Age-dependent impact of streptozotocin on metabolic endpoints and Alzheimer's disease pathologies in 3xTg-AD mice.

Alzheimer's disease (AD) is a multifactorial neurodegenerative disease with a complex origin, thought to involve a combination of genetic, biological and environmental factors. Insulin dysfunction has emerged as a potential factor contributing to AD pathogenesis, particularly in individuals with diabetes, and among those with insulin deficiency or undergoing insulin therapy. The intraperitoneal administration of streptozotocin (STZ) is widely used in rodent models to explore the impact of insulin deficiency on AD pathology, although prior research predominantly focused on young animals, with no comparative analysis across different age groups. Our study aimed to fill this gap by analyzing the impact of insulin dysfunction in 7 and 23 months 3xTg-AD mice, that exhibit both amyloid and tau pathologies. Our objective was to elucidate the age-specific consequences of insulin deficiency on AD pathology. STZ administration led to insulin deficiency in the younger mice, resulting in an increase in cortical amyloid-ß (Aß) and tau aggregation, while tau phosphorylation was not significantly affected. Conversely, older mice displayed an unexpected resilience to the peripheral metabolic impact of STZ, while exhibiting an increase in both tau phosphorylation and aggregation without significantly affecting amyloid pathology. These changes were paralleled with alterations in signaling pathways involving tau kinases and phosphatases. Several markers of blood-brain barrier (BBB) integrity declined with age in 3xTg-AD mice, which might have facilitated a direct neurotoxic effect of STZ in older mice. Overall, our research confirms the influence of insulin signaling dysfunction on AD pathology, but also advises careful interpretation of data related to STZ-induced effects in older animals.

A "double-edged" role for type-5 metabotropic glutamate receptors in pain disclosed by light-sensitive drugs.

Knowing the site of drug action is important to optimize effectiveness and address any side effects. We used light-sensitive drugs to identify the brain region-specific role of mGlu5 metabotropic glutamate receptors in the control of pain. Optical activation of systemic JF-NP-26, a caged, normally inactive, negative allosteric modulator (NAM) of mGlu5 receptors, in cingulate, prelimbic and infralimbic cortices and thalamus inhibited neuropathic pain hypersensitivity. Systemic treatment of alloswitch-1, an intrinsically active mGlu5 receptor NAM, caused analgesia, and the effect was reversed by light-induced drug inactivation in in the prelimbic and infralimbic cortices, and thalamus. This demonstrates that mGlu5 receptor blockade in the medial prefrontal cortex and thalamus is both sufficient and necessary for the analgesic activity of mGlu5 receptor antagonists. Surprisingly, when light was delivered in the basolateral amygdala, local activation of systemic JF-NP-26 reduced pain thresholds, whereas inactivation of alloswitch-1 enhanced analgesia. Electrophysiological analysis showed that alloswitch-1 increased excitatory synaptic responses in prelimbic pyramidal neurons evoked by stimulation of BLA input, and decreased feedforward inhibition of amygdala output neurons by BLA. Both effects were reversed by optical silencing and reinstated by optical reactivation of alloswitch-1. These findings demonstrate for the first time that the action of mGlu5 receptors in the pain neuraxis is not homogenous, and suggest that blockade of mGlu5 receptors in the BLA may limit the overall analgesic activity of mGlu5 receptor antagonists. This could explain the suboptimal effect of mGlu5 NAMs on pain in human studies and validate photopharmacology as an important tool to determine ideal target sites for systemic drugs.

Superiority of the Triple-Acting 5-HT6R/5-HT3R Antagonist and MAO-B Reversible Inhibitor PZ-1922 over 5-HT6R Antagonist Intepirdine in Alleviation of Cognitive Deficits in Rats.

The multifactorial origin and neurochemistry of Alzheimer's disease (AD) call for the development of multitarget treatment strategies. We report a first-in-class triple acting compound that targets serotonin type 6 and 3 receptors (5-HT-Rs) and monoamine oxidase type B (MAO-B) as an approach for treating AD. The key structural features required for MAO-B inhibition and 5-HT6R antagonism and interaction with 5-HT3R were determined using molecular dynamic simulations and cryo-electron microscopy, respectively. Bioavailable PZ-1922 reversed scopolamine-induced cognitive deficits in the novel object recognition test. Furthermore, it displayed superior pro-cognitive properties compared to intepirdine (a 5-HT6R antagonist) in the AD model, which involved intracerebroventricular injection of an oligomeric solution of amyloid-ß peptide (oAß) in the T-maze test in rats. PZ-1922, but not intepirdine, restored levels of biomarkers characteristic of the debilitating effects of oAß. These data support the potential of a multitarget approach involving the joint modulation of 5-HT6R/5-HT3R/MAO-B in AD.

