibitor concentration revealed competitive inhibition of nAChRs by tacrine, with an apparent inhibition constant, K(I), of 0.8 μM. The increase of Φ(-1) in the presence of tacrine suggests that the drug stabilizes a nonconducting open channel form of the receptor. Binding studies with TCP and MK-801 ruled out tacrine binding to common allosteric sites of the receptor. Our study suggests a novel mechanism for action of tacrine on nAChRs besides inhibition of acetylcholine esterase.

Topics: Alzheimer Disease; Animals; Cholinesterase Inhibitors; Dizocilpine Maleate; Kinetics; Nicotinic Antagonists; Patch-Clamp Techniques; Rats; Receptors, Nicotinic; Tacrine

Nerve cell death is the key event in all neurodegenerative disorders, with apoptosis and necrosis being central to both acute and chronic degenerative processes. However, until now, it has not been possible to study these dynamically and in real time. In this study, we use spectrally distinct, well-recognised fluorescent cell death markers to enable the temporal resolution and quantification of the early and late phases of apoptosis and necrosis of single nerve cells in different disease models. The tracking of single-cell death profiles in the same living eye over hours, days, weeks and months is a significant advancement on currently available techniques. We identified a numerical preponderance of late-phase versus early-phase apoptotic cells in chronic models, reinforcing the commonalities between cellular mechanisms in different disease models. We showed that MK801 effectively inhibited both apoptosis and necrosis, but our findings support the use of our technique to investigate more specific anti-apoptotic and anti-necrotic strategies with well-defined targets, with potentially greater clinical application. The optical properties of the eye provide compelling opportunities for the quantitative monitoring of disease mechanisms and dynamics in experimental neurodegeneration. Our findings also help to directly observe retinal nerve cell death in patients as an adjunct to refining diagnosis, tracking disease status and assessing therapeutic intervention.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Apoptosis; Disease Models, Animal; Dizocilpine Maleate; Mice; Necrosis; Neurodegenerative Diseases; Retinal Ganglion Cells

We have investigated the characteristics of a long-term potentiation (LTP)-like facilitation in vivo through GABAA receptor blockade in C57BL/6 and Alzheimer-model transgenic mice dentate gyrus. Bicuculline induced the 'LTP-like' facilitation in a dose-dependent manner. MK-801 inhibited the induction but not maintenance of 'LTP-like' facilitation through bicuculline. Tetanic LTP was further enhanced by bicuculline, but the 'LTP-like' facilitation was conversely attenuated by tetanus. In transgenic mice expressing mutant human tau as an Alzheimer-model, the 'LTP-like' facilitation through bicuculline was significantly greater than tetanic LTP. Bicuculline recovered tetanic LTP impaired in these transgenic mice. These results suggest that GABAA receptor blockade plays an important role in learning and memory, providing a clue for the clinical use of GABAA antagonists to improve cognitive disorders.

Topics: Alzheimer Disease; Animals; Bicuculline; Dentate Gyrus; Disease Models, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; GABA Antagonists; Humans; Long-Term Potentiation; Mice; Mice, Inbred C57BL; Mice, Transgenic; Mutation; Neurons; tau Proteins

There are few studies on the clinical and neurochemical correlates of postsynaptic cholinergic dysfunction in Alzheimer's disease (AD). We have previously found that attenuation of guanine nucleotide-binding (G-) protein coupling to muscarinic M(1) receptors in the neocortex was associated with dementia severity. The present study aims to study whether this loss of M(1)/G-protein coupling is related to alterations in signaling kinases and NMDA receptors. Postmortem frontal cortices of 22 AD subjects and 12 elderly controls were obtained to measure M(1) receptors, M(1)/G-protein coupling, NMDA receptors as well as protein kinase C (PKC) and Src kinase activities. We found that the extent of M(1)/G-protein coupling loss was correlated with reductions in PKC activity and NMDA receptor density. In contrast, Src kinase activity was neither altered nor associated with M(1)/G-protein coupling. Given the well established roles of neuronal PKC signaling and NMDA receptor function in cognitive processes, our results lend further insight into the mechanisms by which postsynaptic cholinergic dysfunction may underlie the cognitive features of AD, and suggest alternative therapeutic targets to cholinergic replacement.

Topics: Aged; Aged, 80 and over; Alzheimer Disease; Brain; Brain Chemistry; Case-Control Studies; Dizocilpine Maleate; Drug Interactions; Excitatory Amino Acid Antagonists; Female; Glutamic Acid; Humans; Male; Muscarinic Antagonists; Pirenzepine; Postmortem Changes; Protein Kinase C; Radioligand Assay; Receptor, Muscarinic M1; src-Family Kinases

