Effects of beta-amyloid protein on serotoninergic, noradrenergic, and cholinergic markers in neurons of the pontomesencephalic tegmentum in the rat

Do patients diagnosed with a neurological disease present increased risk of suicide?

INTRODUCTION

Neurological diseases are the leading cause of disability and the second leading cause of death worldwide. Physical and psychological pain, despair, and disconnection with the environment are observed after the diagnosis of numerous neurological processes, particularly neurodegenerative diseases.

DEVELOPMENT

A higher risk of suicide is observed in patients with such common neurological diseases as epilepsy, migraine, and multiple sclerosis, as well as in those with such degenerative disorders as Alzheimer disease, Huntington disease, amyotrophic lateral sclerosis, and Parkinson's disease. In most cases, suicidal ideation appears in the early stages after diagnosis, in the presence of disabling symptoms, and/or in patients with psychiatric comorbidities (often associated with these neurological diseases).

CONCLUSIONS

Effective suicide prevention in this population group requires assessment of the risk of suicide mainly in newly diagnosed patients, in patients showing unmistakable despair or disabling symptoms, and in patients presenting psychiatric comorbidities (especially depressive symptoms). It is essential to train specialists to detect warning signs in order that they may adopt a suitable approach and determine when psychiatric assessment is required.

Toxicity of Amyloid-β Peptides Varies Depending on Differentiation Route of SH-SY5Y Cells

Alzheimer's disease (AD) is a currently incurable neurodegenerative disorder being the major form of dementia worldwide. AD pathology is initiated by cerebral aggregation of amyloid-β (Aβ) peptides in the form of amyloid plaques; however, the mechanism how Aβ peptide aggregates participate in the disease progression and neurodegeneration is still under debate. Human neuroblastoma cell line SH-SY5Y is a convenient cellular model, which is widely used in biochemical and toxicological studies of neurodegenerative diseases. This model can be further improved by differentiation of the cells toward more neuron-like culture using different protocols. In the current study, dbcAMP, retinoic acid with TPA, or BDNF were used for differentiation of SH-SY5Y cells, and the resulting cultures were tested for the toxicity toward the Aβ42 peptide. The toxicity of Aβ42 peptide depended on the type of differentiated cells: RA and TPA- differentiated cells were most resistant, whereas dbcAMP and RA/BDNF- differentiated cells were more sensitive to Aβ toxicity as compared with non-differentiated cells. The differentiated cultures provide more appropriate cellular models of human origin that can be used for studies of the mechanism of Aβ pathogenesis and for a screening of compounds antagonistic to the toxicity of Aβ peptides.

Do patients diagnosed with a neurological disease present increased risk of suicide?

INTRODUCTION

Neurological diseases are the leading cause of disability and the second leading cause of death worldwide. Physical and psychological pain, despair, and disconnection with the environment are observed after the diagnosis of numerous neurological processes, particularly neurodegenerative diseases.

DEVELOPMENT

A higher risk of suicide is observed in patients with such common neurological diseases as epilepsy, migraine, and multiple sclerosis, as well as in those with such degenerative disorders as Alzheimer disease, Huntington disease, amyotrophic lateral sclerosis, and Parkinson's disease. In most cases, suicidal ideation appears in the early stages after diagnosis, in the presence of disabling symptoms, and/or in patients with psychiatric comorbidities (often associated with these neurological diseases).

CONCLUSIONS

Effective suicide prevention in this population group requires assessment of the risk of suicide mainly in newly diagnosed patients, in patients showing unmistakable despair or disabling symptoms, and in patients presenting psychiatric comorbidities (especially depressive symptoms). It is essential to train specialists to detect warning signs in order that they may adopt a suitable approach and determine when psychiatric assessment is required.

A Complex Relationship Between Suicide, Dementia, and Amyloid: A Narrative Review

Background: Suicide rates are high among older adults and many conditions have been related to suicide in this population: chronic illnesses, physical disabilities, cancer, social isolation, mental disorders and neurocognitive disorders.

Objectives: Among neurocognitive disorders, analysis of the relationships between dementia and suicidal behaviors led to conflicting results and some questions are still without answer. Particularly, it is not known whether (i) Alzheimer's disease (AD) increases the risk of suicidal ideation and suicide attempts (SA) or the frequency of death by suicide; (ii) the presence of suicidal ideation or SA in people older than 65 years of age is an early dementia sign; and (iii) amyloid load in frontal areas facilitates SA by modifying the decision-making pathway.

Methods: Therefore, in this narrative review, we searched the PubMed database using the medical subject heading (MeSH) terms (“Suicide” AND “Depression”) OR (“Amyloid” OR “Dementia”) to identify recent (from 2000 to 2017) original studies on the links between suicidal behavior, dementia and brain amyloid load. We also explored the clinical and pathophysiological role of depression in these relationships.

Results and Discussion: The findings from these studies suggest that late stage dementia could protect against suicidal ideation and SA. Conversely, the risk of complete suicide is increased during the early phase of cognitive decline.

Conclusions: Serious cognitive impairment and decline of executive functions could protect against negative thoughts related to cognitive disability awareness and against suicide planning.Several factors, including brain amyloid load, could be involved in the increased suicide rate early after the diagnosis of dementia.

