Longitudinal analysis of the behavioral phenotype in a novel transgenic rat model of early stages of Alzheimer's disease

GlyT1 Inhibition by NFPS Promotes Neuroprotection in Amyloid-β-Induced Alzheimer's Disease Animal Model

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid-β, leading to N-methyl-D-aspartate (NMDA) receptor-dependent synaptic depression, spine elimination, and memory deficits. Glycine transporter type 1 (GlyT1) modulates glutamatergic neurotransmission via NMDA receptors (NMDAR), presenting a potential alternative therapeutic approach for AD. This study investigates the neuroprotective potential of GlyT1 inhibition in an amyloid-β-induced AD mouse model. C57BL/6 mice were treated with N-[3-([1,1-Biphenyl]-4-yloxy)-3-(4-fluorophenyl)propyl]-N-methylglycine (NFPS), a GlyT1 inhibitor, 24 h prior to intrahippocampal injection of amyloid-β. NFPS pretreatment prevented amyloid-β-induced cognitive deficits in short-term and long-term memory, evidenced by novel object recognition and spatial memory tasks. Moreover, NFPS pretreatment curbed microglial activation, astrocytic reactivity, and subsequent neuronal damage from amyloid-β injection. An extensive label-free quantitative UPLC-MSE proteomic analysis was performed on the hippocampi of mice treated with NFPS. In proteomics, KEGG enrichment analysis revealed increased in dopaminergic synapse, purine-containing compound biosynthetic process and long-term potentiation, and a reduction in Glucose catabolic process and glycolytic process pathways. The western blot analysis confirmed that NFPS treatment elevated BDNF levels, correlating with enhanced TRKB phosphorylation and mTOR activation. Moreover, NFPS treatment reduced the GluN2B expression after 6 h, which was associated with an increase on CaMKIV and CREB phosphorylation. Collectively, these findings demonstrate that GlyT1 inhibition by NFPS activates diverse neuroprotective pathways, enhancing long-term potentiation signaling and countering amyloid-β-induced hippocampal damage.

Effect of simultaneous application of adenosine A1 receptor agonist and A2A receptor antagonist on memory, inflammatory factors, and PSD-95 in lipopolysaccharide-induced memory impairment

The potential role of adenosine, a natural neuroprotective agent, and its receptors in the pathogenesis of Alzheimer's disease has been proposed. The present study aims to examine the effect of administering both an A1 receptor agonist and an A2A adenosine receptor antagonist simultaneously on memory, inflammatory factors, and PSD-95 in an LPS-induced Alzheimer's disease model in rats. Fifty-six male Wistar rats were randomly divided into seven groups: Saline, LPS, Saline + Vehicle, LPS + Vehicle, LPS + SCH58261 (A2A receptor antagonist), LPS + CPA (A1 receptor agonist), LPS + SCH58261+CPA. LPS (3mg/kg/ip) was used to cause memory impairment. Treatment was performed by intraventricular injection of CPA at a dose of 700μg and SCH-58261 at 40μg for ten days. Passive avoidance and Y-maze tests were performed to examine animals' memories. IL-10, TNF-α, and PSD-95 levels were measured in the brain using ELISA and western blot, respectively. Compared to the groups receiving each medication separately, the simultaneous administration of CPA and SCH58261 improved memory (P<0.05). Additionally, compared to the single medication groups, there was a significant increase in IL-10, PSD-95, and a significant decrease in TNF-α in the brain tissue (P<0.05). These findings suggest that the activation of A1 receptors along with A2A receptor inhibition could be a potential therapeutic strategy for Alzheimer's disease. These findings suggest that A1 receptor activation combined with A2A receptor inhibition may be a promising therapeutic approach for Alzheimer's disease.

Early oxidative stress and DNA damage in Aβ-burdened hippocampal neurons in an Alzheimer's-like transgenic rat model

Oxidative stress is a key contributor to AD pathology. However, the earliest role of pre-plaque neuronal oxidative stress, remains elusive. Using laser microdissected hippocampal neurons extracted from McGill-R-Thy1-APP transgenic rats we found that intraneuronal amyloid beta (iAβ)-burdened neurons had increased expression of genes related to oxidative stress and DNA damage responses including Ercc2, Fancc, Sod2, Gsr, and Idh1. DNA damage was further evidenced by increased neuronal levels of XPD (Ercc2) and γH2AX foci, indicative of DNA double stranded breaks (DSBs), and by increased expression of Ercc6, Rad51, and Fen1, and decreased Sirt6 in hippocampal homogenates. We also found increased expression of synaptic plasticity genes (Grin2b (NR2B), CamkIIα, Bdnf, c-fos, and Homer1A) and increased protein levels of TOP2β. Our findings indicate that early accumulation of iAβ, prior to Aβ plaques, is accompanied by incipient oxidative stress and DSBs that may arise directly from oxidative stress or from maladaptive synaptic plasticity.

Nasal application of kisspeptin-54 mitigates motor deficits by reducing nigrostriatal dopamine loss in hemiparkinsonian rats

Parkinson's Disease is a progressive neurodegenerative disorder characterized by motor symptoms resulting from the loss of nigrostriatal dopaminergic neurons. Kisspeptins (KPs) are a family of neuropeptides that are encoded by the Kiss-1 gene, which exert their physiological effects through interaction with the GPR54 receptor. In the current investigation, we investigated the prospective protective effects of central KP-54 treatments on nigrostriatal dopaminergic neurons and consequent motor performance correlates in 6-hydroxydopamine (6-OHDA)-lesioned rats. Male adult Sprague Dawley rats underwent stereotaxic injection of 6-OHDA into the right medial forebrain bundle to induce hemiparkinsonism. Following surgery, rats received chronic central treatments of nasal or intracerebroventricular KP-54 (logarithmically increasing doses) for seven consecutive days. Motor performance was evaluated seven days post-surgery utilizing the open field test and catalepsy test. The levels of dopamine in the striatum were determined with mass spectrometry. Immunohistochemical analysis was conducted to assess the immunoreactivities of tyrosine hydroxylase (TH) and the GPR54 in the substantia nigra. The dose-response curve revealed a median effective dose value of ≈3 nmol/kg for both central injections. Due to its non-invasive and effective nature, nasal administration was utilized in the second phase of our study. Chronic administration of KP-54 (3nmol/kg, nasally) significantly protected 6-OHDA-induced motor deficits. Nasal KP-54 attenuated the loss of nigrostriatal dopaminergic neurons induced by 6-OHDA. Additionally, significant correlations were observed between motor performance and nigrostriatal dopamine levels. Immunohistochemical analysis demonstrated the localization of the GPR54 within TH-positive nigral cells. These findings suggest the potential efficacy of central KP-54 on motor impairments in hemiparkinsonism.

Decreased extrasynaptic δ-GABAA receptors in PNN-associated parvalbumin interneurons correlates with anxiety in APP and tau mouse models of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is associated with gradual memory loss and anxiety which affects ~75% of AD patients. This study investigated whether AD-associated anxiety correlated with modulation of extrasynaptic δ-subunit-containing GABAA receptors (δ-GABAARs) in experimental mouse models of AD.

EXPERIMENTAL APPROACH

We combined behavioural experimental paradigms to measure cognition performance, and anxiety with neuroanatomy and molecular biology, using familial knock-in (KI) mouse models of AD that harbour β-amyloid (Aβ) precursor protein App (AppNL-F) with or without humanized microtubule-associated protein tau (MAPT), age-matched to wild-type control mice at three different age windows.

RESULTS

AppNL-F KI and AppNL-F/MAPT AD models showed a similar magnitude of cognitive decline and elevated magnitude of anxiety correlated with neuroinflammatory hallmarks, including triggering receptor expressed on myeloid cells 2 (TREM2), reactive astrocytes and activated microglia consistent with accumulation of Aβ, tau and down-regulation of Wnt/β-catenin signalling compared to aged-matched WT controls. In both the CA1 region of the hippocampus and dentate gyrus, there was an age-dependent decline in the expression of δ-GABAARs selectively expressed in parvalbumin (PV)-expressing interneurons, encapsulated by perineuronal nets (PNNs) in the AD mouse models compared to WT mice. In vivo positive allosteric modulation of the δ-GABAARs, using a δ-selective-compound DS2, decreased the level of anxiety in the AD mouse models, which was correlated with reduced hallmarks of neuroinflammation, and 'normalisation' of the expression of δ-GABAARs.

CONCLUSIONS

Our data show that the δ-GABAARs could potentially be targeted for alleviating symptoms of anxiety, which would greatly improve the quality of life of AD individuals.

Pharmacological evaluation of newly synthesized benzimidazole derivative for anti-Alzheimer potential

Backgound: Alzheimer disease (AD) is a disastrous disease characterized by accretion of amyloid-beta plaques, neurofibrillary tangles inducing oxidative stress, loss of neuronal functions and continuous progression of cognitive impairment leading to severe dementia.

Material and Methods: The newly synthesized benzimidazole derivative 4-chloro-3-(2-phenyl-1H-benzimidazole-1-sulfonyl) benzoic acid (CB) was evaluated for its anti-Alzheimer activity using in silico, in vivo, in vitro and molecular techniques (ELISA, WB & IHC).