Alzheimer's disease is characterized by extracellular beta-amyloid plaques, intraneuronal Tau-inclusions and cell death of cholinergic neurons. Recent evidence indicates that the vascular system may play an important role in the development of this progressive neurodegenerative disease. The aim of this study was to observe, if brain capillary endothelial cells (BCEC) may produce and secrete factors which induce cell death of cholinergic neurons, and if this effect is counteracted by (1) NGF, MK-801 or vitamin C, (2) modulated by experimentally-induced inflammation with interleukin-1beta and lipopolysaccharide (IL-1beta and LPS) or (3) by blocking of different intracellular signalling pathways. Cholinergic neurons were cultivated in organotypic brain slices of the nucleus basalis of Meynert and treated with conditioned medium derived from BCEC, supplemented with different protective factors. BCEC were stimulated with IL-1beta and LPS or different intracellular pathway inhibitors before collection of conditioned medium. Cholinergic neurons were detected by immunohistochemistry for choline-acetyltransferase. Possible effects on BCEC viability and proliferation were determined by nuclear staining, BrdU incorporation and release of nitrite and lactate-dehydrogenase. BCEC released factors that can kill cholinergic neurons. This neurotoxic effect was blocked by NGF and MK-801 (a NMDA-antagonist), but not by vitamin C. Pretreatment of BCEC with intracellular pathway inhibitors did not change the neurotoxicity, but pretreatment with IL-1beta and LPS abolished the neurotoxic effect. In summary, BCEC produce and secrete molecules which induce excitotoxic cell death of cholinergic neurons. It is concluded that excitotoxic factors secreted by vascular cells may contribute to the development of cholinergic neurodegeneration as it occurs in Alzheimer's disease.

Topics: Alzheimer Disease; Animals; Antioxidants; Ascorbic Acid; Brain; Cell Death; Cells, Cultured; Cholinergic Fibers; Culture Media, Conditioned; Dizocilpine Maleate; Endothelial Cells; Inflammation; Interleukin-1beta; Lipopolysaccharides; Nerve Degeneration; Nerve Growth Factor; Neuroprotective Agents; Rats; Rats, Sprague-Dawley

Millions of Americans suffer from Alzheimer's Disease (AD), which is characterized by significant neurological impairment and an accumulation in brain tissue of senile plaques consisting of beta amyloid (Abeta) peptide. The hippocampus, a region primarily responsible for learning and memory, appears to be particularly susceptible to AD-related injury and chronic alcohol abuse. Although certain risk factors for AD are known, it is unclear if alcohol abuse or dependence may contribute to neuropathology in AD. Recent research suggests that low-to-moderate consumption of alcohol may protect against development of AD, while alcohol dependence may increase risk of developing AD. Therefore, the current studies aimed to investigate the effects of exposure to 50 or 100 mM ethanol (EtOH) and withdrawal on hippocampal injury induced by Abeta peptide treatment.. The present studies exposed organotypic hippocampal slice cultures to 50 or 100 mM ethanol (EtOH) for 10 days, after which the slices underwent ethanol withdrawal (EWD) in the presence of varying concentrations of Abeta 25-35 (0.1, 1, 10 microM), or 35-25 (200 microM), a negative control reverse sequence peptide. Cellular injury, as evidenced by uptake of propidium iodide (PI), was assessed for each subregion of the hippocampal complex (CA1, CA3, and dentate gyrus).. Cellular injury in the CA1 pyramidal cell layer was significantly increased during withdrawal from exposure to 100 mM, but not 50 mM, EtOH. Exposure to Abeta in ethanol-naïve cultures did not produce significant cytotoxicity. However, exposure to Abeta during EWD from 100 mM produced marked increases in CA1 pyramidal cell region cytotoxicity, effects reversed by cotreatment with a nontoxic concentration of the NMDA receptor channel blocker MK-801 (20 microM).. These data suggest that withdrawal from exposure to a high concentration of EtOH produces marked cellular injury in the hippocampus, particularly the CA1 subregion. Further, this EtOH exposure and withdrawal regimen sensitizes the hippocampus to the toxic effects of Abeta treatment in a manner reflecting over activity of NMDA receptor function.

Topics: Alcohol Drinking; Alcoholism; Alzheimer Disease; Amyloid beta-Peptides; Animals; Dizocilpine Maleate; Dose-Response Relationship, Drug; Ethanol; Hippocampus; Propidium; Pyramidal Cells; Rats; Receptors, N-Methyl-D-Aspartate; Tissue Culture Techniques

Alzheimer's disease (AD) and several other neurological disorders have been linked to the overactivation of glutamatergic transmission and excitotoxicity as a common pathway of neuronal injury. The beta-amyloid peptide (Abeta) is centrally related to the pathogenesis of AD, and previous reports have demonstrated that the blockade of glutamate receptors prevents Abeta-induced neuronal death. We show that taurine, a beta-amino acid found at high concentrations in the brain, protects chick retinal neurons in culture against the neurotoxicity of Abeta and glutamate receptor agonists. The protective effect of taurine is not mediated by interaction with glutamate receptors, as demonstrated by binding studies using radiolabeled glutamate receptor ligands. The neuroprotective action of taurine is blocked by picrotoxin, an antagonist of GABA(A) receptors. GABA and the GABA(A) receptor agonists phenobarbital and melatonin also protect neurons against Abeta-induced neurotoxicity. These results suggest that activation of GABA receptors decreases neuronal vulnerability to excitotoxic damage and that pharmacological manipulation of the excitatory and inhibitory neurotransmitter tonus may protect neurons against a variety of insults. GABAergic transmission may represent a promising target for the treatment of AD and other neurological disorders in which excitotoxicity plays a relevant role.

