Considerations for the assessment of suicidal ideation and behavior in older adults with cognitive decline and dementia.

INTRODUCTION: Better understanding of suicide risk and its management in older adults with cognitive impairment and/or dementia remain significant unmet public health needs. Urgency to address them derives from concern that CNS treatments for dementia may impact suicide risk. Regulatory guidances requiring assessment of emergent suicidal ideation and behavior (SI/SB) at every clinical trial visit emphasize the need for understanding their prevalence. METHODS: The literature regarding SI/SB in older persons with cognitive impairment or dementia was reviewed by an Alzheimer's Association Taskforce with emphasis on epidemiology, classification, assessment, and regulatory requirements. RESULTS: Gaps in our knowledge were identified, challenges discussed and recommendations for future work provided. DISCUSSION: Currently available SI/SB data from geriatric persons with dementia do not provide adequate understanding of its epidemiology, identification, assessment, or management. The growing public health burden of this population requires greater attention from clinicians and researchers on tactics and assessment tools to meet these needs.

Suicidal ideation and behavior assessment in dementia studies: An Internet survey.

INTRODUCTION: The AARR task force on suicidal ideation and behavior (SI/SB) in dementia conducted an online survey on the extent of SI/SB in individuals diagnosed with mild cognitive impairment (MCI) or dementia who were participating in clinical trials. METHODS: Investigators with experience in conducting SI/SB assessments in clinical trial subjects with MCI or dementia were invited to complete a global 19-item online survey. RESULTS: A total of 204 evaluable responses were collected with the majority from North America and Europe (83.4%) and the remainder from Asia, Latin America, and Mideast/Africa. The mean (SD) number of subjects personally assessed by the respondents in the past year with MCI, mild-moderate dementia, or severe dementia was 12.8 (26.2), 31.2 (39.6), and 10.1 (34.7), respectively. The mean number of subjects in each diagnostic group with suicidal ideation (SI), suicidal behavior (SB), or completed suicide (CS) was on average quite low (0.3 to 1.1 for SI, 0.1 to 0.2 for SB, and 0.0 to 0.2 for CS). Confidence in subject self-reports of SI/SB over different time periods declined with increasing severity of cognitive impairment and with increasing duration of the recall time period assessed. Of respondents, 56% and 75% had low confidence in self-ratings of SI/SB from subjects with severe dementia over the past 24 hours and the past week to 1 month, respectively. Ratings of the reliability of information collected on SI/SB also decreased with increasing severity of cognitive impairment. Approximately 70% of respondents rated the reliability of the information they obtained from all sources (patient, caregiver, and others) for subjects with MCI as high, but only about half (42.0% to 55.3%) and less than a quarter (17.4% to 24.3%) rated the reliability of information obtained for subjects with mild to moderate dementia or severe dementia as high, respectively. DISCUSSION: These results support the usefulness of prospective SI/SB assessments in MCI and mild dementia, raise questions about the reliability of assessments in moderate dementia, and confirm their lack of clinical utility in severe dementia. The results highlight the need for development of validated assessment instruments adapted to the stage of cognitive decline of the patients under study and may be the most effective in the earliest stages of the disease.

Update on appropriate use criteria for amyloid PET imaging: dementia experts, mild cognitive impairment, and education. Amyloid Imaging Task Force of the Alzheimer's Association and Society for Nuclear Medicine and Molecular Imaging.

Amyloid PET imaging is a novel diagnostic test that can detect in living humans one of the two defining pathologic lesions of Alzheimer disease, amyloid-ß deposition in the brain. The Amyloid Imaging Task Force of the Alzheimer's Association and Society for Nuclear Medicine and Molecular Imaging previously published appropriate use criteria for amyloid PET as an important tool for increasing the certainty of a diagnosis of Alzheimer disease in specific patient populations. Here, the task force further clarifies and expands 3 topics discussed in the original paper: first, defining dementia experts and their use of proper documentation to demonstrate the medical necessity of an amyloid PET scan; second, identifying a specific subset of individuals with mild cognitive impairment for whom an amyloid PET scan is appropriate; and finally, developing educational programs to increase awareness of the amyloid PET appropriate use criteria and providing instructions on how this test should be used in the clinical decision-making process.