The pathomimetic oAß25-35 model of Alzheimer's disease: Potential for screening of new therapeutic agents.

Alzheimer's disease (AD) is the most common form of dementia in the elderly, currently affecting more than 40 million people worldwide. The two main histopathological hallmarks of AD were identified in the 1980s: senile plaques (composed of aggregated amyloid-ß (Aß) peptides) and neurofibrillary tangles (composed of hyperphosphorylated tau protein). In the human brain, both Aß and tau show aggregation into soluble and insoluble oligomers. Soluble oligomers of Aß include their most predominant forms - Aß1-40 and Aß1-42 - as well as shorter peptides such as Aß25-35 or Aß25-35/40. Most animal models of AD have been developed using transgenesis, based on identified human mutations. However, these familial forms of AD represent less than 1% of AD cases. In this context, the idea emerged in the 1990s to directly inject the Aß25-35 fragment into the rodent brain to develop an acute model of AD that could mimic the disease's sporadic forms (99% of all cases). This review aims to: (1) summarize the biological activity of Aß25-35, focusing on its impact on the main structural and functional alterations observed in AD (cognitive deficits, APP misprocessing, tau system dysfunction, neuroinflammation, oxidative stress, cholinergic and glutamatergic alterations, HPA axis dysregulation, synaptic deficits and cell death); and (2) confirm the interest of this pathomimetic model in AD research, as it has helped identify and characterize many molecules (marketed, in clinical development, and in preclinical testing), and to the development of alternative approaches for AD prevention and therapy. Today, the Aß25-35 model appears as a first-intent choice model to rapidly screen the symptomatic or neuroprotective potencies of new compounds, chemical series, or innovative therapeutic strategies.

Intranasal Administration of Nanovectorized Docosahexaenoic Acid (DHA) Improves Cognitive Function in Two Complementary Mouse Models of Alzheimer's Disease.

Polyunsaturated fatty acids (PUFAs) are a class of fatty acids that are closely associated with the development and function of the brain. The most abundant PUFA is docosahexaenoic acid (DHA, 22:6 n-3). In humans, low plasmatic concentrations of DHA have been associated with impaired cognitive function, low hippocampal volumes, and increased amyloid deposition in the brain. Several studies have reported reduced brain DHA concentrations in Alzheimer's disease (AD) patients' brains. Although a number of epidemiological studies suggest that dietary DHA consumption may protect the elderly from developing cognitive impairment or dementia including AD, several review articles report an inconclusive association between omega-3 PUFAs intake and cognitive decline. The source of these inconsistencies might be because DHA is highly oxidizable and its accessibility to the brain is limited by the blood-brain barrier. Thus, there is a pressing need for new strategies to improve DHA brain supply. In the present study, we show for the first time that the intranasal administration of nanovectorized DHA reduces Tau phosphorylation and restores cognitive functions in two complementary murine models of AD. These results pave the way for the development of a new approach to target the brain with DHA for the prevention or treatment of this devastating disease.

Seizure activity triggers tau hyperphosphorylation and amyloidogenic pathways.