Results: In-silico studies revealed that CB has atomic contact energy values of -3.9 to -8.9 kcal/mol against selected targets. In vitro assay showed that CB caused acetylcholinesterase (AChE) and diphenyl-1-picrylhydrazyl inhibition. In-vivo findings revealed improvement in dementia as observed in the morris water maze test and Ymaze test. Amyloid-beta disaggregation, increased level of anti-oxidants, decreased expressions of inflammatory markers and enhanced cellular architecture were found in the cortex and hippocampus of treated rats in the histopathological examination, immunohistochemistry analysis, enzyme-linked immunosorbent assay and western blot analysis.

Conclusions: This study revealed that CB possess different binding affinities with the Alzheimer-related targets and it possess anti-Alzheimer activity, mediated via AChE and amyloid-beta inhibition, anti-oxidant and anti-inflammatory pathways.

Assessing the Safety and Therapeutic Efficacy of Cannabidiol Lipid Nanoparticles in Alleviating Metabolic and Memory Impairments and Hippocampal Histopathological Changes in Diabetic Parkinson's Rats

Diabetic Parkinson's disease (DP) is a progressive neurodegenerative disease with metabolic syndrome that is increasing worldwide. Emerging research suggests that cannabidiol (CBD) is a neuropharmacological compound that acts against this disease, especially CBD in nano-formulation. The safety of cannabidiol lipid nanoparticles (CBD-LNP) was evaluated by assessing in vitro cytotoxicity in neurons and therapeutic outcomes in a DP animal model, including metabolic parameters and histopathology. CBD-LNPs were fabricated by using a microfluidization technique and showed significantly lower cytotoxicity than the natural form of CBD. The DP rats were induced by streptozotocin followed by a 4-week injection of MPTP with a high-fat diet. Rats were treated orally with a vehicle, CBD, CBD-LNP, or levodopa for 4 weeks daily. As a result, vehicle-treated rats exhibited metabolic abnormalities, decreased striatal dopamine levels, and motor and memory deficits. CBD-LNP demonstrated reduced lipid profiles, enhanced insulin secretion, and restored dopamine levels compared to CBD in the natural form. CBD-LNP also had comparable efficacy to levodopa in ameliorating motor deficits and memory impairment in behavior tests. Interestingly, CBD-LNP presented migration of damaged neuronal cells in the hippocampus more than levodopa. These findings suggest that CBD-LNP holds promise as an intervention addressing both metabolic and neurodegenerative aspects of DP, offering a potential therapeutic strategy.

The Effect of Fat Intake with Increased Omega-6-to-Omega-3 Polyunsaturated Fatty Acid Ratio in Animal Models of Early and Late Alzheimer's Disease-like Pathogenesis

This work aims to clarify the effect of dietary polyunsaturated fatty acid (PUFA) intake on the adult brain affected by amyloid pathology. McGill-R-Thy1-APP transgenic (Tg) rat and 5xFAD Tg mouse models that represent earlier or later disease stages were employed. The animals were exposed to a control diet (CD) or an HFD based on corn oil, from young (rats) or adult (mice) ages for 24 or 10 weeks, respectively. In rats and mice, the HFD impaired reference memory in wild-type (WT) animals but did not worsen it in Tg, did not cause obesity, and did not increase triglycerides or glucose levels. Conversely, the HFD promoted stronger microglial activation in Tg vs. WT rats but had no effect on cerebral amyloid deposition. IFN-γ, IL-1β, and IL-6 plasma levels were increased in Tg rats, regardless of diet, while CXCL1 chemokine levels were increased in HFD-fed mice, regardless of genotype. Hippocampal 3-nitrotyrosine levels tended to increase in HFD-fed Tg rats but not in mice. Overall, an HFD with an elevated omega-6-to-omega-3 ratio as compared to the CD (25:1 vs. 8.4:1) did not aggravate the outcome of AD regardless of the stage of amyloid pathology, suggesting that many neurobiological processes relevant to AD are not directly dependent on PUFA intake.

Modeling of Alzheimer's Disease to Study the Efficacy of Cell Therapy (Review)

We analyzed the main approaches to the modeling of Alzheimer's disease for studying the effectiveness of cell therapy. Recent advances in regenerative medicine in the field of neuroscience create prospects for the use of various cell preparations for the treatment of Alzheimer's disease. Experimental data on the use of neural stem/progenitor cells, mesenchymal stem cells, embryonic stem cells, and induced pluripotent stem cells in various models of Alzheimer's disease are presented. Of particular importance is the standardization of protocols. The use of a standardized protocol in modeling of Alzheimer's disease will allow a comparative analysis of the effectiveness and safety of treatment to identify the optimal cell preparation. The data obtained on experimental animals can form the basis for further preclinical and clinical studies of cell therapy for Alzheimer's disease.

Barbigerone prevents scopolamine-induced memory impairment in rats by inhibiting oxidative stress and acetylcholinesterase levels

The current study was designed for the evaluation of barbigerone on memory loss. In this experimental study, 24 Wistar rats (n = 6) were used. Control rats and scopolamine (SCOP)-treated control group rats were orally administered with 3 ml of 0.5% sodium carboxymethyl cellulose (vehicle), whereas barbigerone was (10 and 20 mg kg^-1) administered orally to the rats from the test group. During the 14-day treatment, control group rats were given 3 ml kg^-1 day^-1 saline, and all other groups were administered SCOP (1 mg kg^-1 day^-1, i.p.) 1 h after barbigerone p.o. treatment. The spontaneous alternation activities, learning capacities of a rat's memory were tested with Morris water maze and Y-maze. Reduced glutathione, malondialdehyde, acetylcholine esterase (AChE) and catalase (CAT) levels were measured in rat brain tissue as oxidative stress/antioxidant markers. Moreover, the levels of tumour necrosis factor, interleukin-6 (IL-6) and IL-1β were also estimated. Treatment with barbigerone in SCOP-administered rats dramatically reduced SCOP-induced neurobehavioural deficits, oxidative stress and neuroinflammatory markers, improved endogenous antioxidants, and restored AChE activity. By improving cholinergic function and reducing oxidative damage, barbigerone could mitigate the effects of SCOP-induced changes in the brain.

How does neurokinin 3 receptor agonism affect pathological and cognitive impairments in an Alzheimer's disease-like rat model?

Alzheimer's disease (AD) is accepted as a form of progressive dementia. Cholinergic systems are commonly affected in AD. Neurokinin 3 receptor (NK3R) is involved in learning memory-related processes. It is known that the activation of NK3R affects the release of many neurotransmitters. The aim of this project was to investigate the effects of NK3R agonist senktide administration on neurobehavioral mechanisms in the experimental AD-like rat model. 50 male Wistar albino rats were divided into Control (C), AD, Control + NK3R agonist (CS), AD + NK3R agonist (ADS), AD + NK3Ragonist + antagonist groups (ADSO). We designed AD-like model by intrahippocampal administration of Aβ1-42. After NK3R agonist + antagonist injections, open field (OF), Morris water maze (MWM) tests were applied. Cholinergic mechanism analysis from hippocampus-cortex tissues was performed by ELISA and catecholamine analysis from brain stem tissue were performed by HPLC method. The transitions from edge to center, rearing, grooming parameters were found to be reduced in final values of OF. While the group-time interaction was significant in the OF test findings, there was no significant difference between the groups. In MWM test, ADS group showed a learning level close to control group and animals in AD and ADSO groups could not learn target quadrant in MWM test. The brain stem NA and DA concentrations were not statistically significant. Hippocampal AChE-ChAT levels were supported by positive effects of senktide on learning via the cholinergic mechanisms. As a result, NK3R agonists were found to be effective in improving cognitive functions in rats with AD pathology. In the experimental AD model, positive effects of NK3R on learning memory may be mediated by cholinergic mechanisms.

Pinostrobin alleviates chronic restraint stress‑induced cognitive impairment by modulating oxidative stress and the function of astrocytes in the hippocampus of rats

Chronic stress has been recognized to induce the alterations of neuronal and glial cells in the hippocampus, and is thus implicated in cognitive dysfunction. There is increasing evidence to indicate that natural compounds capable of exerting neuroprotective and antioxidant activities, may function as potential therapeutic agents for cognitive impairment. The present study examined the neuroprotective effects of pinostrobin from Boesenbergia rotunda (L.) against chronic restraint stress (CRS)-induced cognitive impairment associated with the alterations of oxidative stress, neuronal density and glial fibrillary acidic protein (GFAP) of astrocytes in the hippocampus. For this purpose, male Wistar rats were administered once daily with pinostrobin (20 and 40 mg/kg, per os) prior to exposure to CRS (6 h/day) for 21 days. The cognitive behaviors, the concentration of malondialdehyde, and the activities of superoxide dismutase and catalase were determined. Histologically, the alterations in astrocytic GFAP and excitatory amino acid transporter 2 (EAAT2) in the hippocampus were examined. The results revealed that pinostrobin potentially attenuated cognitive impairment in the Y-maze and in novel object recognition tests, with a reduction in oxidative stress. Furthermore, pinostrobin effectively increased neuronal density, as well as the immunoreactivities of GFAP and EAAT2 in the hippocampus. Taken together, these findings indicate that treatment with pinostrobin alleviates chronic stress-induced cognitive impairment by exerting antioxidant effects, reducing neuronal cell damage, and improving the function of astrocytic GFAP and EAAT2. Thus, pinostrobin may have potential for use as a neuroprotective agent to protect against chronic stress-induced brain dysfunction and cognitive deficits.