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Alzheimer Disease; Amyloid beta-Protein Precursor; Animals; Cells, Cultured; Cellular Senescence; Chick Embryo; Dizocilpine Maleate; Excitatory Amino Acid Agonists; Eye Proteins; Glutamic Acid; Kainic Acid; N-Methylaspartate; Neurons; Neuroprotective Agents; Picrotoxin; Receptors, AMPA; Receptors, GABA; Receptors, GABA-A; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Retina; Taurine

We used primary cultures of cortical neurons to examine the relationship between beta-amyloid toxicity and hyperphosphorylation of the tau protein, the biochemical substrate for neurofibrillary tangles of Alzheimer's brain. Exposure of the cultures to beta-amyloid peptide (betaAP) induced the expression of the secreted glycoprotein Dickkopf-1 (DKK1). DKK1 negatively modulates the canonical Wnt signaling pathway, thus activating the tau-phosphorylating enzyme glycogen synthase kinase-3beta. DKK1 was induced at late times after betaAP exposure, and its expression was dependent on the tumor suppressing protein p53. The antisense induced knock-down of DKK1 attenuated neuronal apoptosis but nearly abolished the increase in tau phosphorylation in betaAP-treated neurons. DKK1 was also expressed by degenerating neurons in the brain from Alzheimer's patients, where it colocalized with neurofibrillary tangles and distrophic neurites. We conclude that induction of DKK1 contributes to the pathological cascade triggered by beta-amyloid and is critically involved in the process of tau phosphorylation.

Topics: Aged; Aged, 80 and over; Alzheimer Disease; Amyloid beta-Peptides; Animals; Apoptosis; bcl-2-Associated X Protein; Cells, Cultured; Dizocilpine Maleate; Gene Expression Regulation; Glutamic Acid; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Humans; Immunoenzyme Techniques; Intercellular Signaling Peptides and Proteins; Nerve Degeneration; Nerve Tissue Proteins; Neurofibrillary Tangles; Neurons; Oligodeoxyribonucleotides; Peptide Fragments; Phosphorylation; Protein Processing, Post-Translational; Proteins; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-bcl-2; Quinoxalines; Rats; RNA, Messenger; Signal Transduction; tau Proteins; Tumor Suppressor Protein p53; Wnt Proteins

Psychosis frequently occurs in Alzheimer's disease (AD), being associated with more severe cognitive decline, but the underlying mechanisms are unknown.. To investigate the effect of centrally administered beta-amyloid peptide, a model for AD, in the locomotor response to amphetamine, caffeine and MK-801, which are psychoactive drugs related to neurochemical changes occurring in psychosis.. Mice were intracerebroventricularly injected with beta-amyloid (25-35), and after 1 week they were tested in the passive avoidance, spontaneous alternation and locomotor tasks.. Besides impaired performance in inhibitory avoidance and spontaneous alternation tasks, beta-amyloid-treated mice showed increased spontaneous locomotion, augmented response to amphetamine (1.5 mg/kg), blunted response to caffeine (30 mg/kg) and no difference in MK-801 (0.25 mg/kg)-induced locomotor activation when compared to its respective control.. These results are compatible with the hypothesis that beta-amyloid peptide may predispose to psychotic symptoms of AD by increasing sensitivity of the dopaminergic system, possibly related to a decreased adenosinergic inhibitory tone.

Topics: Adenosine; Adrenergic Agents; Alzheimer Disease; Amphetamine; Amyloid beta-Peptides; Animals; Avoidance Learning; Brain; Caffeine; Central Nervous System Stimulants; Disease Models, Animal; Dizocilpine Maleate; Dopamine; Excitatory Amino Acid Antagonists; Glutamine; Injections, Intraventricular; Male; Mice; Motor Activity; Psychotic Disorders

Huperzine A, a novel cholinesterase inhibitor, was found to inhibit the N-methyl-D-aspartate (NMDA) receptors in the brain. In this study, the mechanisms of the NMDA receptor inhibition were investigated using [3H]dizocilpine (MK-801) binding in synaptic membrane of rat cerebral cortex. Changing the concentrations of L-glutamate and L-glycine did not alter the potency of huperzine A. Spermidine caused rightward shift of the concentration-response curve of huperzine A, and considerably increased its IC(50) value. Huperzine A did not affect the potency of unlabeled (+)-MK-801 in [3H]MK-801 binding. Saturation binding studies reveal that huperzine A exerts a negative allosteric modulation on the MK-801 binding site within the NMDA receptor-channel. The results suggest that huperzine A is a non-competitive antagonist of the NMDA receptors, acting at one of the polyamine binding sites.

