N-Methyl-D-aspartate receptor antagonist MK-801 and radical scavengers protect cholinergic nucleus basalis neurons against beta-amyloid neurotoxicity

Transient expression of the neuropeptide galanin modulates peripheral‑to‑central connectivity in the somatosensory thalamus during whisker development in mice

The significance of transient neuropeptide expression during postnatal brain development is unknown. Here, we show that galanin expression in the ventrobasal thalamus of infant mice coincides with whisker map development and modulates subcortical circuit wiring. Time-resolved neuroanatomy and single-nucleus RNA-seq identified complementary galanin (Gal) and galanin receptor 1 (Galr1) expression in the ventrobasal thalamus and the principal sensory nucleus of the trigeminal nerve (Pr5), respectively. Somatodendritic galanin release from the ventrobasal thalamus was time-locked to the first postnatal week, when Gal1R+ Pr5 afferents form glutamatergic (Slc17a6+) synapses for the topographical whisker map to emerge. RNAi-mediated silencing of galanin expression disrupted glutamatergic synaptogenesis, which manifested as impaired whisker-dependent exploratory behaviors in infant mice, with behavioral abnormalities enduring into adulthood. Pharmacological probing of receptor selectivity in vivo corroborated that target recognition and synaptogenesis in the thalamus, at least in part, are reliant on agonist-induced Gal1R activation in inbound excitatory axons. Overall, we suggest a neuropeptide-dependent developmental mechanism to contribute to the topographical specification of a fundamental sensory neurocircuit in mice.

Contribution of Lysosome and Sigma Receptors to Neuroprotective Effects of Memantine Against Beta-Amyloid in the SH-SY5Y Cells

Purpose: Memantine is an approved drug for the treatment of Alzheimer’s disease (AD). Autophagy, lysosome dysfunction, and sigma receptors have possible roles in the pathophysiology of AD. Therefore, we aimed to investigate the contribution of sigma receptors and lysosome inhibition to the neuroprotective effects of memantine against amyloid-beta (Aβ)-induced neurotoxicity in SH-SY5Y cells.

Methods: We determined the neuroprotective effects of memantine (2.5 µM), dizocilpine (MK801, as a selective N-methyl-D-aspartate (NMDA) receptor antagonist) (5 μM) against Aβ25– 35 (2 μg/μL)-induced neurotoxicity. We used chloroquine (10, 20, and 40 μM) as a lysosome inhibitor and BD-1063 (1, 10, and 30 μM) as a selective sigma receptor antagonist. The MTT assay was used to measure the neurotoxicity in the SH-SY5Y cells. Data were analyzed using the one-way ANOVA.

Results: Memantine (2.5 µM), dizocilpine (5 µM), chloroquine (10 and 20 µM) and BD-1063 (1, 10 and 30 µM) decreased the neurotoxic effects of Aβ on the SH-SY5Y cells. However, chloroquine (40 µM) increased the neurotoxic effects of Aβ. Cell viability in the cells treated with memantine + Aβ + chloroquine (10, 20, and 40 μM) was significantly lower than the memantine + Aβ-treated group. Moreover, cell viability in the memantine + Aβ group was higher than the memantine + Aβ + BD-1063 (10 and 30 μM) groups.

Conclusion: The lysosomal and sigma receptors may contribute to the neuroprotective mechanism of memantine and other NMDA receptor antagonists. Moreover, the restoration of lysosomes function and the modulation of sigma receptors are potential targets in the treatment of AD.

Comparative Effects of Alpha- and Gamma-Tocopherol on Mitochondrial Functions in Alzheimer's Disease In Vitro Model

Vitamin E acts as an antioxidant and reduces the level of reactive oxygen species (ROS) in Alzheimer's disease (AD). Alpha-tocopherol (ATF) is the most widely studied form of vitamin E besides gamma-tocopherol (GTF) which also shows beneficial effects in AD. The levels of amyloid-beta (Aβ) and amyloid precursor protein (APP) increased in the brains of AD patients, and mutations in the APP gene are known to enhance the production of Aβ. Mitochondrial function was shown to be affected by the increased level of Aβ and may induce cell death. Here, we aimed to compare the effects of ATF and GTF on their ability to reduce Aβ level, modulate mitochondrial function and reduce the apoptosis marker in SH-SY5Y cells stably transfected with the wild-type or mutant form of the APP gene. The Aβ level was measured by ELISA, the mitochondrial ROS and ATP level were quantified by fluorescence and luciferase assay respectively whereas the complex V enzyme activity was measured by spectrophotometry. The expressions of genes involved in the regulation of mitochondrial membrane permeability such as voltage dependent anion channel (VDAC1), adenine nucleotide translocase (ANT), and cyclophilin D (CYPD) were determined by quantitative real-time polymerase chain reaction (qRT-PCR), while the expressions of cyclophilin D (CypD), cytochrome c, Bcl2 associated X (BAX), B cell lymphoma-2 (Bcl-2), and pro-caspase-3 were determined by western blot. Our results showed that mitochondrial ROS level was elevated accompanied by decreased ATP level and complex V enzyme activity in SH-SY5Y cells expressing the mutant APP gene (p < 0.05). Treatment with both ATF and GTF reduced the mitochondrial ROS level with maximum reduction was observed in the cells treated with high concentrations of ATF and GTF (p < 0.05). However, only GTF at 80 µM significantly increase the ATP level and complex V enzyme activity (p < 0.05). VDAC1 and CYPD were downregulated and CypD protein was significantly overexpressed in cells transfected with the wild-type (WT) and mutant APP gene (p < 0.05). Cytochrome c release, the ratio of BAX/Bcl-2, and pro-caspase-3 expression increased in cells expressing mutated APP gene (p < 0.05). The expression of CypD and pro-caspase 3 protein, and the ratio of BAX/Bcl-2 were increased in the following order; SH-SY5Y-APP-WT < SH-SY5Y-APP Swe Collapse

Key Words

• preclinical research
• translational research

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MESH Headings

• Alzheimer Disease/drug therapy
• Alzheimer Disease/metabolism
• Amyloid beta-Peptides/metabolism
• Amyloid beta-Protein Precursor/drug effects
• Amyloid beta-Protein Precursor/metabolism
• Apoptosis/drug effects
• Caspase 3/metabolism
• Cell Line, Tumor
• Cytochromes c/metabolism
• Humans
• Mitochondria/drug effects
• Proto-Oncogene Proteins c-bcl-2/metabolism
• Reactive Oxygen Species/metabolism
• Tocopherols/pharmacology
• alpha-Tocopherol/pharmacology
• gamma-Tocopherol/pharmacology

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Grants

• Universiti Kebangsaan Malaysia DIP/2013/003 Universiti Kebangsaan Malaysia FF-2015-025

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Affiliation(s)

Aslina Pahrudin Arrozi Department of Biochemistry, Level 17, Preclinical Building, Universiti Kebangsaan Malaysia Medical Centre, Jalan Yaacob Latif, Bandar Tun Razak, Cheras, 56000, Kuala Lumpur, Malaysia
Siti Nur Syazwani Shukri Department of Biochemistry, Level 17, Preclinical Building, Universiti Kebangsaan Malaysia Medical Centre, Jalan Yaacob Latif, Bandar Tun Razak, Cheras, 56000, Kuala Lumpur, Malaysia
Wan Zurinah Wan Ngah Department of Biochemistry, Level 17, Preclinical Building, Universiti Kebangsaan Malaysia Medical Centre, Jalan Yaacob Latif, Bandar Tun Razak, Cheras, 56000, Kuala Lumpur, Malaysia
Yasmin Anum Mohd Yusof Department of Biochemistry, Level 17, Preclinical Building, Universiti Kebangsaan Malaysia Medical Centre, Jalan Yaacob Latif, Bandar Tun Razak, Cheras, 56000, Kuala Lumpur, Malaysia
Mohd Hanafi Ahmad Damanhuri Department of Biochemistry, Level 17, Preclinical Building, Universiti Kebangsaan Malaysia Medical Centre, Jalan Yaacob Latif, Bandar Tun Razak, Cheras, 56000, Kuala Lumpur, Malaysia
Faizul Jaafar Department of Biochemistry, Level 17, Preclinical Building, Universiti Kebangsaan Malaysia Medical Centre, Jalan Yaacob Latif, Bandar Tun Razak, Cheras, 56000, Kuala Lumpur, Malaysia
Suzana Makpol Department of Biochemistry, Level 17, Preclinical Building, Universiti Kebangsaan Malaysia Medical Centre, Jalan Yaacob Latif, Bandar Tun Razak, Cheras, 56000, Kuala Lumpur, Malaysia.