OBJECTIVE: Although epilepsies and neurodegenerative disorders show pathophysiological similarities, their direct functional associations are unclear. Here, we tested the hypothesis that experimental seizures can induce tau hyperphosphorylation and amyloidogenic modifications over time, with intersections with neuroinflammation. METHODS: We used a model of mesial temporal lobe epilepsy (MTLE) where unilateral intrahippocampal injection of kainic acid (KA) in C57BL/6 mice elicits epileptogenesis and spontaneous focal seizures. We used a model of generalized status epilepticus (SE) obtained by intraperitoneal KA injection in C57BL/6 mice. We performed analyses and cross-comparisons according to a schedule of 72 h, 1 week, and 8 weeks after KA injection. RESULTS: In experimental MTLE, we show AT100, PHF1, and CP13 tau hyperphosphorylation during epileptogenesis (72 h-1 week) and long-term (8 weeks) during spontaneous seizures in the ipsilateral hippocampi, the epileptogenic zone. These pathological modifications extended to the contralateral hippocampus, a seizure propagating zone with no histological lesion or sclerosis. Two kinases, Cdk5 and GSK3ß, implicated in the pathological phosphorylation of tau, were activated. In this MTLE model, the induction of the amyloidogenic pathway (APP, C99, BACE1) was prominent and long-lasting in the epileptogenic zone. These Alzheimer's disease (AD)-relevant markers, established during seizure progression and recurrence, reciprocated an enduring glial (GFAP, Iba1) inflammation and the inadequate activation of the endogenous, anti-inflammatory, glucocorticoid receptor system. By contrast, a generalized SE episode provoked a predominantly transient induction of tau hyperphosphorylation and amyloidogenic markers in the hippocampus, along with resolving inflammation. Finally, we identified overlapping profiles of long-term hippocampal tau hyperphosphorylation by comparing MTLE to J20 mice, the latter a model relevant to AD. SIGNIFICANCE: MTLE and a generalized SE prompt persistent and varying tau hyperphosphorylation or amyloidogenic modifications in the hippocampus. In MTLE, an AD-relevant molecular trajectory intertwines with neuroinflammation, spatiotemporally involving epileptogenic and nonlesional seizure propagating zones.

Chronic Glucocorticoids Consumption Triggers and Worsens Experimental Alzheimer's Disease-Like Pathology by Detrimental Immune Modulations.

INTRODUCTION: Among the risk factors identified in the sporadic forms of Alzheimer's disease (AD), environmental and lifestyle elements are of growing interest. Clinical observations suggest that stressful events can anticipate AD onset, while stress-related disorders can promote AD. Here, we tested the hypothesis that a chronic treatment with glucocorticoids is sufficient to trigger or exacerbate AD molecular hallmarks. METHODS: We first validated a rat model of experimental chronic glucocorticoids (GC) consumption (corticosterone [CORT] in drinking water for 4 weeks). Then, to evaluate the consequences of chronic GC consumption on the onset of amyloid-ß (Aß) toxicity, animals chronically treated with GC were intracerebroventricularly injected with an oligomeric solution of Aß25-35 (oAß) (acute model of AD). We evaluated AD-related cognitive deficits and pathogenic mechanisms, with a special emphasis on neuroinflammatory markers. RESULTS: Chronic CORT consumption caused the inhibition of the nonamyloidogenic pathways, the impairment of Aß clearance processes and the induction of amyloidogenic pathways in the hippocampus. The principal enzymes involved in glucocorticoid receptor activation and Tau phosphorylation were upregulated. Importantly, the AD-like phenotype triggered by chronic CORT was analogous to the one caused by oAß. These molecular commonalities across models were independent from inflammation, as chronic CORT was immunosuppressive while oAß was pro-inflammatory. When chronic CORT consumption anticipated the induction of the oAß pathology, we found a potentiation of neuroinflammatory processes associated with an exacerbation of synaptic and memory deficits but also an aggravation of AD-related hallmarks. DISCUSSION/CONCLUSION: This study unravels new functional outcomes identifying chronic CORT consumption as a main risk factor for AD and suggests that glucocorticoid-based therapies should be prescribed with caution in populations with AD risk.

Mechanistic Insights into Light-Driven Allosteric Control of GPCR Biological Activity.

G protein-coupled receptors (GPCR), including the metabotrobic glutamate 5 receptor (mGlu5), are important therapeutic targets and the development of allosteric ligands for targeting GPCRs has become a desirable approach toward modulating receptor activity. Traditional pharmacological approaches toward modulating GPCR activity are still limited since precise spatiotemporal control of a ligand is lost as soon as it is administered. Photopharmacology proposes the use of photoswitchable ligands to overcome this limitation, since their activity can be reversibly controlled by light with high precision. As this is still a growing field, our understanding of the molecular mechanisms underlying the light-induced changes of different photoswitchable ligand pharmacology is suboptimal. For this reason, we have studied the mechanisms of action of alloswitch-1 and MCS0331; two freely diffusible, mGlu5 phenylazopyridine photoswitchable negative allosteric modulators. We combined photochemical, cell-based, and in vivo photopharmacological approaches to investigate the effects of trans-cis azobenzene photoisomerization on the functional activity and binding ability of these ligands to the mGlu5 allosteric pocket. From these results, we conclude that photoisomerization can take place inside and outside the ligand binding pocket, and this leads to a reversible loss in affinity, in part, due to changes in dissociation rates from the receptor. Ligand activity for both photoswitchable ligands deviates from high-affinity mGlu5 negative allosteric modulation (in the trans configuration) to reduced affinity for the mGlu5 in their cis configuration. Importantly, this mechanism translates to dynamic and reversible control over pain following local injection and illumination of negative allosteric modulators into a brain region implicated in pain control.