Topics: Alkaloids; Alzheimer Disease; Animals; Binding Sites; Binding, Competitive; Cerebral Cortex; Cholinesterase Inhibitors; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Antagonists; Glutamic Acid; Glycine; Neurons; Radioligand Assay; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Sesquiterpenes; Spermidine; Synaptic Membranes

The pharmacology of the N -methyl-d-aspartate (NMDA) receptor site was examined in pathologically affected and relatively spared regions of cerebral cortex tissue obtained at autopsy from Alzheimer's disease cases and matched controls. The affinity and density of the [(3)H]MK-801 binding site were delineated along with the enhancement of [(3)H]MK-801 binding by glutamate and spermine. Maximal enhancement induced by either ligand was regionally variable; glutamate-mediated maximal enhancement was higher in controls than in Alzheimer's cases in pathologically spared regions, whereas spermine-mediated maximal enhancement was higher in controls in areas susceptible to pathological damage. These and other data suggest that the subunit composition of NMDA receptors may be locally variable. Studies with modified conantokin-G (con-G) peptides showed that Ala(7)-con-G had higher affinity than Lys(7)-con-G, and also defined two distinct binding sites in controls. Nevertheless, the affinity for Lys(7)-con-G was higher overall in Alzheimer's brain than in control brain, whereas the reverse was true for Ala(7)-con-G. Over-excitation mediated by specific NMDA receptors might contribute to localized brain damage in Alzheimer's disease. Modified conantokins are useful for identifying the NMDA receptors involved, and may have potential as protective agents.

Topics: Aged; Aged, 80 and over; Alzheimer Disease; Amino Acid Substitution; Binding, Competitive; Cerebral Cortex; Conotoxins; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Female; Glutamic Acid; Humans; Ligands; Male; Middle Aged; Mutagenesis, Site-Directed; Radioligand Assay; Receptors, N-Methyl-D-Aspartate; Spermine

Senile plaques composed mainly by beta-amyloid (Abeta) protein are one of the pathological hallmarks of Alzheimer's disease (AD). In vitro, Abeta and its active fragment 25-35 have been shown either to be directly neurotoxic or to exacerbate the damaging effect of other neurotoxic insults. However, the attempts to replicate Abeta neurotoxicity in vivo have yielded conflicting results. One of the most consistent alterations in AD is a reduced resting glucose utilization. Important evidence suggests that impairment of brain energy metabolism can lead to neuronal damage or facilitate the deleterious effects of some neurotoxic agents. In the present study we have investigated the influence of glycolysis inhibition induced by iodoacetate, and mitochondrial impairment induced by 3-nitropropionic acid (3-NP), in the toxicity of Abeta. We have studied Abeta neurotoxicity during energy deficiency both in vivo in the dentate gyrus of the hippocampal formation and in presynaptic terminals isolated from neocortex and hippocampus. Results show that during metabolic inhibition an enhanced vulnerability of hippocampal neurons to Abeta peptide toxicity occurs, probably resulting from decreased glucose metabolism and mitochondrial ATP production. Synaptosomal response to energy impairment and Abeta toxicity was evaluated by the MTT assay. Results suggest that synapses may be particularly sensitive to metabolic perturbation, which in turn exacerbates Abeta toxicity. The present data provide experimental support to the hypothesis that certain risk factors such as metabolic dysfunction and amyloid accumulation may interact to exacerbate AD, and that metabolic substrates such as pyruvate may play a role as a therapeutic tool.

Topics: Adenosine Triphosphate; Alzheimer Disease; Amyloid beta-Peptides; Animals; Disease Models, Animal; Dizocilpine Maleate; Energy Metabolism; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Glucose; Glycolysis; Hippocampus; Injections, Intraperitoneal; Iodoacetates; Male; Microinjections; Mitochondria; Neocortex; Neuroprotective Agents; Nitro Compounds; Peptide Fragments; Presynaptic Terminals; Propionates; Pyruvic Acid; Rats; Rats, Wistar; Synaptosomes

Whereas a cardinal role for beta-amyloid protein (Abeta) has been postulated as a major trigger of neuronal injury in Alzheimer's disease, the pathogenic mechanism by which Abeta deranges nerve cells remains largely elusive. Here we report correlative in vitro and in vivo evidence that an excitotoxic cascade mediates Abeta neurotoxicity in the rat magnocellular nucleus basalis (MBN). In vitro application of Abeta to astrocytes elicits rapid depolarization of astroglial membranes with a concomitant inhibition of glutamate uptake. In vivo Abeta infusion by way of microdialysis in the MBN revealed peak extracellular concentrations of excitatory amino acid neurotransmitters within 20-30 min. Abeta-triggered extracellular elevation of excitatory amino acids coincided with a significantly enhanced intracellular accumulation of Ca2+ in the Abeta injection area, as was demonstrated by 45Ca2+ autoradiography. In consequence of these acute processes delayed cell death in the MBN and persistent loss of cholinergic fibre projections to the neocortex appear as early as 3 days following the Abeta-induced toxic insult. Such a sequence of Abeta toxicity was effectively antagonized by the N-methyl-D-aspartate (NMDA) receptor ligand dizocilpine maleate (MK-801). Moreover, Abeta toxicity in the MBN decreases with advancing age that may be associated with the age-related loss of NMDA receptor expression in rats. In summary, the present results indicate that Abeta compromises neurons of the rat MBN via an excitotoxic pathway including astroglial depolarization, extracellular glutamate accumulation, NMDA receptor activation and an intracellular Ca2+ overload leading to cell death.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Aspartic Acid; Astrocytes; Basal Nucleus of Meynert; Calcium; Calcium Radioisotopes; Cells, Cultured; Disease Models, Animal; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Glutamic Acid; Microdialysis; Nerve Degeneration; Neuroprotective Agents; Neurotoxins; Rats; Receptors, N-Methyl-D-Aspartate; Taurine