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Life-long epigenetic programming of cortical architecture by maternal 'Western' diet during pregnancy

The evolution of human diets led to preferences toward polyunsaturated fatty acid (PUFA) content with 'Western' diets enriched in ω-6 PUFAs. Mounting evidence points to ω-6 PUFA excess limiting metabolic and cognitive processes that define longevity in humans. When chosen during pregnancy, ω-6 PUFA-enriched 'Western' diets can reprogram maternal bodily metabolism with maternal nutrient supply precipitating the body-wide imprinting of molecular and cellular adaptations at the level of long-range intercellular signaling networks in the unborn fetus. Even though unfavorable neurological outcomes are amongst the most common complications of intrauterine ω-6 PUFA excess, cellular underpinnings of life-long modifications to brain architecture remain unknown. Here, we show that nutritional ω-6 PUFA-derived endocannabinoids desensitize CB₁ cannabinoid receptors, thus inducing epigenetic repression of transcriptional regulatory networks controlling neuronal differentiation. We found that cortical neurons lose their positional identity and axonal selectivity when mouse fetuses are exposed to excess ω-6 PUFAs in utero. Conversion of ω-6 PUFAs into endocannabinoids disrupted the temporal precision of signaling at neuronal CB₁ cannabinoid receptors, chiefly deregulating Stat3-dependent transcriptional cascades otherwise required to execute neuronal differentiation programs. Global proteomics identified the immunoglobulin family of cell adhesion molecules (IgCAMs) as direct substrates, with DNA methylation and chromatin accessibility profiling uncovering epigenetic reprogramming at >1400 sites in neurons after prolonged cannabinoid exposure. We found anxiety and depression-like behavioral traits to manifest in adult offspring, which is consistent with genetic models of reduced IgCAM expression, to suggest causality for cortical wiring defects. Overall, our data uncover a regulatory mechanism whose disruption by maternal food choices could limit an offspring's brain function for life.

The Acute Activation of the CB1 Receptor in the Hippocampus Decreases Neurotoxicity and Prevents Spatial Memory Impairment in Rats Lesioned with β-Amyloid 25-35

Given their anti-inflammatory properties, cannabinoids have been shown to be neuroprotective agents and to reduce excitotoxicity, through the activation of the Cannabinoid receptor type 1 (CB1r). These properties have led to CB1r being proposed as pharmacological targets for the treatment of various neurodegenerative diseases. Amyloid-β 25-35 (Aβ_25-35) induces the expression of inducible nitric oxide synthase (iNOS) and increases nitric oxide (NO●) levels. It has been observed that increased NO● concentrations trigger biochemical pathways that contribute to neuronal death and cognitive damage. This study aimed to evaluate the neuroprotective effect of an acute activation of CB1r on spatial memory and its impact on iNOS protein expression, NO● levels, gliosis and the neurodegenerative process induced by the injection of Aβ_(25-35) into the CA1 subfield of the hippocampus. ACEA [1 μM/1 μL] and Aβ_(25-35) [100 μM/1 μL] and their respective vehicle groups were injected into the CA1 subfield of the hippocampus. The animals were tested for spatial learning and memory in the eight-arm radial maze, with the results revealing that the administration of ACEA plus Aβ_(25-35) improves learning and memory processes, in contrast with the Aβ_(25-35) group. Moreover, ACEA plus Aβ_(25-35) prevented both the increase in iNOS protein and NO● levels and the reactive gliosis induced by Aβ_(25-35). Importantly, neurodegeneration was significantly reduced by the administration of ACEA plus Aβ_(25-35) in the CA1 subfield of the hippocampus. The data obtained in the present research suggest that the acute early activation of CB1r is crucial for neuroprotection.

The modulatory role of phloretin in Aβ25-35 induced sporadic Alzheimer's disease in rat model

Alzheimer's disease (AD) is the leading neurodegenerative disorder with extracellular senile plaques and neurofibrillary tangles as the major hallmarks. The objective was to evaluate the effect of phloretin in a chronic model of sporadic AD by injecting aggregated form of Aβ25-35 peptide sequence intracerebroventricularly (icv) in Wistar rats. To achieve this, male Wistar rats were injected with aggregated Aβ25-35 peptide icv, followed by 21 days phloretin (2.5 mg/kg, 5 mg/kg) administration after recovery period. Barnes maze and elevated plus maze along with the biochemical estimation of antioxidant enzymes activities were conducted. The hippocampus region of the rat brains were stained with Congo red and Nissl stain. TNF-α was estimated in the brain homogenates using the ELISA assay. In this study, phloretin improved the spatial memory formation and retention in Barnes maze test. Additionally, phloretin alleviated the antioxidant defense biomarkers and thereby reduced oxidative stress, decreased TNF-α-mediated neuroinflammation. Furthermore, phloretin treatment showed decreased amyloid beta accumulation in the CA1 region and less number of pyknotic nuclei in the dentate gyrus of the Aβ25-35-injected rat brains. The above experimental findings evinced the promising role of phloretin in Aβ25-35-injected rats and which further envisage its potential to be explored in the treatment of AD.

Hypothalamic CNTF volume transmission shapes cortical noradrenergic excitability upon acute stress

Stress-induced cortical alertness is maintained by a heightened excitability of noradrenergic neurons innervating, notably, the prefrontal cortex. However, neither the signaling axis linking hypothalamic activation to delayed and lasting noradrenergic excitability nor the molecular cascade gating noradrenaline synthesis is defined. Here, we show that hypothalamic corticotropin-releasing hormone-releasing neurons innervate ependymal cells of the 3rd ventricle to induce ciliary neurotrophic factor (CNTF) release for transport through the brain's aqueductal system. CNTF binding to its cognate receptors on norepinephrinergic neurons in the locus coeruleus then initiates sequential phosphorylation of extracellular signal-regulated kinase 1 and tyrosine hydroxylase with the Ca2+-sensor secretagogin ensuring activity dependence in both rodent and human brains. Both CNTF and secretagogin ablation occlude stress-induced cortical norepinephrine synthesis, ensuing neuronal excitation and behavioral stereotypes. Cumulatively, we identify a multimodal pathway that is rate-limited by CNTF volume transmission and poised to directly convert hypothalamic activation into long-lasting cortical excitability following acute stress.

Yokukansan and Yokukansankachimpihange Ameliorate Aggressive Behaviors in Rats with Cholinergic Degeneration in the Nucleus Basalis of Meynert

Yokukansan (YKS) and yokukansankachimpihange (YKSCH) are traditional Japanese Kampo medicines. The latter comprises YKS along with the medicinal herbs Citrus unshiu peel and Pinellia tuber. Both of these Kampo medicines are indicated for the treatment of night crying and irritability in children and for neurosis and insomnia in adults. In recent clinical trials, YKS exhibited ameliorative effects on the behavioral and psychological symptoms of dementia, such as aggressiveness, excitement, and irritability. In the present study, we aimed to clarify the involvement of cholinergic degeneration in the nucleus basalis of Meynert (NBM) in the development of aggressiveness in rats. Subsequently, using this animal model, the effects of YKS and YKSCH on aggressiveness were compared and the mechanisms underlying these effects were investigated. L-Glutamic acid (Glu) was injected into the right NBM of rats to induce deterioration of cholinergic neurons. On day 8 after Glu injection, aggressive behaviors were evaluated using resident–intruder tests. After the evaluation, YKS or YKSCH was administered to rats with aggressive behaviors daily for 7 days. In some groups, the 5-HT_1A receptor antagonist WAY-100635 was coadministered with YKS or YKSCH over the same period. In other groups, locomotor activity was measured on days 12–14 after Glu injection. On day 15, immunohistochemistry was then performed to examine choline acetyltransferase (ChAT) activities in the NBM. Aggressive behaviors had developed on day 8 after Glu injection and were maintained until day 15. YKS and YKSCH significantly ameliorated the aggressive behaviors. These suppressive effects were entirely abolished following coadministration of WAY-100635. Finally, the number of ChAT-positive cells in the right NBM was significantly reduced on day 15 after Glu injection, and treatment with YKS or YKSCH did not ameliorate these reduced cell numbers. Our results show that unilateral Glu injections into the NBM of rats leads to the development of aggressive behaviors, which is thought to reflect cholinergic degeneration. YKS and YKSCH treatments ameliorated Glu-induced aggressive behaviors, and these effects were suggested to be mediated by 5-HT_1A receptor stimulation, but not by improvement of cholinergic degeneration.

