NPY gene transfer in the hippocampus attenuates synaptic plasticity and learning

Recombinant adeno-associated viral (rAAV) vector-induced neuropeptide Y (NPY) overexpression in the hippocampus exerts powerful antiepileptic and antiepileptogenic effects in rats. Such gene therapy approach could be a valuable alternative for developing new antiepileptic treatment strategies. Future clinical progress, however, requires more detailed evaluation of possible side effects of this treatment. Until now it has been unknown whether rAAV vector-based NPY overexpression in the hippocampus alters normal synaptic transmission and plasticity, which could disturb learning and memory processing. Here we show, by electrophysiological recordings in CA1 of the hippocampal formation of rats, that hippocampal NPY gene transfer into the intact brain does not affect basal synaptic transmission, but slightly alters short-term synaptic plasticity, most likely via NPY Y2 receptor-mediated mechanisms. In addition, transgene NPY seems to be released during high frequency neuronal activity, leading to decreased glutamate release in excitatory synapses. Importantly, memory consolidation appears to be affected by the treatment. We found that long-term potentiation (LTP) in the CA1 area is partially impaired and animals have a slower rate of hippocampal-based spatial discrimination learning. These data provide the first evidence that rAAV-based gene therapy using NPY exerts relative limited effect on synaptic plasticity and learning in the hippocampus, and therefore this approach could be considered as a viable alternative for epilepsy treatment.     

Frequency dependency of NMDA receptor‐dependent synaptic plasticity in the hippocampal CA1 region of freely behaving mice

Hippocampal synaptic plasticity in the form of long‐term potentiation (LTP) and long‐term depression (LTD) is likely to enable synaptic information storage in support of memory formation. The mouse brain has been subjected to intensive scrutiny in this regard; however, a multitude of studies has examined synaptic plasticity in the hippocampal slice preparation, whereas very few have addressed synaptic plasticity in the freely behaving mouse. Almost nothing is known about the frequency or N‐methyl‐D‐aspartate receptor (NMDAR) dependency of hippocampal synaptic plasticity in the intact mouse brain. Therefore, in this study, we investigated the forms of synaptic plasticity that are elicited at different afferent stimulation frequencies. We also addressed the NMDAR dependency of this phenomenon. Adult male C57BL/6 mice were chronically implanted with a stimulating electrode into the Schaffer collaterals and a recording electrode into the Stratum radiatum of the CA1 region. To examine synaptic plasticity, we chose protocols that were previously shown to produce either LTP or LTD in the hippocampal slice preparation. Low‐frequency stimulation (LFS) at 1 Hz (900 pulses) had no effect on evoked responses. LFS at 3 Hz (ranging from 200 up to 2 × 900 pulses) elicited short‐term depression (STD, <45 min). LFS at 3 Hz (1,200 pulses) elicited slow‐onset potentiation, high‐frequency stimulation (HFS) at 100 Hz (100 or 200 pulses) or at 50 Hz was ineffective, whereas 100 Hz (50 pulses) elicited short‐term potentiation (STP). HFS at 100 Hz given as 2 × 30, 2 × 50, or 4 × 50 pulses elicited LTP (>24 h). Theta‐burst stimulation was ineffective. Antagonism of the NMDAR prevented STD, STP, and LTP. This study shows for the first time that protocols that effectively elicit persistent synaptic plasticity in the slice preparation elicit distinctly different effects in the intact mouse brain. Persistent LTD could not be elicited with any of the protocols tested. Plasticity responses are NMDAR dependent, suggesting that these phenomena are relevant for hippocampus‐dependent learning. © 2012 Wiley Periodicals, Inc.     

Learning deficits and dysfunctional synaptic plasticity induced by aggregated amyloid deposits in the dentate gyrus are rescued by chronic treatment with indomethacin

The amyloid pathology in Alzheimer's disease is accompanied by a chronic inflammatory response characterized by gliosis and activated microglial cells surrounding senile plaques. Epidemiological studies have shown nonsteroidal anti-inflammatory drug treatment reduces the risk of Alzheimer's disease. We have previously shown that injection of a combination of Abeta40 and Abeta43 in the dentate gyrus of the rat induces aggregated amyloid deposits and inflammation associated with dysfunctional synaptic plasticity and learning deficits. Here we characterize the effectiveness of nonsteroidal anti-inflammatory treatment in this model and show that this treatment restores the working memory deficit and decremental long-term potentiation in the dentate gyrus. Importantly, we observe no qualitative difference in the presence of aggregated material but a substantial reduction in microglial-induced inflammation, suggesting that mature aggregated plaques may not be directly responsible for the deficits but may trigger an inflammatory response which has a detrimental effect on synaptic function and memory.     