The inhibition of huperzine A, a potential therapeutic agent to treat Alzheimer's disease, on rat cortical acetylcholinesterase was found to be highly stereospecific. In the present study the effect of the enantiomers of huperzine A on [(3)H]dizocilpine (MK-801) binding to synaptic membrane of rat cerebral cortex was compared. The natural (-)-huperzine A and the synthetic (+)-huperzine A inhibited the specific binding of [(3)H]MK-801 with a similar potency. The IC(50) values were 65+/-7 and 82+/-12 microM (n=5 for each enantiomer, P=0.248), respectively. The result indicates that huperzine A inhibits N-methyl-D-aspartate (NMDA) receptor in rat cerebral cortex without stereoselectivity.

Topics: Alkaloids; Alzheimer Disease; Animals; Binding Sites; Cerebral Cortex; Cholinesterase Inhibitors; Dizocilpine Maleate; Drug Interactions; Neurons; Neuroprotective Agents; Radioligand Assay; Rats; Receptors, N-Methyl-D-Aspartate; Sesquiterpenes; Stereoisomerism; Synaptic Membranes

Glutamatergic hypofunction occurs in Alzheimer's disease (AD). MK801, a noncompetitive blocker of glutamate N-methyl-D-aspartate receptors, was used to disrupt the cognitive performance of rats trained on a delayed nonmatching to sample radial maze task. Drugs which act by blocking serotonin (5-HT) receptors were evaluated for their ability to reduce the cognitive impairment produced by MK801. Specifically, WAY-100635, a selective 5-HT1A receptor antagonist, buspirone, a 5-HT1A partial agonist, ritanserin, a 5-HT2 antagonist, and ondansetron, a 5-HT3 antagonist, were assessed. In addition, the muscarinic agonist arecoline was evaluated for its potential cognitive benefit in this model. It was found that WAY-100635 significantly reduced the cognitive impairment induced by MK801. Treatment with single doses of ritanserin, ondansetron, or arecoline in combination with MK801 did not result in a cognitive impairment, indicating that these drugs attenuated the MK801 impairment. The combination of buspirone and MK801 resulted in an inability of the animals to complete the task. These results suggest that interactions between 5-HT and glutamate may mediate the beneficial effects of reducing cognitive impairment and that 5-HT antagonists, especially selective 5-HT1A antagonists, may be useful in treating AD. Further, it is indicated that the MK801 model of cognitive impairment may add to the armamentarium of tools available to predict treatment efficacy in AD.

Topics: Alzheimer Disease; Animals; Arecoline; Cognition Disorders; Disease Models, Animal; Dizocilpine Maleate; Drug Synergism; Glutamates; Male; Maze Learning; Muscarinic Agonists; Neuroprotective Agents; Piperazines; Pyridines; Rats; Rats, Sprague-Dawley; Serotonin Antagonists

Huperzine A, a selective inhibitor of acetylcholinesterase, was recently demonstrated to exert an antagonist effect on N-methyl-D-aspartate (NMDA) receptor in rat cerebral cortex. In the present study, the effects of six cholinesterase inhibitors, e.g. huperzine A, huperzine B, tacrine, donepezil (E2020), physostigmine and galanthamine on [3H]dizocilpine (MK-801) binding to synaptic membrane of rat cerebral cortex were compared. Their IC50 values (mean +/- SD) were 36.9 +/- 12.1, 316.8 +/- 93.2, 33.2 +/- 3.7, 135.0 +/- 15.1, 50.4 +/- 7.4, and 3344 +/- 295 microM, respectively. The rank order of potency is tacrine approximately huperzine A > physostigmine > donepezil > huperzine B >> galanthamine. There is no correlation between their activities to inhibit [3H]MK-801 binding and to inhibit acetylcholinesterase (r = +0.563, P = 0.245). The results suggest that most cholinesterase inhibitors available exhibit an antagonist effect on NMDA receptor in rat cerebral cortex in addition to their inhibitory effect on acetylcholinesterase.

Topics: Alzheimer Disease; Animals; Cerebral Cortex; Cholinesterase Inhibitors; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Inhibitory Concentration 50; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate

Amyloid precursor protein, which gives rise to the A beta polypeptide found in senile plaques in the brains of patients with Alzheimer's disease, is a member of a family of proteins which includes amyloid precursor-like protein 2 (APLP2). To date, little is known of the involvement of this protein in Alzheimer's disease or any other neurodegenerative condition. The present study set out to determine whether APLP2 expression could be modified in cultured rat cortical neurones exposed to an excitotoxic insult. Treatment of cultures with glutamate (500 microM) for 30 min resulted in increased lactate dehydrogenase liberation into the bathing medium 24 h after removal of the insult indicating neuronal damage. This was accompanied by a decrease in APLP2 recovery in the medium but no change in its intracellular level. Both the increase in LDH release and APLP2 recovery were prevented by pretreatment with the N-methyl-D-aspartate receptor antagonist MK-801. These data show that neuronal APLP2 metabolism is altered in response to an excitotoxic insult.