Update on appropriate use criteria for amyloid PET imaging: dementia experts, mild cognitive impairment, and education.

Amyloid PET imaging is a novel diagnostic test that can detect in living humans one of the two defining pathologic lesions of Alzheimer disease, amyloid-ß deposition in the brain. The Amyloid Imaging Task Force of the Alzheimer's Association and Society for Nuclear Medicine and Molecular Imaging previously published appropriate use criteria for amyloid PET as an important tool for increasing the certainty of a diagnosis of Alzheimer disease in specific patient populations. Here, the task force further clarifies and expands 3 topics discussed in the original paper: first, defining dementia experts and their use of proper documentation to demonstrate the medical necessity of an amyloid PET scan; second, identifying a specific subset of individuals with mild cognitive impairment for whom an amyloid PET scan is appropriate; and finally, developing educational programs to increase awareness of the amyloid PET appropriate use criteria and providing instructions on how this test should be used in the clinical decision-making process.

Can we prevent Alzheimer's disease? Secondary "prevention" trials in Alzheimer's disease.

Current research including the basic biology of Alzheimer's disease (AD) provides a foundation to explore whether our current state of knowledge is sufficient to initiate prevention studies and allow us to believe prevention of AD is possible. Current research and recently revised criteria for the diagnosis of AD by the National Institutes on Aging and the Alzheimer's Association suggest a continuum of disease from preclinical asymptomatic to symptomatic Alzheimer's dementia. In light of these revised criteria, the possibility of secondary prevention and even primary prevention is under discussion. The Alzheimer's Association Research Roundtable convened a meeting to discuss the rationale and feasibility of conducting secondary prevention trials in AD.

Appropriate use criteria for amyloid PET: a report of the Amyloid Imaging Task Force, the Society of Nuclear Medicine and Molecular Imaging, and the Alzheimer's Association.

Positron emission tomography (PET) of brain amyloid ß is a technology that is becoming more available, but its clinical utility in medical practice requires careful definition. To provide guidance to dementia care practitioners, patients, and caregivers, the Alzheimer's Association and the Society of Nuclear Medicine and Molecular Imaging convened the Amyloid Imaging Taskforce (AIT). The AIT considered a broad range of specific clinical scenarios in which amyloid PET could potentially be used appropriately. Peer-reviewed, published literature was searched to ascertain available evidence relevant to these scenarios, and the AIT developed a consensus of expert opinion. Although empirical evidence of impact on clinical outcomes is not yet available, a set of specific appropriate use criteria (AUC) were agreed on that define the types of patients and clinical circumstances in which amyloid PET could be used. Both appropriate and inappropriate uses were considered and formulated, and are reported and discussed here. Because both dementia care and amyloid PET technology are in active development, these AUC will require periodic reassessment. Future research directions are also outlined, including diagnostic utility and patient-centered outcomes.

Appropriate use criteria for amyloid PET: a report of the Amyloid Imaging Task Force, the Society of Nuclear Medicine and Molecular Imaging, and the Alzheimer's Association.

Positron emission tomography (PET) of brain amyloid b is a technology that is becoming more available, but its clinical utility in medical practice requires careful definition. To provide guidance to dementia care practitioners, patients, and caregivers, the Alzheimer's Association and the Society of Nuclear Medicine and Molecular Imaging convened the Amyloid Imaging Taskforce (AIT). The AIT considered a broad range of specific clinical scenarios in which amyloid PET could potentially be used appropriately. Peer-reviewed, published literature was searched to ascertain available evidence relevant to these scenarios, and the AIT developed a consensus of expert opinion. Although empirical evidence of impact on clinical outcomes is not yet available, a set of specific appropriate use criteria (AUC) were agreed on that define the types of patients and clinical circumstances in which amyloid PET could be used. Both appropriate and inappropriate uses were considered and formulated,and are reported and discussed here. Because both dementia care and amyloid PET technology are in active development, these AUC will require periodic reassessment. Future research directions are also outlined, including diagnostic utility and patient-centered outcomes.

Intraneuronal Aß detection in 5xFAD mice by a new Aß-specific antibody.