GABAergic neurotransmission and new strategies of neuromodulation to compensate synaptic dysfunction in early stages of Alzheimer's disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disease characterized by cognitive decline, brain atrophy due to neuronal and synapse loss, and formation of two pathological lesions: extracellular amyloid plaques, composed largely of amyloid-beta peptide (Aβ), and neurofibrillary tangles formed by intracellular aggregates of hyperphosphorylated tau protein. Lesions mainly accumulate in brain regions that modulate cognitive functions such as the hippocampus, septum or amygdala. These brain structures have dense reciprocal glutamatergic, cholinergic, and GABAergic connections and their relationships directly affect learning and memory processes, so they have been proposed as highly susceptible regions to suffer damage by Aβ during AD course. Last findings support the emerging concept that soluble Aβ peptides, inducing an initial stage of synaptic dysfunction which probably starts 20–30 years before the clinical onset of AD, can perturb the excitatory–inhibitory balance of neural circuitries. In turn, neurotransmission imbalance will result in altered network activity that might be responsible of cognitive deficits in AD. Therefore, Aβ interactions on neurotransmission systems in memory-related brain regions such as amygdaloid complex, medial septum or hippocampus are critical in cognitive functions and appear as a pivotal target for drug design to improve learning and dysfunctions that manifest with age. Since treatments based on glutamatergic and cholinergic pharmacology in AD have shown limited success, therapies combining modulators of different neurotransmission systems including recent findings regarding the GABAergic system, emerge as a more useful tool for the treatment, and overall prevention, of this dementia. In this review, focused on inhibitory systems, we will analyze pharmacological strategies to compensate neurotransmission imbalance that might be considered as potential therapeutic interventions in AD.

Memantine protects cholinergic and glutamatergic septal neurons from Aβ1-40-induced toxicity

The medial septal region (medial septum and diagonal band of Broca, MS/DB) controls hippocampal excitability and synaptic plasticity. MS/DB cholinergic neurons degenerate early in Alzheimer's disease (AD). The presence of MS/DB glutamatergic neurons that project to the hippocampus and are vulnerable to Aβ suggests that excitotoxicity plays a role in AD septal degeneration and hippocampal dysfunction. To demonstrate the presence of excitotoxicity in Aβ-induced septal damage, we compared rats injected with Aβ1-40 into the MS/DB with animals treated with memantine prior, during and after Aβ1-40 injections. Controls were injected with phosphate buffered saline (PBS). MS/DB cholinergic, glutamatergic and GABAergic neurons were immunochemically identified. The number of MS/DB neurons was estimated using stereology. Our results show that memantine blocks Aβ1-40-induced septal damage and suggest that excitotoxicity plays a role in basal forebrain neurodegeneration.

Alzheimer's disease, β-amyloid, glutamate, NMDA receptors and memantine--searching for the connections

β-amyloid (Aβ) is widely accepted to be one of the major pathomechanisms underlying Alzheimer's disease (AD), although there is presently lively debate regarding the relative roles of particular species/forms of this peptide. Most recent evidence indicates that soluble oligomers rather than plaques are the major cause of synaptic dysfunction and ultimately neurodegeneration. Soluble oligomeric Aβ has been shown to interact with several proteins, for example glutamatergic receptors of the NMDA type and proteins responsible for maintaining glutamate homeostasis such as uptake and release. As NMDA receptors are critically involved in neuronal plasticity including learning and memory, we felt that it would be valuable to provide an up to date review of the evidence connecting Aβ to these receptors and related neuronal plasticity. Strong support for the clinical relevance of such interactions is provided by the NMDA receptor antagonist memantine. This substance is the only NMDA receptor antagonist used clinically in the treatment of AD and therefore offers an excellent tool to facilitate translational extrapolations from in vitro studies through in vivo animal experiments to its ultimate clinical utility.

Schizandrin, an antioxidant lignan from Schisandra chinensis, ameliorates Aβ1-42-induced memory impairment in mice

In the present study, we examined the effect of schisandrin (SCH) of Schisandra chinensis on the amyloid-beta_1–42- (Aβ_1–42-) induced memory impairment in mice and elucidated the possible antioxidative mechanism. Mice were intracerebroventricular (i.c.v.) injected with the aggregated Aβ_1–42 and then treated with SCH (4, 12, and 36 mg/kg body weight) or donepezil (DPZ), a reference drug (0.65 mg/kg) by intragastric infusion for 14 days. Noncognitive disturbances and cognitive performance were evaluated by locomotor activity test, Y-maze test, and water maze test. Antioxidative enzyme activities including superoxide dismutase (SOD) and glutathione peroxidase (GSH-px) and levels of malondialdehyde (MDA), glutathione (GSH), and oxidized glutathione (GSSG) within the cerebral cortex and hippocampus of mice were measured to elucidate the mechanism. Our results showed that SCH significantly improved Aβ_1–42-induced short-term and spatial reference memory impairments in Y-maze test and water maze test. Furthermore, in the cerebral cortex and hippocampus of mice, SOD and GSH-px activities, GSH level, and GSH/GSSG ratio were increased, and levels of MDA and GSSG were decreased by the treatment of SCH. These results suggest that SCH is a potential cognitive enhancer against Alzheimer's disease through antioxidative action.

Experimental inhibition of peptide fibrillogenesis by synthetic peptides, carbohydrates and drugs

Peptide fibrillogenesis generally begins by the transformation of normally soluble proteins into elongated aggregates which are called as amyloid. These fibrils mainly consist of ß-sheets. They share certain common characteristics such as a cross-ß x-ray diffraction pattern, association with other common proteins and typical staining by the dye Congo Red. The individual form of the deposit consists of a disease-specific peptide/protein. The disease-specific protein serves as the basis for the classification of the amyloids. The association of fibril-forming peptides/proteins with diseases makes them primary disease-targets. Understanding the molecular interactions involved in the fibril formation becomes the foremost requirement to characterize the target. Interference with these interactions of ß-sheets in vitro prevents and sometimes reverses the fibril assembly. A small molecule capable of interfering with the formation of fibril could have therapeutic applications in these diseases. This anti-aggregation approach appears to be a viable treatment option. A search for such a molecule is pursued actively world over. All types of compounds and approaches to slow down or prevent the aggregation process have been described in the literature. These efforts are reviewed in this chapter.

Behavioural and cellular effects of exogenous amyloid-β peptides in rodents

A better understanding of Alzheimer's disease (AD) and the development of disease modifying therapies are some of the biggest challenges of the 21st century. One of the core features of AD are amyloid plaques composed of amyloid-beta (Aβ) peptides. The first hypothesis proposed that cognitive deficits are linked to plaque-development and transgenic mice have been generated to study this link, thereby providing a good model to develop new therapeutic approaches. Since later it was recognised that in AD patients the cognitive deficit is rather correlated to soluble amyloid levels, consequently, a new hypothesis appeared associating the earliest amyloid toxicity to these soluble species. The purpose of this review is to give a summary of behavioural and cellular data obtained after soluble Aβ peptide administration into rodents' brain, thereby showing that this model is a valid tool to investigate AD pathology when no plaques are present. Additionally, this method offers an excellent, efficient model to test compounds which could act at such early stages of the disease.

Effect of N-methyl-D-aspartate (NMDA) receptor antagonists on alpha-synuclein-evoked neuronal nitric oxide synthase activation in the rat brain

alpha-Synuclein (ASN), a small presynaptic protein that is abundant in the brain, is implicated in the pathogenesis of neurodegenerative disorders including Parkinson's and Alzheimer's disease. The central domain of alpha-synuclein, the non-amyloid beta component of the Alzheimer's disease amyloid (NAC) is probably responsible for its toxicity. However, the molecular mechanism of alpha-synuclein action remains largely elusive. The present study examined the effect of alpha-synuclein and the NAC peptide on nitric oxide synthase (NOS) activity in rat brain cortical and hippocampal slices using a radiochemical technique. Moreover, nitrite levels in brain slices incubated in the presence of alpha-synuclein were measured using the Griess reaction. ASN and the NAC stimulated NOS activity by about 70% and 40%, respectively. beta-Synuclein, a homologous protein of ASN that lacks the NAC domain, had no effect on NOS activity. Under the same experimental conditions, alpha-synuclein increased nitrite levels by 27%. alpha-Synuclein and the NAC affected the activity of constitutive neuronal isoform of NOS, but had no impact on the endothelial or inducible NOS isoforms. The effect of alpha-synuclein and the NAC peptide on NOS activity was inhibited by MK-801 and APV, antagonists of the NMDA receptor. These results indicate that the NMDA receptor plays an important role in alpha-synuclein-evoked nitric oxide synthesis. We suggest that nitric oxide liberated by the over-activated neuronal isoform of NOS could react with superoxide to form peroxynitrite, which modulates the function of a variety of biomolecules including proteins, lipids, and DNA.