Amyloid Hypothesis: Is There a Role for Antiamyloid Treatment in Late-Life Depression?

Antidepressants have modest efficacy in late-life depression (LLD), perhaps because various neurobiologic processes compromise frontolimbic networks required for antidepressant response. We propose that amyloid accumulation is an etiologic factor for frontolimbic compromise that predisposes to depression and increases treatment resistance in a subgroup of older adults. In patients without history of depression, amyloid accumulation during the preclinical phase of Alzheimer disease (AD) may result in the prodromal depression syndrome that precedes cognitive impairment. In patients with early-onset depression, pathophysiologic changes during recurrent episodes may promote amyloid accumulation, further compromise neurocircuitry required for antidepressant response, and increase treatment resistance during successive depressive episodes. The findings that support the amyloid hypothesis of LLD are (1) Depression is a risk factor, a prodrome, and a common behavioral manifestation of AD; (2) amyloid deposition occurs during a long predementia period when depression is prevalent; (3) patients with lifetime history of depression have significant amyloid accumulation in brain regions related to mood regulation; and (4) amyloid deposition leads to neurobiologic processes, including vascular damage, neurodegeneration, neuroinflammation, and disrupted functional connectivity, that impair networks implicated in depression. The amyloid hypothesis of LLD is timely because availability of ligands allows in vivo assessment of amyloid in the human brain, a number of antiamyloid agents are relatively safe, and there is evidence that some antidepressants may reduce amyloid production. A model of LLD introducing the role of amyloid may guide the design of studies aiming to identify novel antidepressant approaches and prevention strategies of AD.

On cognitive ecology and the environmental factors that promote Alzheimer disease: lessons from Octodon degus (Rodentia: Octodontidae)

Cognitive ecologist posits that the more efficiently an animal uses information from the biotic and abiotic environment, the more adaptive are its cognitive abilities. Nevertheless, this approach does not test for natural neurodegenerative processes under field or experimental conditions, which may recover animals information processing and decision making and may explain, mechanistically, maladaptive behaviors. Here, we call for integrative approaches to explain the relationship between ultimate and proximate mechanisms behind social behavior. We highlight the importance of using the endemic caviomorph rodent Octodon degus as a valuable natural model for mechanistic studies of social behavior and to explain how physical environments can shape social experiences that might influence impaired cognitive abilities and the onset and progression of neurodegenerative disorders such as Alzheimer disease. We consequently suggest neuroecological approaches to examine how key elements of the environment may affect neural and cognitive mechanisms associated with learning, memory processes and brain structures involved in social behavior. We propose the following three core objectives of a program comprising interdisciplinary research in O. degus, namely: (1) to determine whether diet types provided after weaning can lead to cognitive impairment associated with spatial memory, learning and predisposing to develop Alzheimer disease in younger ages; (2) to examine if early life social experience has long term effects on behavior and cognitive responses and risk for development Alzheimer disease in later life and (3) To determine if an increase of social interactions in adult degu reared in different degree of social stressful conditions alter their behavior and cognitive responses.

Experimental models of Alzheimer's disease for deciphering the pathogenesis and therapeutic screening (Review)

Despite decades of laboratory and clinical research, Alzheimer's disease (AD) is still the leading cause of dementia in adults and there are no curative therapies currently available for this disease. This may be due to the pathological features of AD, which include extensive extracellular amyloid plaques and intracellular neurofibrillary tangles, as well as subsequent neuronal and synaptic loss, which begin to appear several years prior to memory loss and the damge is already irreversible and extensive at the time of clinical diagnosis. The poor therapeutic effects of current treatments necessitate the introduction of experimental models able to replicate AD pathology, particularly in the pre-symptomatic stage, and then to explore preventive and therapeutic strategies. In response to this necessity, various experimental models reproducing human AD pathology have been developed, which are also useful tools for therapeutic screening. Although none of these models fully reproduce the key features of human AD, the experimental models do provide important insight into the pathological changes which occur in AD. This review summarizes the commonly used experimental models of AD and also discusses how the models may be used to decipher the pathogenesis underlying AD and to screen novel therapies for this disease.

Accelerating Alzheimer's research through 'natural' animal models

PURPOSE OF REVIEW

Alzheimer's disease is a complex multifactorial age-related neurodegenerative disorder. Current transgenic animal models do not fully recapitulate human Alzheimer's disease at the molecular, cellular and behavioural levels. This review aims to address the clinical relevance of using 'physiologically' aged rats, dogs and Octodon degus, as more representative 'natural' ecologically valid models to elucidate mechanistic aspects of Alzheimer's disease, and for the development of therapeutic agents to attenuate age-related cognitive decline.

