Working memory deficits and related disinhibition of the cAMP/PKA/CREB are alleviated by prefrontal α4β2*-nAChRs stimulation in aged mice

The present study investigates in aged mice the working memory (WM) enhancing potential of the selective α4β2* nicotinic receptor agonist S 38232 as compared with the cholinesterase inhibitor donepezil, and their effect on cAMP response element binding protein (CREB) phosphorylation (pCREB) as a marker of neuronal activity. We first showed that aged mice exhibit a WM deficit and an increase of pCREB in the prelimbic cortex (PL) as compared with young mice, whereas no modification appears in the CA1. Further, we showed that systemic administration of S 38232 restored WM in aged mice and alleviated PL CREB overphosphorylation. Donepezil alleviated age-related memory deficits, however, by increasing pCREB in the CA1, while pCREB in PL remained unaffected. Finally, whereas neuronal inhibition by lidocaine infusion in the PL appeared deleterious in young mice, the infusion of Rp-cAMPS (a compound known to inhibit CREB phosphorylation) or S 38232 rescued WM in aged animals. Thus, by targeting the α4β2*-nicotinic receptor of the PL, S 38232 alleviates PL CREB overphosphorylation and restores WM in aged mice, which opens new pharmacologic perspectives of therapeutic strategy.     

Influence of dopamine D3 receptor knockout on age-related decline of spatial memory

There is evidence indicating that the brain's dopaminergic system is involved in age-associated memory impairment. However, specific roles in this process for the different dopamine receptor subtypes have not been elucidated. The cAMP-response element binding protein (CREB) is one of the cellular molecules that have been strongly implicated in the synaptic plasticity deficits occurring in age-related memory and cognitive impairment. In the present study, dopamine D₃ receptor mutant mice were tested in the Morris water maze task. We found that aged D₃ receptor mutant mice perform comparatively better than their even-aged wild-type counterparts in both spatial learning training and a subsequent memory test. The degree of hippocampal CREB phosphorylation is significantly higher in aged D₃ receptor mutants compared to aged wild-type mice, whereas no difference in CREB activation was observed in the prefrontal cortex. These results suggest that blockade of D₃ receptors ameliorates age-related memory decline and that D₃ receptor-regulated CREB signaling in the hippocampus may be involved in these age-associated alterations.     

Oxytocin improves long-lasting spatial memory during motherhood through MAP kinase cascade

Oxytocin is an essential hormone for mammalian labor and lactation. Here, we show a new function of oxytocin in causing plastic changes in hippocampal synapses during motherhood. In oxytocin-perfused hippocampal slices, one-train tetanus stimulation induced long-lasting, long-term potentiation (L-LTP) and phosphorylation of cyclic AMP-responsive element binding protein (CREB), and MAP kinase inhibitors blocked these inductions. An increase in CREB phosphorylation and L-LTP induced by one-train tetanus were observed in the multiparous mouse hippocampus without oxytocin application. Furthermore, intracerebroventricular injection of oxytocin in virgin mice improved long-term spatial learning in vivo, whereas an injection of oxytocin antagonist in multiparous mice significantly inhibited the improved spatial memory, L-LTP and CREB phosphorylation. These findings indicate that oxytocin is critically involved in improving hippocampus-dependent learning and memory during motherhood in mice.     

Occlusal disharmony induces spatial memory impairment and hippocampal neuron degeneration via stress in SAMP8 mice

We examined the effect of occlusal disharmony in senescence-accelerated (SAMP8) mice on plasma corticosterone levels, hippocampal neuron number, and spatial performance in the water maze. The bite-raised condition was associated with an accelerated age-related decline in spatial memory, increased plasma corticosterone levels, and a decreased number of neurons in the hippocampal CA3 region. The findings suggest that the bite-raised condition in aged SAMP8 mice induces hippocampal neuron loss, thereby leading to senile memory deficits.     