Action of estrogen on survival of basal forebrain cholinergic neurons: promoting amelioration

Extensive studies during the past two decades provide compelling evidence that the gonadal steroid, estrogen, has the potential to affect the viability of basal forebrain cholinergic neurons. These observations reflect a unique ameliorative feature of estrogen as it restores and protects the cholinergic neurons against noxious stimuli or neurodegenerative processes. Hence, we first address the ameliorative function of estrogen on basal forebrain cholinergic neurons such as the actions of estrogen on neuronal plasticity of cholinergic neurons, estrogen-induced memory enhancement and the ameliorative role of estrogen on cholinergic neuron related neurodegenerative processes such as Alzheimer's disease. Second, we survey recent data as to possible mechanisms underlying the ameliorative actions of estrogen; influencing the amyloid precursor protein processing, enhancement in neurotrophin receptor signaling and estrogen-induced non-classical actions on second messenger systems. In addition, clinical relevance, pitfalls and future aspects of estrogen therapy on basal forebrain cholinergic neurons will be discussed.

Neuroprotective effect of alpha-asarone on spatial memory and nitric oxide levels in rats injected with amyloid-beta((25-35))

The chemical alpha-asarone is an important active substance of the Acori graminei rhizome (AGR). It has pharmacological effects that include antihyperlipidemic, antiinflammatory, and antioxidant activity. Our aim was to study the effects alpha-asarone on nitric oxide (NO) levels in the hippocampus and temporal cortex of the rat after injection of the fraction 25-35 from amyloid-beta (Abeta((25-35))). In addition we examined the working spatial memory in an eight-arm radial maze. Our results showed a significant increase of nitrites in the hippocampus and temporal cortex of Abeta((25-35))-treated rats. Other evidence of neuronal damage was the expression of a glial-fibrillar-acid protein and a silver staining. There were impairments in the spatial memory evaluated in the eight-arm radial maze. We wanted to determine whether alpha-asarone improves the memory correlated with NO overproduction and neuronal damage caused by the injection of Abeta((25-35)) into rats. Then animals received a 16-day treatment of alpha-asarone before the Abeta((25-35)) injection. Our results show a significant decrease of nitrite levels in the hippocampus and temporal cortex, without astrocytosis and silver-staining cells, which correlates with memory improvement in the alpha-asarone-treated group. Our results suggest that alpha-asarone may protect neurons against Abeta((25-35))-caused neurotoxicity by inhibiting the effects of NO overproduction in the hippocampus and temporal cortex.

Difluoromethylornithine decreases long-lasting protein oxidation induced by neonatal ethanol exposure in the hippocampus of adolescent rats

BACKGROUND

Ethanol exposure and withdrawal during central nervous system development can cause oxidative stress and produce severe and long-lasting behavioral and morphological alterations in which polyamines seem to play an important role. However, it is not known if early ethanol exposure causes long-lasting protein oxidative damage and if polyamines play a role in such a deleterious effect of ethanol.

METHODS

In this study we investigated the effects of early ethanol exposure (6 g/kg/d, by gavage), from postnatal day (PND) 1 to 8, and of the administration of difluoromethylornithine (DFMO, 500 mg/kg, i.p., on PND 8), a polyamine biosynthesis inhibitor, on the extent of oxidative modification of proteins. Indices of oxidative modification of proteins included protein carbonyls, 3-nitrotyrosine (3-NT), and protein bound 4-hydroxynonenal (HNE) in the hippocampus, cerebellum, hypothalamus, striatum, and cerebral cortex of Sprague-Dawley rats at PND 40.

RESULTS

Both ethanol and DFMO administration alone increased protein carbonyl immunoreactivity in the hippocampus at PND 40, but the combination of DFMO and ethanol resulted in no effect on protein carbonyl levels. No alterations in the content of protein-bound HNE, 3-NT, or carbonyl were found in any other cerebral structure.

CONCLUSIONS

These results suggest that the hippocampus is selectively affected by early ethanol exposure and by polyamine synthesis inhibition. In addition, the results suggest a role for polyamines in the long-lasting increase of protein carbonyls induced by ethanol exposure and withdrawal.

Differential effects of tumor necrosis factor-alpha co-administered with amyloid beta-peptide (25-35) on memory function and hippocampal damage in rat

Effects of concurrent intracerebroventricular administration of amyloid-beta peptide 25-35 (Abeta(25-35)) and the proinflammatory cytokine tumor necrosis factor-alpha (TNFalpha) to rats were investigated. A battery of behavioral tests including radial arm maze, passive avoidance, elevated plus-maze and forced swim test as well as histological methods were used. A single administration of Abeta(25-35) induced delayed behavioral deficits manifested in reference and working memory disturbances in the radial maze task involving spatial memory. However, no effects of Abeta(25-35) on learning or retention in a passive avoidance test could be revealed. Abeta(25-35) appeared to decrease anxiety without affecting depression-like behavior in the rats. Abeta(25-35)-induced cognitive deficits could be related to the moderate neuronal cell loss found in the hippocampal CA1 field. Though administration of TNFalpha did not impair learning and memory of rats in the radial maze, it induced gross changes in their behavior during passive avoidance training. Though TNFalpha did not protect against Abeta(25-35)-induced neuronal cell loss in the CA1 field of hippocampus, co-administration of TNFalpha with Abeta(25-35) resulted in an improvement of reference memory impaired by the amyloid peptide, but not of working memory.

Anti-amyloidogenic effects of antioxidants: Implications for the prevention and therapeutics of Alzheimer's disease

Alzheimer's disease (AD) is one of the most common dementing disorders and has profound medical and social consequences. The initiating molecular event is unknown, and its pathophysiology is highly complex. However, free radical injury appears to be a fundamental process contributing to the neuronal death seen in this disorder, and many studies using surrogate markers of oxidative damage have provided evidence supporting this hypothesis. Various compounds with antioxidant ability attenuated the oxidative stress induced by amyloid beta-protein (Abeta) in studies done in vitro and in vivo. Moreover, various antioxidants have been reported to inhibit the formation and extension of beta-amyloid fibrils (fAbeta), as well as to destabilize preformed fAbeta in vitro. In cell culture experiments, destabilized fAbeta were suggested to be less toxic than intact fAbeta. In transgenic mice model studies, some antioxidant compounds reduced plaque burden in vivo. In this article, we review the recent advances in the research on the antioxidants that inhibit the formation of fAbeta, as well as destabilize preformed fAbeta. Although the mechanisms by which these compounds inhibit fAbeta formation from Abeta, and destabilize preformed fAbeta are still unclear, they could be key molecules for the development of preventives and therapeutics for AD.

Simultaneous release of glutamate and acetylcholine from single magnocellular "cholinergic" basal forebrain neurons

Basal forebrain (BF) neurons provide the principal cholinergic drive to the hippocampus and cortex. Their degeneration is associated with the cognitive defects of Alzheimer's disease. Immunohistochemical studies suggest that some of these neurons contain glutamate, so might also release it. To test this, we made microisland cultures of single BF neurons from 12- to 14-d-old rats. Over 1-8 weeks in culture, neuronal processes made autaptic connections onto the neuron. In 34 of 36 cells tested, a somatically generated action potential was followed by a short-latency EPSC that was blocked by 1 mM kynurenic acid, showing that they released glutamate. To test whether the same neuron also released acetylcholine, we placed a voltage-clamped rat myoball expressing nicotinic receptors in contact with a neurite. In six of six neurons tested, the glutamatergic EPSC was accompanied by a nicotinic (hexamethonium-sensitive) myoball current. Stimulation of the M2-muscarinic presynaptic receptors (characterized using tripitramine and pirenzepine) produced a parallel inhibition of autaptic glutamatergic and myoball nicotinic responses; metabotropic glutamate receptor stimulation produced similar but less consistent and weaker effects. Atropine enhanced the glutamatergic EPSCs during repetitive stimulation by 25 +/- 6%; the anti-cholinesterase neostigmine reduced the train EPSCs by 37 +/- 6%. Hence, synaptically released acetylcholine exerted a negative-feedback inhibition of coreleased glutamate. We conclude that most cholinergic basal forebrain neurons are capable of releasing glutamate as a cotransmitter and that the release of both transmitters is subject to simultaneous feedback inhibition by synaptically released acetylcholine. This has implications for BF neuron function and for the use of cholinesterase inhibitors in Alzheimer's disease.