Topics: Alzheimer Disease; Amyloid beta-Protein Precursor; Animals; Cells, Cultured; Cerebral Cortex; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Glutamic Acid; L-Lactate Dehydrogenase; Nerve Tissue Proteins; Neurons; Rats; Receptors, N-Methyl-D-Aspartate

This work has explored the relationship between excitotoxicity and the amyloid precursor protein gene (APP) which may be relevant to future therapeutic developments in Alzheimer's disease. The excitotoxic effects of kainic acid (KA) and pentylenetetrazole (PTZ) have been compared and contrasted on the two major mRNA isoforms of APP using in situ hybridization and quantitative analysis of gene expression in rat brain. The Kunitz Protease Inhibitor containing isoform APP 770 KPI+, the major glial cell isoform, has been shown to be stimulated after KA and was related to neuronal loss and astrocyte activation as gauged by GFAP mRNA. This was associated with reduced expression of APP695 KPI- isoform, the major neuronal isoform. These changes were not observed after PTZ where there was no neuronal loss and no glial reaction. The KA induced changes in APP were prevented by pretreatment with the non-competitive NMDA receptor antagonist dizocilpine and the barbiturate pentobarbitone, but not with the kappa-opioid receptor agonist enadoline. These findings were related to the suppression of seizures and the survival of neurons. In conclusion, excitotoxic stimulation leading to neuronal death was associated with increased expression of APP KPI+ mRNA and decreased APP KPI- mRNA, a finding which may relate to the plasticity of the central nervous system.

Topics: Alzheimer Disease; Amyloid beta-Protein Precursor; Animals; Benzofurans; Brain; Dizocilpine Maleate; Gene Expression Regulation; Glial Fibrillary Acidic Protein; Humans; Kainic Acid; Male; Neuroprotective Agents; Neurotoxins; Organ Specificity; Pentobarbital; Pentylenetetrazole; Pyrrolidines; Rats; Rats, Wistar; RNA, Messenger; Transcription, Genetic; Trypsin Inhibitor, Kunitz Soybean

Blockade of N-methyl-D-aspartate (NMDA) glutamate receptors by MK-801 induces neuronal degeneration in the posterior cingulate/retrosplenial cortex and other corticolimbic regions although damage in the latter has not been adequately characterized. This disseminated corticolimbic damage is of interest since NMDA hypofunction, the mechanism that triggers this neurodegenerative syndrome, has been postulated to play a role in the pathophysiology of Alzheimer's disease (AD). Several histological methods, including electron microscopy, were used to evaluate the neurotoxic changes in various corticolimbic regions of rat brain following MK-801 or a combination of MK-801 plus pilocarpine. We found that MK-801 triggers neuronal degeneration in a widespread pattern similar to that induced by phencyclidine and that females showed more damage than males. The neurotoxic reaction involved additional brain regions when muscarinic receptors were hyperactivated by administering pilocarpine with MK-801. Ultrastructural evaluation revealed that a major feature of the neurotoxic action involves degeneration of dendritic spines which entails loss of synaptic complexes. The ultrastructural appearance of degenerating neurons was generally inconsistent with an apoptotic mechanism, although evidence equivocally consistent with apoptosis was observed in some instances. The cell death process evolved relatively slowly and was still ongoing 7 days posttreatment. Relevance of these results to AD is discussed.

Topics: Alzheimer Disease; Animals; Cerebral Cortex; Dizocilpine Maleate; Drug Combinations; Excitatory Amino Acid Antagonists; Female; Limbic System; Male; Nerve Degeneration; Pilocarpine; Rats; Rats, Sprague-Dawley; Sex Characteristics; Time Factors

This study used [3H]dizocilpine ([3H]MK-801) binding to the N-methyl-D-aspartate (NMDA) receptor to examine redox, polyamine, and glycine modulatory sites in membranes derived from the superior frontal and the superior temporal cortex of patients with Alzheimer's disease. In control subjects the competitive polyamine site antagonist arcaine inhibited [3H]dizocilpine binding in a dose-dependent fashion and this curve was shifted to the right by the addition of 50 microM spermidine. Arcaine inhibition of binding was more potent in the temporal cortex than in the frontal cortex, in both the absence and presence of 50 microM spermidine. In Alzheimer's disease, arcaine inhibition of [3H]dizocilpine binding (in both the absence and the presence of spermidine) was not different from control in either of the two brain areas examined. The sulfhydryl redox site of the NMDA receptor was assessed using the oxidizing agent 5,5'-dithio-bis(2-nitrobenzoic acid), which inhibited binding in a dose-dependent fashion. This inhibition was similar in patients with Alzheimer's disease and control subjects. Glycine-stimulated [3H]dizocilpine binding was also unaffected in patients with Alzheimer's disease. However, in the temporal cortex there was a significant age-associated decline in [3H]dizocilpine binding in the presence of 100 microM glutamate (Rs = -0.71) and 100 microM glutamate plus 30 microM glycine (Rs = -0.90). There was also an age-related increase in arcaine IC50 (which reflects an age-related decrease in arcaine affinity) in the frontal cortex, determined both in the absence (Rs = 0.83) and the presence (Rs = 0.79) of spermidine. These data indicate that the NMDA receptor and its modulatory redox, polyamine, and glycine subsites are intact in patients with Alzheimer's disease and that the modulatory activity of polyamine and glycine sites decline with aging.