Functional and molecular heterogeneity of D2R neurons along dorsal ventral axis in the striatum.

Action control is a key brain function determining the survival of animals in their environment. In mammals, neurons expressing dopamine D2 receptors (D2R) in the dorsal striatum (DS) and the nucleus accumbens (Acb) jointly but differentially contribute to the fine regulation of movement. However, their region-specific molecular features are presently unknown. By combining RNAseq of striatal D2R neurons and histological analyses, we identified hundreds of novel region-specific molecular markers, which may serve as tools to target selective subpopulations. As a proof of concept, we characterized the molecular identity of a subcircuit defined by WFS1 neurons and evaluated multiple behavioral tasks after its temporally-controlled deletion of D2R. Consequently, conditional D2R knockout mice displayed a significant reduction in digging behavior and an exacerbated hyperlocomotor response to amphetamine. Thus, targeted molecular analyses reveal an unforeseen heterogeneity in D2R-expressing striatal neuronal populations, underlying specific D2R's functional features in the control of specific motor behaviors.

Glucocorticoid receptors signaling impairment potentiates amyloid-ß oligomers-induced pathology in an acute model of Alzheimer's disease.

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis occurs early in Alzheimer's disease (AD), associated with elevated circulating glucocorticoids (GC) and glucocorticoid receptors (GR) signaling impairment. However, the precise role of GR in the pathophysiology of AD remains unclear. Using an acute model of AD induced by the intracerebroventricular injection of amyloid-ß oligomers (oAß), we analyzed cellular and behavioral hallmarks of AD, GR signaling pathways, processing of amyloid precursor protein, and enzymes involved in Tau phosphorylation. We focused on the prefrontal cortex (PFC), particularly rich in GR, early altered in AD and involved in HPA axis control and cognitive functions. We found that oAß impaired cognitive and emotional behaviors, increased plasma GC levels, synaptic deficits, apoptosis and neuroinflammatory processes. Moreover, oAß potentiated the amyloidogenic pathway and enzymes involved both in Tau hyperphosphorylation and GR activation. Treatment with a selective GR modulator (sGRm) normalized plasma GC levels and all behavioral and biochemical parameters analyzed. GR seems to occupy a central position in the pathophysiology of AD. Deregulation of the HPA axis and a feed-forward effect on PFC GR sensitivity could participate in the etiology of AD, in perturbing Aß and Tau homeostasis. These results also reinforce the therapeutic potential of sGRm in AD.

Is AD a Stress-Related Disorder? Focus on the HPA Axis and Its Promising Therapeutic Targets.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that has important health and economic impacts in the elderly. Despite a better understanding of the molecular mechanisms leading to the appearance of major pathological hallmarks (senile plaques and neurofibrillary tangles), effective treatments are still lacking. Sporadic AD forms (98% of all cases) are multifactorial, and a panoply of risk factors have been identified. While the major risk factor is aging, growing evidence suggests that chronic stress or stress-related disorders increase the probability to develop AD. An early dysregulation of the hypothalamic-pituitary-adrenal axis (HPA axis or stress axis) has been observed in patients. The direct consequence of such perturbation is an oversecretion of glucocorticoids (GC) associated with an impairment of its receptors (glucocorticoid receptors, GR). These steroids hormones easily penetrate the brain and act in synergy with excitatory amino acids. An overexposure could be highly toxic in limbic structures (prefrontal cortex and hippocampus) and contribute in the cognitive decline occurring in AD. GC and GR dysregulations seem to be involved in lots of functions disturbed in AD and a vicious cycle appears, where AD induces HPA axis dysregulation, which in turn potentiates the pathology. This review article presents some preclinical and clinical studies focusing on the HPA axis hormones and their receptors to fight AD. Due to its primordial role in the maintenance of homeostasis, the HPA axis appears as a key-actor in the etiology of AD and a prime target to tackle AD by offering multiple angles of action.

Central Role of Glucocorticoid Receptors in Alzheimer's Disease and Depression.