Nicotinamide as potential biomarker for Alzheimer's disease: A translational study based on metabolomics

Introduction: The metabolic routes altered in Alzheimer's disease (AD) brain are poorly understood. As the metabolic pathways are evolutionarily conserved, the metabolic profiles carried out in animal models of AD could be directly translated into human studies. Methods: We performed untargeted Nuclear Magnetic Resonance metabolomics in hippocampus of McGill-R-Thy1-APP transgenic (Tg) rats, a model of AD-like cerebral amyloidosis and the translational potential of these findings was assessed by targeted Gas Chromatography-Electron Impact-Mass Spectrometry in plasma of participants in the German longitudinal cohort AgeCoDe. Results: In rat hippocampus 26 metabolites were identified. Of these 26 metabolites, nine showed differences between rat genotypes that were nominally significant. Two of them presented partial least square-discriminant analysis (PLS-DA) loadings with the larger absolute weights and the highest Variable Importance in Projection (VIP) scores and were specifically assigned to nicotinamide adenine dinucleotide (NAD) and nicotinamide (Nam). NAD levels were significantly decreased in Tg rat brains as compared to controls. In agreement with these results, plasma of AD patients showed significantly reduced levels of Nam in respect to cognitively normal participants. In addition, high plasma levels of Nam showed a 27% risk reduction of progressing to AD dementia within the following 2.5 years, this hazard ratio is lost afterwards. Discussion: To our knowledge, this is the first report showing that a decrease of Nam plasma levels is observed couple of years before conversion to AD, thereby suggesting its potential use as biomarker for AD progression.

Butin Mitigates Memory Impairment in Streptozotocin-Induced Diabetic Rats by Inhibiting Oxidative Stress and Inflammatory Responses

It has been reported from the previous literature that butin restores mitochondrial dysfunction by modulation of oxidative stress and glutamate-induced neurotoxicity in mouse hippocampus HT22 cells. Butin also possesses an anti-Huntington's effect in rats. Considering the current background, this study was designed to evaluate the neuroprotective effect of butin against memory loss caused by streptozotocin (STZ). STZ (40 mg/kg) was intraperitoneally injected into rats. Three days later, diabetic rats were identified and included in the study. A total of 30 rats (12 nondiabetic and 18 diabetics) were grouped as Group A (control-non-diabetic rats) and Group B (STZ diabetic control) were treated with 1 mL of sodium CMC (0.5% w/v). Group C (STZ+ butin 25) were treated with butin 25 mg/kg. Group D (STZ+ butin 50) and Group E (butin per se) were administered with butin 50 mg/kg. Each therapy was administered orally once each day for 15-day. The Morris water maze and the Y-maze behavioural tests were run throughout the experimental programme. Animals were put to death on day 15 and their brains were removed for biochemical assays (CAT, SOD, GSH, MDA, nitrite, acetylcholinesterase (AchE), IL-1, and mitochondrial enzyme complexes). Rats with neurobehavioral impairments brought on by STZ have less spontaneous movement, learning capacity, and memory. Additionally, STZ decreased endogenous antioxidants and increased pro-inflammatory cytokines, nitrite, MDA, and AchE. Neurobehavioral deficits and metabolic markers were dramatically improved by butin.

Spatio-temporal metabolic rewiring in the brain of TgF344-AD rat model of Alzheimer's disease

Brain damage associated with Alzheimer's disease (AD) occurs even decades before the symptomatic onset, raising the need to investigate its progression from prodromal stages. In this context, animal models that progressively display AD pathological hallmarks (e.g. TgF344-AD) become crucial. Translational technologies, such as magnetic resonance spectroscopy (MRS), enable the longitudinal metabolic characterization of this disease. However, an integrative approach is required to unravel the complex metabolic changes underlying AD progression, from early to advanced stages. TgF344-AD and wild-type (WT) rats were studied in vivo on a 7 Tesla MRI scanner, for longitudinal quantitative assessment of brain metabolic profile changes using MRS. Disease progression was investigated at 4 time points, from 9 to 18 months of age, and in 4 regions: cortex, hippocampus, striatum, and thalamus. Compared to WT, TgF344-AD rats replicated common findings in AD patients, including decreased N-acetylaspartate in the cortex, hippocampus and thalamus, and decreased glutamate in the thalamus and striatum. Different longitudinal evolution of metabolic concentration was observed between TgF344-AD and WT groups. Namely, age-dependent trajectories differed between groups for creatine in the cortex and thalamus and for taurine in cortex, with significant decreases in Tg344-AD animals; whereas myo-inositol in the thalamus and striatum showed greater increase along time in the WT group. Additional analysis revealed divergent intra- and inter-regional metabolic coupling in each group. Thus, in cortex, strong couplings of N-acetylaspartate and creatine with myo-inositol in WT, but with taurine in TgF344-AD rats were observed; whereas in the hippocampus, myo-inositol, taurine and choline compounds levels were highly correlated in WT but not in TgF344-AD animals. Furthermore, specific cortex-hippocampus-striatum metabolic crosstalks were found for taurine levels in the WT group but for myo-inositol levels in the TgF344-AD rats. With a systems biology perspective of metabolic changes in AD pathology, our results shed light into the complex spatio-temporal metabolic rewiring in this disease, reported here for the first time. Age- and tissue-dependent imbalances between myo-inositol, taurine and other metabolites, such as creatine, unveil their role in disease progression, while pointing to the inadequacy of the latter as an internal reference for quantification.

Differential neuroprotective effect of curcuminoid formulations in aluminum chloride-induced Alzheimer's disease

Alzheimer's disease (AD) is a slowly progressive brain degenerative disorder which gradually impairs memory, thinking, and ability to perform easy routine tasks. This degenerative disorder mainly targets the elderly people and has imposed an endemic burden on society. Hence, there is a crucial need to investigate the efficacious herbal pharmacotherapies that can effectively mitigate and prevent the pathological hallmarks of AD. The current study aims to explore the potential efficacy of curcuminoid-rich extract (CRE) and its ternary complex (TC). Experimental rodents were administered with AlCl₃ (300 mg/kg) to induce AD and treated with rivastigmine, curcuminoid crude extract, CRE, and TC orally for three consecutive weeks. Neurobehavioral, biochemical, and histopathological studies were performed from the last week of the study period. The mRNA expression of different pathological biomarkers was estimated by RT-qPCR analysis. The results of the study suggested that CRE and TC significantly improved the behavioral, biochemical parameters and acetylcholinesterase inhibitory activity in treatment groups. Histological analysis was also carried out indicating that the neurodegenerative changes and neuronal loss were stabilized by CRE and TC supplementation. CRE and TC supplementation remarkably downregulated the interleukin-1α, tumor necrosis factor-α, interleukin-1β, acetylcholinesterase, and β-secretase pathological gene expression. Hence, it was concluded that CRE and TC may act as promising candidates in the prevention of AD via numerous underlying signaling pathways.

The dorsal hippocampal protein targeting to glycogen maintains ionotropic glutamate receptor subunits expression and contributes to working and short-term memories in mice

Brain glycogen metabolism is known to be involved in the learning and memory processes. Protein targeting to glycogen (PTG) is a crucial molecule for glycogenesis, and its expression level is shown to be increased in the dorsal hippocampus during fear memory acquisition and recall, suggesting that PTG may contribute to the memory process. However, its detailed role in the dorsal hippocampus remains unclear. Therefore, we knocked down the expression of PTG in the dorsal hippocampus and attempted to analyze its function behaviorally. PTG expression was found to be enriched in astrocytes. Furthermore, short hairpin RNA against PTG suppressed the expression of PTG in astrocytes. Mice with knockdown of PTG in the dorsal hippocampus showed suppressed alternation behavior in the Y-maze test and reduced memory recall at the first hour after acquisition in the passive avoidance test. Knockdown of mouse dorsal hippocampal astrocyte-specific PTG also impaired working memory in the Y-maze test. GluR1, GluR2, and NR2a subunits expressions were significantly down-regulated in the dorsal hippocampus of mice in which PTG was knocked down. These results indicate that PTG in the dorsal hippocampal astrocytes may contribute to working and short-term memories by maintaining the expression of glutamate receptor subunits.