CB1 receptor‐mediated signaling underlies the hippocampal synaptic,learning, and memory deficits following treatment with JWH‐081, a new component of spice/K2 preparations

Recently, synthetic cannabinoids have been sprayed onto plant material, which is subsequently packaged and sold as “Spice” or “K2” to mimic the effects of marijuana. A recent report identified several synthetic additives in samples of “Spice/K2”, including JWH‐081, a synthetic ligand for the cannabinoid receptor 1 (CB1). The deleterious effects of JWH‐081 on brain function are not known, particularly on CB1 signaling, synaptic plasticity, learning and memory. Here, we evaluated the effects of JWH‐081 on pCaMKIV, pCREB, and pERK1/2 signaling events followed by long‐term potentiation (LTP), hippocampal‐dependent learning and memory tasks using CB1 receptor wild‐type (WT) and knockout (KO) mice. Acute administration of JWH‐081 impaired CaMKIV phosphorylation in a dose‐dependent manner, whereas inhibition of CREB phosphorylation in CB1 receptor WT mice was observed only at higher dose of JWH‐081 (1.25 mg/kg). JWH‐081 at higher dose impaired CaMKIV and CREB phosphorylation in a time‐dependent manner in CB1 receptor WT mice but not in KO mice and failed to alter ERK1/2 phosphorylation. In addition, SR treated or CB1 receptor KO mice have a lower pCaMKIV/CaMKIV ratio and higher pCREB/CREB ratio compared with vehicle or WT littermates. In hippocampal slices, JWH‐081 impaired LTP in CB1 receptor WT but not in KO littermates. Furthermore, JWH‐081 at higher dose impaired object recognition, spontaneous alternation and spatial memory on the Y‐maze in CB1 receptor WT mice but not in KO mice. Collectively our findings suggest that deleterious effects of JWH‐081 on hippocampal function involves CB1 receptor mediated impairments in CaMKIV and CREB phosphorylation, LTP, learning and memory in mice. © 2013 Wiley Periodicals, Inc.     

DYRK1A BAC transgenic mice show altered synaptic plasticity with learning and memory defects

Among the various phenotypes seen in Down syndrome (DS), mental retardation is the most common and most debilitating condition suffered by individuals with DS. The DYRK1A gene on human chromosome 21q22.2 encodes a subfamily of protein kinases that displays dual substrate specificities and is known to play a critical role in neurodevelopment. To study DS mental retardation, we have generated transgenic mice that contain only one copy of the complete human DYRK1A gene in a bacterial artificial chromosome. The transgenic mice showed significant impairment in hippocampal-dependent memory tasks in a Morris water maze. Interestingly, we observed shifts in both long-term potentiation and long-term depression, which suggests a role for DYRK1A in bidirectional synaptic plasticity. These mice represent the most clinically relevant DYRK1A mouse model to date and provide us a valuable tool for the in vivo study of mechanisms that underlie the learning and memory deficit in DS.     

Sexual dimorphisms in the effect of low-level p25 expression on synaptic plasticity and memory

p25, a degradation product of p35, has been reported to accumulate in the forebrain of patients with Alzheimer's disease. p25 as well as p35 are activators of cyclin-dependent kinase 5 (Cdk5) although p25/Cdk5 and p35/Cdk5 complexes have distinct properties. Several mouse models with high levels of p25 expression exhibit signs of neurodegeneration. On the contrary, we have shown that low levels of p25 expression do not cause neurodegeneration and are even beneficial for particular types of learning and memory [Angelo et al., (2003) Eur J. Neurosci., 18, 423-431]. Here, we have studied the influence of low-level p25 expression in hippocampal synaptic plasticity and in learning and memory for each sex separately in two different genetic backgrounds (129B6F1 and C57BL/6). Surprisingly, we found that low-level p25 expression had different consequences in male and female mutants. In the two genetic backgrounds LTP induced by a strong stimulation of the Schaffer's collaterals (four trains, 1-s duration, 5-min interval) was severely impaired in male, but not in female, p25 mutants. Furthermore, in the two genetic backgrounds spatial learning in the Morris water maze was faster in female p25 mutants than in male transgenic mice. These results suggest that, in women, the production of p25 in Alzheimer's disease could be a compensation for some early learning and memory deficits.     