Alzheimer's disease (AD) is the principal neurodegenerative pathology in the world displaying negative impacts on both the health and social ability of patients and inducing considerable economic costs. In the case of sporadic forms of AD (more than 95% of patients), even if mechanisms are unknown, some risk factors were identified. The principal risk is aging, but there is growing evidence that lifetime events like chronic stress or stress-related disorders may increase the probability to develop AD. This mini-review reinforces the rationale to consider major depressive disorder (MDD) as an important risk factor to develop AD and points the central role played by the hypothalamic-pituitary-adrenal (HPA) axis, glucocorticoids (GC) and their receptors (GR) in the etiology of MDD and AD. Several strategies directly targeting GR were tested to neutralize the HPA axis dysregulation and GC overproduction. Given the ubiquitous expression of GR, antagonists have many undesired side effects, limiting their therapeutic potential. However, a new class of molecules was developed, highly selective and acting as modulators. They present the advantage to selectively abrogate pathogenic GR-dependent processes, while retaining beneficial aspects of GR signaling. In fact, these "selective GR modulators" induce a receptor conformation that allows activation of only a subset of downstream signaling pathways, explaining their capacity to combine agonistic and antagonistic properties. Thus, targeting GR with selective modulators, alone or in association with current strategies, becomes particularly attractive and relevant to develop novel preventive and/or therapeutic strategies to tackle disorders associated with a dysregulation of the HPA axis.

Exogenous LRRK2G2019S induces parkinsonian-like pathology in a nonhuman primate.

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease among the elderly. To understand its pathogenesis and to test therapies, animal models that faithfully reproduce key pathological PD hallmarks are needed. As a prelude to developing a model of PD, we tested the tropism, efficacy, biodistribution, and transcriptional effect of canine adenovirus type 2 (CAV-2) vectors in the brain of Microcebus murinus, a nonhuman primate that naturally develops neurodegenerative lesions. We show that introducing helper-dependent (HD) CAV-2 vectors results in long-term, neuron-specific expression at the injection site and in afferent nuclei. Although HD CAV-2 vector injection induced a modest transcriptional response, no significant adaptive immune response was generated. We then generated and tested HD CAV-2 vectors expressing leucine-rich repeat kinase 2 (LRRK2) and LRRK2 carrying a G2019S mutation (LRRK2G2019S), which is linked to sporadic and familial autosomal dominant forms of PD. We show that HD-LRRK2G2019S expression induced parkinsonian-like motor symptoms and histological features in less than 4 months.

Illuminating Phenylazopyridines To Photoswitch Metabotropic Glutamate Receptors: From the Flask to the Animals.

Phenylazopyridines are photoisomerizable compounds with high potential to control biological functions with light. We have obtained a series of phenylazopyridines with light dependent activity as negative allosteric modulators (NAM) of metabotropic glutamate receptor subtype 5 (mGlu5). Here we describe the factors needed to achieve an operational molecular photoisomerization and its effective translation into in vitro and in vivo receptor photoswitching, which includes zebrafish larva motility and the regulation of the antinociceptive effects in mice. The combination of light and some specific phenylazopyridine ligands displays atypical pharmacological profiles, including light-dependent receptor overactivation, which can be observed both in vitro and in vivo. Remarkably, the localized administration of light and a photoswitchable compound in the peripheral tissues of rodents or in the brain amygdalae results in an illumination-dependent analgesic effect. The results reveal a robust translation of the phenylazopyridine photoisomerization to a precise photoregulation of biological activity.

Coxsackievirus Adenovirus Receptor Loss Impairs Adult Neurogenesis, Synapse Content, and Hippocampus Plasticity.

UNLABELLED: Although we are beginning to understand the late stage of neurodegenerative diseases, the molecular defects associated with the initiation of impaired cognition are poorly characterized. Here, we demonstrate that in the adult brain, the coxsackievirus and adenovirus receptor (CAR) is located on neuron projections, at the presynapse in mature neurons, and on the soma of immature neurons in the hippocampus. In a proinflammatory or diseased environment, CAR is lost from immature neurons in the hippocampus. Strikingly, in hippocampi of patients at early stages of late-onset Alzheimer's disease (AD), CAR levels are significantly reduced. Similarly, in triple-transgenic AD mice, CAR levels in hippocampi are low and further reduced after systemic inflammation. Genetic deletion of CAR from the mouse brain triggers deficits in adult neurogenesis and synapse homeostasis that lead to impaired hippocampal plasticity and cognitive deficits. We propose that post-translational CAR loss of function contributes to cognitive defects in healthy and diseased-primed brains. SIGNIFICANCE STATEMENT: This study addressed the role of the coxsackievirus and adenovirus receptor (CAR), a single-pass cell adhesion molecule, in the adult brain. Our results demonstrate that CAR is expressed by mature neurons throughout the brain. In addition, we propose divergent roles for CAR in immature neurons, during neurogenesis, and at the mature synapse. Notably, CAR loss of function also affects hippocampal plasticity.