RECENT FINDINGS

Aged rats, dogs and O. degus decline cognitively and ultimately develop Alzheimer's disease-like symptoms in response to the natural ageing process. Aged rats provide a tractable and popular model to examine the neurobiological basis underlying cognitive decline with age, but they do not develop Alzheimer's disease pathology. Progressive accumulation of abnormal amyloid-beta in extracellular plaques and surrounding cerebral vasculature is a common feature in human Alzheimer's disease, aged canine model and most nonhuman primates. Interestingly, the O. degus develops amyloid-beta deposits, neurofibrillary tangles containing hyperphosphorylated tau protein, altered cholinergic transmission and cognitive deficits analogous to those observed in Alzheimer's disease. Natural animal models better represent the full pathophysiology of Alzheimer's disease and are not only a viable alternative to transgenic models, but also are arguably the preferable model.

SUMMARY

'Natural' models are useful to elucidate the neurobiological basis of Alzheimer's disease and develop effective therapeutic strategies that can be translated into human clinical trials.

Neurodegeneration, β-amyloid and mood disorders: state of the art and future perspectives

OBJECTIVE

Depression may increase the risk of developing Alzheimer's disease (AD). Recent studies have shown modifications in blood beta-amyloid (Aβ) levels in depressed patients. This literature review examines the potential relationship between Aβ-mediated neurotoxicity and pathophysiology of mood disorders.

DESIGN

We conducted a review of the literature focusing on recent studies reporting alterations of plasma and serum Aβ peptides levels in patients suffering from mood disorders.

RESULTS

Different data suggest that patients with mood disorders are at great risk of developing cognitive impairment and dementia. In particular, low plasma levels of Aβ42 peptide and a high Aβ40/Aβ42 ratio have been found in depressed patients. In addition, changes in Aβ protein levels in patients with mood disorders have been associated with the severity of cognitive impairment and correlated positively with the number of episodes and severity of illness course.

CONCLUSIONS

Given the intriguing association between change in plasma level of Aβ, depression and cognitive impairment, future work should focus on the relationship between Aβ peripheral level(s), biomarkers of neurodegeneration and development of dementia in patients affected by mood disorders.

Plasma amyloid β, depression, and dementia in community-dwelling elderly

Plasma amyloid β (Aβ) levels have been associated with an increased risk of Alzheimer's disease (AD). As depression is common before the onset of AD, a few clinical studies tested the cross-sectional association of Aβ levels with depression in elderly and showed incongruous findings. Hence, we tested the longitudinal association between Aβ levels and depressive symptoms in community-dwelling elderly. The study is embedded in a population-based cohort of 980 participants aged 60 years or older from the Rotterdam Study with Aβ levels. Participants were evaluated for depressive symptoms with the Centre for Epidemiological Studies-Depression scale at baseline and repeatedly over the mean follow-up of 11 years. We first performed cross-sectional analyses. Then, we tested the longitudinal association between Aβ levels and depressive symptoms after excluding participants with dementia during follow-up. In cross-sectional analyses, persons with high Aβ(1-40) levels had more clinically relevant depressive symptoms. However, this association was accounted for by persons with clinically relevant depressive symptoms who developed dementia within the next 11 years. In longitudinal analyses, persons with low levels of Aβ(1-40) and Aβ(1-42) without dementia had a higher risk of clinically relevant depressive symptoms during the follow-up. These findings suggest that the cross-sectional association between high plasma Aβ levels and clinically relevant depressive symptoms in the elderly is due to prodromal dementia. In contrast, the longitudinal association between low plasma Aβ levels and depressive symptoms could not be explained by dementia during follow-up suggesting that Aβ peptides may play a distinct role on depression etiology.

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.

β-Amyloid induced effects on cholinergic, serotonergic, and dopaminergic neurons is differentially counteracted by anti-inflammatory drugs

β-Amyloid (Aβ) is a small peptide that plays a potent role in synaptic plasticity as well as forms amyloid plaques in Alzheimer's disease (AD). Recent studies suggest that Aβ deposition is deleterious not only in AD, but also in Parkinson's disease (PD) and depression. This Aβ effect is associated with inflammatory processes. However, further evaluation is needed to understand how Aβ and inflammation interact and contribute to the regulation of the cholinergic, serotonergic, and dopaminergic neuronal populations. The aim of the present study was to investigate the effects of Aβ(1-42) on cholinergic neurons of the nucleus basalis of Meynert (which degenerate in AD), on serotonergic neurons of the dorsal raphe nucleus (which play a role in depression), and on dopaminergic neurons of the ventral mesencephalon (which degenerate in PD) in rat organotypic brain slices. Furthermore, we investigated whether anti-inflammatory drugs (celecoxib, citalopram, cyclooxygenase-2 inhibitor, ibuprofen, indomethacin, piclamilast) modulate or counteract Aβ-induced effects. Two-week-old organotypic brain slices of the nucleus basalis of Meynert, dorsal raphe nucleus, and ventral mesencephalon were incubated with 50 ng/ml Aβ(1-42) with or without anti-inflammatory agents for 3 days. Our results reveal that Aβ significantly decreased the number of choline acetyltransferase-positive cholinergic, tryptophan hydroxylase-positive serotonergic, and tyrosine hydroxylase-positive dopaminergic neurons and that anti-inflammatory drugs partially counteracted the Aβ-induced neuronal decline. This decline was not due to apoptotic processes (as evaluated by TUNEL, propidium iodide, caspase), oxidative stress (as measured by nitrite, catalase, or superoxide dismutase-2), or inflammation, but was most likely caused by a downregulation of these key enzymes.