银杏叶提取物GBE50对实验性衰老大鼠海马CA1 区突触可塑性及学习记忆功能的影响

The content of total flavonoids in an extract of Ginkgo biloba,called GBE50,is 44% by weight.This is significantly greater than that in a standard extract of Ginkgo biloba,designated EGB761.To date,the mechanisms by which GBE50 and EGB761 function remain poorly understood.In the present study,an experimental rat model of aging was induced by intraperitoneal injection of D-galactose,followed by intragastric perfusion of GBE50 (30,60mg/kg),or EGB761 (60mg/kg).The water maze scores and hippocampal CA1 synaptic plasticity were evaluated.In the place navigation test,the GBE50 group rats did better than EGB761,while similar scores were obtained in the spatial probe test,and in the platform-switched test.In addition,long-term potentiation was significantly enhanced following high-frequency stimulation in the GBE50 and EGB761 groups,compared with the model group.These results demonstrate that GBE50 and EGB761 improved the learning and memory of aging rats.In particular,GBE50 administered at the 60mg/kg dose exhibited superior effects over EGB761 at the same 60mg/kg dose.Furthermore,the enhancement of hippocampal synaptic plasticity may be an underlying mechanism.     

Long-term homocysteine exposure induces alterations in spatial learning, hippocampal signalling and synaptic plasticity

Abnormally high levels of homocysteine (HCY) have been linked to neurodegenerative diseases, but it remains unclear whether this is the cause or effect of degenerative processes. Here, we investigated the effects of prolonged HCY exposure on cognitive abilities and physiological parameters by injecting rats daily with either 20 or 200 mg/kg HCY over a period of up to 14 weeks. Notwithstanding a significant weight reduction in the 200 mg HCY group, HCY-exposed animals did not show a behavioural deficit when tested repeatedly (in weeks 1, 3, 5, 7 and 13) in a reference memory version of the water maze. Unexpectedly, some improvement in repeated reversal learning was observed in HCY exposed animals compared to controls. Pre-treatment with HCY for 3 weeks before water maze training did not uncover any cognitive alterations. Increased plasma concentrations of HCY were revealed only for the 200 mg HCY group after 14 weeks of injections, but no evidence for DNA damage was obtained. Immunocytochemically, HCY was detected in the brain after 14 weeks of treatment (both 20 and 200 mg/kg), but not after 5 weeks. Bidirectional changes in basic synaptic transmission and long-term potentiation of hippocampal CA1 pyramidal cells were observed at 5, 7 and 14 weeks in both HCY groups, indicative of complex, multifactorial time- and concentration-dependent changes. Overall, it is concluded that healthy adult rats are able to cope with continuous exposure to HCY. While HCY affects growth and neuronal excitability, this does not precipitate into an immediate impairment of cognitive function.     

Activity and plasticity in the CA1, the dentate gyrus, and the amygdala following controllable vs. uncontrollable water stress

The level of controllability has been shown to modulate the effects of stress on physiology and behavior. In the present study, we investigated the effects of controllable vs. uncontrollable stressors on plasticity in hippocampal CA1, the dentate gyrus (DG), and basal amygdala nucleus (B) in the rat, using the electrophysiological procedure of long-term potentiation (LTP). A naive group was left undisturbed until the electrophysiological recording commenced. Rats of the two controllable stress groups were trained in the Morris water maze to locate an invisible underwater platform (the first group), or visible platform (the second group), thus escaping from the water, before the recording. The uncontrollable stress group underwent the same procedure (exposure time to water was adjusted to the averaged exposure time of the first controllable group) without the escape platform. We first assessed the effects of stress and controllability on LTP in CA1. Both controllable stressors and the uncontrollable stress impaired CA1 LTP, with a more robust effect induced by the uncontrollable stress. We further assessed the effects of the same procedures on LTP in DG and B. The uncontrollable stress enhanced LTP in DG and increased baseline responses (suggesting uncontrollable stress-induced plasticity) in the amygdala. All the stressors decreased amygdalar LTP. An assessment of plasma levels of corticosterone (CORT), following the behavioral procedures, revealed an enhancement in CORT release following the uncontrollable, but not controllable stress, indicating the uncontrollable condition as the most stressful. These findings provide insight into the differential effects of stress and stress controllability on different hippocampal subregions and the amygdala.     

Impairment in long-term memory formation and learning-dependent synaptic plasticity in mice lacking glycogen synthase in the brain

Glycogen is the only carbohydrate reserve of the brain, but its overall contribution to brain functions remains unclear. Although it has traditionally been considered as an emergency energetic reservoir, increasing evidence points to a role of glycogen in the normal activity of the brain. To address this long-standing question, we generated a brain-specific Glycogen Synthase knockout (GYS1^Nestin-KO) mouse and studied the functional consequences of the lack of glycogen in the brain under alert behaving conditions. These animals showed a significant deficiency in the acquisition of an associative learning task and in the concomitant activity-dependent changes in hippocampal synaptic strength. Long-term potentiation (LTP) evoked in the hippocampal CA3-CA1 synapse was also decreased in behaving GYS1^Nestin-KO mice. These results unequivocally show a key role of brain glycogen in the proper acquisition of new motor and cognitive abilities and in the underlying changes in synaptic strength.     

Presenilins and APP in neuritic and synaptic plasticity: implications for the pathogenesis of Alzheimer's disease

A key neuropathological hallmark of Alzheimer’s disease (AD) is the loss of neocortical and hippocampal synapses, which is closely correlated with the degree of memory impairment. Mutations in the genes encoding the amyloid precursor protein (APP) and presenilins are responsible from some cases of early-onset autosomal-dominant AD. This article reviews the current understanding of how alterations in the cellular functions of APP and presenilins may result in the dysfunction and degeneration of synapses in AD. APP mutations result in increased production/aggregation of amyloid β-peptide (Aβ), which induces oxidative stress, resulting in the impairment of synaptic membrane ion, glutamate, and glucose transporters. APP mutations may also compromise the production and/or function of secreted forms of APP that are believed to play important roles in learning and memory processes. Presenilin (PS1) mutations result in a major defect in endoplasmic reticulum (ER) calcium regulation, which may perturb synaptic function in ways that lead to impaired synaptic plasticity and neuronal degeneration. Studies in transgenic mice that express APP and PS1 mutations have provided evidence that the mutations result in altered cellular calcium homeostasis and synaptic plasticity, and impaired learning and memory. This article provides a brief review of the pathophysiological interactions of APP and presenilins with synaptic proteins, and discusses how AD-linked mutations in APP and PS1 may disrupt synaptic processes that contribute to memory formation.     

Association between a polymorphism of ubiquitin carboxy-terminal hydrolase L1 (UCH-L1) gene and sporadic Parkinson's disease

We found a novel polymorphism (S/Y18) of ubiquitin carboxy-terminal hydrolase L1 (UCH-L1) gene a mutation of which is expected to contribute to the etiology of a form of familial Parkinson's disease (PD). We report the frequency of this polymorphism in 313 patients with sporadic PD and 302 control subjects (Japanese and Caucasians). The frequency of the mutant allele (Y) was significantly higher in Japanese control subjects (51.2%) than in Japanese PD patients (43.4%) (χ²=3.917, p=0.048<0.05). It appears that this polymorphism has a weak protective factor against PD in at least the Japanese population. The frequencies of Y allele and S/Y and Y/Y genotypes in the PD patients and the controls were more significantly higher in Japanese than in Caucasian population (p<0.0001). It seems that the role of this polymorphism in PD may be different between Caucasian and Japanese populations.     

AF64A, a cholinergic neurotoxin, selectively depletes acetylcholine in hippocampus and cortex, and produces long-term passive avoidance and radial-arm maze deficits in the rat

The behavioral and biochemical effects of AF64A, a presynaptic cholinergic neurotoxin, were investigated. Bilateral administration of this compound into the lateral cerebral ventricles produced transient and dose-related effects on sensorimotor function and long-term impairments of cognitive behavior. Male Fischer-F344 rats dosed with either 15 or 30 nmol of AF64A reacted 29–62% faster than CSF-injected controls in a hot-plate test 14 (but not 1, 7, 21 or 28) days following dosing. The group administered 15 nmol of AF64A was also significantly more active (41%) than controls 28 days following dosing. The activity level of this group was comparable to that of controls at other times and hyperactivity was never observed in the 30 nmol group. Retention of a step-through passive avoidance task, assessed 35 days after dosing, was impaired in both 15 and the 30 nmol groups. Their step-through latencies were significatlly shorter than the control latencies, and they exhibited more partial entries during the 24-h retention test. Radial-arm maze performance, measured 60–80 days following treatment, was markedly impaired in the treated groups. Animals treated with AF64A made fewer correct responses in their first 8 choices, required more total selections to complete the task, and had an altered pattern of spatial responding in the maze. The neurochemical changes produced by AF64A, determined 120 days after dosing, were specific to the cholinergic system and consisted of decreases of ACh in both the hippocampus (15 and 30 nmol groups) and the frontal cortex (30 nmol group). The concentrations of catecholamines, indoleamines, their metabolites and choline in various brain regions were not affected by AF64A. Furthermore, histological analysis revealed that the doses of AF64A used in the present study did not damage the hippocampus, the fimbria-fornix, the septum or the caudate nucleus. These data support the contention that cholinergic processes in the hippocampus, nd/or frontal cortex play an important role in learning and memory processes. Furthermore, based upon the behavioral and biochemical data presented, it is suggested that AF64A could be a useful pharmacological tool for examining the neurobiological substrates of putative cholinergic disorder such as senile dementia of the Alzheimer's type.     

JNK1 contributes to metabotropic glutamate receptor-dependent long-term depression and short-term synaptic plasticity in the mice area hippocampal CA1

Several recent reports implicate an important role played by c-Jun N-terminal kinases (JNKs) in long-term potentiation (LTP). However, little is known about how the isoforms of JNKs participate in synaptic plasticity. Here we showed that short-term synaptic plasticity was impaired in the hippocampal area CA1 of JNK1-deficient (JNK1-/-) mice; these mice showed normal LTP in response to a strong tetanus and no alteration of N-methyl-D-aspartate receptor-dependent long-term depression (LTD) in the hippocampus. However, LTD induced either by group I metabotropic glutamate receptors (mGluRs) agonist dihydroxyphenylglycine or by paired-pulse low-frequency stimulation was absent in both the JNK1-/- slices and in JNK inhibitor anthrax [1, 9-cd] pyrazol-6(2H)-1 (SP600125)-pretreated slices. Induction of mGluR-dependent LTD resulted in an increase in phosphorylation of JNK1 substrates, including p-c-Jun and p-ATF2 in wild-type (WT) mice, and these increases failed to occur in the JNK1-/- or SP600125-pretreated mice. These results demonstrated that JNK1 played a crucial role in the short-term synaptic plasticity and mGluR-dependent LTD, whereas hippocampus LTP was not affected by JNK1 deficiency.     

Impaired long-term memory retention and working memory in sdy mutant mice with a deletion in Dtnbp1, a susceptibility gene for schizophrenia

Background

Schizophrenia is a complex genetic disorder caused by multiple genetic and environmental factors. The dystrobrevin-binding protein 1 (DTNBP1: dysbindin-1) gene is a major susceptibility gene for schizophrenia. Genetic variations in DTNBP1 are associated with cognitive functions, general cognitive ability and memory function, and clinical features of patients with schizophrenia including negative symptoms and cognitive decline. Since reduced expression of dysbindin-1 has been observed in postmortem brains of patients with schizophrenia, the sandy (sdy) mouse, which has a deletion in the Dtnbp1 gene and expresses no dysbindin-1 protein, could be an animal model of schizophrenia. To address this issue, we have carried out a comprehensive behavioral analysis of the sdy mouse in this study.

Results

In a rotarod test, sdy mice did not exhibit motor learning whilst the wild type mice did. In a Barnes circular maze test both sdy mice and wild type mice learned to selectively locate the escape hole during the course of the training period and in the probe trial conducted 24 hours after last training. However, sdy mice did not locate the correct hole in the retention probe tests 7 days after the last training trial, whereas wild type mice did, indicating impaired long-term memory retention. A T-maze forced alternation task, a task of working memory, revealed no effect of training in sdy mice despite the obvious effect of training in wild type mice, suggesting a working memory deficit.

Conclusion

Sdy mouse showed impaired long-term memory retention and working memory. Since genetic variation in DTNBP1 is associated with both schizophrenia and memory function, and memory function is compromised in patients with schizophrenia, the sdy mouse may represent a useful animal model to investigate the mechanisms of memory dysfunction in the disorder.     

小檗碱对三转基因阿尔茨海默病小鼠的学习记忆和海马PSD95突触相关蛋白表达水平的影响

目的 探讨小檗碱(BBR)对三转基因阿尔茨海默病(AD)小鼠的学习记忆及海马组织PSD95突触蛋白表达水平的影响。方法 将30只三转基因(APP/Tau/PS1)AD小鼠按随机数字表法分成3组,即AD对照组、AD+25 mgBBR组、AD+50 mgBBR,每组各10只,后2组以灌胃方式且剂量分别为25 mg·kg^-1·d^-1、50 mg·kg^-1·d^-1,对照组给予等剂量生理盐水连续3个月灌胃处理; 采用Morris水迷宫方法探测各组AD小鼠行为学改变、空间记忆及探索情况; 免疫荧光染色检测各组小鼠海马组织突触后致密蛋白95(PSD95)阳性表达水平; Western blotting(WB)法检测各组三转基因AD小鼠海马脑组织PSD95蛋白、磷酸化蛋白激酶B(p-Akt)和磷酸化雷帕霉素靶蛋白(p-mTOR)表达水平及微管相关蛋白轻链3-Ⅱ(LC3-Ⅱ)自噬水平。结果 AD+25 mgBBR组的逃避潜伏期的学习记忆能力、免疫荧光PSD95表达水平以及PSD995、LC3-Ⅱ、p-Akt、p-mTOR蛋白表达水平与AD对照组比较均有明显差异(P<0.05); AD+50 mgBBR组逃避潜伏期的学习记忆能力、免疫荧光PSD95表达水平以及LC3-Ⅱ、p-Akt、p-mTOR表达水平与AD对照组比较差异均更明显(P<0.05,P<0.01)。结论 应用50 mg小檗碱能较好改善三转基因AD小鼠的学习记忆、空间探索能力,其机制可能是通过增加自噬水平LC3-Ⅱ调控Akt/mTOR信号通路,增加突触蛋白PSD95的表达水平及突触数量,以改善AD相关临床症状。     

The effects of MyD88 deficiency on exploratory activity, anxiety, motor coordination, and spatial learning in C57BL/6 and APPswe/PS1dE9 mice

Toll-like receptors (TLRs) are a family of pattern-recognition receptors in innate immunity and provide a first line defense against pathogens and tissue injuries. In addition to important roles in infection, inflammation, and immune diseases, recent studies show that TLR signaling is involved in modulation of learning, memory, mood, and neurogenesis. Because MyD88 is essential for the downstream signaling of all TLRs, except TLR3, we investigated the effects of MyD88 deficiency (MyD88−/−) on behavioral functions in mice. Additionally, we recently demonstrated that a mouse model of Alzheimer's disease (AD) deficient for MyD88 had decreases in Aβ deposits and soluble Aβ in the brain as compared with MyD88 sufficient AD mouse models. Because accumulation of Aβ in the brain is postulated to be a causal event leading to cognitive deficits in AD, we investigated the effects of MyD88 deficiency on behavioral functions in the AD mouse model at 10 months of age. MyD88 deficient mice showed more anxiety in the elevated plus-maze. In the motor coordination tests, MyD88 deficient mice remained on a beam and a bar for a longer time, but with slower initial movement on the bar. In the Morris water maze test, MyD88 deficiency appeared to improve spatial learning irrespective of the transgene. Our findings suggest that the MyD88-dependent pathway contributes to behavioral functions in an AD mouse model and its control group.     

Myricetin protects hippocampal CA3 pyramidal neurons and improves learning and memory impairments in rats with Alzheimer's disease

There is currently no treatment for effectively slowing the progression of Alzheimer's disease, so early prevention is very important. Numerous studies have shown that flavonoids can improve memory impairment. The present study investigated the effects of myricetin, a member of the flavonoids, on intracerebroventricular streptozotocin induced neuronal loss and memory impairment in rat models of Alzheimer's disease. Myricetin at 5 or 10 mg/kg was intraperitoneally injected into rats over 21 days. Control rats were treated with 10 m L/kg saline. Behavioral test(the shuttle box test) was performed on day 22 to examine learning and memory in rats. Immediately after that, hematoxylin-eosin staining was performed to observe the morphological change in hippocampal CA3 pyramidal neurons. Myricetin greatly increased the number of hippocampal CA3 pyramidal neurons and improved learning and memory impairments in rats with Alzheimer's disease. These findings suggest that myricetin is beneficial for treatment of Alzheimer's disease.