Platelet-activating factor-induced synaptic facilitation is associated with increased calcium/calmodulin-dependent protein kinase II,protein kinase C and extracellular signal-regulated kinase activities in the rat hippocampal CA1 region

Platelet-activating factor (PAF) is an important inflammatory lipid mediator affecting neural plasticity. In the present study, we demonstrated how PAF affects synaptic efficacy through activation of protein kinases in the rat hippocampal CA1 region. In cultured hippocampal neurons, 10 to 1000 nM PAF stimulated autophosphorylation of calcium/calmodulin-dependent protein kinase II (CaMKII) and phosphorylation of synapsin I and myristoylated alanine-rich protein kinase C substrate (MARCKS). In hippocampal CA1 slices, field excitatory postsynaptic potentials (fEPSPs) induced by stimulation of the Schaffer collateral/commissural pathways were significantly increased 10–50 min after exposure to 100 to 1000 nM PAF. Immunoblotting analysis showed that 100 nM PAF treatment for 10 or 50 min significantly and persistently increased CaMKII autophosphorylation in the hippocampal CA1 region. Increased protein kinase Cα (PKCα) autophosphorylation was also seen at the same time point after PAF exposure. By contrast, extracellular signal-regulated kinase (ERK) phosphorylation was slightly but significantly increased at 10 min after PAF exposure. Consistent with increased CaMKII autophosphorylation, AMPA-type glutamate receptor subunit 1 (GluR1) (Ser-831) phosphorylation as a CaMKII postsynaptic substrate significantly increased after 10 or 50 min of treatment, whereas synapsin I (Ser-603) phosphorylation as a presynaptic substrate increased at 10 min in the hippocampal CA1 region. Phosphorylation of MARCKS (Ser-152/156) and NMDA receptor subunit 1 (NR1) (Ser-896) as PKCα substrates also significantly increased after 10 min but had not further increased by 50 min in the CA1 region. Increased of fEPSPs induced by PAF treatment completely and/or partly inhibited by KN93 and/or U0126 treatment. These results suggest that PAF induces synaptic facilitation through activation of CaMKII, PKC and ERK in the hippocampal CA1 region.     

热应激预适应对小鼠学习记忆的影响

目的观察热应激对脑缺血处理的小鼠空间学习记忆能力、海马CA1区神经元CREB的影响。方法采用Morris水迷宫筛选空间学习记忆能力正常的昆明小鼠60只,体重(40±5)g,雌雄不限。将实验动物分为4组:正常对照组(Normal)、热应激预处理后缺血再灌注组(HS/IR)、缺血再灌注组(IR)、单纯热应激组(HS);处理后存活时间分别为3h、24h、72h,每个时间点6只,动物处死前再作水迷宫检测。用免疫组织化学方法检测CREB的表达。常规尼氏染色法镜下计数海马CA1区存活神经元。结果水迷宫检测IR组小鼠潜伏期增加,其搜索策略以边缘式和限制式为主,与其它3组比较有显著的统计学意义(P<0.01)。尼氏染色证实IR组锥体细胞神经元减少;24h的HS/IR组的CREB的表达高于IR组。结论热应激预处理可以改善动物因脑缺血引起的学习记忆功能下降。其机制可能涉及到热应激对CREB表达的上调。     

Peroxiredoxin II preserves cognitive function against age-linked hippocampal oxidative damage

Reactive oxygen species (ROS), routinely produced in biological reactions, contribute to both normal aging and age-related decline in cognitive function. However, little is known regarding the involvement of specific antioxidants in the underlying mechanism(s). Here, we examined if peroxiredoxin II (Prx II) scavenges intracellular ROS that cause age-dependent mitochondrial decay in hippocampal CA1 pyramidal neurons and subsequent impairment of learning and memory. Age-dependent mitochondrial ROS generation and long-term potentiation (LTP) decline were more prominent in hippocampal neurons in Prx II^−/− than in wild-type mice. Additionally, Prx II^−/− mice failed to activate synaptic plasticity-related cellular signaling pathways involving CREB, CaMKII, and ERK, or to maintain functional integrity of their mitochondria. Dietary vitamin E alleviated Prx II deficiency-related deficits, including mitochondrial decay and CREB signaling, resulting in restoration of the abrupt cognitive decline in aged Prx II^−/− mice. These results suggest that Prx II help maintain hippocampal synaptic plasticity against age-related oxidative damage.     

Age-related impairments in memory and in CREB and pCREB expression in hippocampus and amygdala following inhibitory avoidance training

This experiment examined whether age-related changes in CREB and pCREB contribute to the rapid forgetting seen in aged animals. Young (3-month-old) and aged (24-month-old) Fischer-344 rats received inhibitory avoidance training with a low (0.2 mA, 0.4 s) or moderate (0.5 mA, 0.5 s) foot shock; memory was measured 7 days later. Other rats were euthanized 30 min after training, and CREB and pCREB expression levels were examined in the hippocampus, amygdala, and piriform cortex using immunohistochemistry. CREB levels decreased with age in the hippocampus and amygdala. After training with either shock level, young rats exhibited good memory and increases in pCREB levels in the hippocampus and amygdala. Aged rats exhibited good memory for the moderate but not the low shock but did not show increases in pCREB levels after either shock intensity. These results suggest that decreases in total CREB and in pCREB activation in the hippocampus and amygdala may contribute to rapid forgetting in aged rats. After moderate foot shock, the stable memory in old rats together with absence of CREB activation suggests either that CREB was phosphorylated in a spatiotemporal pattern other than analyzed here or that the stronger training conditions engaged alternate mechanisms that promote long-lasting memory.     

Prandial increase of leptin in the brain activates spatial learning and memory

Leptin is well known to be involved in the control of feeding, thermogenesis, reproduction and neuroendocrine functions through its actions on the rodents hypothalamic receptors. Leptin facilitated the presynaptic transmitter release and postsynaptic sensitivity to the transmitters in the hippocampal CA1 neurons. Thus long-term potentiation (LTP) and the phosphorylation of Ca²⁺/calmodulin protein kinase II (CaMKII) were facilitated in the CA1 neurons. Therefore behavioral performance related to spatial learning and memory was improved by leptin in vivo applications. We also investigated LTP and spatial learning and memory function in two leptin receptor-deficient rodents, Zucker fatty rats and db/db mice. The CA1 region of both strains showed impairments of LTP and leptin application did not improve these impairments. These strains showed lower basal levels of CaMKII activity in the CA1 region than the respective controls, and the levels did not respond to a brief tetanic stimulation. These strains also showed impaired spatial learning and memory. The present studies suggest that leptin signaling in the brain may have important implications for cognitive function.     

Long-term administration of green tea catechins prevents age-related spatial learning and memory decline in C57BL/6 J mice by regulating hippocampal cyclic amp-response element binding protein signaling cascade

Flavonoid-rich foods have been shown to be effective at reversing age-related deficits in learning and memory in both animals and humans. However, little investigation of the preventative effects of flavonoids on the naturally aged animals was reported. In our study, 14-month-old female C57BL/6 J mice were orally administered 0.025%, 0.05% and 0.1% green tea catechins (GTC, w/v) in drinking water for 6 months; we found that a supplementation with 0.05% or 0.1% GTC prevented age-related spatial learning and memory decline of mice in the Morris water maze. Better performance of GTC-treated mice was associated with increased levels of cAMP-response element binding protein (CREB) phosphorylation in the hippocampus. The expressions of brain-derived neurotrophic factor (BDNF) and Bcl-2, two target genes of CREB which can exhibit long-term regulatory roles in synaptic plasticity and synaptic structure, were also increased. We also found that long-term 0.05% or 0.1% GTC administration prevented age-related reductions of two representative post-synaptic density proteins PSD95 and Ca²⁺/calmodulin-dependent protein kinase II, suggesting that synaptic structural changes may be involved. These results demonstrated that long-term 0.05% or 0.1% green tea catechin administration may prevent age-related spatial learning and memory decline of female C57BL/6 J mice by regulating hippocampal CREB signaling cascade.     