Reduced tissue levels of noradrenaline are associated with behavioral phenotypes of the TgCRND8 mouse model of Alzheimer's disease

Noradrenergic cell loss is well documented in Alzheimer's disease (AD). We have measured the tissue levels of catecholamines in an amyloid precursor protein-transgenic 'TgCRND8' mouse model of AD and found reductions in noradrenaline (NA) within hippocampus, temporoparietal and frontal cortices, and cerebellum. An age-related increase in cortical NA levels was observed in non-Tg controls, but not in TgCRND8 mice. In contrast, NA levels declined with aging in the TgCRND8 hippocampus. Dopamine levels were unaffected. Reductions in the tissue content of NA were found to coincide with altered expression of brain-derived neurotrophic factor (BDNF) mRNA and to precede the onset of object memory impairment and behavioral despair. To test whether these phenotypes might be associated with diminished NA, we treated mice with dexefaroxan, an antagonist of presynaptic inhibitory α(2)-adrenoceptors on noradrenergic and cholinergic terminals. Mice 12 weeks of age were infused systemically for 28 days with dexefaroxan or rivastigmine, a cholinesterase inhibitor. Both dexefaroxan and rivastigmine improved TgCRND8 behavioral phenotypes and increased BDNF mRNA expression without affecting amyloid-β peptide levels. Our results highlight the importance of noradrenergic depletion in AD-like phenotypes of TgCRND8 mice.

Dysfunctional nucleus tractus solitarius: its crucial role in promoting neuropathogenetic cascade of Alzheimer's dementia--a novel hypothesis

The pathophysiological mechanism(s) underlying Alzheimer's disease (AD) still remain unclear, and no disease-modifying or prophylactic therapies are currently available. Unraveling the fundamental neuropathogenesis of AD is an important challenge. Several studies on AD have suggested lesions in a number of CNS areas including the basal forebrain, hippocampus, entorhinal cortex, amygdale/insula, and the locus coeruleus. However, plausible unifying studies on the upstream factors that involve these heterogeneous regions and herald the onset of AD pathogenesis are not available. The current article presents a novel nucleus tractus solitarius (NTS) vector hypothesis that underpins several disparate biological mechanisms and neural circuits, and identifies relevant hallmarks of major presumptive causative factor(s) linked to the NTS, in older/aging individuals. Aging, obesity, infection, sleep apnea, smoking, neuropsychological states, and hypothermia-all activate inflammatory cytokines and oxidative stress. The synergistic impact of systemic proinflammatory mediators activates microglia and promotes neuroinflammation. Acutely, the innate immune response is protective defending against pathogens/toxins; however, when chronic, it causes neuroinflammation and neuronal dysfunction, particularly in brainstem and neocortex. The NTS in the brainstem is an essential multiple signaling hub, and an extremely important central integration site of baroreceptor, chemoreceptor, and a multitude of sensory afferents from gustatory, gastrointestinal, cardiac, pulmonary, and upper airway systems. Owing to persistent neuroinflammation, the dysfunctional NTS exerts deleterious impact on nucleus ambiguus, dorsal motor nucleus of vagus, hypoglossal, parabrachial, locus coeruleus and many key nuclei in the brainstem, and the hippocampus, entorhinal cortex, prefrontal cortex, amygdala, insula, and basal forebrain in the neocortex. The neuronal and synaptic dysfunction emanating from the inflamed NTS may affect its interconnected pathways impacting almost the entire CNS--which is already primed by neuroinflammation, thus promoting cognitive and neuropsychiatric symptoms. The upstream factors discussed here may underpin the neuropathopgenesis of AD. AD pathology is multifactorial; the current perspective underscores the value of attenuating disparate upstream factors--in conjunction with anticholinesterase, anti-inflammatory, immunosuppressive, and anti-oxidant pharmacotherapy. Amelioration of the NTS pathology may be of central importance in countering the neuropathological cascade of AD. The NTS, therefore, may be a potential target of novel therapeutic strategies.

Recent rodent models for Alzheimer's disease: clinical implications and basic research

Alzheimer's disease (AD) is the most common origin of dementia in the elderly. Although the cause of AD remains unknown, several factors have been identified that appear to play a critical role in the development of this debilitating disorder. In particular, amyloid precursor protein (APP), tau hyperphosphorylation, and the secretase enzymes, have become the focal point of recent research. Over the last two decades, several transgenic and non-transgenic animal models have been developed to elucidate the mechanistic aspects of AD and to validate potential therapeutic targets. Transgenic rodent models over-expressing human β-amyloid precursor protein (β-APP) and mutant forms of tau have become precious tools to study and understand the pathogenesis of AD at the molecular, cellular and behavioural levels, and to test new therapeutic agents. Nevertheless, none of the transgenic models of AD recapitulate fully all of the pathological features of the disease. Octodon degu, a South American rodent has been recently found to spontaneously develop neuropathological signs of AD in old age. This review aims to address the limitations and clinical relevance of transgenic rodent models in AD, and to highlight the potential for O. degu as a natural model for the study of AD neuropathology.