BACKGROUND: The form(s) of amyloid-ß peptide (Aß) associated with the pathology characteristic of Alzheimer's disease (AD) remains unclear. In particular, the neurotoxicity of intraneuronal Aß accumulation is an issue of considerable controversy; even the existence of Aß deposits within neurons has recently been challenged by Winton and co-workers. These authors purport that it is actually intraneuronal APP that is being detected by antibodies thought to be specific for Aß. To further address this issue, an anti-Aß antibody was developed (MOAB-2) that specifically detects Aß, but not APP. This antibody allows for the further evaluation of the early accumulation of intraneuronal Aß in transgenic mice with increased levels of human Aß in 5xFAD and 3xTg mice. RESULTS: MOAB-2 (mouse IgG2b) is a pan-specific, high-titer antibody to Aß residues 1-4 as demonstrated by biochemical and immunohistochemical analyses (IHC), particularly compared to 6E10 (a commonly used commercial antibody to Aß residues 3-8). MOAB-2 did not detect APP or APP-CTFs in cell culture media/lysates (HEK-APPSwe or HEK-APPSwe/BACE1) or in brain homogenates from transgenic mice expressing 5 familial AD (FAD) mutation (5xFAD mice). Using IHC on 5xFAD brain tissue, MOAB-2 immunoreactivity co-localized with C-terminal antibodies specific for Aß40 and Aß42. MOAB-2 did not co-localize with either N- or C-terminal antibodies to APP. In addition, no MOAB-2-immunoreactivity was observed in the brains of 5xFAD/BACE-/- mice, although significant amounts of APP were detected by N- and C-terminal antibodies to APP, as well as by 6E10. In both 5xFAD and 3xTg mouse brain tissue, MOAB-2 co-localized with cathepsin-D, a marker for acidic organelles, further evidence for intraneuronal Aß, distinct from Aß associated with the cell membrane. MOAB-2 demonstrated strong intraneuronal and extra-cellular immunoreactivity in 5xFAD and 3xTg mouse brain tissues. CONCLUSIONS: Both intraneuronal Aß accumulation and extracellular Aß deposition was demonstrated in 5xFAD mice and 3xTg mice with MOAB-2, an antibody that will help differentiate intracellular Aß from APP. However, further investigation is required to determine whether a molecular mechanism links the presence of intraneuronal Aß with neurotoxicity. As well, understanding the relevance of these observations to human AD patients is critical.

Endogenous galanin protects mouse hippocampal neurons against amyloid toxicity in vitro via activation of galanin receptor-2.

Expression of the neuropeptide galanin is known to be upregulated in the brain of patients with Alzheimer's disease (AD). We and others have shown that galanin plays a neuroprotective role in a number of excitotoxic injury paradigms, mediated by activation of the second galanin receptor subtype (GAL2). In the present study, we investigated whether galanin/GAL2 plays a similar protective role against amyloid-ß(Aß) toxicity. Here we report that galanin or the GAL2/3-specific peptide agonist Gal2-11, both equally protect primary dispersed mouse wildtype (WT) neonatal hippocampal neurons from 250 nM Aß1-42 toxicity in a dose dependent manner. The amount of Aß1-42 induced cell death was significantly greater in mice with loss-of-function mutations in galanin (Gal-KO) or GAL2 (GAL2-MUT) compared to strain-matched WT controls. Conversely, cell death was significantly reduced in galanin over-expressing (Gal-OE) transgenic mice compared to strain-matched WT controls. Exogenous galanin or Gal2-11 rescued the deficits in the Gal-KO but not the GAL2-MUT cultures, confirming that the protective effects of endogenous or exogenous galanin are mediated by activation of GAL2. Despite the high levels of endogenous galanin in the Gal-OE cultures, the addition of exogenous 100 nM or 50 nM galanin or 100 nM Gal2-11 further significantly reduced cell death, implying that GAL2-mediated neuroprotection is not at maximum in the Gal-OE mice. These data further support the hypothesis that galanin over-expression in AD is a neuroprotective response and imply that the development of a drug-like GAL2 agonist might reduce the progression of symptoms in patients with AD.

Preparation and characterization of toxic Abeta aggregates for structural and functional studies in Alzheimer's disease research.