Non-fibrillar β-amyloid abates spike-timing-dependent synaptic potentiation at excitatory synapses in layer 2/3 of the neocortex by targeting postsynaptic AMPA receptors

Cognitive decline in Alzheimer's disease (AD) stems from the progressive dysfunction of synaptic connections within cortical neuronal microcircuits. Recently, soluble amyloid beta protein oligomers (Abeta(ol)s) have been identified as critical triggers for early synaptic disorganization. However, it remains unknown whether a deficit of Hebbian-related synaptic plasticity occurs during the early phase of AD. Therefore, we studied whether age-dependent Abeta accumulation affects the induction of spike-timing-dependent synaptic potentiation at excitatory synapses on neocortical layer 2/3 (L2/3) pyramidal cells in the APPswe/PS1dE9 transgenic mouse model of AD. Synaptic potentiation at excitatory synapses onto L2/3 pyramidal cells was significantly reduced at the onset of Abeta pathology and was virtually absent in mice with advanced Abeta burden. A decreased alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)/N-methyl-D-aspartate (NMDA) receptor-mediated current ratio implicated postsynaptic mechanisms underlying Abeta synaptotoxicity. The integral role of Abeta(ol)s in these processes was verified by showing that pretreatment of cortical slices with Abeta((25-35)ol)s disrupted spike-timing-dependent synaptic potentiation at unitary connections between L2/3 pyramidal cells, and reduced the amplitude of miniature excitatory postsynaptic currents therein. A robust decrement of AMPA, but not NMDA, receptor-mediated currents in nucleated patches from L2/3 pyramidal cells confirmed that Abeta(ol)s perturb basal glutamatergic synaptic transmission by affecting postsynaptic AMPA receptors. Inhibition of AMPA receptor desensitization by cyclothiazide significantly increased the amplitude of excitatory postsynaptic potentials evoked by afferent stimulation, and rescued synaptic plasticity even in mice with pronounced Abeta pathology. We propose that soluble Abeta(ol)s trigger the diminution of synaptic plasticity in neocortical pyramidal cell networks during early stages of AD pathogenesis by preferentially targeting postsynaptic AMPA receptors.

Effects of a Novel Cognitive Enhancer, Spiro[imidazo-[1,2-a]pyridine-3,2-indan]-2(3H)-one (ZSET1446), on Learning Impairments Induced by Amyloid-β1–40 in the Rat

We have previously shown that intracerebroventricular (i.c.v.) infusion of amyloid-beta (Abeta)1-40 produces oxidative stress and cholinergic dysfunction, as well as learning and memory deficits, in rats. In the present study, effects of a newly synthesized azaindolizinone derivative, spiro[imidazo[1,2-a]pyridine-3,2-indan]-2(3H)-one (ZSET1446), were assessed in rats with learning deficits induced by Abeta1-40 or scopolamine. The i.c.v. infusion of Abeta1-40 caused impairments in spontaneous alternation behavior in a Y-maze task, spatial reference and short-term memory in a water-maze task, and retention of passive-avoidance learning. Abeta1-40-infused rats also showed reduction in choline acetyltransferase (ChAT) activity in the medial septum and hippocampus, but not in the basal forebrain and cortex, and a decrease in glutathione S-transferase (GST)-like immunoreactivity in the cortex. Nicotine-stimulated acetylcholine (ACh) release in Abeta1-40-infused rats was lower than that in vehicle-infused rats. Oral administration of ZSET1446 at the dose range of 0.01 to 1 mg/kg ameliorated Abeta1-40-induced learning impairment in Y-maze, water-maze, and passive-avoidance tasks. ZSET1446 reversed the decrease of ChAT activity in the medial septum and hippocampus, GST-like immunoreactivity in the cortex, and nicotine-stimulated ACh release of Abeta1-40-treated rats to the levels of vehicle-infused control rats. Furthermore, 0.001 to 0.1 mg/kg ZSET1446 showed ameliorative effects on learning impairments caused by scopolamine in a passive-avoidance task. These results suggest that ZSET1446 may be a potential candidate for development as a therapeutic agent to manage cognitive impairment associated with conditions such as Alzheimer's disease.

Effect of vitamin E on memory retention in rats: possible involvement of cholinergic system

This study concerned effects of vitamin E and the cholinergic system on memory retention of passive avoidance learning in rats. Post-training intracerebroventricular (i.c.v.) injections were carried out in all experiments. Administrations of vitamin E (10, 25 and 50 microg/rat), nicotine (0.1 microg/rat) and pilocarpine (0.5 microg/rat), the muscarinic receptor agonist increased memory retention, while mecamylamine (0.01, 0.1 and 0.5 microg/rat), the nicotinic receptor antagonist and scopolamine (0.1, 1 and 5 microg/rat), the muscarinic receptor antagonist decreased memory retention. The combination of vitamin E with nicotine or pilocarpine showed potentiation. Effects of mecamylamine or scopolamine were attenuated by vitamin E. It is concluded that vitamin E has a close interaction with cholinergic system in memory retention process.

Neuroprotective Role of Neurokinin B (NKB) on β-amyloid (25–35) Induced Toxicity in Aging Rat Brain Synaptosomes: Involvement in Oxidative Stress and Excitotoxicity

The brain tissue has a large oxidative capacity, but its ability to combat oxidative stress is limited. In aging brain tissue the oxidative stress increases due to decreased activity of antioxidant enzymes and increased oxidative stress leading to neurodegeneration associated with excitotoxicity. The aim of the present study was to determine the effect of neuropeptides, neurokinin B (NKB) and amyloid beta protein fragment Abeta (25-35) and neurotransmitters N-methyl D-aspartate (NMDA) and Glutamate on rat brain synaptosomes of different age groups. Aging brain functions were assessed by measuring the activities of superoxide dismutase (Mn-SOD) and monoamine oxidase (MAO) and intrasynaptosomal [Ca(2+)](i )levels in presence of neuropeptides and neurotransmitters. Increase in age decreased the SOD and MAO enzyme activities; Abeta (25-35) addition further had damaging/toxic effects on the enzymes, whereas NKB alone and in combination with amyloid lowered the toxic effects caused by Abeta (25-35) addition, which was concentration (peptide) and age dependent. Oxidative stress and excitotoxicity are major consequences associated with the age, [Ca(2+)](i )was increased with the age and the neuropeptides and neurotransmitters elicited significant modulatory effects on it. Our study elucidates an increased activity of SOD, decreased activity of MAO and restoration of [Ca(2+)](i) levels in the presence of NKB and suggests an antioxidant, neuromodulatory and neuroprotective role of tachykinin peptide NKB against the beta amyloid induced toxicity.

Basal forebrain cholinergic dysfunction in Alzheimer's disease--interrelationship with beta-amyloid, inflammation and neurotrophin signaling

Alzheimer's disease, the most common neurodegenerative disorder of senile dementia, is characterized by two major morpho-pathological hallmarks. Deposition of extracellular neuritic, beta-amyloid peptide-containing plaques (senile plaques) in cerebral cortical regions of Alzheimer patients is accompanied by the presence of intracellular neurofibrillary tangles in cerebral pyramidal neurons. Basal forebrain cholinergic dysfunction is also a consistent feature of Alzheimer's disease, which has been suggested to cause, at least partly, the cognitive deficits observed in patients with Alzheimer's disease. Impaired cortical cholinergic neurotransmission may also contribute to beta-amyloid plaque pathology in Alzheimer's disease by affecting expression and processing of the beta-amyloid precursor protein (APP). Vice versa, low level of soluble beta-amyloid has been observed to inhibit cholinergic synaptic function. Deposition of beta-amyloid plaques in Alzheimer's disease is also accompanied by a significant plaque-associated glial up-regulation of interleukin-1, which has been attributed to affect expression and metabolism of APP and to interfere with cholinergic transmission. Understanding the molecular mechanisms underlying the interrelationship between cortical cholinergic dysfunction, beta-amyloid formation and deposition, as well as local inflammatory upregulation, would allow to derive potential treatment strategies to pharmacologically intervene in the disease-causing signaling cascade.