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.

Rat hippocampal proteomic alterations following intrahippocampal injection of amyloid beta peptide (1-40)

Amyloid beta peptide 1-40 (Aβ(1-40)) is closely associated with the progressive neuronal loss and cognitive decline observed in Alzheimer's disease (AD). This study aimed to establish a proteomic strategy for the profiling of AD tissues for disease-specific changes in protein abundance. Intrahippocampal injection of Aβ(1-40) induced spatial memory and learning decline in rats. Proteomic analysis revealed the changes in protein expression in the rat hippocampus treated with Aβ(1-40). Four proteins of interest which was in abundance was significantly altered in Aβ(1-40)-treated rats were identified by peptide mass fingerprint (PMF). These proteins corresponded to synapsin Ib, protein disulfide-isomerase A3 precursor, tubulin β chain and ATP synthase β subunit. Our results provide new insights into the relationship between Aβ and the pathogenesis of AD, and suggest potential targets for the therapy of AD.

Inflammatory stimuli reduce survival of serotonergic neurons and induce neuronal expression of indoleamine 2,3-dioxygenase in rat dorsal raphe nucleus organotypic brain slices

Neuroinflammation results in dysregulation of serotonergic neurons in the dorsal raphe nucleus (doR) and is considered to play an important role in the pathophysiology of depression. The aim of the present study was to induce neuroinflammation in a simple doR brain slice model using lipopolysaccharide (LPS), interferon-gamma (IFNγ), beta-amyloid₁₋₄₂ or tumor necrosis factor-alpha and to explore the survival of serotonergic neurons and the expression of the tryptophan degrading enzyme indoleamine 2,3-dioxygenase (IDO). Administration of pro-inflammatory stimuli reduced survival of serotonergic neurons in doR slices and increased IDO expression. IFNγ most potently induced IDO expression, which co-localized with neurons, including serotonergic neurons, but not with microglia or astrocytes. IFNγ did not induce PI-positive staining in slices, but increased the average nuclei size of IDO-positive cells. The inflammation-induced decline did not return to control levels, when slices were withdrawn from inflammation, pointing to neurodegeneration. The growth factors BDNF or GDNF did not counteract the inflammation-induced decrease in serotonergic neurons, except for LPS-induced neuronal decline. The inflammation-induced effect was not blocked by the NMDA-receptor antagonist MK-801. Further LPS, but not IFNγ increased inflammatory markers and microglia activity. In conclusion, our data show that a range of inflammatory stimuli decline serotonergic neurons in doR slices and upregulate IDO expression. The data suggest that IDO does not contribute to serotonergic decline, but may serve as a marker of neurodegeneration. Neuroinflammation may contribute to the development of depression.

Brain neurotoxic amyloid-beta peptides: their potential role in the pathophysiology of depression and as molecular therapeutic targets

The monoamine hypothesis ascribes an important role to the under activity of brain monoamines such as 5-HT, noradrenaline and dopamine to the pathophysiology of depression. This view emerged more than 50 years ago and has guided development of most medications currently used for the treatment of this disorder. However, large numbers of depressed individuals treated with currently available antidepressant agents, or even with various combinations, do not respond. Residual symptoms, relapses and recurrences are common while receiving adequate doses of these medications. In a recent issue of the BJP, Colaianna et al.describe results suggesting that a new neurobiological mechanism with treatment implications should be considered for the development of depression in humans, namely, elevations in potentially neurotoxic brain amyloid-ß peptides.

Plasma amyloid beta-42 independently predicts both late-onset depression and Alzheimer disease

OBJECTIVES

Depression in the elderly might represent a prodromal phase of Alzheimer disease (AD). High levels of plasma amyloid beta-42 (Aβ42) were found in prestages of AD and also in depressed patients in cross-sectional studies. This study examined the association of emerging late-onset depression (LOD) and AD with plasma Aβ42 in a sample of never depressed and not demented persons at baseline.

DESIGN

Prospective 5-year longitudinal study.

PARTICIPANTS

A community dwelling of older adults (N = 331) from the Vienna Transdanube Aging study.

MEASUREMENTS

Laboratory measurements, cognitive functioning, and depressive symptoms were assessed at baseline, 2.5, and 5 years follow-ups.

RESULTS

After exclusion of converters to AD, regression analysis revealed that higher plasma Aβ42 at baseline was a positive predictor for conversion to first episode of LOD. Independent of whether persons with mild cognitive impairment (MCI) at 2.5 years were included or excluded into regressions, higher plasma Aβ42 at baseline was a significant predictor for the development of probable or possible AD at 5 years. Higher conversion to AD was also associated with male gender but not with either higher scores on the Geriatric Depression Scale (GDS), with stroke or cerebral infarction nor apolipoprotein E ε4 allele. No association was found for an interaction between plasma Aβ42 levels and GDS.

CONCLUSIONS

Higher plasma Aβ42 at baseline predicted the development of first episode of LOD and conversion to probable or possible AD. Emerging depression as measured by scores on GDS at the 2.5-year follow-up, either alone or as an interaction factor with plasma Aβ42, failed to predict the conversion to AD at 5 years.