The amyloid cascade hypothesis, supported by strong evidence from genetics, pathology and studies using animal models, implicates amyloid-beta (Abeta) oligomerization and fibrillogenesis as central causative events in the pathogenesis of Alzheimer's disease (AD). Today, significant efforts in academia, biotechnology and the pharmaceutical industry are devoted to identifying the mechanisms by which the process of Abeta aggregation contributes to neurodegeneration in AD and to the identity of the toxic Abeta species. In this paper, we describe methods and detailed protocols for reproducibly preparing Abeta aggregates of defined size distribution and morphology, including monomers, protofibrils and fibrils, using size exclusion chromatography. In addition, we describe detailed biophysical procedures for elucidating the structural features, aggregation kinetics and toxic properties of the different Abeta aggregation states, with special emphasis on protofibrillar intermediates. The information provided by this approach allows for consistent correlation between the properties of the aggregates and their toxicity toward primary neurons and/or cell lines. A better understanding of the molecular and structural basis of Abeta aggregation and toxicity is crucial for the development of effective strategies aimed at prevention and/or treatment of AD. Furthermore, the identification of specific aggregation states, which correlate with neurodegeneration in AD, could lead to the development of diagnostic tools to detect and monitor disease progression. The procedures described can be performed in as little as 1 day, or may take longer, depending on the exact toxicity assays used.

Transgenerational rescue of a genetic defect in long-term potentiation and memory formation by juvenile enrichment.

The idea that qualities acquired from experience can be transmitted to future offspring has long been considered incompatible with current understanding of genetics. However, the recent documentation of non-Mendelian transgenerational inheritance makes such a "Lamarckian"-like phenomenon more plausible. Here, we demonstrate that exposure of 15-d-old mice to 2 weeks of an enriched environment (EE), that includes exposure to novel objects, elevated social interactions and voluntary exercise, enhances long-term potentiation (LTP) not only in these enriched mice but also in their future offspring through early adolescence, even if the offspring never experience EE. In both generations, LTP induction is augmented by a newly appearing cAMP/p38 MAP kinase-dependent signaling cascade. Strikingly, defective LTP and contextual fear conditioning memory normally associated with ras-grf knock-out mice are both masked in the offspring of enriched mutant parents. The transgenerational transmission of this effect occurs from the enriched mother to her offspring during embryogenesis. If a similar phenomenon occurs in humans, the effectiveness of one's memory during adolescence, particularly in those with defective cell signaling mechanisms that control memory, can be influenced by environmental stimulation experienced by one's mother during her youth.

Transglutaminase induces protofibril-like amyloid beta-protein assemblies that are protease-resistant and inhibit long-term potentiation.

An increasing body of evidence suggests that soluble assemblies of amyloid beta-protein (Abeta) play an important role in the initiation of Alzheimer disease (AD). In vitro studies have found that synthetic Abeta can form soluble aggregates through self-assembly, but this process requires Abeta concentrations 100- to 1000-fold greater than physiological levels. Tissue transglutaminase (TGase) has been implicated in neurodegeneration and can cross-link Abeta. Here we show that TGase induces rapid aggregation of Abeta within 0.5-30 min, which was not observed with chemical cross-linkers. Both Abeta40 and Abeta42 are good substrates for TGase but show different aggregation patterns. Guinea pig and human TGase induced similar Abeta aggregation patterns, and oligomerization was observed with Abeta40 concentrations as low as 50 nm. The formed Abeta40 species range from 5 to 6 nm spheres to curvilinear structures of the same width, but up to 100 nm in length, that resemble the previously described self-assembled Abeta protofibrils. TGase-induced Abeta40 assemblies are resistant to a 1-h incubation with either neprilysin or insulin degrading enzyme, whereas the monomer is rapidly degraded by both proteases. In support of these species being pathological, TGase-induced Abeta40 assemblies (100 nm) inhibited long term potentiation recorded in the CA1 region of mouse hippocampus slices. Our data suggest that TGase can contribute to AD by initiating Abeta oligomerization and aggregation at physiological levels, by reducing the clearance of Abeta due to the generation of protease-resistant Abeta species, and by forming Abeta assemblies that inhibit processes involved in memory and learning. Our data suggest that TGase might constitute a specific therapeutic target for slowing or blocking the progression of AD.