Topics: Aged; Aged, 80 and over; Alzheimer Disease; Analysis of Variance; Biguanides; Binding Sites; Brain; Cell Membrane; Cerebral Cortex; Dithionitrobenzoic Acid; Dizocilpine Maleate; Female; Frontal Lobe; Glycine; Humans; Male; Middle Aged; Organ Specificity; Oxidation-Reduction; Radioligand Assay; Receptors, N-Methyl-D-Aspartate; Spermidine; Temporal Lobe

Binding to adenosine A1 receptors and the status of their coupling to G proteins were studied in the hippocampus and parahippocampal gyrus of Alzheimer individuals and age-matched controls. The binding to A1 receptors was compared with binding to the N-methyl-D-aspartate receptor complex channel-associated sites (labeled with (+)-[3H]5-methyl-10,11-dihydro-5H- dibenzo[a,d]cyclohepten-5,10-imine maleate). In vitro quantitative autoradiography demonstrated a similar anatomical distribution of A1 receptors labeled either with an agonist ((-)-[3H]phenylisopropyladenosine) or antagonist ([3H]8-cyclopentyl-1,3-dipropylxanthine) in the brains of elderly controls. In Alzheimer patients, significant decreases in the density of both agonist and antagonist binding sites were found in the molecular layer of the dentate gyrus. Decreased A1 agonist binding was also observed in the CA1 stratum oriens and outer layers of the parahippocampal gyrus, while reduced antagonist binding was found in the subiculum and CA3 region. Reduced density of the N-methyl-D-aspartate receptor channel sites was found in the CA1 region and parahippocampal gyrus. The reductions in binding to adenosine A1 and N-methyl-D-aspartate receptors were due to a decrease in the density of binding sites (Bmax), and not changes in receptor affinity (KD). In both elderly control and Alzheimer subjects, GTP substantially reduced the density of A1 agonist binding sites with a concomitant increase in the KD values, whereas antagonist binding was unaffected by GTP. The results suggest that adenosine A1 receptor agonists and antagonists recognize overlapping populations of binding sites. Reduced density of A1 receptors in the molecular layer of the dentate gyrus most probably reflects damage of the perforant path input in Alzheimer's disease, while altered binding in the CA1 and CA3 regions is probably due to loss of intrinsic neurons. Similar effects of GTP on binding to A1 receptors in control and Alzheimer individuals suggest lack of alterations in coupling of A1 receptors to G proteins in Alzheimer's disease, thus supporting the notion of normal receptor coupling to their effector systems in Alzheimer's disease.

Topics: Adenosine; Aged; Aged, 80 and over; Alzheimer Disease; Autoradiography; Dizocilpine Maleate; Female; GTP-Binding Proteins; Hippocampus; Humans; Kinetics; Male; Organ Specificity; Pyramidal Tracts; Receptors, N-Methyl-D-Aspartate; Receptors, Purinergic; Tritium; Xanthines

[3H]Glycine binding and glycine modulation of [3H]MK-801 binding have been used to study the glycine allosteric site associated with the N-methyl-D-aspartate receptor complex in postmortem human brain. The effect of glycine on [3H]MK-801 binding appeared sensitive to duration of terminal coma, and possibly postmortem delay. Thirty percent of the binding occurred in a subfraction of brain tissue and did not show enhancement by glycine and glutamic acid. [3H]Glycine binding to a subfraction free from this component was studied and showed high specific binding. KD and Bmax values showed considerable intersubject variability which did not appear to be due to demographic features or to tissue content of amino acids with an affinity for this site. The pharmacological characteristics of binding in this subfraction and a correlation between Bmax values and the maximal enhancement of [3H]MK-801 binding by glycine are consistent with [3H]glycine binding occurring to an N-methyl-D-aspartate receptor complex associated site. Further support for this is provided by a significantly lower Bmax value for [3H]glycine binding in subjects with Alzheimer's disease and reduced glycine enhancement of [3H]MK-801 binding. However, the effect of perimortem factors makes it difficult to confidently attribute this solely to a disease-related change in the receptor. The possible role of the glycine allosteric site in the treatment of neuropsychiatric disorders is discussed.