Effects of yokukansan, a traditional Japanese medicine, on aggressiveness induced by intracerebroventricular injection of amyloid beta protein into mice

The effects of yokukansan, a traditional Japanese medicine, on aggressiveness and motor activities were examined in mice after injection of amyloid beta protein (Abeta) into the lateral ventricle of the brain. The results were compared with those of conventional (haloperidol) and atypical (risperidone) antipsychotic medicines. A significant increase in aggressiveness was observed on day 7 after injection of Abeta, and it lasted until day 28. A single oral administration of yokukansan (1.0 g/kg) did not ameliorate the aggressiveness observed on day 7. However, a tendency toward amelioration of the aggressiveness was observed after the administration of yokukansan (0.5 and 1.0 g/kg) for 1 week (days 7-14). The 3 week administration (days 7-28) of yokukansan significantly ameliorated the aggressiveness in a dose-dependent manner without inhibition of motor activity. In contrast, a single administration of intraperitoneal haloperidol (0.03-0.1 mg/kg) or oral risperidone (0.1-0.3 mg/kg) on day 28 significantly reduced aggressiveness in a dose-dependent manner. However, motor activities were significantly suppressed. These results suggest yokukansan reduces aggressiveness without suppressing physical activity.

Natural non-trasgenic animal models for research in Alzheimer's disease

The most common animal models currently used for Alzheimer disease (AD) research are transgenic mice that express a mutant form of human Aβ precursor protein (APP) and/or some of the enzymes implicated in their metabolic processing. However, these transgenic mice carry their own APP and APP-processing enzymes, which may interfere in the production of different amyloid-beta (Aβ) peptides encoded by the human transgenes. Additionally, the genetic backgrounds of the different transgenic mice are a possible confounding factor with regard to crucial aspects of AD that they may (or may not) reproduce. Thus, although the usefulness of transgenic mice is undisputed, we hypothesized that additional relevant information on the physiopathology of AD could be obtained from other natural non-transgenic models. We have analyzed the chick embryo and the dog, which may be better experimental models because their enzymatic machinery for processing APP is almost identical to that of humans. The chick embryo is extremely easy to access and manipulate. It could be an advantageous natural model in which to study the cell biology and developmental function of APP and a potential assay system for drugs that regulate APP processing. The dog suffers from an age-related syndrome of cognitive dysfunction that naturally reproduces key aspects of AD including Aβ cortical pathology, neuronal degeneration and learning and memory disabilities. However, dense core neuritic plaques and neurofibrillary tangles have not been consistently demonstrated in the dog. Thus, these species may be natural models with which to study the biology of AD, and could also serve as assay systems for Aβ-targeted drugs or new therapeutic strategies against this devastating disease.

Effects of amyloid-β peptides on the serotoninergic 5-HT1A receptors in the rat hippocampus

A recent [(18)F]MPPF-positron emission tomography study has highlighted an overexpression of 5-HT(1A) receptors in the hippocampus of patients with mild cognitive impairment compared to a decrease in those with Alzheimer's disease (AD) [Truchot, L., Costes, S.N., Zimmer, L., Laurent, B., Le Bars, D., Thomas-Antérion, C., Croisile, B., Mercier, B., Hermier, M., Vighetto, A., Krolak-Salmon, P., 2007. Up-regulation of hippocampal serotonin metabolism in mild cognitive impairment. Neurology 69 (10), 1012-1017]. We used in vivo and in vitro neuroimaging to evaluate the longitudinal effects of injecting amyloid-β (Aβ) peptides (1-40) into the dorsal hippocampus of rats. In vivo microPET imaging showed no significant change in [(18)F]MPPF binding in the dorsal hippocampus over time, perhaps due to spatial resolution. However, in vitro autoradiography with [(18)F]MPPF (which is antagonist) displayed a transient increase in 5-HT(1A) receptor density 7 days after Aβ injection, whereas [(18)F]F15599 (a radiolabelled 5-HT(1A) agonist) binding was unchanged suggesting that the overexpressed 5-HT(1A) receptors were in a non-functional state. Complementary histology revealed a loss of glutamatergic neurons and an intense astroglial reaction at the injection site. Although a neurogenesis process cannot be excluded, we propose that Aβ injection leads to a transient astroglial overexpression of 5-HT(1A) receptors in compensation for the local neuronal loss. Exploration of the functional consequences of these serotoninergic modifications during the neurodegenerative process may have an impact on therapeutics targeting 5-HT(1A) receptors in AD.

Dogs with canine counterpart of Alzheimer's disease lose noradrenergic neurons

Degeneration of noradrenergic neurons in the locus ceruleus is a well-described feature of Alzheimer's disease (AD). In spite of extensive utilization of the dog as a model for human degenerative diseases, there is no data on the response to aging of the noradrenergic system in dogs. We have used modern unbiased stereology to estimate the total number of A6-A7 noradrenergic neurons in normal, aged dogs and dogs with the canine counterpart of AD. In small-breed dogs with no cognitive impairments, the total mean number of tyrosine hydroxylase immunolabeled A6-A7 neurons was 17,228+/-1655, with no differences between young and aged dogs. In contrast, aged dogs with cognitive impairments exhibited a significant reduction in the total number of A6-A7 neurons (13,487+/-1374; P=0.001). Additionally, we found a negative correlation between the number of A6-A7 neurons and the extent of beta-amyloid deposits in the prefrontal cortex. These results suggest that the canine model could be useful in exploring the potential benefits of noradrenergic drugs for the treatment of AD.