Selective inhibition of NF-kappaB activation prevents dopaminergic neuronal loss in a mouse model of Parkinson's disease.

Parkinson's disease (PD) is the second most common neurodegenerative disorder. Despite intense investigations, no effective therapy is available to stop its onset or halt its progression. The present study evaluates the ability of peptide corresponding to the NF-kappaB essential modifier-binding domain (NBD) of IkappaB kinase alpha (IKKalpha) or IKKbeta to prevent nigrostriatal degeneration in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD and establish a role for NF-kappaB in human parkinsonism. First, we found that NF-kappaB was activated within the substantia nigra pars compacta of PD patients and MPTP-intoxicated mice. However, i.p. injection of wild-type NBD peptide reduced nigral activation of NF-kappaB, suppressed nigral microglial activation, protected both the nigrostriatal axis and neurotransmitters, and improved motor functions in MPTP-intoxicated mice. These findings were specific because mutated NBD peptide had no effect. We conclude that selective inhibition of NF-kappaB activation by NBD peptide may be of therapeutic benefit for PD patients.

A brief, but repeated, swimming protocol is sufficient to overcome amyloid beta-protein inhibition of hippocampal long-term potentiation.

Alzheimer's disease starts as an almost imperceptible malady, first observed clinically as a mild memory problem. Accumulating genetic and biochemical data have suggested that amyloid beta-protein (Abeta) plays an important role in this memory loss, and Abeta has been shown to suppress long-term potentiation (LTP), a cellular model for memory and learning. Here we show that a very brief (3 min) swimming, twice daily for 2 weeks, rescues LTP inhibition in the CA1 region of hippocampal slices caused by Abeta(42) or Abeta(40) carrying the Arctic mutation using a theta burst stimulation (TBS) protocol. Whereas the input-output curve was not affected, the paired-pulse ratio was reduced in mice receiving our repeated swimming protocol, suggesting a possible involvement of presynaptic facilitation. Similar to swimming, Abeta's inhibition of LTP could be rescued with the adenylyl cyclase, forskolin. Interestingly, this swimming protocol produced conditions in which a weak-TBS could invoke LTP not observed in naïve mice, which again was mimicked by forskolin. In contrast, the protein kinase A (PKA) inhibitor, H89, blocked both the forskolin and swimming potentiation of LTP; these data implicate cAMP/PKA signaling in the protective effect of swimming and mediating Abeta' detrimental effects. Our data add a new simple behavior paradigm that shows the importance of an environmental factor in reversing the pathophysiological effects of Abeta, and suggest new therapeutic avenues.

Gemfibrozil ameliorates relapsing-remitting experimental autoimmune encephalomyelitis independent of peroxisome proliferator-activated receptor-alpha.

The present study underlines the importance of gemfibrozil, a lipid-lowering drug and an activator of peroxisome proliferator-activated receptor-alpha (PPAR-alpha), in inhibiting the disease process of adoptively transferred experimental allergic encephalomyelitis (EAE), an animal model of relapsing-remitting multiple sclerosis. Clinical symptoms of EAE, infiltration of mononuclear cells, and demyelination were significantly lower in SJL/J female mice receiving gemfibrozil through food chow than those without gemfibrozil. It is noteworthy that the drug was equally effective in treating EAE in PPAR-alpha wild-type as well as knockout mice. Gemfibrozil also inhibited the encephalitogenicity of MBP-primed T cells and switched the immune response from a Th1 to a Th2 profile independent of PPAR-alpha. Gemfibrozil consistently inhibited the expression and DNA-binding activity of T-bet, a key regulator of interferon-gamma (IFN-gamma) expression and stimulated the expression and DNA-binding activity of GATA3, a key regulator of IL-4. Gemfibrozil treatment decreased the number of T-bet-positive T cells and increased the number of GATA3-positive T cells in spleen of donor mice. The histological and immunohistochemical analyses also demonstrate the inhibitory effect of gemfibrozil on the invasion of T-bet-positive T cells into the spinal cord of EAE mice. Furthermore, we demonstrate that the differential effect of gemfibrozil on the expression of T-bet and GATA3 was due to its inhibitory effect on NO production. Although excess NO favored the expression of T-bet, scavenging of NO stimulated the expression of GATA-3. Taken together, our results suggest gemfibrozil, an approved drug for hyperlipidemia in humans, may find further therapeutic use in multiple sclerosis.