Topics: Aged; Aged, 80 and over; Allosteric Site; Alzheimer Disease; Animals; Cell Membrane; Cerebral Cortex; Coma; Dizocilpine Maleate; Female; Frontal Lobe; Glutamates; Glutamic Acid; Glycine; Humans; Male; Papio; Postmortem Changes; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate

L-Phosphoserine is one of the phosphomonoesters elevated in Alzheimer's disease brain and has close structural similarity to L-glutamate. This study attempts to define precisely the actions of L-phosphoserine at L-glutamate receptor subtypes. L-Phosphoserine is shown to bind to N-methyl-D-aspartate and kainic acid receptor subtypes, but not to the quisqualic acid subtype. Studies of [3H]MK-801 binding in the presence and absence of L-glutamate and glycine show L-phosphoserine to be a competitive N-methyl-D-aspartate antagonist. The IC50 of L-phosphoserine in these studies varies from 373 to 721 microM. This may indicate a physiologically relevant action of L-phosphoserine in Alzheimer's disease brain because whole brain concentrations may reach over 1 mM.

Topics: 2-Amino-5-phosphonovalerate; Alzheimer Disease; Animals; Dizocilpine Maleate; Dose-Response Relationship, Drug; Glutamates; Glycine; Kainic Acid; N-Methylaspartate; Phosphoserine; Rats; Receptors, Glutamate; Receptors, Neurotransmitter

Topics: 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; Aging; Alzheimer Disease; Animals; Dizocilpine Maleate; Haplorhini; Humans; Huntington Disease; Nerve Degeneration; Neurotoxins; Parkinson Disease; Quinolinic Acid; Quinolinic Acids; Receptors, Dopamine

The action of D-Cycloserine (DCS) at the strychnine-insensitive glycine recognition site of the NMDA receptor-ionophore complex has been studied with membranes from inferior parietal cortex of patients with Alzheimer's disease. The maximal response of the site, measured using [3H]MK-801 binding, was 64% of that observed with glycine. Stimulation of binding induced by DCS in the presence of fixed concentrations of glycine resulted in a family of dose-response curves, consistent with the antibiotic having the property of a partial agonist at this glycine site. It is proposed that because of circumscribed glutamatergic pyramidal cell pathology DCS will have benefit for Alzheimer's patients over and above all other types of cognitive impairment.

Topics: Aged; Aged, 80 and over; Alzheimer Disease; Brain; Cognition; Cycloserine; Dizocilpine Maleate; Female; Humans; Ionophores; Radioligand Assay; Receptors, N-Methyl-D-Aspartate; Stereoisomerism

The binding of [3H]MK-801 to the N-methyl-D-aspartate receptor complex of well-washed cortical membranes from brains of examples of Alzheimer's disease and controls has been determined in incubations containing either glutamate or glycine plus glutamate. No changes were detected in the IC50 values for inhibition by zinc in the Alzheimer's samples compared to control although 'glycine-dependent' binding of the [3H]-ligand was significantly reduced in Alzheimer's disease.

Topics: Aged; Aged, 80 and over; Alzheimer Disease; Brain; Dibenzocycloheptenes; Dizocilpine Maleate; Female; Glycine; Humans; Male; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Zinc

The novel N-methyl-D-aspartate receptor channel ligand (+)-[3H]5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5, 10-imine maleate ([3H]MK-801) has been utilized to label this receptor in human brain tissue. Characteristics of [3H]MK-801 binding to well-washed membranes from 17 control subjects and 16 patients with Alzheimer's disease were determined in frontal, parietal, and temporal cerebral cortex and cerebellar cortex. In control tissue the pharmacological specificity of the binding of this substance is entirely consistent with the profile previously reported for rat brain. Binding could be stimulated by the addition of glutamic acid to the incubation medium; addition of glycine produced further enhancement which was not prevented by strychnine. The specificity of the effects of these and other amino acids on the binding was the same as in the rat. In Alzheimer's disease significantly less binding was observed in the frontal cortex under glutamate- and glycine-stimulated conditions. This appears to be associated with a reduced affinity of the site whereas the pharmacological specificity of the site remained unchanged. The effect did not appear to be due to differences in mode of death between Alzheimer's disease and control subjects and is unlikely to be related to factors for which the groups were matched. In contrast, binding was not altered in the absence of added amino acids and presence of glutamate alone. These results imply that in the cerebral cortex the agonist site and a site in the cation channel of the receptor are not selectively altered, but that their coupling to a strychnine-insensitive glycine recognition site is impaired.

Topics: Aged; Aged, 80 and over; Alzheimer Disease; Brain; Cell Membrane; Cerebellar Cortex; Dibenzocycloheptenes; Dizocilpine Maleate; Female; Frontal Lobe; Glutamates; Glutamic Acid; Glycine; Humans; Male; Middle Aged; Parietal Lobe; Postmortem Changes; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Temporal Lobe; Time Factors

The density of [3H]MK-801 binding sites was studied in homogenates prepared from different cortical regions of postmortem brains of Alzheimer patients and age matched controls. Highest number of binding sites for this noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) receptor was in temporal pole (Brodmann area A-38) in both groups. There were no consistent differences between patients and controls in either binding density or affinity constant in any of the areas studied. Involvement of glutamatergic neurotransmission in Alzheimer's disease does not seem to be at the level of the MK-801 recognition site on the NMDA receptor complex.

Topics: Aged; Aged, 80 and over; Alzheimer Disease; Anticonvulsants; Binding Sites; Cerebral Cortex; Dibenzocycloheptenes; Dizocilpine Maleate; Female; Hippocampus; Humans; Male; Middle Aged; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter