Aggravation of chronic stress effects on hippocampal neurogenesis and spatial memory in LPA₁ receptor knockout mice

Background

The lysophosphatidic acid LPA₁ receptor regulates plasticity and neurogenesis in the adult hippocampus. Here, we studied whether absence of the LPA₁ receptor modulated the detrimental effects of chronic stress on hippocampal neurogenesis and spatial memory.

Methodology/Principal Findings

Male LPA₁-null (NULL) and wild-type (WT) mice were assigned to control or chronic stress conditions (21 days of restraint, 3 h/day). Immunohistochemistry for bromodeoxyuridine and endogenous markers was performed to examine hippocampal cell proliferation, survival, number and maturation of young neurons, hippocampal structure and apoptosis in the hippocampus. Corticosterone levels were measured in another a separate cohort of mice. Finally, the hole-board test assessed spatial reference and working memory. Under control conditions, NULL mice showed reduced cell proliferation, a defective population of young neurons, reduced hippocampal volume and moderate spatial memory deficits. However, the primary result is that chronic stress impaired hippocampal neurogenesis in NULLs more severely than in WT mice in terms of cell proliferation; apoptosis; the number and maturation of young neurons; and both the volume and neuronal density in the granular zone. Only stressed NULLs presented hypocortisolemia. Moreover, a dramatic deficit in spatial reference memory consolidation was observed in chronically stressed NULL mice, which was in contrast to the minor effect observed in stressed WT mice.

Conclusions/Significance

These results reveal that the absence of the LPA₁ receptor aggravates the chronic stress-induced impairment to hippocampal neurogenesis and its dependent functions. Thus, modulation of the LPA₁ receptor pathway may be of interest with respect to the treatment of stress-induced hippocampal pathology.     

Effects of amyloid β-protein on hippocampal long-term potentiation

The accumulation of amyloid β-protein (Aβ) plaques is identified as a major pathological feature of Alzheimer's disease (AD). Recent studies show that soluble species of Aβ are involved in the early memory dysfunction long before neurodegenerative changes. However, the mechanism underlying the neurotoxicity of soluble Aβ is still unclear. Long-term potentiation (LTP) has been thought as an important cellular model of synaptic plasticity for many years. The studies on the hippocampal LTP and Aβ, especially those using AD transgenic models, provided more evidence for the Aβ-induced dysfunction of learning and memory. Based on the recent researches on AD, this article reviewed the effects of Aβ, especially soluble Aβ and its active fragments, on the hippocampal LTP. The possible mechanisms by which Aβ impairs hippocampal LTP are also discussed.     

The effect of the use of copper carbonate and copper nanoparticles in the diet of rats on the level of β-amyloid and acetylcholinesterase in selected organs

BackgroundCopper has an important role in nervous system function, as a cofactor of many enzymes and in the synthesis of neurotransmitters. Both the dose and the chemical form of copper can determine the impact of this element on metabolism, the neurological system and the immune system.AimsThe aim of the study was to determine whether and in what form the addition of copper changes the level of amyloid beta and acetylcholinesterase level in selected rat tissues.MethodsThirty, healthy, male, albino Wistar rats aged 7 weeks were randomly divided into 3 groups. Three experimental treatments were used to evaluate the effects of different levels and sources of Cu (6.5 mg kg of diet) in the diet: Cu₀ – rats fed a diet without Cu supplementation; Cu_salt – rats fed a diet with CuCO₃ (6.5 mg kg of diet) during two months of feeding; Cu_NPs - rats fed a diet with Cu nanoparticles (6.5 mg kg of diet) during two months of feeding. In blood serum and tissue homogenates there rated the indicators proving the potential neurodegenerative effect and epigenetic DNA damage induced by chemical form of copper or lack of additional copper supplementation in diet were determined. There were analysed: level of acetylcholinesterase, β-amyloid, low-density lipoprotein receptor-related protein 1, apyrimidinic endonuclease, thymidine glycosidase, alkylpurine-DNA-N-glycosylase and glycosylated acetylcholinesterase.ResultsIrrespective of the form of copper added, it was found to increase acetylcholinesterase level in the brain, spleen and liver, as well as in the blood plasma of the rats. Copper in the form of CuCO₃ was found to increase acetylcholinesterase level in the kidneys. The addition of both forms of copper caused a marked increase in the plasma concentration of β-amyloid in comparison with the diet with no added Cu. The addition of both forms of copper caused a marked increase in the plasma concentration of β-amyloid in comparison with the diet with no added Cu.ConclusionsA lack of added Cu in the diet of rats reduces the concentration of amyloid-β in the blood, whereas administration of copper, in the form of either CuNPs or CuCO₃, increases the level of this peptide in the blood. The use of copper in the form of CuNPs in the diet of rats does not increase the level of β-amyloid more than the use of the carbonate form of this element. The use of CuNPs or CuCO₃ in the diet of rats increases acetylcholinesterase level in the brain, spleen, liver, and blood. CuNPs in the diet of rats were not found to increase acetylcholinesterase level to a greater extent than Cu⁺² carbonate.     

Internal and environmental effects on folding and dimerisation of Alzheimer's β-amyloid peptide

Amyloid deposits are a hallmark of many diseases. In the case of Alzheimer's disease, a turn between 21Ala and 30Ala, stabilised by a salt bridge between 22Glu/23Asp and 28Lys, may nucleate folding and aggregation of the amyloid β (Aβ) peptide. In the present paper, we test this hypothesis by studying how salt bridge and turn formation vary with intrinsic and environmental changes, and how these changes affect folding and aggregation of the Aβ-peptide.     

Exogenous seeding of cerebral β-amyloid deposition in βAPP-transgenic rats

Deposition of the amyloid-β (Aβ) peptide in senile plaques and cerebral Aβ angiopathy (CAA) can be stimulated in Aβ-precursor protein (APP)-transgenic mice by the intracerebral injection of dilute brain extracts containing aggregated Aβ seeds. Growing evidence implicates a prion-like mechanism of corruptive protein templating in this phenomenon, in which aggregated Aβ itself is the seed. Unlike prion disease, which can be induced de novo in animals that are unlikely to spontaneously develop the disease, previous experiments with Aβ seeding have employed animal models that, as they age, eventually will generate Aβ lesions in the absence of seeding. In the present study, we first established that a transgenic rat model expressing human APP (APP21 line) does not manifest endogenous deposits of Aβ within the course of its median lifespan (30?months). Next, we injected 3-month-old APP21 rats intrahippocampally with dilute Alzheimer brain extracts containing aggregated Aβ. After a 9-month incubation period, these rats had developed senile plaques and CAA in the injected hippocampus, whereas control rats remained free of such lesions. These findings underscore the co-dependence of agent and host in governing seeded protein aggregation, and show that cerebral Aβ-amyloidosis can be induced even in animals that are relatively refractory to the spontaneous origination of parenchymal and vascular deposits of Aβ.     

Change of cholinergic transmission and memory deficiency induced by injection of β-amyloid protein into NBM of rats

The change of cholinergic transmission of p-amyloid protein (P-AP) treated rats was studied by intracerebral microdialysis sampling combined with HPLC analysis. β-AP1-40 was injected into nucleus basalis magnocellularis (NBM). Passive avoidance response test (step-down test) and delayed alternation task were used for memory testing. The impairment of memory after injection of β-AP1-40 into NBM exhibited mainly the deficiency of short-term working memory. One week after injection of β-AP1-40 the release of acetylcholine (ACh) from frontal cortex of freely-moving rats decreased significantly, and the response of cholinergic nerve ending to the action of high [K+] solution was rather weak. In control animals the percentage of increase of ACh-release during behavioral performance was 57%, while in β-AP1-40-treated rats it was 34%. The temporary increase of the ACh-release of the rat put into a new place was also significantly diminished in β-AP1-40 -treated rats. The results show that the injection of      

The effects of β-glucan on iron levels and lipid peroxidation in intra-abdominal sepsis in rats

Sepsis is defined as a systemic response of organisms to microorganisms and toxins. Sepsis is associated with the enhanced generation of reactive oxygen metabolites, leading to multiple organ dysfunctions. β-glucan is accepted to be one of the most powerful immune response modifiers. The aim of this study was to investigate the putative protective effect of β-glucan on changes of iron and malondialdehyde (MDA) levels in various tissue and blood after experimental sepsis in rats. Sepsis was induced by cecal ligation and perforation (CLP) in 32 male Wistar albino rat. To evaluate this, rats were divided into four groups as sham operated, β-glucan treated sham operated, CLP and β-glucan treated CLP. Sixteen hours after operation, rats were decapitated and MDA and iron levels were measured in the liver, kidney, heart, diaphragm tissues and blood. Also, whole tissue histopathology was evaluated by a light microscope. The results demonstrate that sepsis significantly decreased iron levels of all tissues and blood. The decrease in tissue iron levels and the increase MDA levels demonstrate the role of trace elements and free radicals in sepsis-induced tissue damage. Our results indicate that the given dose of β-glucan was probably insufficient to prevent sepsis-induced organ injury.     

Effects of treadmill exercise on brain insulin signaling and β-amyloid in intracerebroventricular streptozotocin induced-memory impairment in rats

[Purpose]

The purpose of the study is to explore effect of 6 weeks treadmill exercise on brain insulin signaling and β-amyloid(Aβ).

[Methods]

The rat model of Alzheimer’s disease(AD) used in the present study was induced by the intracerebroventricular(ICV) streptozotocin(STZ). To produce the model of animal with AD, STZ(1.5mg/kg) was injected to a cerebral ventricle of both cerebrums of Sprague-Dawley rat(20 weeks). The experimental animals were divided into ICV-Sham(n=7), ICV-STZ CON(n=7), ICV-STZ EXE(n=7). Treadmill exercise was done for 30 min a day, 5 days a week for 6 weeks. Passive avoidance task was carried out before and after treadmill exercise.

[Results]

The results of this study show that treadmill exercise activated Protein kinase B(AKT)/ Glycogen synthase kinase 3α (GSK3α), possibly via activation of insulin receptor(IR) and insulin receptor substrate(IRS) and reduced Aβ in the brain of ICV-STZ rats. More interestingly, treadmill exercise improved cognitive function of ICV-STZ rats. Finally, physical exercise or physical activity gave positive influences on brain insulin signaling pathway.

[Conclusion]

Therefore, treadmill exercise can be applied to improve AD as preventive and therapeutic method.     

Change of cholinergic transmission and memory deficiency induced by injection of β-amyloid protein into NBM of rats

The change of cholinergic transmission of ?-amyloid protein (β-AP) treated rats was studied by intracerebral microdialysis sampling combined with HPLC analysis. β-AP_1—40 was injected into nucleus basalis magnocellularis (NBM). Passive avoidance response test (step-down test) and delayed alternation task were used for memory testing. The impairment of memory after injection of β-AP_1—40 into NBM exhibited mainly the deficiency of short-term working memory. One week after injection of β-AP_1—40 the release of acetylcholine (ACh) from frontal cortex of freely-moving rats decreased significantly, and the response of cholinergic nerve ending to the action of high [K⁺] solution was rather weak. In control animals the percentage of increase of ACh-release during behavioral performance was 57%, while in β-AP_1—40-treated rats it was 34%. The temporary increase of the ACh-release of the rat put into a new place was also significantly diminished in β-AP_1—40-treated rats. The results show that the injection of β-AP_1—40 into NBM impairs the cholinergic transmission in frontal cortex, and the impairment of cholinergic transmission may be the main cause of the deficit of working memory.     

Impaired hippocampal long-term potentiation and failure of learning in β1,4-N-acetylgalactosaminyltransferase gene transgenic mice

Gangliosides (sialic acid-containing glycosphingolipids) play important roles in many physiological functions, including synaptic plasticity in the hippocampus, which is considered as a cellular mechanism of learning and memory. In the present study, three types of synaptic plasticity, long-term potentiation (LTP), long-term depression (LTD) and reversal of LTP (depotentiation, DP), in the field excitatory post-synaptic potential in CA1 hippocampal neurons and learning behavior were examined in β1,4-N-acetylgalactosaminyltransferase (β1,4 GalNAc-T; GM2/GD2 synthase) gene transgenic (TG) mice, which showed a marked decrease in b-pathway gangliosides (GQ1b, GT1b and GD1b) in the brain and isolated hippocampus compared with wild-type (WT) mice. The magnitude of the LTP induced by tetanus (100 pulses at 100?Hz) in TG mice was significantly smaller than that in control WT mice, whereas there was no difference in the magnitude of the LTD induced by three short trains of low-frequency stimulation (LFS) (200 pulses at 1?Hz) at 20?min intervals between the two groups of mice. The reduction in the LTP produced by delivering three trains of LFS (200 pulses at 1?Hz, 20?min intervals) was significantly greater in the TG mice than in the WT mice. Learning was impaired in the four-pellet taking test (4PTT) in TG mice, with no significant difference in daily activity or activity during the 4PTT between TG and WT mice. These results suggest that the overexpression of β1,4 GalNAc-T resulted in altered synaptic plasticity of LTP and DP in hippocampal CA1 neurons and learning in the 4PTT, and this is attributable to the shift from b-pathway gangliosides to a-pathway gangliosides.     

