[Chronic sleep deprivation exacerbates cognitive and pathological impairments in APP/PS1/tau triple transgenic Alzheimer's disease model mice].

Sleep exerts important functions in the regulation of cognition and emotion. Recent studies have found that sleep disorder is one of the important risk factors for Alzheimer's disease (AD), but the effects of chronic sleep deprivation on the cognitive functions of AD model mice and its possible mechanism are still unclear. In the present study, 8-month-old male APP/PS1/tau triple transgenic AD model (3xTg-AD) mice and wild type (WT) mice (n = 8 for each group) were subjected to chronic sleep deprivation by using the modified multiple platform method, with 20 h of sleep deprivation each day for 21 days. Then, open field test, elevated plus maze test, sugar water preference test, object recognition test, Y maze test and conditioned fear memory test were performed to evaluate anxiety- and depression-like behaviors, and multiple cognitive functions. In addition, the immunohistochemistry technique was used to observe pathological characteristics in the hippocampus of mice. The results showed that: (1) Chronic sleep deprivation did not affect anxiety- (P = 0.539) and depression-like behaviors (P = 0.874) in 3xTg-AD mice; (2) Chronic sleep deprivation exacerbated the impairments of object recognition memory (P < 0.001), working memory (P = 0.002) and the conditioned fear memory (P = 0.039) in 3xTg-AD mice; (3) Chronic sleep deprivation increased amyloid ß (Aß) deposition (P < 0.001) and microglial activation (P < 0.001) in the hippocampus of 3xTg-AD mice, without inducing abnormal tau phosphorylation and neurofibrillary tangles. These results indicate that chronic sleep deprivation exacerbates the impairments of recognition memory, working memory and conditioned fear memory in 3xTg-AD mice by aggravating Aß deposition and the excessive activation of microglia in the hippocampus.

A dual GLP-1 and Gcg receptor agonist rescues spatial memory and synaptic plasticity in APP/PS1 transgenic mice.

Alzheimer's disease (AD) is a neurodegenerative disease that severely affects the health and lifespan of the elderly worldwide. Recently, the correlation between AD and type 2 diabetes mellitus (T2DM) has received intensive attention, and a promising new anti-AD strategy is the use of anti-diabetic drugs. Oxyntomodulin (Oxm) is a peptide hormone and growth factor that acts on neurons in the hypothalamus. OXM activates glucagon-like peptide 1 (GLP-1) and glucagon (Gcg) receptors, facilitates insulin signaling and has neuroprotective effects against Aß1-42-induced cytotoxicity in primary hippocampal neurons. Here, we tested the effects of the protease-resistant analogue (D-Ser2)Oxm on spatial memory and synaptic plasticity and the underlying molecular mechanisms in the APP/PS1 transgenic mouse model of AD. The results showed that (D-Ser2)Oxm not only alleviated the impairments of working memory and long-term spatial memory, but also reduced the number of Aß plaques in the hippocampus, and reversed the suppression of hippocampal synaptic long-term potentiation (LTP). Moreover, (D-Ser2)Oxm administration significantly increased p-PI3K/p-AKT1 expression and decreased p-GSK3ß levels in the hippocampus. These results are the first to show an in vivo neuroprotective role of (D-Ser2)Oxm in APP/PS1 mice, and this role involves the improvement of synaptic plasticity, clearance of Aß and normalization of PI3K/AKT/GSK3ß cell signaling in the hippocampus. This study suggests that (D-Ser2)Oxm holds promise for the prevention and treatment of AD.

A novel GLP-1/GIP/Gcg triagonist reduces cognitive deficits and pathology in the 3xTg mouse model of Alzheimer's disease.

Type 2 diabetes mellitus (T2DM) is an important risk factor for Alzheimer's disease (AD). Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) have been identified to be effective in T2DM treatment and neuroprotection. In this study, we further explored the effects of a novel unimolecular GLP-1/GIP/Gcg triagonist on the cognitive behavior and cerebral pathology in the 7-month-old triple transgenic mouse model of AD (3xTg-AD), and investigated its possible electrophysiological and molecular mechanisms. After chronic administration of the GLP-1/GIP/Gcg triagonist (10 nmol/kg bodyweight, once daily, i.p.) for 30 days, open field, Y maze and Morris water maze tests were performed, followed by in vivo electrophysiological recording, immunofluorescence and Western blotting experiments. We found that the chronic treatment with the triagonist could improve long-term spatial memory of 3xTg-AD mice in Morris water maze, as well as the working memory in Y maze task. The triagonist also alleviated the suppression of long-term potentiation (LTP) in the CA1 region of hippocampus. In addition, the triagonist significantly reduced hippocampal pathological damages, including amyloid-ß (Aß) and phosphorylated tau aggregates, and upregulated the expression levels of S133 p-CREB, T286 p-CAMKII and S9 p-GSK3ß in the hippocampus of the 3xTg-AD mice. These results demonstrate for the first time that the novel GLP-1/GIP/Gcg triagonist is efficacious in ameliorating cognitive deficits and pathological damages of 3xTg-AD mice, suggesting that the triagonist might be potentially beneficial in the treatment of AD.

Lixisenatide reduces amyloid plaques, neurofibrillary tangles and neuroinflammation in an APP/PS1/tau mouse model of Alzheimer's disease.

Type 2 diabetes mellitus (T2DM) has been identified as a high risk factor for Alzheimer's disease (AD). The impairment of insulin signaling has been found in AD brain. Glucagon-like peptide-1 (GLP-1) is an incretin hormone, normalises insulin signaling and acts as a neuroprotective growth factor. We have previously shown that the long-lasting GLP-1 receptor (GLP-1R) agonist lixisenatide plays an important role in memory formation, synaptic plasticity and cell proliferation of rats. In the follow-up study, we analysed the neuroprotective effect and mechanism of lixisenatide, injected for 60 days at 10 nmol/kg i.p. once daily in APP/PS1/tau female mice and C57BL/6J female mice (as control) aged 12 month. The results showed that lixisenatide could reduce amyloid plaques, neurofibrillary tangles and neuroinflammation in the hippocampi of 12-month-old APP/PS1/tau female mice; activation of PKA-CREB signaling pathway and inhibition of p38-MAPK might be the important mechanisms in the neuroprotective function of lixisenatide. The study demonstrated that GLP-1R agonists such as lixisenatide might have the potential to be developed as a novel therapy for AD.

[Application of wireless neuronal recording system in fear conditioning of Alzheimer's disease mice - hippocampal Theta oscillation observation].

APP/PS1/tau triple transgenic (3xTg) mouse is a classical animal model of Alzheimer's disease (AD), which has abnormalities in recognition and electrophysiological properties at early 6-month-old age. However, few studies were performed by using simultaneously recording cognitive behavior and brain electrical activity in the conscious 3xTg mice. By using a new wireless recording system, we recorded hippocampal Theta oscillations in 3xTg mice during the process of fear conditioning test. The results showed that: (1) in training session, no significant difference in the fear behavior and hippocampal Theta activity was found between 3xTg mice and WT mice; (2) in test session, 3xTg mice showed a significant decrease in freezing ratio compared with WT mice when they were exposed to conditioning stimulus (CS); (3) the 3xTg mice showed lower peak power in Theta oscillation in both Pre-CS and CS duration compared with WT mice; (4) CS effectively induced an increase in the peak frequency of Theta oscillation in WT mice, but not in 3xTg mice. These results indicated that the impairment of cognition behavior in 3xTg mice was accompanied with the decreased peak power and peak frequency of Theta oscillation in the hippocampus, suggesting that a decline in Theta oscillation might be involved in the impairments of the fear conditioning, and the enhanced hippocampal Theta oscillation may be beneficial for improving AD cognitive function.

Amyloid ß protein injection into medial septum impairs hippocampal long-term potentiation and cognitive behaviors in rats.

The specific loss of cholinergic neurons and the progressive deficits of cognitive function are the most primary characteristics of Alzheimer's disease (AD). Although the neurotoxicity of amyloid ß protein (Aß) in AD has been investigated extensively, it is still unclear whether the Aß aggregated in the medial septum (MS), a major cholinergic nucleus projecting to the hippocampus, could affect hippocampal synaptic plasticity and further impair the memory behaviors. The present study investigated the effects of Aß injection into the MS on hippocampal long-term potentiation (LTP) and cognitive behaviors of rats by using Morris water maze (MWM), Y maze and in vivo hippocampal LTP recording. The effects of kainic acid (KA), an agent with specific neurotoxicity to GABAergic neurons, were also observed. The results showed that: (1) Intra-MS injection of Aß25-35, not KA, impaired spatial learning and memory of rats in classical and reversal MWM tests; (2) Both Aß25-35 and KA impaired novelty-seeking behavior of rats in Y maze; (3) Intra-MS injection of Aß25-35, not KA, suppressed in vivo hippocampal LTP in the CA1 region of rats; (4) Both Aß25-35 and KA did not affect the motor ability in behavioral tests and the hippocampal paired-pulse facilitation (PPF) in electrophysiological recording. These results indicate that intra-MS injection of Aß could impair spatial memory, cognitive flexibility and exploratory motivation, as well as hippocampal LTP in rats, suggesting that the cholinergic neurons in the MS and the septo-hippocampal projection could be important targets of neurotoxic Aß, and the specific damage of cholinergic neurons in the MS is likely responsible for the impairments of hippocampal synaptic plasticity and cognitive function in AD.

A novel antibody targeting sequence 31-35 in amyloid ß protein attenuates Alzheimer's disease-related neuronal damage.

Amyloid ß protein (Aß) plays a critical role in pathogenesis of Alzheimer's disease (AD). Our previous studies indicated that the sequence 31-35 in Aß molecule is an effective active center responsible for Aß neurotoxicity in vivo and in vitro. In the present study, we prepared a novel antibody specifically targeting the sequence 31-35 of amyloid ß protein, and investigated the neuroprotection of the anti-Aß31-35 antibody against Aß1-42 -induced impairments in neuronal viability, spatial memory, and hippocampal synaptic plasticity in rats. The results showed that the anti-Aß31-35 antibody almost equally bound to both Aß31-35 and Aß1-42 , and pretreatment with the antibody dose-dependently prevented Aß1-42 -induced cytotoxicity on cultured primary cortical neurons. In behavioral study, intracerebroventricular (i.c.v.) injection of anti-Aß31-35 antibody efficiently attenuated Aß1-42 -induced impairments in spatial learning and memory of rats. In vivo electrophysiological experiments further indicated that Aß1-42 -induced suppression of hippocampal synaptic plasticity was effectively reversed by the antibody. These results demonstrated that the sequence 31-35 of Aß may be a new therapeutic target, and the anti-Aß31-35 antibody could be a novel immunotheraputic approach for the treatment of AD. © 2016 Wiley Periodicals, Inc.

High-intensity treadmill running impairs cognitive behavior and hippocampal synaptic plasticity of rats via activation of inflammatory response.

Although appropriate exercise is beneficial for enhancing brain functions, high-intensity exercise (HIE)-induced cognitive dysfunction is causing more and more concerns nowadays. In the present study, we observed the effects of high-intensity treadmill running on the spatial learning of the adult Sprague Dawley male rats in Y-maze (n = 16 per group), and investigated its possible electrophysiological and molecular mechanisms by examining in vivo hippocampal long-term potentiation (LTP), central inflammatory responses, and JNK/p38/ERK signal pathway. The Y-maze active avoidance test showed that high-intensity treadmill running impaired spatial learning ability of rats, with increased error times and prolonged training time in recognizing safety condition. Associated with the cognitive dysfunction, the induction and maintenance of hippocampal LTP were also impaired by the HIE. Furthermore, accompanied by elevated levels of inflammatory factors IL-1ß, TNF-α, and iNOS, overactivation of microglia and astrocytes was also found in the CA1 region of hippocampus in the excessive exercise group, indicating an inflammatory response induced by HIE. In addition, Western blot assay showed that the phosphorylation of JNK/p38/ERK proteins was enhanced in the exercise group. These results suggest that exercise stress-induced neuronal inflammatory responses in the hippocampus are associated with HIE-induced cognitive deficits, which may be involved in the upregulation of the JNK/p38/ERK pathway. © 2016 Wiley Periodicals, Inc.

[Real-time measurement of Ca2+ flux in hippocampal slice with non-invasive micro-test technique].

The deposition of amyloid-ß protein (Aß) in the brain is the most important pathological feature of Alzheimer's disease (AD). The mechanism of Aß neurotoxicity may be closely related to the disturbance of intracellular Ca2+ homeostasis. Non-invasive micro-test technique (NMT) is a novel technique developed in recent years, which can be used to directly record transmembrane ion influx and efflux in a non-contact way by detecting the diffusion potentials outside of the membrane. The present study examined the effects of Aß31-35 pretreatment on glutamate (Glu)-induced Ca2+ influx and low [Ca2+] solution-induced Ca2+ efflux in the hippocampal slices of C57BL/6 mice using NMT. The results showed that: (1) acute administration of Glu (2.5, 5, 10 mmol/L) evoked a persistent transmembrane Ca2+ influx in hippocampal CA1 neurons, with a rapid onset and subsequent decay; (2) pretreatment with Aß dose-dependently increased the average rate of Ca2+ influx induced by Glu during the initial 5 min, which was blocked by NMDA receptor antagonist D-APV; (3) perfusion with low [Ca2+] artificial cerebrospinal fluid (aCSF) induced a continuous Ca2+ efflux, which was mostly blocked by KB-R7943, a specific antagonist of Na+/Ca2+ exchanger; (4) Aß31-35 pretreatment partially inhibited the low [Ca2+] aCSF-induced Ca2+ efflux. These results indicate that Aß not only facilitates Ca2+ influx but also inhibits Ca2+ efflux, which jointly contribute to the Aß-induced intracellular Ca2+ overload; the potentiation of Aß on Glu excitotoxicity is mainly mediated by NMDA receptors, while the target for Aß to affect Ca2+ efflux was mainly Na+/Ca2+ exchanger. NMT showed multiple advantages in detecting transmembrane Ca2+ flux in brain slices, such as non-invasiveness to target cells, fast, convenient and real-time acquisition of Ca2+ flux. Therefore, this study provided new experimental evidence for Aß-induced Ca2+ overload, as well as a novel application for NMT in measuring transmembrane Ca2+ flux of neurons in the brain.

[GLP-1/GIP/Gcg receptor Triagonist improves the cognitive behaviors in triple-transgenic mice of Alzheimer's disease].

Alzheimer's disease (AD) is a progressively neurodegenerative disorder, which seriously affects human health but is still irreversible up to now. Recent studies indicate that type 2 diabetes mellitus (T2DM) is an important risk factor for AD, and the drugs used for treatment of T2DM have shown some neuroprotective effects in the treatment of AD. Glucagon-like peptide-1 (GLP-1)/ glucose-dependent insulinotropic polypeptide (GIP)/glucagon (Gcg) receptor Triagonist is a new monomeric polypeptide equally activating the GLP-1/GIP/Gcg receptors, which is built on the basis of GLP-1/Gcg receptor coagonist core sequence, and incorporated with partial amino acids of GIP. Recently, the Triagonist has been reported to be effective in alleviating diabetic complications in rodent models of obesity. The present study observed for the first time the cognitive improvement effects of the Triagonist in the triple-transgenic AD mice (3xTg-AD) by using multiple behavioral techniques, and explored its probable molecular mechanisms using ELISA and Western blot. The results showed that the chronic treatment with the Triagonist (i.p.) significantly reversed the impairments in working memory of 3xTg-AD mice, with an obvious increase in the percentage of correct spontaneous alternation in the Y maze; the Triagonist treatment also improved long-term spatial memory and re-learning ability of 3xTg-AD mice in classical Morris water maze and reverse water maze tests, with decreased escape latency in under water platform tests and increased swimming time in probe tests. ELISA and Western blot experiments showed that the Triagonist up-regulated the levels of cAMP, PKA and p-CREB in the hippocampus of 3xTg-AD mice. These results indicate that GLP-1/GIP/Gcg receptor Triagonist can improve the cognitive behaviors in 3xTg-AD mice, and the up-regulation of hippocampal cAMP/PKA/CREB signal pathway may mediate the neuroprotection of the Triagonist, suggesting that the GLP-1/GIP/Gcg receptor Triagonist may be a novel therapeutic strategy for the treatment of AD.

Steroid sulfatase inhibitor DU-14 protects spatial memory and synaptic plasticity from disruption by amyloid ß protein in male rats.

Alzheimer's disease (AD) is an age-related mental disorder characterized by progressive loss of memory and multiple cognitive impairments. The overproduction and aggregation of Amyloid ß protein (Aß) in the brain, especially in the hippocampus, are closely involved in the memory loss in the patients with AD. Accumulating evidence indicates that the Aß-induced imbalance of dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS) in the brain plays an important role in the AD pathogenesis and progression. The level of DHEA is elevated, while DHEAS is dramatically decreased in the AD brain. The present study tried to restore the balance between DHEA and DHEAS by using a non-steroidal sulfatase inhibitor DU-14, which increases endogenous DHEAS through preventing DHEAS converted back into DHEA. We found that: (1) DU-14 effectively attenuated the Aß1-42-induced cognitive deficits in spatial learning and memory of rats in Morris water maze test; (2) DU-14 prevented Aß1-42-induced decrease in the cholinergic theta rhythm of hippocampal local field potential (LFP) in the CA1 region; (3) DU-14 protected hippocampal synaptic plasticity against Aß1-42-induced suppression of long term potentiation (LTP). These results provide evidence for the neuroprotective action of DU-14 against neurotoxic Aß, suggesting that up-regulation of endogenous DHEAS by DU-14 could be beneficial to the alleviation of Aß-induced impairments in spatial memory and synaptic plasticity.

Desipramine improves depression-like behavior and working memory by up-regulating p-CREB in Alzheimer's disease associated mice.

Aggregation of amyloid [Formula: see text] protein (A[Formula: see text] and progressive loss of memory are the main characteristics of Alzheimer's disease (AD). It is noteworthy that approximately 40% of AD patients have depressive symptom. The close correlation between cognitive deficits and mental depression suggests a possibility that antidepression treatment might be beneficial to cognitive improvement in AD. The present study, by using tail-suspension test (TST), forced swimming, alternative electro-stimulus Y maze test and immunohistochemistry, examined the neuroprotective effects of desipramine, a newer generation tricyclic antidepressants (TCA), and investigated its possible molecular mechanism. The results showed that: (1) intra-hippocampal injection of A[Formula: see text] induced depression-like behavior and associative learning deficits in mice, with an increased mean immobility time in tail-suspension and forced swimming test and an increased mean error times in Y maze test; (2) after treatment with desipramine (10[Formula: see text]mg/kg, i.p.), the average immobility time significantly decreased, from [Formula: see text][Formula: see text]s in A[Formula: see text] group to [Formula: see text][Formula: see text]s in A[Formula: see text] plus desipramine group ([Formula: see text]) in TST and from [Formula: see text][Formula: see text]s to [Formula: see text][Formula: see text]s ([Formula: see text] or 9, [Formula: see text]) in forced swimming test, respectively;the mean error times of mice in Y maze test also significantly decreased, from [Formula: see text] in A[Formula: see text] group to [Formula: see text] in A[Formula: see text] plus desipramine group ([Formula: see text], [Formula: see text]); (3) desipramine administration significantly prevented against A[Formula: see text]-induced down-regulation of phosphorylated cAMP response element binding protein (p-CREB) in the hippocampus. These results indicate that A[Formula: see text] could concurrently mimic the depression-like behavior and working memory disorder in mice, while desipramine could effectively reverse both the deficits induced by A[Formula: see text]. The neuroprotection of desipramine may be involved in the up-regulation of p-CREB level in the hippocampus of mice.

[Neuroprotective effects of a novel antidiabetic drug (D-Ser2)Oxm on amyloid ß protein-induced cytotoxicity].

The accumulation and neurotoxicity of amyloid ß protein (Aß) in the brain is one of major pathological hallmarks of Alzheimer's disease (AD). The effective drugs against Aß have been still deficient up to now. According to a most recent study, (D-Ser2) Oxm, a new antidiabetic drug, not only improves the disorders in plasma glucose and insulin in type 2 diabetes mellitus (T2DM) rats, but also exerts positive effects on hippocampal neurogenesis and synaptogenesis. However, it is still unclear whether (D-Ser2)Oxm can directly protect cultured neurons against Aß1-42-induced cytotoxicity. In the present study, we investigated the neuroprotective effects of (D-Ser2)Oxm on the cultured primary hippocampal neurons by testing the cell viability, neuronal apoptosis, mitochondrial membrane potential and intracellular calcium concentration. The results showed that treatment with (D-Ser2)Oxm effectively reversed Aß1-42-induced decline in cell viability (P < 0.001), and this protective effect could be inhibited by the pretreatment with exendin(9-39), a GLP-1 receptor blocker. (D-Ser2)Oxm treatment also decreased Aß1-42-induced neuronal early apoptosis and down-regulated apoptotic protein caspase3. Meantime, (D-Ser2)Oxm treatment inhibited Aß1-42-induced [Ca(2+)]i elevation, mitochondrial membrane potential depolarization, and glycogen synthase kinase-3ß (GSK3ß) activation. These results suggest that (D-Ser2)Oxm can protect hippocampal neurons against Aß1-42-induced cytotoxicity and this effect may be related to activation of GLP-1 receptors, regulation of intracellular calcium homeostasis and stabilization of mitochondrial membrane potential.

Colivelin ameliorates amyloid ß peptide-induced impairments in spatial memory, synaptic plasticity, and calcium homeostasis in rats.

Amyloid ß peptide (Aß) has been thought to be neurotoxic and responsible for the impairment of learning and memory in Alzheimer's disease (AD). Humanin (HN), a 24 amino acid polypeptide first identified from the unaffected occipital lobe of an AD patient, is believed to be neuroprotective against the AD-related neurotoxicity. In this study, we investigated the neuroprotective effects of Colivelin (CLN), a novel HN derivative, against Aß by using behavioral test, in vivo electrophysiological recording, and intracellular calcium imaging. Our results showed that intrahippocampal injection of CLN (0.2 nmol) effectively prevented Aß25-35 (4 nmol)-induced deficits in spatial learning and memory of rats in Morris water maze test; the suppression of in vivo hippocampal long term potentiation (LTP) by Aß25-35 was nearly completely prevented by CLN; in addition, CLN pretreatment also effectively inhibited Aß25-35-induced calcium overload in primary cultured hippocampal neurons. These results indicate that CLN has significant neuroprotective properties against Aß, and CLN may holds great promise for the treatment and prevention of AD.

Leptin attenuates the detrimental effects of ß-amyloid on spatial memory and hippocampal later-phase long term potentiation in rats.

ß-Amyloid (Aß) is the main component of amyloid plaques developed in the brain of patients with Alzheimer's disease (AD). The increasing burden of Aß in the cortex and hippocampus is closely correlated with memory loss and cognition deficits in AD. Recently, leptin, a 16kD peptide derived mainly from white adipocyte tissue, has been appreciated for its neuroprotective function, although less is known about the effects of leptin on spatial memory and synaptic plasticity. The present study investigated the neuroprotective effects of leptin against Aß-induced deficits in spatial memory and in vivo hippocampal late-phase long-term potentiation (L-LTP) in rats. Y maze spontaneous alternation was used to assess short term working memory, and the Morris water maze task was used to assess long term reference memory. Hippocampal field potential recordings were performed to observe changes in L-LTP. We found that chronically intracerebroventricular injection of leptin (1µg) effectively alleviated Aß1-42 (20µg)-induced spatial memory impairments of Y maze spontaneous alternation and Morris water maze. In addition, chronic administration of leptin also reversed Aß1-42-induced suppression of in vivo hippocampal L-LTP in rats. Together, these results suggest that chronic leptin treatments reversed Aß-induced deficits in learning and memory and the maintenance of L-LTP.

The neuroprotection of Rattin against amyloid ß peptide in spatial memory and synaptic plasticity of rats.

Rattin, a specific derivative of humanin in rats, shares the ability with HN to protect neurons against amyloid ß (Aß) peptide-induced cellular toxicity. However, it is still unclear whether Rattin can protect against Aß-induced deficits in cognition and synaptic plasticity in rats. In the present study, we observed the effects of Rattin and Aß31-35 on the spatial reference memory and in vivo hippocampal Long-term potentiation of rats by using Morris water maze test and hippocampal field potential recording. Furthermore, the probable molecular mechanism underlying the neuroprotective roles of Rattin was investigated. We showed that intra-hippocampal injection of Rattin effectively prevented the Aß31-35-induced spatial memory deficits and hippocampal LTP suppression in rats; the Aß31-35-induced activation of Caspase-3 and inhibition of STAT3 in the hippocampus were also prevented by Rattin treatment. These findings indicate that Rattin treatment can protect spatial memory and synaptic plasticity of rats against Aß31-35-induced impairments, and the underlying protective mechanism of Rattin may be involved in STAT3 and Caspases-3 pathways. Therefore, application of Rattin or activation of its signaling pathways in the brain might be beneficial to the prevention of Aß-related cognitive deficits.

[Amyloid ß protein suppresses hippocampal theta rhythm and induces behavioral disinhibition and spatial memory deficit in rats].

Hippocampal neuronal network oscillation is closely related to the memory, anxiety and behavioral inhibition of mammalian. The cognitive decline and behavioral disinhibition in the patients with Alzheimer's disease (AD) may be relevant to amyloid ß protein (Aß)-induced impairment in hippocampal neuronal cooperative activity. However, it is not well known whether intrahippocampal injection of Aß could induce behavioral disinhibition and neuronal network disorder, as well as cognition decline in animals. In the present study, we observed the effects of intracerebral injection of Aß(1-42) on the spatial memory and behavioral inhibition of rats by using Morris water maze and elevated plus-maze tests. Further, we analyzed hippocampal theta rhythm by recording hippocampal local field potential. The results showed that: (1) bilateral hippocampal injection of Aß(1-42) reduced the anxious behavior of rats, with a significant behavioral disinhibition in the elevated plus-maze test, representing as an increase in the mean entering times and mean residence time in the open arm; (2) Aß(1-42) injection resulted in a significant impairment of spatial memory in rats, with significantly increased mean escape latencies in hidden platform test; (3) Aß(1-42) disrupted the induction of theta rhythm induced by tail pinch, with a significant reduction in the peak power, not the peak power frequency of the theta rhythm. These experimental results indicate that intrahippocampal injection of Aß(1-42) can induce behavioral disinhibition and theta rhythm suppression, as well as spatial memory impairment in rats, which suggests that the cognition deficits and behavior impairments in AD are probably associated with the Aß-induced disruption of hippocampal theta rhythm and consequent down-regulation of synaptic plasticity.

Val8-GLP-1 remodels synaptic activity and intracellular calcium homeostasis impaired by amyloid ß peptide in rats.

Type 2 diabetes mellitus (T2DM) is a risk factor for Alzheimer's disease (AD) in the elderly. Glucagon-like peptide-1 (GLP-1), a modulator in T2DM therapy, has been shown to have neuroprotective properties. However, the native GLP-1 can be rapidly degraded by the enzyme dipeptidyl peptidase IV (DPP IV); the neuroprotective mechanism of GLP-1 in the central nervous system is still an open question, and whether GLP-1 can prevent amyloid ß (Aß)-induced synaptic dysfunction and calcium disorder is still unclear. The present study, by using patch clamp and calcium imaging techniques, investigated the effects of Val8-GLP-1(7-36), a GLP-1 analogue with profound resistance to DPP IV, on the excitatory and inhibitory synaptic transmission and intracellular calcium concentration ([Ca²âº](i) ) in the absence or presence of Aß1-40. The results showed that 1) Aß1-40 significantly reduced the frequency of miniature excitatory postsynaptic currents (mEPSCs) and miniature inhibitory postsynaptic currents (mIPSCs) in CA1 pyramidal neurons of rat brain slices; 2) Val8-GLP-1(7-36) did not affect the activity of miniature postsynaptic currents but effectively protected against the Aß1-40-induced decrease in mEPSC and mIPSC frequency; 3) Aß1-40 significantly increased [Ca²âº](i) in primary neuronal cultures; and 4) Val8-GLP-1(7-36) alone did not change the intracellular calcium level but prevented Aß1-40-induced persistent elevation of [Ca²âº](i). These findings demonstrate for the first time that central application of Val8-GLP-1(7-36) could protect against Aß-induced synaptic dysfunction and intracellular calcium overloading, suggesting that the neuroprotection of GLP-1 may be involved in the remodeling of synaptic activity and intracellular calcium homeostasis in the brain.

Amyloid ß-protein suppressed nicotinic acetylcholine receptor-mediated currents in acutely isolated rat hippocampal CA1 pyramidal neurons.

Amyloid ß protein (Aß) is responsible for the deficits of learning and memory in Alzheimer's disease (AD). The high affinity between Aß and nicotinic acetylcholine receptors (nAChRs) suggests that the impairment of cognitive function in AD might be involved in the Aß-induced damage of nAChRs. This study investigated the effects of Aß fragments on nAChR-mediated membrane currents in acutely isolated rat hippocampal pyramidal neurons by using whole-cell patch clamp technique. The results showed that: (1) nonspecific nAChR agonist nicotine, selective α7 nAChR agonist choline, and α4ß2 nAChR agonist epibatidine all effectively evoked inward currents in CA1 neurons at normal resting membrane potential, with different desensitization characteristics; (2) acute application of different concentrations (pM-µM) of Aß25-35, Aß31-35, or Aß35-31 alone did not trigger any membrane current, but pretreatment with 1 µM Aß25-35 and Aß31-35 similarly and reversibly suppressed the nicotine-induced currents; (3) further, choline- and epibatidine-induced currents were also reversibly suppressed by the Aß pretreatment, but more prominent for the choline-induced response. These results demonstrate that the functional activity of both α7 and α4ß2 nAChRs in the membrane of acutely isolated hippocampal neurons was significantly downregulated by Aß treatment, suggesting that nAChRs, especially α7 nAChRs, in the brain may be the important biological targets of neurotoxic Aß in AD. In addition, the similar suppression of nAChR currents by Aß25-35 and Aß31-35 suggests that the sequence 31-35 in Aß molecule may be a shorter active center responsible for the neurotoxicity of Aß in AD.

Melatonin protects against amyloid-ß-induced impairments of hippocampal LTP and spatial learning in rats.

Alzheimer's disease (AD), the most prevalent neurodegenerative disease in the elderly, leads to progressive loss of memory and cognitive deficits. Amyloid-ß protein (Aß) in the brain is thought to be the main cause of memory loss in AD. Melatonin, an indole hormone secreted by the pineal gland, has been reported to produce neuroprotective effects. We examined whether melatonin could protect Aß-induced impairments of hippocampal synaptic plasticity, neuronal cooperative activity, and learning and memory. Rats received bilateral intrahippocampal injection of Aß1-42 or Aß31-35 followed by intraperitoneal application of melatonin for 10 days, and the effects of chronic melatonin treatment on in vivo hippocampal long-term potentiation (LTP) and theta rhythm and Morris water maze performance were examined. We showed that intrahippocampal injection of Aß1-42 or Aß31-35 impaired hippocampal LTP in vivo, while chronic melatonin treatment reversed Aß1-42- or Aß31-35-induced impairments in LTP induction. Intrahippocampal injection of Aß31-35 impaired spatial learning and decreased the power of theta rhythm in the CA1 region induced by tail pinch, and these synaptic, circuit, and learning deficits were rescued by chronic melatonin treatment. These results provide evidence for the neuroprotective action of melatonin against Aß insults and suggest a strategy for alleviating cognition deficits of AD.