Enduring glucocorticoid-evoked exacerbation of synaptic plasticity disruption in male rats modelling early Alzheimer's disease amyloidosis

Synaptic dysfunction is a likely proximate cause of subtle cognitive impairment in early Alzheimer's disease. Soluble oligomers are the most synaptotoxic forms of amyloid ß-protein (Aß) and mediate synaptic plasticity disruption in Alzheimer's disease amyloidosis. Because the presence and extent of cortisol excess in prodromal Alzheimer's disease predicts the onset of cognitive symptoms we hypothesised that corticosteroids would exacerbate the inhibition of hippocampal synaptic long-term potentiation in a rat model of Alzheimer's disease amyloidosis. In a longitudinal experimental design using freely behaving pre-plaque McGill-R-Thy1-APP male rats, three injections of corticosterone or the glucocorticoid methylprednisolone profoundly disrupted long-term potentiation induced by strong conditioning stimulation for at least 2 months. The same treatments had a transient or no detectible detrimental effect on synaptic plasticity in wild-type littermates. Moreover, corticosterone-mediated cognitive dysfunction, as assessed in a novel object recognition test, was more persistent in the transgenic animals. Evidence for the involvement of pro-inflammatory mechanisms was provided by the ability of the selective the NOD-leucine rich repeat and pyrin containing protein 3 (NLRP3) inflammasome inhibitor Mcc950 to reverse the synaptic plasticity deficit in corticosterone-treated transgenic animals. The marked prolongation of the synaptic plasticity disrupting effects of brief corticosteroid excess substantiates a causal role for hypothalamic-pituitary-adrenal axis dysregulation in early Alzheimer's disease.

Activation of PPARα enhances astroglial uptake and degradation of β-amyloid

[Figure: see text].

Polyethylene Glycol 3350 Changes Stool Consistency and the Microbiome but not Behavior of CD1 Mice

OBJECTIVES

Polyethylene Glycol 3350 (PEG3350) is a laxative commonly used to treat constipation in children. The Food and Drug Administration has received reports of increased anxiety, aggression, and obsessive--compulsive behaviors in children administered PEG3350. Thus, we assessed whether daily administration of PEG3350 leads to anxiety-like behavior in mice.

METHODS

Outbred CD-1 IGS mice were administered either a high or a low dose of PEG3350 via daily oral gavage for 2 weeks. As a laxative comparison and control, additional mice were given a high or low dose of magnesium citrate or vehicle (water). Weight and stool consistency were assessed after each gavage to determine laxative effectiveness. Anxiety-like behaviors were assessed using light/dark, open field, and elevated plus maze (EPM) tests at baseline, after 2 weeks of daily gavage, and after a 2 week washout in experiment 1, and after 2 weeks of daily gavage in experiment 2. Stool samples were collected for microbiome analysis in experiment 2 at baseline, after 2 weeks of daily gavage, and after 2 weeks washout.

RESULTS

PEG3350 and magnesium citrate significantly changed stool consistency, as well as microbiome alpha and beta diversity. Anxiety-like behaviors were not, however, different in mice administered low or high doses of PEG3350 or magnesium citrate.

CONCLUSIONS

Although changes in stool consistency and the gut microbiome occurred, administration of PEG3350 did not alter anxiety-like behaviors.

Pseudoginsenoside-F11 attenuates cognitive dysfunction and tau phosphorylation in sporadic Alzheimer's disease rat model

We previously reported that pseudoginsenoside-F11 (PF11), an ocotillol-type saponin, significantly ameliorated Alzheimer's disease (AD)-associated cognitive defects in APP/PS1 and SAMP8 mice by inhibiting Aβ aggregation and tau hyperphosphorylation, suggesting a potential therapeutic effect of PF11 in the treatment of AD. In the present study we further evaluated the therapeutic effects of PF11 on relieving cognitive impairment in a rat model of sporadic AD (SAD). SAD was induced in rats by bilateral icv infusion of streptozotocin (STZ, 3 mg/kg). The rats were treated with PF11 (2, 4, 8 mg·kg^-1·d^-1, ig) or a positive control drug donepezil (5 mg·kg^-1·d^-1, ig) for 4 weeks. Their cognitive function was assessed in the nest building, Y-maze, and Morris water maze tests. We showed that STZ icv infusion significantly affected the cognitive function, tau phosphorylation, and insulin signaling pathway in the hippocampus. Furthermore, STZ icv infusion resulted in significant upregulation of the calpain I/cyclin-dependent protein kinase 5 (CDK5) signaling pathway in the hippocampus. Oral administration of PF11 dose-dependently ameliorated STZ-induced learning and memory defects. In addition, PF11 treatment markedly reduced the neuronal loss, protected the synapse structure, and modulated STZ-induced expression of tau phosphorylation by regulating the insulin signaling pathway and calpain I/CDK5 signaling pathway in the hippocampus. Donepezil treatment exerted similar beneficial effects in STZ-infused rats as the high dose of PF11 did. This study highlights the excellent therapeutic potential of PF11 in managing AD.

The Interplay of Tau Protein and β-Amyloid: While Tauopathy Spreads More Profoundly Than Amyloidopathy, Both Processes Are Almost Equally Pathogenic

Alzheimer's disease (AD) is a neurodegenerative disorder, in which amyloid precursor protein (APP) misprocessing and tau protein hyperphosphorylation are well-established pathogenic cascades. Despite extensive considerations, the central mediator of neuronal cell death upon AD remains under debate. Therefore, we examined the direct interplay between tauopathy and amyloidopathy processes. We employed primary culture neurons and examined pathogenic P-tau and Aβ oligomers upon hypoxia treatment by immunofluorescence and immunoblotting. We observed both tauopathy and amyloidopathy processes upon the hypoxia condition. We also applied Aβ1-42 or P-tau onto primary cultured neurons. We overexpressed P-tau in SH-SY5Y cells and found Aβ accumulation. Furthermore, adult male rats received Aβ1-42 or pathogenic P-tau in the dorsal hippocampus and were examined for 8 weeks. Learning and memory performance, as well as anxiety behaviors, were assessed by Morris water maze and elevated plus-maze tests. Both Aβ1-42 and pathogenic P-tau significantly induced learning and memory deficits and enhanced anxiety behavior after treatment 2 weeks. Aβ administration induced robust tauopathy distribution in the cortex, striatum, and corpus callosum as well as CA1. On the other hand, P-tau treatment developed Aβ oligomers in the cortex and CA1 only. Our findings indicate that Aβ1-42 and pathogenic P-tau may induce each other and cause almost identical neurotoxicity in a time-dependent manner, while tauopathy seems to be more distributable than amyloidopathy.

Anxiety and Alzheimer's disease: Behavioral analysis and neural basis in rodent models of Alzheimer's-related neuropathology

Alzheimer's disease (AD) pathology is commonly associated with cognitive decline but is also composed of neuropsychiatric symptoms including psychological distress and alterations in mood, including anxiety and depression. Emotional dysfunction in AD is frequently modeled using tests of anxiety-like behavior in transgenic rodents. These tests often include the elevated plus-maze, light/dark test and open field test. In this review, we describe prototypical behavioral paradigms used to examine emotional dysfunction in transgenic models of AD, specifically anxiety-like behavior. Next, we summarize the results of studies examining anxiety-like behavior in transgenic rodents, noting that the behavioral outcomes using these paradigms have produced inconsistent results. We suggest that future research will benefit from using a battery of tests to examine emotional behavior in transgenic AD models. We conclude by discussing putative, overlapping neurobiological mechanisms underlying AD-related neuropathology, stress and anxiety-like behavior reported in AD models.

Hippocampal hyperactivity in a rat model of Alzheimer's disease

Neuronal network dysfunction is a hallmark of Alzheimer's disease (AD). However, the underlying pathomechanisms remain unknown. We analyzed the hippocampal micronetwork in transgenic McGill-R-Thy1-APP rats (APPtg) at the beginning of extracellular amyloid beta (Aβ) deposition. We established two-photon Ca²⁺ -imaging in vivo in the hippocampus of rats and found hyperactivity of CA1 neurons. Patch-clamp recordings in brain slices in vitro revealed increased neuronal input resistance and prolonged action potential width in CA1 pyramidal neurons. We did neither observe changes in synaptic inhibition, nor in excitation. Our data support the view that increased intrinsic excitability of CA1 neurons may precede inhibitory dysfunction at an early stage of Aβ-deposition and disease progression.

Early Long-Term Memory Impairment and Changes in the Expression of Synaptic Plasticity-Associated Genes, in the McGill-R-Thy1-APP Rat Model of Alzheimer's-Like Brain Amyloidosis

Accruing evidence supports the hypothesis that memory deficits in early Alzheimer Disease (AD) might be due to synaptic failure caused by accumulation of intracellular amyloid beta (Aβ) oligomers, then secreted to the extracellular media. Transgenic mouse AD models provide valuable information on AD pathology. However, the failure to translate these findings to humans calls for models that better recapitulate the human pathology. McGill-R-Thy1-APP transgenic (Tg) rat expresses the human amyloid precursor protein (APP751) with the Swedish and Indiana mutations (of familial AD), leading to an AD-like slow-progressing brain amyloid pathology. Therefore, it offers a unique opportunity to investigate learning and memory abilities at early stages of AD, when Aβ accumulation is restricted to the intracellular compartment, prior to plaque deposition. Our goal was to further investigate early deficits in memory, particularly long-term memory in McGill-R-Thy1-APP heterozygous (Tg+/–) rats. Short-term- and long-term habituation to an open field were preserved in 3-, 4-, and 6-month-old (Tg+/–). However, long-term memory of inhibitory avoidance to a foot-shock, novel object-recognition and social approaching behavior were seriously impaired in 4-month-old (Tg+/–) male rats, suggesting that they are unable to either consolidate and/or evoke such associative and discriminative memories with aversive, emotional and spatial components. The long-term memory deficits were accompanied by increased transcript levels of genes relevant to synaptic plasticity, learning and memory processing in the hippocampus, such as Grin2b, Dlg4, Camk2b, and Syn1. Our findings indicate that in addition to the previously well-documented deficits in learning and memory, McGill-R-Thy1-APP rats display particular long-term-memory deficits and deep social behavior alterations at pre-plaque early stages of the pathology. This highlights the importance of Aβ oligomers and emphasizes the validity of the model to study AD-like early processes, with potentially predictive value.