Dynamic interplays between memory systems depend on practice: the hippocampus is not always the first to provide solution

Previous studies showed that the optimization of behavioral performance through extended training depends on a switch from hippocampus-based memory to striatum-based habit. Here we investigate whether the amount of training within one learning session influences the retention of memory for hippocampal versus striatal strategies. Mice were trained to search for a submerged cue-marked platform which remained in the same spatial location in the water-maze for each of three training regimens (4, 12 or 22 trials). Subsequently, they were either tested for retention of memory 1 h or 24 h later on a probe test or killed at different time points over a 7-h period to determine the kinetic of cAMP response element binding protein (CREB) phosphorylation in both memory systems. During the probe test mice had to choose between a submerged platform located in the same position as during the acquisition phase (spatial solution) and a platform marked by the cue but located in the opposite quadrant of the pool (cue-guided solution). Results showed that the animals first preferred the cue-marked platform, which represents a strategy that was selectively impaired by lesions of the dorsolateral caudate-putamen. With further practice, or context pre-exposure, animals transiently favored the hippocampus-dependent place solution but finally, both strategies became interchangeable and insensitive to either lesion. CREB phosphorylation increased in both memory systems following acquisition but training-dependent changes selectively occurred in the hippocampus wherein biphasic activation was initiated by the four-trial training and blocked by training for 22 trials. These findings indicate that learning in one session consists of three acquisition stages with parallel engagement of multiple memory systems at the beginning of learning. They suggest, however, that, in a later phase, dynamic interplays promote the use of the most adapted brain system depending on practice and this is accompanied by specific patterns of CREB phosphorylation in the hippocampus.     

Rac1信号通路在小鼠可卡因情景线索记忆过程中的作用

目的:探讨Rac1信号通路在小鼠可卡因情景线索记忆过程中的作用。方法:将成年雄性C57BL/6J小鼠随机分为对照组(control)、可卡因配对的条件性位置偏爱组(CPP)和Rac1抑制剂NSC23766处理组(NSC),利用CPP实验检测可卡因是否可诱导小鼠产生CPP,利用立体定位技术注射AAV-GFP病毒于小鼠海马CA1区并做免疫荧光染色观察海马CA1区神经元的形态;利用Western Blot及GST-pull down方式检测蛋白表达及活性变化;采用Rac1抑制剂NSC23766阻断信号通路探讨其对小鼠可卡因诱导的CPP的影响。结果:可卡因可以诱导小鼠形成CPP,并导致Rac1 GTPase活性增强及其下游信号分子cofilin磷酸化活性升高,并最终导致海马CA1区锥体神经元发生神经可塑性变化。结论:Rac1信号通路通过影响小鼠海马CA1区锥体神经元发生结构可塑性,从而参与调控可卡因情景线索记忆。     

热应激对小鼠海马神经元的保护作用

本文观察了热应激预处理对脑缺血/再灌注昆明小鼠海马神经元的保护作用。实验采用昆明小鼠以双侧颈总动脉夹闭7min后再通制作脑缺血/再灌注模型,在缺血/再灌注前予以热应激预处理。根据不同的处理方法将动物随机分为四组:(1)正常对照组,(2)热应激预处理后缺血再灌注组(HS/IR),(3)缺血再灌注组(IR),(4)单纯热应激组(HS),后3组又分别分为1d、4d和14d三个亚组。水迷宫检测小鼠学习记忆的行为改变,免疫组织化学染色结合图像分析技术检测缺血/再灌注对海马CA1区神经元微管相关蛋白-2(MAP-2)的影响,Nissl染色计数CA1区神经元的数目。结果表明:与正常组、HS和HS/IR组比较,IR组小鼠水迷宫检测逃避潜伏期增加(P<0.01),其搜索策略以边缘式和限制式为主,而其它三组搜索策略则以趋向式和直线式为主。Nissl染色显示IR组和HS/IR组海马锥体细胞减少,且IR组细胞丢失比HS/IR组更多(P<0.05);MAP-2免疫组化染色显示4d时海马CA1区辐射层的树突发生紊乱和断裂,MAP-2有明显减少(P<0.05),14d时IR组MAP-2阳性表达主要聚集于胞浆中。以上实验结果提示,热应激预处理可以通过对海马神经元的保护作用改善动物脑缺血/再灌注引起的学习记忆能力的下降。     

Age-related alterations of oxidative stress markers in the mouse hippocampal CA1 sector