Divergent effects of Abeta1-42 on ionotropic glutamate receptor-mediated responses in CA1 neurons in vivo

Aggregated Abeta1-42 is hypothesized to be the central cause of Alzheimer's disease. However, early changes in synaptic activity may be detected in the disease long before a significant cell loss is manifested. Despite the fact that Abeta1-42 interference with long-term potentiation (LTP) and the field excitatory postsynaptic potential (fEPSP) is well documented, the exact mechanism of these events remains to be clarified. Here we studied the effects of iontophoretically applied Abeta1-42 on the neuronal firing evoked in vivo on the CA1 hippocampal neurons of Wistar rats by different agonists of the ionotropic glutamate receptors: N-methyl-d-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and kainic acid (KA). NMDA elicited firing enhanced in all of the measured cells; in contrast, the AMPA-mediated responses decreased significantly after Abeta1-42 ejection. The changes in KA-evoked responses to Abeta1-42 revealed two types of cells. In the first type, the KA-mediated firing remained at the control level, while in the second type, Abeta1-42 attenuated the KA-evoked responses. A protective pentapeptide, Leu-Pro-Tyr-Phe-Asp-amide, was used to verify the specificity of these beta-amyloid-elicited effects. The pentapeptide protected against the modulatory effects of Abeta1-42 on the NMDA and AMPA responses. In conclusion, we have shown that Abeta1-42 exerts divergent effects on the activity of the ionotropic glutamate receptors in vivo. These results suggest that the LTP disruption and fEPSP attenuation seen after Abeta1-42 application are in part due to the altered function of these receptors.

Studies of the effects of fragment (25?35) of beta-amyloid peptide on the behavior of rats in a radial maze

Decreases in cognitive functions, particularly long-term (episodic) and working memory, are among the earliest prognostic signs of Alzheimer's disease. The toxicity of beta-amyloid peptide is regarded as a major cause of neurodegeneration and cognitive impairment in this disease. The present report describes studies of the effects of intracerebroventricular administration of beta-amyloid peptide (25-35) (Abeta(25-35)) on the reproduction of a previously assimilated habit consisting of finding food in an eight-arm radial maze in rats. Abeta(25-35) was given bilaterally at doses of 15 and 30 nmol/animal seven days after preliminary training. Testing was performed 60 days after peptide administration. The results showed that Abeta(25-35) impaired working memory in rats without having any significant effect on the retention of responses. We were unable to demonstrate any relationship between memory impairment and the dose of peptide given. These data provide evidence of the ability of Abeta(25-35) to produce greater degradation of working memory function than long-term memory function.

Identification, design, synthesis, and pharmacological activity of (4-ethyl-piperazin-1-yl)-phenylmethanone derivatives with neuroprotective properties against beta-amyloid-induced toxicity

In search of novel therapeutic approaches for Alzheimer's disease (AD), we report herein the identification, design, synthesis, and pharmacological activity of (4-ethyl-piperaz-1-yl)-phenylmethanone derivatives with neuroprotective properties against beta-amyloid-induced toxicity. (4-ethyl-piperaz-1-yl)-phenylmethanone is a common substructure shared by molecules isolated from plants of the Asteraceae genus, traditionally used as restorative of lost or declining mental functions. (4-Ethyl-piperaz-1-yl)-phenylmethanone displayed strong neuroprotective properties against Abeta1-42 and reversed Abeta1-42-induced ATP depletion on neuronal cells, suggesting a mitochondrial site of action. Abeta1-42 has been described to induce a hyperactivity of the glutamate network in neuronal cells. (4-Ethyl-piperaz-1-yl)-phenylmethanone also inhibited the neurotoxic effect that glutamate displayed on PC12 cells, suggesting that the reduction of glutamate-induced neurotoxicity may be one of the mechanisms by which this compound exerts its neuroprotective properties against the deleterious effects of the Abeta1-42. These data suggest that the identified (4-ethyl-piperaz-1-yl)-phenylmethanone chemical entity exerts neuroprotective properties and may serve as a lead compound for the development of novel therapies for AD.

Local anesthetic procaine protects rat pheochromocytoma PC12 cells against beta-amyloid-induced neurotoxicity

Alzheimer's disease (AD) is the most common dementia occurring in elderly. We report herein the neuroprotective properties of procaine and other anesthetic agents against beta-amyloid-induced neurotoxicity. Procaine displayed strong neuroprotective properties against the amyloid peptide Abeta(1-42) and preserved Abeta(1-42)-induced ATP depletion on rat pheochromocytoma PC12 cells. Procaine also inhibited the neurotoxic effect that glutamate displayed on PC12 cells, suggesting that the reduction of glutamate-induced neurotoxicity may be the mechanism by which these compounds exert their 'antiamyloid' effects. In search of a mechanism of action we observed that procaine is a ligand for the sigma1 receptor, a protein which ligands have been shown to protect mitochondrial function and to exert antidepressant properties. Procaine binds also to muscarinic receptors but the true meaning of this feature needs to be clarified. In conclusion, these data suggest that procaine exerts neuroprotective properties and may serve either as a treatment for AD or as a starting point for the development of novel therapies for AD.

Activation of NR1a/NR2B receptors by soluble factors from APP-stimulated monocyte-derived macrophages: implications for the pathogenesis of Alzheimer's disease

Amyloid-beta peptide (Abeta), the major component of amyloid plaques, can activate brain mononuclear phagocytes (MP; macrophages and microglia), leading to their secretion of neurotoxins. Recent studies strongly suggest that MP-mediated neurotoxicity plays an important role in the pathogenesis of Alzheimer's disease (AD). To further explore this notion, human monocyte-derived macrophages (MDM) were stimulated with naturally secreted alpha-processing soluble amyloid precursor protein/p3 (alphaAPPs/p3) or beta-processing APP/Abeta (betaAPPs/Abeta). MDM conditioned media (MCM) was recovered and tested for its ability to activate recombinant N-methyl-d-aspartate (NMDA) receptor subtype NR1a/NR2B expressed in Xenopus oocytes. Pressure ejection of alphaAPPs/p3- and betaAPPs/Abeta-stimulated MCM produced inward currents of 59.5 +/- 8.9 nA (mean +/- S.E.M., n = 31) and 111.1 +/- 21.0 nA (n = 42) in NR1a/NR2B-expressing oocytes, respectively. The MCM-induced currents were concentration dependent and blocked by 50 microM of the NMDA receptor antagonist 2-amino-5-phosphnovalerate, but not by a non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (20 microM). The alphaAPPs/p3- and betaAPPs/Abeta-stimulated MCM placed in non-injected oocytes failed to generate inward current. These results demonstrate that APPs/Abeta-stimulated MCM directly activate NMDA receptor subtypes relevant in the pathogenesis of AD.

The focality of the global Alzheimer brain process: is the selective vulnerability of neurons a specific phenomenon of primary neuronal pathobiology?

A focality in the development of a global series of predisposing factors that conditions a progressiveness in the neurodegenerative process of Alzheimer type would appear to arise as a specific lesion of the neuron. Such a neuronal lesion would perhaps disrupt functional connectivity of neuronal networks in a process involving loss of neuronal viability. Indeed, a strict concept of selective vulnerability of neurons in the Alzheimer brain might be simply a preconditioning by microenvironmental factors that interacts with the individual neuron in terms of cellular component depletion or in terms of plasmalemmal disruption. In a final analysis, perhaps, the individual neuron would appear as the essential focus of a process that would account for a conditioning globality of the Alzheimer process that promotes both progressiveness and irreversibility of the brain pathology.