Bim contributes to the progression of Huntington's disease-associated phenotypes

Huntington's disease (HD) is a neurodegenerative disorder caused by an expanded polyglutamine tract in the huntingtin (HTT) protein. Mutant HTT (mHTT) toxicity is caused by its aggregation/oligomerization. The striatum is the most vulnerable region, although all brain regions undergo neuronal degeneration in the disease. Here we show that the levels of Bim, a BH3-only protein, are significantly increased in HD human post-mortem and HD mouse striata, correlating with neuronal death. Bim reduction ameliorates mHTT neurotoxicity in HD cells. In the HD mouse model, heterozygous Bim knockout significantly mitigates mHTT accumulation and neuronal death, ameliorating disease-associated phenotypes and lifespan. Therefore, Bim could contribute to the progression of HD.

Synchrotron Fourier transform infrared microspectroscopy (sFTIRM) analysis of Al-induced Alzheimer's disease in rat brain cortical tissue

Aluminium (Al) is reported to promote beta amyloid (Aβ) aggregation, free radical production and disturb acetylcholine metabolism leading to cognitive dysfunction that are strongly associated with Alzheimer's disease (AD). Here we utilized synchrotron Fourier transform infrared microspectroscopy (sFTIRM) to analyse the fine structure of proteins and lipids in the rat cortical brain tissues in response to AlCl₃ toxicity and Lepidium sativum (LS) treatment after 42 and 65 days. For statistical analysis, we used principal component analysis (PCA). Our results showed profusion of gauche rotomers form in membrane lipid acyl chains that increases the membrane fluidity and disorder only in AD group indicated by the detected sνCH₂ band shift to higher frequency. All half bands width (HBW) values of the decomposed amide I band showed marked decrease in AD group compared to the other tested groups, together with an increase in the amounts of β-sheets (1641 cm^-1) protein and random coil structure (1654 cm^-1). These were indicated by a drastic increase in the percentage areas ratios of (1638 cm^-1/1654 cm^-1) and (1641 cm^-1/1654 cm^-1) that may be attributed to a stronger the hydrogen bonds that stabilize the protein conformational structure and/or the increase of the β-strand length due to misfolded Aβ formation in response to Al toxicity through transit phase/phases dominated by random coil structure. In curative group, LS treatment reversed these changes and restored the protein and lipid integrities. To conclude, sFTIRM is a powerful tool that shed light on the biomolecular structure of AD-like cortical brain tissue and considered the therapeutic potential of LS as a promising natural AD treatment.

Rodent Models of Amyloid-Beta Feature of Alzheimer's Disease: Development and Potential Treatment Implications

Alzheimer's disease (AD) is the most common neurodegenerative disorder worldwide and causes severe financial and social burdens. Despite much research on the pathogenesis of AD, the neuropathological mechanisms remain obscure and current treatments have proven ineffective. In the past decades, transgenic rodent models have been used to try to unravel this disease, which is crucial for early diagnosis and the assessment of disease-modifying compounds. In this review, we focus on transgenic rodent models used to study amyloid-beta pathology in AD. We also discuss their possible use as promising tools for AD research. There is still no effective treatment for AD and the development of potent therapeutics are urgently needed. Many molecular pathways are susceptible to AD, ranging from neuroinflammation, immune response, and neuroplasticity to neurotrophic factors. Studying these pathways may shed light on AD pathophysiology as well as provide potential targets for the development of more effective treatments. This review discusses the advantages and limitations of these models and their potential therapeutic implications for AD.

Brain connectivity during Alzheimer's disease progression and its cognitive impact in a transgenic rat model

The research of Alzheimer's disease (AD) in its early stages and its progression till symptomatic onset is essential to understand the pathology and investigate new treatments. Animal models provide a helpful approach to this research, since they allow for controlled follow-up during the disease evolution. In this work, transgenic TgF344-AD rats were longitudinally evaluated starting at 6 months of age. Every 3 months, cognitive abilities were assessed by a memory-related task and magnetic resonance imaging (MRI) was acquired. Structural and functional brain networks were estimated and characterized by graph metrics to identify differences between the groups in connectivity, its evolution with age, and its influence on cognition. Structural networks of transgenic animals were altered since the earliest stage. Likewise, aging significantly affected network metrics in TgF344-AD, but not in the control group. In addition, while the structural brain network influenced cognitive outcome in transgenic animals, functional network impacted how control subjects performed. TgF344-AD brain network alterations were present from very early stages, difficult to identify in clinical research. Likewise, the characterization of aging in these animals, involving structural network reorganization and its effects on cognition, opens a window to evaluate new treatments for the disease.

Early intraneuronal amyloid triggers neuron-derived inflammatory signaling in APP transgenic rats and human brain

This work provides evidence that soluble and oligomeric amyloid protein stokes neuronal inflammation during the earliest stages of Alzheimer’s disease. Identifying neuron-derived factors that engage the brain’s immune system will provide insight into how vulnerable neurons might interact with other immune cells to propagate cytotoxic signaling cascades and cellular dysfunction during disease development.

Chronic inflammation during Alzheimer’s disease (AD) is most often attributed to sustained microglial activation in response to amyloid-β (Aβ) plaque deposits and cell death. However, cytokine release and microgliosis are consistently observed in AD transgenic animal models devoid of such pathologies, bringing into question the underlying processes that may be at play during the earliest AD-related immune response. We propose that this plaque-independent inflammatory reaction originates from neurons burdened with increasing levels of soluble and oligomeric Aβ, which are known to be the most toxic amyloid species within the brain. Laser microdissected neurons extracted from preplaque amyloid precursor protein (APP) transgenic rats were found to produce a variety of potent immune factors, both at the transcript and protein levels. Neuron-derived cytokines correlated with the extent of microglial activation and mobilization, even in the absence of extracellular plaques and cell death. Importantly, we identified an inflammatory profile unique to Aβ-burdened neurons, since neighboring glial cells did not express similar molecules. Moreover, we demonstrate within disease-vulnerable regions of the human brain that a neuron-specific inflammatory response may precede insoluble Aβ plaque and tau tangle formation. Thus, we reveal the Aβ-burdened neuron as a primary proinflammatory agent, implicating the intraneuronal accumulation of Aβ as a significant immunological component in the AD pathogenesis.

Oral treatment with royal jelly improves memory and presents neuroprotective effects on icv-STZ rat model of sporadic Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive decline in cognitive function. Intracerebroventricular injection of streptozotocin (icv-STZ) has been used as an experimental model of Sporadic AD (SAD) in rodents and represents a promising tool for etiopathogenic analysis and evaluation of new therapeutic proposals for AD. The icv-STZ model shows many aspects of SAD abnormalities, resulting in decreased brain glucose and energy metabolism, cognitive impairment, oxidative stress, neuronal loss, and amyloid angiopathy. Royal jelly (RJ), a substance produced by worker honeybees of the Apis mellifera species, has been popularly used for more than 30 years in areas related to health eating and natural medicine. Researches indicate that RJ has a several pharmacological activities, including neuroprotective and improvement of cognitive function. The objective of this study was to investigate the effects of oral treatment with royal jelly during 2 weeks in Wistar rats submitted to icv-STZ on a working memory and neuroprotection, as evaluated by neurogenesis, neurodegeneration and oxidative stress. In this study, icv-STZ injection induced deleterious effects in the hippocampus, associated with cognitive impairments, and developed marked neurodegeneration, besides the reduction of neurogenesis and increased oxidative stress. On the other hand, RJ long-term oral administration induced beneficial effects in animals injured by icv-STZ injection, increasing retention time for working spatial memory, reducing neurodegeneration and oxidative stress level and increasing the proliferation of new neurons in the hippocampus. Thus, RJ promotes beneficial effects on cognitive functions and exhibits a neuroprotective action in the STZ experimental model of SAD.