Comparative effects of β-carotene and fucoxanthin on retinol deficiency induced oxidative stress in rats

This study aimed at comparing antioxidant potential of fucoxanthin (FUCO) with β-carotene in relieving lipid peroxidation (Lpx) caused by retinol deficiency (RD) in rats. RD rats (n = 45) were fed a dose of either β-carotene (0.81 μmol) or FUCO (0.83 μmol). Plasma and liver lipid peroxide levels and activity of antioxidant enzymes catalase (CAT) and glutathione transferase (GST) were measured for 8 h. Results revealed that RD increased (P < 0.05) Lpx in plasma and liver by 34.3% and 19.4%, while the CAT activity in plasma (89%) and liver microsomes (91%) and GST in liver homogenate (31%) and liver microsomes (30%) were decreased (P < 0.05) compared to control (rats fed basal diet). FUCO suppressed (P < 0.05) the Lpx level by 7–85% (plasma) and 24–72% (liver) as compared to β-carotene (51–76%, 33–65%) over a period of 8 h. The activity of CAT in plasma and liver microsomes was higher (P < 0.05) in FUCO (90–95%, 85–93%) and β-carotene (87–96%, 79–91%) groups as compared to RD group. Similarly, the activity of GST in liver and its microsomes was also elevated (P < 0.05) in FUCO (44–51%, 22–51%) and β-carotene (19–54%, 30–43%) groups as compared to RD group. Results demonstrate that FUCO has greater potential than β-carotene in modulating Lpx, CAT, GST in plasma and liver of RD rats.     

Effects of hypericin on the structure and aggregation properties of β-amyloid peptides

We have determined the secondary structure of 1–40 β-amyloid peptides by Fourier-transform infrared spectroscopy (FTIR) and characterized the peptide photophysical properties before and after self-assembly by using intrinsic tyrosine steady-state and time-resolved fluorescence. All measurements were performed in the presence and absence of hypericin (Hyp), an exogenous natural polycyclic pigment that has been shown to inhibit fibril formation and has also been used as a fluorescent probe. We monitored the time course of the aggregation process measuring 405 nm light diffusion at 90° and used thioflavin T to reveal the presence of fibrils. FTIR quantitative analysis evidenced a prevalent random conformation at t = 0 with and without Hyp. Fibrils showed a predominant parallel β-sheet structure and a small percentage of α-helix. The results of fluorescence measurements showed that Hyp does significantly interact with peptides in β-sheet conformation. In conclusion, hypericin does hinder the formation of fibrils, but the percentages of parallel β-sheets were not significantly different from those found in samples not treated with Hyp.     

β-adrenergic modulation of in vivo long-term potentiation in area CA1 and its role in spatial learning in rats

The hippocampus plays a key role in declarative learning and memory [1]. Hippocampal long-term potentiation (LTP) is a type of synaptic plasticity that has been widely studied as a syn-aptic mechanism underlying learning and memory[27]. It has been reported that in vitro LTP in area CA1 is subjected to b-adrenergic modulation. For example, the theta-pulse stimulation (510 Hz), a neutral frequency not modifying synaptic strength, can elicit a robust LTP in area CA1 in slice when the b-adr…     