Amyloid-β(25–35)-induced memory impairments correlate with cell loss in rat hippocampus

Amyloid beta-peptide (Abeta) plays an important role in the pathophysiology of Alzheimer's disease. The relationship between amnesia induced by central administration of aggregated Abeta(25-35) and neurodegeneration in the hippocampus was investigated. One month after a single intracerebroventricular injection of Abeta(25-35) (15 nmol), male Wistar rats were tested in an eight-arm radial maze. A quantitative evaluation of cell number in hippocampal regions was carried out on H&E-stained brain sections of rats used in the behavioral study. Indices of free radical-mediated processes in the hippocampus were evaluated in additional groups of animals 1, 3, 5, and 30 days after surgery. Abeta(25-35) induced impairments of working and reference memory (RM) as well as neurodegeneration in the CA1 but not in the CA3 field of the hippocampus. A significant correlation between both reference and working memory (WM) impairments and the neuronal cell loss in the hippocampal CA1 region was demonstrated. A gradually developing oxidative stress was evident in the hippocampus of rats treated with Abeta(25-35) as indicated by the increase in 2-thiobarbituric acid (TBARS) reactive substances and superoxide generation. These data suggest the involvement of oxidative stress in Abeta(25-35)-induced neurodegeneration and a relation between memory impairment and neurodegeneration in the CA1 subfield of the hippocampus.

Neonatal handling increases sensitivity to acute neurodegeneration in adult rats

Environmental stimuli during the perinatal period can result in persistent individual differences in neural viability and cognitive functions. Earlier studies have shown that brief daily maternal separation and/or handling of rat pups during the first weeks of life reduces stress reactivity during adulthood and attenuates neuronal loss and cognitive decline during aging. In the present study we examined whether neonatal handling also affects the sensitivity of the adult brain to an acute neurotoxic insult. Postnatally handled and nonhandled control rats were left undisturbed from weaning onwards until the age of 11 months. At this age, the animals were subjected to a neurotoxic challenge by unilateral infusion of 60 mM of the glutamate analogue N-methyl-D-aspartate (NMDA) into the nucleus basalis magnocellularis (NBM). The brains were collected to measure cholinergic cell and fiber loss. In the nonlesioned side of the brain, cholinergic cell number in the NBM and fiber density in the cortex were not different between postnatally handled and control rats. However, in the lesioned hemisphere handled animals exhibited a significantly higher loss of choline-acetyltransferase-immunoreactive and acetylcholinesterase-positive fibers in the somatosensory cortex. The present results provide evidence for an enhanced vulnerability of postnatally handled rats to acute neurodegeneration in contrast to the previously reported attenuation of spontaneous aging-related neurodegenerative processes.

Association between antioxidant nutritional indicators and the incidence of dementia: results from the PAQUID prospective cohort study

OBJECTIVE

To analyse the relation between antioxidant vitamins A, E, and malondialdehyde (MDA) lipoperoxidation product plasma concentrations with incident dementia.

DESIGN

: A nested case-control within the PAQUID (Personnes Agées QUID) cohort.

SETTING

The PAQUID population-based prospective cohort in southwestern France.

SUBJECTS

Among 626 subjects with blood collection at baseline, 46 developed a dementia during the follow-up and were considered to be cases. Each case was matched (on age and sex) to three controls.

RESULTS

Plasma vitamin E concentrations were lower among cases (mean value at 22.62 micromol/l (s.d.: 7.38) vs 24.99 (s.d.: 6.73 among controls). The same trend was observed for vitamin A concentrations, but the difference was not significant. On the contrary, MDA concentrations tended to be higher (mean value 1.35 micromol/l (s.d.: 0.53) vs 1.23 (s.d.: 0.44)) among cases. In logistic regression models, plasma values were split into tertiles. Adjusted for confounders, the risk of dementia was significantly increased in the lowest vitamin E tertile (< or =21.0 micromol/l) (OR=3.12, P=0.033) compared to the highest one (> or =25.5 micromol/l). The risk of Alzheimer's disease was also increased, with borderline significance (OR=3.06, P=0.053). Risks associated with vitamin A were nonsignificant. Similarly, there was a trend to an increased risk of dementia in the highest tertile of MDA (OR=1.67, P=0.31).

CONCLUSIONS

These results suggest that subjects with low plasma vitamin E concentrations are at a higher risk of developing a dementia in subsequent years.

Single intracerebroventricular administration of amyloid-beta (25-35) peptide induces impairment in short-term rather than long-term memory in rats

Ample experimental evidence indicates that intracerebral injection or infusion of amyloid-beta peptides (Abeta) to rodents induces learning and memory impairments as well as neurodegeneration in brain areas related to cognitive function. In the present study, we assessed the effects of a single intracerebroventricular (i.c.v.) injection of aggregated Abeta fragment (25-35) at a dose of 15nmol/rat on short-term and long-term memory in rats during the 6-month post-surgery period. The results demonstrate that Abeta(25-35)-induced memory impairments in spontaneous alternation behavior in a Y-maze at 17, 36, and 180 days after the surgery as well as in a social recognition task 110 days post-surgery. Abeta(25-35) also impaired spatial memory in an 8-arm radial maze, but did not influence performance of the step-down passive avoidance task. These results suggest that Abeta(25-35) preferably induces impairments of spatial and non-spatial short-term (working) memory rather than long-term memory in rats.

Functional recovery of cholinergic basal forebrain neurons under disease conditions: old problems, new solutions?

Recognition of the involvement of cholinergic neurons in the modulation of cognitive functions and their severe dysfunction in neurodegenerative disorders, such as Alzheimer's disease, initiated immense research efforts aimed at unveiling the anatomical organization and cellular characteristics of the basal forebrain (BFB) cholinergic system. Concomitant with our unfolding knowledge about the structural and functional complexity of the BFB cholinergic projection system, multiple pharmacological strategies were introduced to rescue cholinergic nerve cells from noxious attacks; however, a therapeutic breakthrough is still awaited. In this review, we collected recent findings that significantly contributed to our better understanding of cholinergic functions under disease conditions, and to the design of effective means to restore lost or damaged cholinergic functions. To this end, we first provide a brief survey of the neuroanatomical organization of BFB nuclei with emphasis on major evolutionary differences among mammalian species, in particular rodents and primates, and discuss limitations of the translation of experimental data to human therapeutic applications. Subsequently, we summarize the involvement of cholinergic dysfunction in the pathogenesis of severe neurological conditions, including stroke, traumatic brain injury, virus encephalitis and Alzheimer's disease, and emphasize the critical role of pro-inflammatory cytokines as common mediators of cholinergic neuronal damage. Moreover, we review leading functional concepts on the limited recovery of cholinergic neurons and their impaired plastic re-modeling, as well as on the hampered interplay of the ascending cholinergic and monoaminergic projection systems under neurodegenerative conditions. In addition, recent advances in the dynamic labeling of living cholinergic neurons by fluorochromated antibodies, referred to as in vivo labeling, and novel neuroimaging approaches as potential diagnostic tools of progressive cholinergic decline are surveyed. Finally, the potential of cell replacement strategies using embryonic and adult stem cells, and multipotent neural progenitors, as a means to recover damaged cholinergic functions, is discussed.

Involvement of oxidative stress in the enhancement of acetylcholinesterase activity induced by amyloid beta-peptide

Acetylcholinesterase (AChE) activity is increased within and around amyloid plaques, which are present in Alzheimer's disease (AD) patient's brain. In this study, using cultured retinal cells as a neuronal model, we analyzed the effect of the synthetic peptide Abeta(25-35) on the activity of AChE, the degradation enzyme of acetylcholine, as well as the involvement of oxidative stress in this process. The activity of AChE was increased when retinal cells were incubated with Abeta(25-35) (25 microM, 24 h) and antioxidants such as alpha-tocopherol acetate and nitric oxide synthase (NOS) inhibitors were capable of preventing this effect. Despite Abeta(25-35) did not affect cell membrane integrity, the redox capacity of cells decreased. The incubation with this amyloidogenic peptide led to an increment of reactive oxygen species formation (20%), of lipid peroxidation (65%), and basal intracellular calcium levels (40%). The data obtained show that the enhancement of AChE activity induced by Abeta(25-35) is mediated by oxidative stress, and that vitamin E and NOS inhibitors, by preventing the compromise of the enzyme activity, can have an important role in the maintenance of acetylcholine synaptic levels, thus preventing or improving cognitive and memory functions of AD patients.