Perturbed mitochondria-ER contacts in live neurons that model the amyloid pathology of Alzheimer's disease

The use of fixed fibroblasts from familial and sporadic Alzheimer's disease patients has previously indicated an upregulation of mitochondria-ER contacts (MERCs) as a hallmark of Alzheimer's disease. Despite its potential significance, the relevance of these results is limited because they were not extended to live neurons. Here we performed a dynamic in vivo analysis of MERCs in hippocampal neurons from McGill-R-Thy1-APP transgenic rats, a model of Alzheimer's disease-like amyloid pathology. Live FRET imaging of neurons from transgenic rats revealed perturbed 'lipid-MERCs' (gap width <10 nm), while 'Ca²⁺-MERCs' (10-20 nm gap width) were unchanged. In situ TEM showed no significant differences in the lipid-MERCs:total MERCs or lipid-MERCs:mitochondria ratios; however, the average length of lipid-MERCs was significantly decreased in neurons from transgenic rats as compared to controls. In accordance with FRET results, untargeted lipidomics showed significant decreases in levels of 12 lipids and bioenergetic analysis revealed respiratory dysfunction of mitochondria from transgenic rats. Thus, our results reveal changes in MERC structures coupled with impaired mitochondrial functions in Alzheimer's disease-related neurons.This article has an associated First Person interview with the first author of the paper.

Resting State Networks in the TgF344-AD Rat Model of Alzheimer's Disease Are Altered From Early Stages

A better and non-invasive characterization of the preclinical phases of Alzheimer's disease (AD) is important to advance its diagnosis and obtain more effective benefits from potential treatments. The TgF344-AD rat model has been well characterized and shows molecular, behavioral and brain connectivity alterations that resemble the silent period of the pathology. Our aim was to longitudinally investigate functional brain connectivity in established resting-state networks (RSNs) obtained by independent component analysis (ICA) in a cohort of TgF344-AD and control rats every 3 months, from 5 to 18 months of age, to cover different stages of the disease. Before each acquisition, working memory performance was evaluated by the delayed non match-to-sample (DNMS) task. Differences in the temporal evolution were observed between groups in the amplitude and shape of the somatosensorial and sensorimotor networks but not in the whole default mode network (DMN). Subsequent high dimensional ICA analysis showed early alterations in the anterior DMN subnetwork activity of TgF344-AD rats compared to controls. Performance of DNMS task was positively correlated with somatosensorial network at 5 months of age in the wild-type (WT) animals but not in the Tg-F344 rats. At different time points, DMN showed negative correlation with cognitive performance in the control group while in the transgenic group the correlation was positive. In addition, behavioral differences observed at 5 months of age correlated with alterations in the posterior DMN subnetwork. We have demonstrated that functional connectivity using ICA represents a useful biomarker also in animal models of AD such as the TgF344AD rats, as it allows the identification of alterations associated with the progression of the disease, detecting differences in specific networks even at very early stages.

Experimental Pharmacology in Transgenic Rodent Models of Alzheimer's Disease

This Mini Review discusses the merits and shortfalls of transgenic (tg) rodents modeling aspects of the human Alzheimer’s disease (AD) pathology and their application to evaluate experimental therapeutics. It addresses some of the differences between mouse and rat tg models for these investigations. It relates, in a condensed fashion, the experience of our research laboratory with the application of anti-inflammatory compounds and S-adenosylmethionine (SAM) at the earliest stages of AD-like amyloid pathology in tg mice. The application of SAM was intended to revert the global brain DNA hypomethylation unleashed by the intraneuronal accumulation of amyloid-β-immunoreactive material, an intervention that restored levels of DNA methylation including of the bace1 gene. This review also summarizes experimental pharmacology observations made in the McGill tg rat model of AD-like pathology by applying “nano-lithium” or a drug with allosteric M1 muscarinic and sigma 1 receptor agonistic properties (AF710B). Extremely low doses of lithium (up to 400 times lower than used in the clinic) had remarkable beneficial effects on lowering pathology and improving cognitive functions in tg rats. Likewise, AF710B treatment, even at advanced stages of the pathology, displayed remarkable beneficial effects. This drug, in experimental conditions, demonstrated possible “disease-modifying” properties as pathology was frankly diminished and cognition improved after a month of “wash-out” period. The Mini-Review ends with a discussion on the predictive value of similar experimental pharmacological interventions in current rodent tg models. It comments on the validity of some of these approaches for early interventions at preclinical stages of AD, interventions which may be envisioned once definitive diagnosis of AD before clinical presentation is made possible.

Preclinical Models of Alzheimer's Disease: Relevance and Translational Validity

The only drugs currently approved for the treatment of Alzheimer's Disease (AD) are four acetylcholinesterase inhibitors and the NMDA antagonist memantine. Apart from these drugs, which have minimal to no clinical benefit, the 40-year search for effective therapeutics to treat AD has resulted in a clinical failure rate of 100% not only for compounds that prevent brain amyloid deposition or remove existing amyloid plaques but also those acting by a variety of other putative disease-associated mechanisms. This indicates that the preclinical data generated from current AD targets to support the selection, optimization, and translation of new chemical entities (NCEs) and biologics to clinical trials is seriously compromised. While many of these failures reflect flawed hypotheses or a lack of adequate characterization of the preclinical pharmacodynamic and pharmacokinetic (PD/PK) properties of lead NCEs-including their bioavailability and toxicity-the conceptualization, validation, and interrogation of the current animal models of AD represent key limitations. The overwhelming majority of these AD models are transgenic, based on aspects of the amyloid hypothesis and the genetics of the familial form of the disease. As a result, these generally lack construct and predictive validity for the sporadic form of the human disease. The 170 or so transgenic models, perhaps the largest number ever focused on a single disease, use rodents, mainly mice, and in addition to amyloid also address aspects of tau causality with more complex multigene models including other presumed causative factors together with amyloid. This overview discusses the current animal models of AD in the context of both the controversies surrounding the causative role of amyloid in the disease and the need to develop validated models of cognitive function/dysfunction that more appropriately reflect the phenotype(s) of human aged-related dementias. © 2019 by John Wiley & Sons, Inc.

Nonlinear analysis of local field potentials and motor cortex EEG in spinocerebellar ataxia 3

This study explores the potential usefulness of EEG for patient diagnosis by analyzing SCA3 and wt mice. Self-made implantable electrodes were constructed and implanted to extract EEG signals from the cerebral motor cortex and the cerebellar areas that are affected by the disease. Nonlinear dynamic analysis and EEG energy were used to distinguish between SCA3 and WT mice, and we found that all four were increased in SCA3 mice. The alpha and theta bands of LZ complexity were significantly higher in SCA3 mice than in the control group. Therefore, it was possible to distinguish between the two groups by the LZ complexity of their alpha and theta bands. Analysis of C₀ complexity and approximate entropy showed that the random part in the disease group was larger than in the control group, and that in addition the randomness was increased in SCA3 mice. The spatial learning and memory were analyzed by means of the Morris water maze test (MWM), The results showed that the swimming velocity, distance traveled and latency to reach the platform in SCA3 mice were increased when compared with WT mice during the 4 training days (p < 0.05, 0.01 or 0.001). And the results are conform to the results of EEG signals. In conclusion, EEG signals could be used to identify SCA3 in mice. They may also be clinically useful for the diagnosis of cerebellar ataxia in patients, and for additional studies aimed at gaining a deeper understanding of spinal cerebral ataxia.

Social housing protects against age-related working memory decline independently of physical enrichment in rats

Longitudinal human studies suggest that as we age, sociality provides protective benefits against cognitive decline. However, little is known about the underlying neural mechanisms. Rodent studies, which are ideal for studying cognition, fail to examine the independent effects of social housing while controlling for physical enrichment in all groups. In this study, rats were socially housed or nonsocially housed throughout their lifespan and tested in the radial arm maze to measure working memory (WM) and reference memory longitudinally at 3 ages. In old age, exclusively, socially housed rats made significantly less WM errors than nonsocially housed rats, while reference memory errors did not differ between groups at any age. Anxiety, as assessed behaviorally and physiologically, could not account for the observed differences in WM. These data provide the first evidence that social enrichment alone can prevent age-related WM deficits in spite of the effects of practice seen in longitudinal designs. Importantly, our model will facilitate future investigations into the mechanisms underlying the neuroprotective benefits of sociability in old age.

Platelets Bioenergetics Screening Reflects the Impact of Brain Aβ Plaque Accumulation in a Rat Model of Alzheimer

Alzheimer's disease (AD) is associated to depressed brain energy supply and impaired cortical and hippocampal synaptic function. It was previously reported in McGill-R-Thy1-APP transgenic (Tg(+/+)) rats that Aβ deposition per se is sufficient to cause abnormalities in glucose metabolism and neuronal connectivity. These data support the utility of this animal model as a platform for the search of novel AD biomarkers based on bioenergetic status. Recently, it has been proposed that energy dysfunction can be dynamically tested in platelets (PLTs) of nonhuman primates. PLTs are good candidates to find peripheral biomarkers for AD because they may reflect in periphery the bioenergetics deficits and the inflammatory and oxidative stress processes taking place in AD brain. In the present study, we carried out a PLTs bioenergetics screening in advanced-age (12-14 months old) control (WT) and Tg(+/+) rats. Results indicated that thrombin-activated PLTs of Tg(+/+) rats showed a significantly lower respiratory rate, as compared to that measured in WT animals, when challenged with the same dose of FCCP (an uncoupler of oxidative phosphorylation). In summary, our results provide original evidence that PLTs bioenergetic profiling may reflect brain bioenergetics dysfunction mediated by Aβ plaque accumulation. Further studies on human PLTs from control and AD patients are required to validate the usefulness of PLTs bioenergetics as a novel blood-based biomarker for AD.