The environment versus genetics in controlling the contribution of MAP kinases to synaptic plasticity.

BACKGROUND: A challenge in biomedical research is to design experimental paradigms that reflect a natural setting. Even when freshly isolated tissues are used, they are almost always derived from animals housed in cages that poorly reflect the animal's native environment. This issue is highlighted by studies on brain function, where mice housed in a more natural "enriched environment" display enhanced learning and memory and delayed onset of symptoms of neurodegenerative diseases compared to mice housed conventionally. How the environment mediates its effects on brain function is poorly understood. RESULTS: We show that after exposure of adolescent mice to an "enriched environment," the induction of long-term potentiation (LTP), a form of synaptic plasticity that is thought to contribute to learning and memory, involves a novel signal transduction pathway that is nonfunctional in comparable mice housed conventionally. This environmentally gated signaling pathway, which rescues defective LTP induction in adolescent Ras-GRF knockout mice, consists of NMDA glutamate receptor activation of p38, a MAP kinase that does not contribute to LTP in mice housed conventionally. Interestingly, the same exposure to environmental enrichment does not have this effect in adult mice. CONCLUSIONS: This study reveals a new level of cell signaling control whereby environmental factors gate the efficacy of a specific signaling cascade to control how LTP is induced in adolescent animals. The suppression of this gating mechanism in mature animals represents a new form of age-dependent decline in brain plasticity.

Interleukin-1alpha stimulates non-amyloidogenic pathway by alpha-secretase (ADAM-10 and ADAM-17) cleavage of APP in human astrocytic cells involving p38 MAP kinase.

Interleukin-1alpha (IL-1alpha) stimulates a disintegrin and metalloproteinase, ADAM-17 synthesis, consistent with activation of the soluble fragment of Amyloid Precursor Protein, APP, (sAPPalpha) in human primary astrocytes. To characterize the mechanism by which IL-1alpha promotes the non-amyloidogenic pathway of APP metabolism, we used U373 MG astrocytoma cells. IL-1alpha significantly increased levels of ADAM-10 and ADAM-17 mRNA in 16 hr. Upregulation of ADAM-17 mRNA by IL-1alpha was more pronounced despite higher basal levels of ADAM-10 mRNA. This pattern was also observed at the protein level with the upregulation of alpha-secretase. RNA interference (RNAi) of ADAM-10 and ADAM-17 inhibited IL-1alpha-stimulated sAPPalpha release and the effect was more pronounced with ADAM-17 RNAi. Concomitantly, the level of sAPPalpha was significantly increased by IL-1alpha in 48 hr; however, IL-1alpha stimulated cell-associated APP levels maximally at 6 h but the induction declined at 48 hr. IL-1alpha treatment of cells for 48 h reduced both intracellular and secreted levels of amyloid-beta, Abeta-40, and Abeta-42 peptides. Multiple MAP kinases (MAPK), including MEK/ERK, p38 kinase, PI3 kinase (PI3K) but not JNK were involved in the regulation of IL-1alpha-stimulated alpha-secretase activity and sAPPalpha release. p38 MAPK seems to be the most proximal of these MAPKs, as it was the earliest to be activated by IL-1alpha and blocking this pathway attenuated activation of IL-1alpha-induced MEK and PI3K pathways. Our data show a complex mechanism of sAPPalpha regulation by IL-1alpha that involves ADAM-10, ADAM-17 and p38 MAPK upstream of MEK and PI3K.

Distinct roles for Ras-guanine nucleotide-releasing factor 1 (Ras-GRF1) and Ras-GRF2 in the induction of long-term potentiation and long-term depression.