Medial septal beta-amyloid 1-40 injections alter septo-hippocampal anatomy and function

Degeneration of septal neurons in Alzheimer's disease (AD) results in abnormal information processing at cortical circuits and consequent brain dysfunction. The septum modulates the activity of hippocampal and cortical circuits and is crucial to the initiation and occurrence of oscillatory activities such as the hippocampal theta rhythm. Previous studies suggest that amyloid beta peptide (Abeta) accumulation may trigger degeneration in AD. This study evaluates the effects of single injections of Abeta 1-40 into the medial septum. Immunohistochemistry revealed a decrease in septal cholinergic (57%) and glutamatergic (53%) neurons in Abeta 1-40 treated tissue. Additionally, glutamatergic terminals were significantly less in Abeta treated tissue. In contrast, septal GABAergic neurons were spared. Unitary recordings from septal neurons and hippocampal field potentials revealed an approximately 50% increase in firing rates of slow firing septal neurons during theta rhythm and large irregular amplitude (LIA) hippocampal activities and a significantly reduced hippocampal theta rhythm power (49%) in Abeta 1-40 treated tissue. Abeta also markedly reduced the proportion of slow firing septal neurons correlated to the hippocampal theta rhythm by 96%. These results confirm that Abeta alters the anatomy and physiology of the medial septum contributing to septo-hippocampal dysfunction. The Abeta induced injury of septal cholinergic and glutamatergic networks may contribute to an altered hippocampal theta rhythm which may underlie the memory loss typically observed in AD patients.

Huperzine A Reverses Cholinergic and Monoaminergic Dysfunction Induced by Bilateral Nucleus Basalis Magnocellularis Injection of β-Amyloid Peptide (1–40) in Rats

(1) Huperzine A, a promising therapeutic agent for Alzheimer's disease (AD), was tested for its effects on cholinergic and monoaminergic dysfunction induced by injecting beta-amyloid peptide-(1-40) into nucleus basalis magnocellularis of the rat. (2) Bilateral injection of 10 microg beta-amyloid peptide-(1-40) into nucleus basalis magnocellularis produced local deposits of amyloid plaque and functional abnormalities detected by microdialysis. In medial prefrontal cortex, reductions in the basal levels and stimulated release of acetylcholine, dopamine, norepinephrine, and 5-hydroxytryptamine were observed. However, oral huperzine A (0.18 mg/kg, once daily for 21 consecutive days) markedly reduced morphologic abnormalities at the injection site in rats infused with beta-amyloid peptide-(1-40). Likewise, this treatment ameliorated the beta-amyloid peptide-(1-40)-induced deficits in extracellular acetylcholine, dopamine, and norepinephrine (though not 5-hydroxytryptamine) in medial prefrontal cortex, and lessened the reduction in nicotine or methoctramine-stimulated release of acetylcholine and K(+)-evoked releases of acetylcholine and dopamine. (3) The present results provide the first direct evidence that huperzine A acts to oppose neurotoxic effects of beta-amyloid peptide on cholinergic, dopaminergic, and noradrenergic systems of the rat forebrain.

Effects of beta-amyloid protein on M1 and M2 subtypes of muscarinic acetylcholine receptors in the medial septum-diagonal band complex of the rat: relationship with cholinergic, GABAergic, and calcium-binding protein perikarya

Cortical cholinergic dysfunction has been correlated with the expression and processing of beta-amyloid precursor protein. However, it remains unclear as to how cholinergic dysfunction and beta-amyloid (Abeta) formation and deposition might be related to one another. Since the M1- and M2 subtypes of muscarinic acetylcholine receptors (mAChRs) are considered key molecules that transduce the cholinergic message, the purpose of the present study was to assess the effects of the injected Abeta peptide on the number of M1mAchR- and M2mAChR-immunoreactive cells in the medial septum-diagonal band (MS-nDBB) complex of the rat. Injections of Abeta protein into the retrosplenial cortex resulted in a decrease in M1mAChR and M2mAChR immunoreactivity in the MS-nDBB complex. Quantitative analysis revealed a significant reduction in the number of M1mAChR- and M2mAChR-immunoreactive cells in the medial septum nucleus (MS) and in the horizontal nucleus of the diagonal band of Broca (HDB) as compared to the corresponding hemisphere in control animals and with that seen in the contralateral hemisphere, which corresponds to the PBS-injected side. Co-localization studies showed that the M1mAChR protein is localized in GABA-immunoreactive cells of the MS-nDBB complex, in particular those of the MS nucleus, while M2mAChR protein is localized in both the cholinergic and GABAergic cells. Moreover, GABAergic cells containing M2mAChR are mainly localized in the MS nucleus, while cholinergic cells containing M2mAChR are localized in the MS and the HDB nuclei. Our findings suggest that Abeta induces a reduction in M1mAChR- and M2mAChR-containing cells, which may contribute to impairments of cholinergic and GABAergic transmission in the MS-nDBB complex.