The McGill Transgenic Rat Model of Alzheimer's Disease Displays Cognitive and Motor Impairments, Changes in Anxiety and Social Behavior, and Altered Circadian Activity

The McGill-R-Thy1-APP transgenic rat is an animal model of the familial form of Alzheimer's disease (AD). This model mirrors several neuropathological hallmarks of the disease, including the accumulation of beta-amyloid and the formation of amyloid plaques (in homozygous animals only), neuroinflammation and the gradual deterioration of cognitive functions even prior to plaque formation, although it lacks the tauopathy observed in human victims of AD. The goal of the present study was a thorough characterization of the homozygous model with emphasis on its face validity in several domains of behavior known to be affected in AD patients, including cognitive functions, motor coordination, emotionality, sociability, and circadian activity patterns. On the behavioral level, we found normal locomotor activity in spontaneous exploration, but problems with balance and gait coordination, increased anxiety and severely impaired spatial cognition in 4–7 month old homozygous animals. The profile of social behavior and ultrasonic communication was altered in the McGill rats, without a general social withdrawal. McGill rats also exhibited changes in circadian profile, with a shorter free-running period and increased total activity during the subjective night, without signs of sleep disturbances during the inactive phase. Expression of circadian clock gene Bmal1 was found to be increased in the parietal cortex and cerebellum, while Nr1d1 expression was not changed. The clock-controlled gene Prok2 expression was found to be elevated in the parietal cortex and hippocampus, which might have contributed to the observed changes in circadian phenotype. We conclude that the phenotype in the McGill rat model is not restricted to the cognitive domain, but also includes gait problems, changes in emotionality, social behavior, and circadian profiles. Our findings show that the model should be useful for the development of new therapeutic approaches targeting not only memory decline but also other symptoms decreasing the quality of life of AD patients.

Chronic Hippocampal Expression of Notch Intracellular Domain Induces Vascular Thickening, Reduces Glucose Availability, and Exacerbates Spatial Memory Deficits in a Rat Model of Early Alzheimer

The specific roles of Notch in progressive adulthood neurodegenerative disorders have begun to be unraveled in recent years. A number of independent studies have shown significant increases of Notch expression in brains from patients at later stages of sporadic Alzheimer's disease (AD). However, the impact of Notch canonical signaling activation in the pathophysiology of AD is still elusive. To further investigate this issue, 2-month-old wild-type (WT) and hemizygous McGill-R-Thy1-APP rats (Tg(+/-)) were injected in CA1 with lentiviral particles (LVP) expressing the transcriptionally active fragment of Notch, known as Notch Intracellular Domain (NICD), (LVP-NICD), or control lentivirus particles (LVP-C). The Tg(+/-) rat model captures presymptomatic aspects of the AD pathology, including intraneuronal amyloid beta (Aβ) accumulation and early cognitive deficits. Seven months after LVP administration, Morris water maze test was performed, and brains isolated for biochemical and histological analysis. Our results showed a learning impairment and a worsening of spatial memory in LVP-NICD- as compared to LVP-C-injected Tg(+/-) rats. In addition, immuno histochemistry, ELISA multiplex, Western blot, RT-qPCR, and ¹H-NMR spectrometry of cerebrospinal fluid (CSF) indicated that chronic expression of NICD promoted hippocampal vessel thickening with accumulation of Aβ in brain microvasculature, alteration of blood-brain barrier (BBB) permeability, and a decrease of CSF glucose levels. These findings suggest that, in the presence of early Aβ pathology, expression of NICD may contribute to the development of microvascular abnormalities, altering glucose transport at the BBB with impact on early decline of spatial learning and memory.

Early brain connectivity alterations and cognitive impairment in a rat model of Alzheimer's disease

BACKGROUND

Animal models of Alzheimer's disease (AD) are essential to understanding the disease progression and to development of early biomarkers. Because AD has been described as a disconnection syndrome, magnetic resonance imaging (MRI)-based connectomics provides a highly translational approach to characterizing the disruption in connectivity associated with the disease. In this study, a transgenic rat model of AD (TgF344-AD) was analyzed to describe both cognitive performance and brain connectivity at an early stage (5 months of age) before a significant concentration of β-amyloid plaques is present.

METHODS

Cognitive abilities were assessed by a delayed nonmatch-to-sample (DNMS) task preceded by a training phase where the animals learned the task. The number of training sessions required to achieve a learning criterion was recorded and evaluated. After DNMS, MRI acquisition was performed, including diffusion-weighted MRI and resting-state functional MRI, which were processed to obtain the structural and functional connectomes, respectively. Global and regional graph metrics were computed to evaluate network organization in both transgenic and control rats.

RESULTS

The results pointed to a delay in learning the working memory-related task in the AD rats, which also completed a lower number of trials in the DNMS task. Regarding connectivity properties, less efficient organization of the structural brain networks of the transgenic rats with respect to controls was observed. Specific regional differences in connectivity were identified in both structural and functional networks. In addition, a strong correlation was observed between cognitive performance and brain networks, including whole-brain structural connectivity as well as functional and structural network metrics of regions related to memory and reward processes.

CONCLUSIONS

In this study, connectivity and neurocognitive impairments were identified in TgF344-AD rats at a very early stage of the disease when most of the pathological hallmarks have not yet been detected. Structural and functional network metrics of regions related to reward, memory, and sensory performance were strongly correlated with the cognitive outcome. The use of animal models is essential for the early identification of these alterations and can contribute to the development of early biomarkers of the disease based on MRI connectomics.

Anxiety-like behavior as an early endophenotype in the TgF344-AD rat model of Alzheimer's disease

Alzheimer's disease (AD) is characterized by progressive cognitive decline and the presence of aggregates of amyloid beta (plaques) and hyperphosphorylated tau (tangles). Early diagnosis through neuropsychological testing is difficult due to comorbidity of symptoms between AD and other types of dementia. As a result, there is a need to identify the range of behavioral phenotypes expressed in AD. In the present study, we utilized a transgenic rat (TgF344-AD) model that bears the mutated amyloid precursor protein as well as presenilin-1 genes, resulting in progressive plaque and tangle pathogenesis throughout the cortex. We tested young adult male and female TgF344-AD rats in a spatial memory task in the Morris water maze and for anxiety-like behavior in the elevated plus-maze. Results indicated that regardless of sex, TgF344-AD rats exhibited increased anxiety-like behavior in the elevated plus-maze, which occurred without significant deficits in the spatial memory. Together, these results indicate that enhanced anxiety-like behavior represents an early-stage behavioral marker in the TgF344-AD rat model.

Multimodal Imaging in Rat Model Recapitulates Alzheimer's Disease Biomarkers Abnormalities

Imaging biomarkers are frequently proposed as endpoints for clinical trials targeting brain amyloidosis in Alzheimer's disease (AD); however, the specific impact of amyloid-β (Aβ) aggregation on biomarker abnormalities remains elusive in AD. Using the McGill-R-Thy1-APP transgenic rat as a model of selective Aβ pathology, we characterized the longitudinal progression of abnormalities in biomarkers commonly used in AD research. Middle-aged (9–11 months) transgenic animals (both male and female) displayed mild spatial memory impairments and disrupted cingulate network connectivity measured by resting-state fMRI, even in the absence of hypometabolism (measured with PET [¹⁸F]FDG) or detectable fibrillary amyloidosis (measured with PET [¹⁸F]NAV4694). At more advanced ages (16–19 months), cognitive deficits progressed in conjunction with resting connectivity abnormalities; furthermore, hypometabolism, Aβ plaque accumulation, reduction of CSF Aβ_1-42 concentrations, and hippocampal atrophy (structural MRI) were detectable at this stage. The present results emphasize the early impact of Aβ on brain connectivity and support a framework in which persistent Aβ aggregation itself is sufficient to impose memory circuits dysfunction, which propagates to adjacent brain networks at later stages.

SIGNIFICANCE STATEMENT The present study proposes a “back translation” of the Alzheimer pathological cascade concept from human to animals. We used the same set of Alzheimer imaging biomarkers typically used in large human cohorts and assessed their progression over time in a transgenic rat model, which allows for a finer spatial resolution not attainable with mice. Using this translational platform, we demonstrated that amyloid-β pathology recapitulates an Alzheimer-like profile of biomarker abnormalities even in the absence of other hallmarks of the disease such as neurofibrillary tangles and widespread neuronal losses.