Studies of the effects of aminopterin on the crypts of Lieberkühn in rats

Summary Studies have been made on the effects of an intramuscular injection of aminopterin on the crypts of Lieberkühn in rats. A decrease in the mitotic counts was accompanied by a rapid increase in the number of abnormal cells present in the epithelium of the crypt. Three hours after administration of the aminopterin, an almost complete absence of true metaphase chromosoms was found. By 24 hours, a partial return towards normal mitotic activity was observed but the number of abnormal cells present was still very high. It is suggested that the mitotic changes are in keeping with the conclusion of Grampa and Dustin (1952) of an arrest at interphase but that a secondary arrest at metaphase cannot be excluded.A morphological feature of some of the abnormal cells was the presence of a Feulgen positive granule in the cytoplasm, which by electron microscopy was also shown to contain many cytoplasmic constituents. It is suggested that material is lost from the nucleus and incorporated into a granule in the cytoplasm. A possible explanation of the purpose and function of the granule, as a means of disposing of unwanted or aberrant material, is put forward.Acknowledgements. I am grateful to Professor R. J. Brocklehurst for his continued interest and support of this work, and to the Stage II, B. Sc. students (1964) who counted the cells in many of the specimens as a laboratory exercise. My thanks are also due to Mr. J. Clements for technical assistance.     

Samuel Butler and human long term memory: Is the cupboard bare?

Memory studies in biological systems distinguish three informational processes that are generally sequential—production/acquisition, storage, and retrieval/use. Identification of DNA as a storage form for hereditary information accelerated progress in that field. Assuming the path of successful elucidation in one memory field (heredity) to be heuristic for elucidation in another (brain), then progress in neuroscience should accelerate when a storage form is identified. In the 19th century Ewald Hering and Samuel Butler held that heredity and brain memory both involved the storage of information and that the two forms of storage were the same. Hering specified storage as ‘molecular vibrations’ but, while making a fuller case, Butler was less committal. In the 20th century, the ablation studies of Karl Lashley failed to identify unique sites for storage of brain information, and Donald Hebb's ‘synaptic plasticity’ hypothesis of distributed storage over a neuronal network won favor. In the 21st century this has come under attack, and the idea that brain and hereditary information are stored as DNA is advocated. Thus, albeit without attribution, Butler's idea is reinstated. Yet, while the case is still open, the synaptic plasticity and DNA hypotheses have problems. Two broad alternatives remain on the table. Long term memory is located: (1) in the brain, either in some other macromolecular form (e.g. protein, lipid) or in some sub-molecular form (e.g. quantum computing and ‘brain as holograph’ hypotheses) or (2) outside the brain. The suggestion of the medieval physician Avicenna that the brain ‘cupboard’ is bare—i.e. the brain is a perceptual, not storage, organ—is consistent with a mysterious ‘universe as holograph’ model. Understanding how Butler came to contribute could be heuristic for future progress in a field fraught with ‘fractionation and disunity’.     

Involvement of the nitric oxide signaling in modulation of naringin against intranasal manganese and intracerbroventricular β-amyloid induced neurotoxicity in rats

Manganese -induced aggregation of the amyloid-β peptide (Aβ) is a hallmark molecular feature of Alzheimer's disease (AD). The current study was designed to investigate the effects of chronic administration of naringin against β-A_1–42 and manganese induced experimental model. Wistar rats received intracerebroventricular (ICV) β-A_1–42 once, intranasal manganese, naringin and nitric oxide modulators for 21 days and behavioral alterations were assessed. Mitochondrial enzymes, oxidative parameters, TNF-α, β-A_1–42 acetylcholinesterase (AChE) levels and manganese concentration were measured. ICV β-A_1–42 and intranasal manganese treated rats showed a memory deficit and significantly increased in β-A_1–42 level and manganese concentration, mitochondrial oxidative damage, AChE level and inflammatory mediator in the hippocampus and cortex. Chronic administration of naringin (40 and 80 mg/kg) significantly improved memory performance and attenuated the oxidative damage and mitochondrial dysfunction in Aβ with Mn treated rats. In addition, naringin also attenuates the pro-inflammatory cytokines like TNF-α, AChE, Amyloid deposition and Mn concentration. Further, pretreatment of N(G)-Nitro-L-arginine methyl ester (L-NAME) with (5 mg/kg) with lower dose of naringin significantly potentiated its protective effect. These results demonstrate that naringin offers protection against ICV β-A_1–42 and intranasal manganese induced memory dysfunction possibly due to its antioxidant, anti-inflammatory, anti-amyloidogenesis therefore, could have a therapeutic potential in Alzheimer's disease.     

Activation of the c-Jun N-terminal kinase signaling cascade mediates the effect of amyloid-beta on long term potentiation and cell death in hippocampus: a role for interleukin-1beta?