Effects of tumor necrosis factor-alpha central administration on hippocampal damage in rat induced by amyloid beta-peptide (25-35)

Male Wistar rats received unilateral intrahippocampal injections of 3 nmol (3.18 microg) aggregated Abeta(25-35), intracerebroventricular bilateral injections of 0.5 microg human recombinant TNFalpha or both (Abeta(25-35) + TNFalpha-treated animals). Seven days after the surgery brain sections were stained with cresyl violet (Nissl), for fragmented DNA (TUNEL), glial fibrillar acidic protein (GFAP) and isolectin B4-reactive microglia. In addition, caspase-3 activity in brain regions was measured fluorometrically. The morphology of the hippocampus after the injection of Abeta(25-35) or both Abeta(25-35) and TNFalpha (but not TNFalpha alone) showed cell loss in the CA1 pyramidal cell layer. The extension of neuronal degeneration measured in the CA1 field was significantly larger in Abeta(25-35)-treated groups compared to the contralateral hemisphere of both vehicle-treated controls and animals injected with TNFalpha alone. TNFalpha augmented the Abeta(25-35)-induced damage, significantly increasing the extension of degenerating area. Administration of Abeta(25-35) caused reactive gliosis in the ipsilateral hemisphere as demonstrated by upregulation of GFAP expression and the presence of hypertrophic astrocytes in the hippocampus. This effect was much more prominent in the hippocampi of rats treated with Abeta(25-35) + TNFalpha but absent after administration of TNFalpha alone. In both Abeta(25-35)-treated groups, the damaged area of the hippocampal CA1 field and lateral band of dentate gyrus displayed many darkly stained round isolectin B4-positive phagocyte-like microglial cells. Sparse TUNEL-positive nuclei were found in the hippocampi of rats treated with Abeta(25-35) alone or together with TNFalpha, but not in the control brain sections or in brain sections of TNFalpha-injected animals. The activity of caspase-3 increased significantly in the ipsilateral hippocampus after the injection of Abeta(25-35). Surprisingly, administration of TNFalpha into the cerebral ventricles prevented this Abeta(25-35)-induced increase in hippocampal caspase-3 activity. The results are discussed from the perspective of dual (neuroprotective and neurodestructive) roles of TNF in the brain.

Amyloid beta-peptide 25-35 reduces [3H]acetylcholine release in retinal neurons. Involvement of metabolic dysfunction

Cholinergic pathways serve important functions in learning and memory processes. The loss of basal forebrain cholinergic neurons and the presence of senile plaques composed by amyloid beta-peptide (A beta) are found in post-mortem brains of Alzheimer's disease (AD) patients. However, the role of A beta in the cholinergic dysfunction observed in AD is not yet clarified. In this study, we observed that the release of [3H]acetylcholine evoked by K(+)-depolarization was significantly lower in cells treated with A beta 25-35 peptide, than in untreated cells or in cells exposed to the reverse sequence peptide A beta 35-25. The levels of pyruvate, the substrate for pyruvate dehydrogenase, the enzyme involved in acetyl coenzyme A synthesis in the brain, which is rate-limiting for the synthesis of acetylcholine, were significantly decreased, about 40%, in A beta treated cells. A beta 25-35 did not affect choline acetyltransferase activity or [3H]choline uptake. 2-[3H]-deoxyglucose uptake was decreased when cells were exposed to A beta 25-35 or to A beta 1-40. Taken together these data suggest that an impairment of glycolysis, and the consequent decrease in pyruvate levels, may be responsible for the decrement of acetylcholine release observed in A beta treated cells, thus sustaining the hypothesis that the cholinergic dysfunction, observed in AD patients, might be associated with extracellular A beta accumulation.

Alzheimer's disease and the basal forebrain cholinergic system: relations to beta-amyloid peptides, cognition, and treatment strategies

Alzheimer's disease (AD) is the most common form of degenerative dementia and is characterized by progressive impairment in cognitive function during mid- to late-adult life. Brains from AD patients show several distinct neuropathological features, including extracellular beta-amyloid-containing plaques, intracellular neurofibrillary tangles composed of abnormally phosphorylated tau, and degeneration of cholinergic neurons of the basal forebrain. In this review, we will present evidence implicating involvement of the basal forebrain cholinergic system in AD pathogenesis and its accompanying cognitive deficits. We will initially discuss recent results indicating a link between cholinergic mechanisms and the pathogenic events that characterize AD, notably amyloid-beta peptides. Following this, animal models of dementia will be discussed in light of the relationship between basal forebrain cholinergic hypofunction and cognitive impairments in AD. Finally, past, present, and future treatment strategies aimed at alleviating the cognitive symptomatology of AD by improving basal forebrain cholinergic function will be addressed.

Antiamnesic effects of azaindolizinone derivative ZSET845 on impaired learning and decreased ChAT activity induced by amyloid-beta 25-35 in the rat

Antiamnesic effects of a newly synthesized azaindolizinone derivative ZSET845 were assessed in rats made learning ability deficient by amyloid-beta (Abeta)25-35 treatment. Intracerebroventricular injection of Abeta25-35 induced a marked decrease in step-through latency in passive avoidance task and reduction in choline acetyltransferase (ChAT) activity in the medial septum and hippocampus, but not in the basal forebrain and cortex. The number of ChAT-immunoreactive cells was decreased in the medial septum. Oral administration of ZSET845 at a dose of 1 or 10 mg/kg ameliorated learning impairment in passive avoidance task and enhanced ChAT activity in the basal forebrain, medial septum and hippocampus, and increased in the number of ChAT-immunoreactive cells in the medial septum in Abeta-treated rats to the levels of vehicle-injected control rats. These results suggest that ZSET845 is worth testing for further preclinical study aimed for the treatment of senile dementia such as Alzheimer's disease.

Amyloid beta-peptide induces cholinergic dysfunction and cognitive deficits: a minireview

Amyloid beta-peptide (Abeta) plays a critical role in the development of Alzheimer's disease (AD). Much progress has been made in understanding this age-related neurodegenerative disorder, thus an insight into the cellular actions of Abeta and resulting functional consequences may contribute to preventive and therapeutic approaches for AD. In this review, recent evidence of Abeta-induced brain dysfunction, particularly of cholinergic impairment and memory deficits is summarized. Moreover, proposed mechanisms for Abeta-induced neurotoxicity such as oxidative stress, ion-channel formation, and Abeta-receptor interaction are discussed.

Oral post-lesion administration of 5-HT(1A) receptor agonist repinotan hydrochloride (BAY x 3702) attenuates NMDA-induced delayed neuronal death in rat magnocellular nucleus basalis

Recent evidence indicates that stimulation of postsynaptic 5-HT(1A) receptors abates excitotoxic neuronal death. Here we investigated whether oral post-lesion administration of the 5-HT(1A) receptor agonist (-)-(R)-2-[4-[[(3,4-dihydro-2H-1-benzopyran-2-yl)methyl]amino]butyl]-1,2-benzisothiazol-3(2H)-one 1,1-dioxide monohydrochloride (Repinotan HCl) attenuates N-methyl-D-aspartate (NMDA) excitotoxicity (60 nmol/microl) in the rat magnocellular nucleus basalis. Repinotan HCl (1 mg/kg) was administered from day 1, 2, 3, or 6 post-surgery twice daily for five consecutive days. This delayed drug administration protocol was employed to investigate the initiation period during which 5-HT(1A) receptor agonists may significantly influence ongoing neurodegeneration processes. 8-Hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, 1 mg/kg) served as reference compound. Twenty-four hours after drug delivery a small open-field test, while on day 14 post-surgery a passive avoidance test was performed. Effects of Repinotan HCl treatment on the survival of cholinergic magnocellular nucleus basalis neurons and their cortical projections were determined by quantitative acetylcholinesterase (AChE) and choline-acetyltransferase (ChAT) histochemistry. Moreover, AChE and ChAT activities were biochemically measured both in the cerebral cortex and in the magnocellular nucleus basalis. Repinotan HCl treatment markedly increased spontaneous activities in the small open-field at any time-point investigated. Improved memory performance was only demonstrated when Repinotan HCl was administered from day 1 post-lesion on wards. Repinotan HCl treatment from day 2 and 3 post-lesion on markedly attenuated both histochemical and neurochemical characteristics of NMDA excitotoxicity on cholinergic magnocellular nucleus basalis neurons and on their cortical projections. Whereas the neuroprotective profile of Repinotan HCl was superior to that of 8-OH-DPAT, oral administration of both 5-HT(1A) receptor agonists yielded largely equivalent behavioral recovery after NMDA infusion in the magnocellular nucleus basalis. In conclusion, the present data indicate the potent neuroprotective action of the 5-HT(1A) receptor agonist Repinotan HCl with a peak efficacy of delayed (2-3 day) post-lesion drug treatment in vivo. Post-lesion treatment with 5-HT(1A) receptor agonists may therefore be of significance in the intervention of neuronal damage associated with acute excitotoxic conditions.