Arginine vasopressin relates with spatial learning and memory in a mouse model of spinocerebellar ataxia type 3

Spinocerebellar ataxia is an inherited neurodegenerative disorder that the most prevalent type is type 3 (SCA3). Arginine vasopressin (AVP) is released within the lateral septum for controlling the learning and memory. This communication studied the effect of AVP on the spatial learning and memory of SCA3 mice. The spatial learning and memory were analyzed by Morris water maze test (MWM), and AVP concentration was measured by radioimmunoassay. The results showed that (Alves et al., 2010) the swimming velocity, distance traveled and latency to the platform of MWM in SCA3 mice were reduced slower than those in WT mice over 4 training days (p<0.05, 0.01 or 0.001); (Antunes and Zimmerman, 1978) SCA3 mice showed a lower performance of spatial learning and memory of MWM during the fifth day (test day) compared to WT mice; (Bao et al., 2014) SCA3 mice had a decrease of AVP concentration in cerebral cortex (6.3±0.6pg/mg vs. 11.4±1.0pg/mg, p<0.01), hypothalamus (6.1±1.3ng/mg vs. 10.3±2.1ng/mg, p<0.05), hippocampus (3.2±0.5pg/mg vs. 5.2±1.0pg/mg, p<0.01) and cerebellum (4.7±0.9pg/mg vs. 8.3±1.1pg/mg, p<0.01), not in spinal cord, pituitary and serum; and (Barberies and Tribollet, 1996) intraventricular AVP could significantly quicken swimming velocity, cut down distance traveled and reduce latency to the platform of MWM in a dose-dependent manner, but intraventricular AVP receptor antagonist weakened the spatial learning and memory of MWM in SCA3 mice during the fifth day. The data suggested that AVP in the brain, not spinal cord and peripheral system of SCA3 mice related with the change of the spatial learning and memory of MWM.

Differential deregulation of NGF and BDNF neurotrophins in a transgenic rat model of Alzheimer's disease

Evidence from human neuropathological studies indicates that the levels of the neurotrophins nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are compromised in Alzheimer's disease. However, the causes and temporal (pathology-dependent) evolution of these alterations are not completely understood. To elucidate these issues, we investigated the McGill-R-Thy1-APP transgenic rat, which exhibits progressive intracellular and extracellular amyloid-beta (Aβ) pathology and ensuing cognitive deficits. Neurochemical analyses revealed a differential dysregulation of NGF and BDNF transcripts and protein expression. While BDNF mRNA levels were significantly reduced at very early stages of amyloid pathology, before plaques appeared, there were no changes in NGF mRNA expression even at advanced stages. Paradoxically, the protein levels of the NGF precursor were increased. These changes in neurotrophin expression are identical to those seen during the progression of Alzheimer's disease. At advanced pathological stages, deficits in the protease cascade controlling the maturation and degradation of NGF were evident in McGill transgenic rats, in line with the paradoxical upregulation of proNGF, as seen in Alzheimer's disease, in the absence of changes in NGF mRNA. The compromise in NGF metabolism and BDNF levels was accompanied by downregulation of cortical cholinergic synapses; strengthening the evidence that neurotrophin dysregulation affects cholinergic synapses and synaptic plasticity. Our findings suggest a differential temporal deregulation of NGF and BDNF neurotrophins, whereby deficits in BDNF mRNA appear at early stages of intraneuronal Aβ pathology, before alterations in NGF metabolism and cholinergic synapse loss manifest.

Streptozotocin-induced hippocampal astrogliosis and insulin signaling malfunction as experimental scales for subclinical sporadic Alzheimer model

AIMS

Insulin signaling malfunction has recently been suggested as a preliminary event involved in the etiology of Sporadic Alzheimer's disease (SAD). In order to develop insulin resistance-related SAD model, rats were treated with streptozotocin, intracerebroventricularly (icv-STZ). Nevertheless, given the lack of knowledge regarding sub-clinical stages of SAD, the current challenging issue is establishing a practical pre-clinical SAD model. Despite some proposed mechanisms, such as insulin malfunction, neuroinflammation, and gliosis, icv-STZ mechanism of action is not fully understood yet and Streptozotocin-induced rat model of Alzheimer has still major shortcomings.

MAIN METHODS

Using three STZ doses (0.5, 1, and 3mg/kg) and three testing time (short-term, medium-term and long-term), we sought the best dose of STZ in order to mimic the characteristic feature of sAD in rats. So, we conducted a series of fifteen-week follow-up cognitive and non-cognitive studies. Besides, IR, tau and ChAT mRNA levels were measured, along with histological analysis of astrocyte, dark neuron numbers, and pyramidal layer thickness, in order to compare the effects of different doses of icv-STZ.

KEY FINDINGS

STZ 3mg/kg caused cognitive and insulin signaling disturbance from the very first testing-time. STZ1-injected animals, however, showed an augmented hippocampal astrocyte numbers in a short time; they, also, were diagnosed with disturbed insulin signaling in medium-term post icv-STZ-injection. Moreover, behavioral, molecular and histological impairments induced by 0.5mg/kg icv-STZ were slowly progressing in comparison to high doses of STZ.

SIGNIFICANCE

STZ1 and 0.5mg/kg-treated animals are, respectively, suggested as a suitable experimental model of MCI, and sub-clinical stage.

BACE1 inhibition by microdose lithium formulation NP03 rescues memory loss and early stage amyloid neuropathology

Lithium is first-line therapy for bipolar affective disorder and has recently been shown to have protective effects in populations at risk for Alzheimer's disease (AD). However, the mechanism underlying this protection is poorly understood and consequently limits its possible therapeutic application in AD. Moreover, conventional lithium formulations have a narrow therapeutic window and are associated with a severe side effect profile. Here we evaluated a novel microdose formulation of lithium, coded NP03, in a well-characterized rat model of progressive AD-like amyloid pathology. This formulation allows microdose lithium delivery to the brain in the absence of negative side effects. We found that NP03 rescued key initiating components of AD pathology, including inactivating GSK-3β, reducing BACE1 expression and activity, and reducing amyloid levels. Notably, NP03 rescued memory loss, impaired CRTC1 promoter binding of synaptic plasticity genes and hippocampal neurogenesis. These results raise the possibility that NP03 be of therapeutic value in the early or preclinical stages of AD.

Cav1.2 channels mediate persistent chronic stress-induced behavioral deficits that are associated with prefrontal cortex activation of the p25/Cdk5-glucocorticoid receptor pathway

Chronic stress is known to precipitate and exacerbate neuropsychiatric symptoms, and exposure to stress is particularly pathological in individuals with certain genetic predispositions. Recent genome wide association studies have identified single nucleotide polymorphisms (SNPs) in the gene CACNA1C, which codes for the Ca_v1.2 subunit of the L-type calcium channel (LTCC), as a common risk variant for multiple neuropsychiatric conditions. Ca_v1.2 channels mediate experience-dependent changes in gene expression and long-term synaptic plasticity through activation of downstream calcium signaling pathways. Previous studies have found an association between stress and altered Ca_v1.2 expression in the brain, however the contribution of Ca_v1.2 channels to chronic stress-induced behaviors, and the precise Ca_v1.2 signaling mechanisms activated are currently unknown. Here we report that chronic stress leads to a delayed increase in Ca_v1.2 expression selectively within the prefrontal cortex (PFC), but not in other stress-sensitive brain regions such as the hippocampus or amygdala. Further, we demonstrate that while Ca_v1.2 heterozygous (Ca_v1.2^+/−) mice show chronic stress-induced depressive-like behavior, anxiety-like behavior, and deficits in working memory 1–2 days following stress, they are resilient to the effects of chronic stress when tested 5–7 days later. Lastly, molecular studies find a delayed upregulation of the p25/Cdk5-glucocorticoid receptor (GR) pathway in the PFC when examined 8 days post-stress that is absent in Ca_v1.2^+/− mice. Our findings reveal a novel Ca_v1.2-mediated molecular mechanism associated with the persistent behavioral effects of chronic stress and provide new insight into potential Ca_v1.2 channel mechanisms that may contribute to CACNA1C-linked neuropsychiatric phenotypes.

Synaptosomal bioenergetic defects are associated with cognitive impairment in a transgenic rat model of early Alzheimer's disease

Synaptic bioenergetic deficiencies may be associated with early Alzheimer's disease (AD). To explore this concept, we assessed pre-synaptic mitochondrial function in hemizygous (+/-)TgMcGill-R-Thy1-APP rats. The low burden of Aβ and the wide array of behavioral and cognitive impairments described in 6-month-old hemizygous TgMcGill-R-Thy1-APP rats (Tg(+/-)) support their use to investigate synaptic bioenergetics deficiencies described in subjects with early Alzheimer's disease (AD). In this report, we show that pre-synaptic mitochondria from Tg(+/-) rats evidence a decreased respiratory control ratio and spare respiratory capacity associated with deficits in complex I enzymatic activity. Cognitive impairments were prevented and bioenergetic deficits partially reversed when Tg(+/-) rats were fed a nutritionally complete diet from weaning to 6-month-old supplemented with pyrroloquinoline quinone, a mitochondrial biogenesis stimulator with antioxidant and neuroprotective effects. These results provide evidence that, as described in AD brain and not proven in Tg mice models with AD-like phenotype, the mitochondrial bioenergetic capacity of synaptosomes is not conserved in the Tg(+/-) rats. This animal model may be suitable for understanding the basic biochemical mechanisms involved in early AD.