Amyloid-beta (Abeta) is a major constituent of the neuritic plaque found in the brain of Alzheimer's disease patients, and a great deal of evidence suggests that the neuronal loss that is associated with the disease is a consequence of the actions of Abeta. In the past few years, it has become apparent that activation of c-Jun N-terminal kinase (JNK) mediates some of the effects of Abeta on cultured cells; in particular, the evidence suggests that Abeta-triggered JNK activation leads to cell death. In this study, we investigated the effect of intracerebroventricular injection of Abeta(1-40) on signaling events in the hippocampus and on long term potentiation in Schaffer collateral CA1 pyramidal cell synapses in vivo. We report that Abeta(1-40) induced activation of JNK in CA1 and that this was coupled with expression of the proapoptotic protein, Bax, cytosolic cytochrome c, poly-(ADP-ribose) polymerase cleavage, and Fas ligand expression in the hippocampus. These data indicate that Abeta(1-40) inhibited expression of long term potentiation, and this effect was abrogated by administration of the JNK inhibitor peptide, D-JNKI1. In parallel with these findings, we observed that Abeta-induced changes in caspase-3 activation and TdT-mediated dUTP nick-end labeling staining in neuronal cultured cells were inhibited by D-JNKI1. We present evidence suggesting that interleukin (IL)-1beta plays a significant role in mediating the effects of Abeta(1-40) because Abeta(1-40) increased hippocampal IL-1beta and because several effects of Abeta(1-40) were inhibited by the caspase-1 inhibitor Ac-YVAD-CMK. On the basis of our findings, we propose that Abeta-induced changes in hippocampal plasticity are likely to be dependent upon IL-1beta-triggered activation of JNK.     

Leptin boosts cellular metabolism by activating AMPK and the sirtuins to reduce tau phosphorylation and β-amyloid in neurons

Leptin is a pleiotropic hormone primarily secreted by adipocytes. A high density of functional Leptin receptors has been reported to be expressed in the hippocampus and other cortical regions of the brain, the physiological significance of which has not been explored extensively. Alzheimer’s disease (AD) is marked by impaired brain metabolism with decreased glucose utilization in those regions which often precede pathological changes. Recent epidemiological studies suggest that plasma Leptin is protective against AD. Specifically, elderly with plasma Leptin levels in the lowest quartile were found to be four times more likely to develop AD than those in the highest quartile. We have previously reported that Leptin modulates AD pathological pathways in vitro through a mechanism involving the energy sensor, AMP-activated protein kinase (AMPK). To this end, we investigated the extent to which activation of AMPK as well as another class of sensors linking energy availability to cellular metabolism, the sirtuins (SIRT), mediate Leptin’s biological activity. Leptin directly activated neuronal AMPK and SIRT in cell lines. Additionally, the ability of Leptin to reduce tau phosphorylation and β-amyloid production was sensitive to the AMPK and sirtuin inhibitors, compound C and nicotinamide, respectively. These findings implicate that Leptin normally acts as a signal for energy homeostasis in neurons. Perhaps Leptin deficiency in AD contributes to a neuronal imbalance in handling energy requirements, leading to higher Aβ and phospho-tau, which can be restored by replenishing low Leptin levels. This may also be a legitimate strategy for therapy.     

Models of β-amyloid induced Tau-pathology: the long and “folded” road to understand the mechanism

The amyloid cascade hypothesis has been the prevailing hypothesis in Alzheimer’s Disease research, although the final and most wanted proof i.e. fully successful anti-amyloid clinical trials in patients, is still lacking. This may require a better in depth understanding of the cascade. Particularly, the exact toxic forms of Aβ and Tau, the molecular link between them and their respective contributions to the disease process need to be identified in detail. Although the lack of final proof has raised substantial criticism on the hypothesis per se, accumulating experimental evidence in in vitro models, in vivo models and from biomarkers analysis in patients supports the amyloid cascade and particularly Aβ-induced Tau-pathology, which is the focus of this review. We here discuss available models that recapitulate Aβ-induced Tau-pathology and review some potential underlying mechanisms. The availability and diversity of these models that mimic the amyloid cascade partially or more complete, provide tools to study remaining questions, which are crucial for development of therapeutic strategies for Alzheimer’s Disease.