Mesopontine cholinergic projections to the hypoglossal motor nucleus

Mesopontine cholinergic (ACh) neurons have increased discharge during wakefulness, rapid eye movement (REM) sleep, or both. Hypoglossal (12) motoneurons, which play an important role in the control of upper airway patency, are postsynaptically excited by stimulation of nicotinic receptors, whereas muscarinic receptors presynaptically inhibit inputs to 12 motoneurons. These data suggest that ACh contributes to sleep/wake-related changes in the activity of 12 motoneurons by acting within the hypoglossal motor nucleus (Mo12), but the origins of ACh projections to Mo12 are not well established. We used retrograde tracers to assess the projections of ACh neurons of the mesopontine pedinculopontine tegmental (PPT) and laterodorsal tegmental (LDT) nuclei to the Mo12. In six Sprague-Dawley rats, Fluorogold or B subunit of cholera toxin, were pressure injected (5-20nl) into the Mo12. Retrogradely labeled neurons, identified as ACh using nitric oxide synthase (NOS) immunohistochemistry, were found bilaterally in discrete subregions of both PPT and LDT nuclei. Most retrogradely labeled PPT cells (96%) were located in the PPT pars compacta region adjacent to the ventrolateral tip of the superior cerebellar peduncle. In the LDT, retrogradely labeled neurons were located exclusively in its pars alpha region. Over twice as many ACh neurons projecting to the Mo12 were located in the PPT than LDT. The results demonstrate direct mesopontine ACh projections to the Mo12. These projections may contribute to the characteristic of wakefulness and REM sleep increases, as well as REM sleep-related decrements, of 12 motoneuronal activity.

Effects of lipids and aging on the neurotoxicity and neuronal loss caused by intracerebral injections of the amyloid-β peptide in the rat

The influence of diet and age on the area of lesion and on the neuronal density in the cerebral cortex was studied in rats following local injections of the amyloid-beta peptide (Abeta1-40) in PBS vehicle into the left frontal and cingulate cortices and compared with effects of injections of PBS alone into the corresponding regions of the right hemisphere The experiments were carried out in two groups of animals: one group of young adult rats and a second group of aged rats. Each group of animals, depending on the diet received, was divided into high-cholesterol, high-fat, and a control group. In order to evaluate the interaction of Abeta/PBS-cholesterol and of Abeta/PBS-fat, animals without dietary manipulation receiving Abeta and PBS injection were used as controls. The results showed that the greatest area of lesion was at Abeta injection sites in the high-cholesterol fed group of aged animals. The results also revealed a significant variance in the neuronal density by group and by injection type. Thus, high-cholesterol fed animals showed a greater reduction in neuronal density at Abeta and PBS-injected sites than that seen in the high-fat or control groups. The results also indicate that the loss of neurons at the Abeta injection site exceeds that seen in the PBS-injected area. The greatest reduction in the neuronal density was found at Abeta-injected site in the high-cholesterol fed group of aged animals. In conclusion, our findings indicate an interaction between lipids, age, and Abeta neurotoxicity, and might provide insights into the basic mechanisms involved in a short-term (acute-to-subchronic) response to Abeta peptide.

Amyloid beta peptide-induced cholinergic fibres loss in the cerebral cortex of the rat is modified by diet high in lipids and by age

The influence of diet and age on the effects of intracerebral injection of beta-amyloid peptide (Abeta1-40) in vehicle phosphate-buffered saline (PBS) and on the effects of vehicle alone on cholinergic fibres of the cerebral cortex was studied in rats. The experiments were carried in two groups of animals: one group of young adult rats and a second group of aged rats. Each group of animals, depending on the diet received, was divided into high-cholesterol, high-fat, and a control diet group. In order to evaluate the interaction of Abeta/PBS-cholesterol and of Abeta/PBS-fat, animals without dietary manipulation receiving Abeta and PBS injection were used as controls. High-cholesterol fed animals showed a statistically significant reduction of 49.62% in the number of cholinergic fibres at the Abeta injection site as compared with that at PBS injection site, while the high-fat and control animals showed a significant reduction of 28.13 and 26.81%, respectively. In all diet groups, the loss of cholinergic fibres caused by Abeta as compared to that caused by PBS injection was significantly greater in aged rats in comparison with that observed in the young animals. Furthermore, the results of a multivariate linear regression model revealed that the greatest reduction in cholinergic fibres was in the high-cholesterol fed animals (35 fibres/mm) as compared with that seen in the high-fat and control animals. A significantly greater reduction was also observed at Abeta injection site (28 fibres/mm) as compared with that caused by PBS injection, and a reduction of 16 cholinergic fibres per mm was found in aged animals as compared to that seen in young adult rats. These results show that high-cholesterol diet enhances the toxicity of Abeta peptide and that this is also age-dependent. Therefore, this study increases the evidences of the role of cholesterol in the pathology of Alzheimer's disease (AD).