NMDA-type glutamate receptors (NMDARs) contribute to many forms of long-term potentiation (LTP) and long-term depression (LTD). NMDARs are heteromers containing calcium-permeating neuronal receptor 1 (NR1) subunits and a variety of NR2 subunits. Evidence suggests that, in the CA1 region of the hippocampus, NR2A-containing NMDARs promote LTP whereas NR2B-containing receptors promote LTD. However, the calcium sensors that distinguish between these signals to promote the appropriate form of synaptic plasticity are not known. Ras-guanine nucleotide-releasing factor 1 (Ras-GRF1) and Ras-GRF2 are highly similar calcium-stimulated exchange factors that activate Ras and Rac GTPases. Here, using a set of Ras-GRF knock-out mice, we show that Ras-GRF2 contributes predominantly to the induction of NMDAR-dependent LTP, whereas Ras-GRF1 contributes predominantly to the induction of NMDAR-dependent LTD in the CA1 region of the hippocampus of postpubescent mice (postnatal days 25-36). In contrast, neither Ras-GRF protein influences synaptic plasticity in prepubescent mice (postnatal days 14-18). Ras-GRF2 mediates signaling from (R)-[(S)-1-(4-bromo-phenyl)-ethylamino]-(2,3-dioxo-1,2,3,4-tetrahydroquinoxalin-5-yl)-methyl-phosphonic acid-sensitive (NVP-AAM077-sensitive) (NR2A-containing) NMDARs to the Ras effector extracellular signal-related protein kinase 1/2 (Erk1/2) mitogen-activated protein (MAP) kinase, a promoter of NMDAR-induced LTP at this site. In contrast, Ras-GRF1 mediates signaling from ifenprodil-sensitive (NR2B-containing) NMDARs to the Rac effector p38 MAP kinase, a promoter of LTD. These findings show that, despite their similar functional domain organization, Ras-GRF1 and Ras-GRF2 mediate opposing forms of synaptic plasticity by coupling different classes of NMDARs to distinct MAP kinase pathways. Moreover, the postnatal appearance of Ras-GRF-dependent LTP and LTD coincides with the emergence of hippocampal-dependent behavior, implying that Ras-GRF proteins contribute to forms of synaptic plasticity that are required specifically for mature hippocampal function.

Small non-fibrillar assemblies of amyloid beta-protein bearing the Arctic mutation induce rapid neuritic degeneration.

Recent studies suggest that soluble intermediates formed during amyloid beta-protein (Abeta) fibrillogenesis are neurotoxic. We studied early aggregation assemblies of wild-type and mutant Abeta bearing the E22G ("Arctic") familial Alzheimer's disease mutation. Using a novel method to present purified, disaggregated Abeta peptides to primary cortical neurons, the detailed temporal pattern of neurotoxicity was assessed. Neurons exposed to Arctic Abeta showed a progressive degeneration that was much more rapid than that with wild-type Abeta, beginning in dendrites and axons and leading to frank cell death. This neurotoxicity paralleled the aggregation process, with neuritic injury first appearing in the presence of small spherical Abeta oligomers, which were followed by a time-dependent elongation of curvilinear Abeta assemblies. One of the earliest neuritic changes was the formation of neurofilament-positive ringlets within axons, which disappeared as neurites followed by cell body degeneration. Our data support the hypothesis that small Abeta intermediates formed early in the aggregation process initiate cellular dysfunction beginning in neurites, leading to neuronal loss. A similar pattern of degeneration may occur during the preclinical and early clinical phases of Alzheimer's disease.

Certain inhibitors of synthetic amyloid beta-peptide (Abeta) fibrillogenesis block oligomerization of natural Abeta and thereby rescue long-term potentiation.

Recent studies support the hypothesis that soluble oligomers of amyloid beta-peptide (Abeta) rather than mature amyloid fibrils are the earliest effectors of synaptic compromise in Alzheimer's disease. We took advantage of an amyloid precursor protein-overexpressing cell line that secretes SDS-stable Abeta oligomers to search for inhibitors of the pathobiological effects of natural human Abeta oligomers. Here, we identify small molecules that inhibit formation of soluble Abeta oligomers and thus abrogate their block of long-term potentiation (LTP). Furthermore, we show that cell-derived Abeta oligomers can be separated from monomers by size exclusion chromatography under nondenaturing conditions and that the isolated, soluble oligomers, but not monomers, block LTP. The identification of small molecules that inhibit early Abeta oligomer formation and rescue LTP inhibition offers a rational approach for therapeutic intervention in Alzheimer's disease and highlights the utility of our cell-culture paradigm as a useful secondary screen for compounds designed to inhibit early steps in Abeta oligomerization under biologically relevant conditions.