OptoGluNAM4.1, a Photoswitchable Allosteric Antagonist for Real-Time Control of mGlu4 Receptor Activity.

OptoGluNAM4.1, a negative allosteric modulator (NAM) of metabotropic glutamate receptor 4 (mGlu4) contains a reactive group that covalently binds to the receptor and a blue-light-activated, fast-relaxing azobenzene group that allows reversible receptor activity photocontrol in vitro and in vivo. OptoGluNAM4.1 induces light-dependent behavior in zebrafish and reverses the activity of the mGlu4 agonist LSP4-2022 in a mice model of chronic pain, defining a photopharmacological tool to better elucidate the physiological roles of the mGlu4 receptor in the nervous system.

Disruption of the coxsackievirus and adenovirus receptor-homodimeric interaction triggers lipid microdomain- and dynamin-dependent endocytosis and lysosomal targeting.

The coxsackievirus and adenovirus receptor (CAR) serves as a docking factor for some adenovirus (AdV) types and group B coxsackieviruses. Its role in AdV internalization is unclear as studies suggest that its intracellular domain is dispensable for some AdV infection. We previously showed that in motor neurons, AdV induced CAR internalization and co-transport in axons, suggesting that CAR was linked to endocytic and long-range transport machineries. Here, we characterized the mechanisms of CAR endocytosis in neurons and neuronal cells. We found that CAR internalization was lipid microdomain-, actin-, and dynamin-dependent, and subsequently followed by CAR degradation in lysosomes. Moreover, ligands that disrupted the homodimeric CAR interactions in its D1 domains triggered an internalization cascade involving sequences in its intracellular tail.

Study of adenovirus and CAR axonal transport in primary neurons.

Vectors derived from the canine adenovirus serotype 2 (CAV-2) possess a high neurotropism and efficient retrograde transport that lead to widespread neuronal transduction in the central nervous system (CNS) of various animals. These abilities are due to the engagement of virions to the coxsackievirus and adenovirus receptor at the surface of neurons, which is linked to the endocytic and axonal transport machineries. The trafficking of CAV-2 and the coxsackievirus and adenovirus receptor (CAR) can be visualized ex vivo by incubating primary neurons (e.g., motoneurons and hippocampal neurons) with fluorescently labeled virions or recombinant viral proteins. Using this approach, we could recapitulate the mechanisms responsible for long-range transport of adenovirus in neurons.

Deregulation of hypothalamic-pituitary-adrenal axis functions in an Alzheimer's disease rat model.

Elevated cortisol evidence in Alzheimer's disease (AD) patients prompted the hypothesis that stress and glucocorticoids are involved in the development and/or maintenance of AD. We investigated the hypothalamic-pituitary-adrenal (HPA) axis activity, functionality, and reactivity for up to 6 weeks after an intracerebroventricular injection of amyloid-ß(25-35) peptide (Aß(25-35)) in rat, a validated acute model of AD. Aß(25-35) induces memory impairment, alteration of anxiety responses, HPA axis hyperactivity, and glucocorticoid (GR) and mineralocorticoid (MR) receptor increases in brain regions related to HPA axis functions. GR are progressively translocated in neurons nucleus, while membrane version of MR is evidenced in all structures considered. The MR/GR ratio was modified in all structures considered. Aß(25-35) induces a subtle disturbance in the feedback of the HPA axis, without modifying its functionality. The reactivity alteration is long-lasting, suggesting that amyloid toxicity affects the HPA axis adaptive response to stress. These findings are evidence of progressive HPA axis deregulation after Aß(25-35), which is associated with an imbalance of MR/GR ratio and a disruption of the glucocorticoid receptors nucleocytoplasmic shuttling, and suggest that elevated glucocorticoids observed in AD could be first a consequence of amyloid toxicity.