We investigated the age-related alterations of Cu/Zn-SOD, Mn-SOD, cytochrome c, and HNE (4-hydroxy-2-nonenal) in the hippocampal CA1 sector of 2-, 18-, 40-, 42- and 50-59-week-old mice as compared with 8-week-old mice under the same conditions. Two-week-old mice exhibited small number of Cu/Zn-SOD-positive cells in the hippocampal CA1 sector. Thereafter, Cu/Zn-SOD-positive cells were increased gradually in the hippocampal CA1 sector from 18 to 50-59 weeks of birth. Mn-SOD-positive cells in 2-week-old mice showed a weak staining in the hippocampal CA1 sector. However, Mn-SOD-positive cells were unchanged in the hippocampal CA1 sector from 8 to 50-59 weeks of birth. Cytochrome c-positive cells in 2-week-old mice showed a weak staining in the hippocampal CA1 sector. In contrast, cytochrome c-positive cells were unchanged in the hippocampal CA1 sector up to 40-42 weeks of birth. Thereafter, cytochrome c-positive cells were decreased in the hippocampal CA1 sector of 50-59-week-old mice. HNE immunoreactivity in 2-week-old mice showed a weak density in the hippocampal CA1 sector. In contrast, the density of HNE immunoreactivity was unchanged in the hippocampal CA1 sector up to 40-42 weeks of birth. Thereafter, densities of HNE immunoreactivity were increased significantly in the hippocampal CA1 sector of 50-59-week-old mice. The present results show that the alteration of cytoplasmic Cu/Zn-SOD and lipid peroxidation was more pronounced than that of mitochondrial Mn-SOD in the vulnerable hippocampal CA1 sector during aging processes. Furthermore, the present study demonstrates that the decrease in the number of cytochrome c-positive cells and the increase of densities of HNE immunoreactivity may reflect the mitochondrial dysfunction in the hippocampal CA1 sector of aged animals. These findings suggest that the damage of mitochondrial membrane may occur in the hippocampal CA1 sector during aging processes.     

Impairment of long-term potentiation and spatial memory in leptin receptor-deficient rodents

Leptin is well known to be involved in the control of feeding, reproduction and neuroendocrine functions through its action on the hypothalamus. However, leptin receptors are found in brain regions other than the hypothalamus (including the hippocampus and cerebral cortex) suggesting extrahypothalamic functions. We investigated hippocampal long-term potentiation (LTP) and long-term depression (LTD), and the spatial-memory function in two leptin receptor-deficient rodents (Zucker rats and db/db mice). In brain slices, the CA1 hippocampal region of both strains showed impairments of LTP and LTD; leptin (10(-12) M) did not improve these impairments in either strain. These strains also showed lower basal levels of Ca(2+)/calmodulin-dependent protein kinase II activity in the CA1 region than the respective controls, and the levels did not respond to tetanic stimulation. These strains also showed impaired spatial memory in the Morris water-maze test (i.e. longer swim-path lengths during training sessions and less frequent crossings of the platform's original location in the probe test.From these results we suggest that the leptin receptor-deficient animals show impaired LTP in CA1 and poor spatial memory due, at least in part, to a deficiency in leptin receptors in the hippocampus.     

表没食子儿茶素没食子酸酯对APP/PS1双转基因小鼠神经元突触可塑性和神经细胞黏附分子表达的影响

目的 观察表没食子儿茶素没食子酸酯 (EGCG) 对淀粉样前体蛋白（APP）/早老素1(PS1)双转基因小鼠空间学习记忆能力、海马 CA1 区突触超微结构和神经细胞黏附分子表达的影响。方法 选用 8 周龄雄性APP/PS1双转基因小鼠随机分为模型组、EGCG组、盐酸多奈哌齐组,另以同窝阴性小鼠设立正常组,每组 12 只。连续灌胃给药 6 个月后进行相关指标检测。采用 Morris 水迷宫实验观测APP/PS1转基因小鼠空间学习记忆能力;透射电子显微镜观察小鼠海马CA1区突触超微结构; 分别采用免疫荧光法及免疫印迹法检测APP/PS1转基因小鼠海马CA1区神经细胞黏附分子（NCAM）和唾液酸转移酶（ST8Sia Ⅱ）的蛋白表达。结果 与正常组比较,模型组逃避潜伏期延长;与模型组比较,EGCG组、盐酸多奈哌齐组小鼠逃避潜伏期下降 (P＜0.05)。电子显微镜结果显示,与模型组比较,EGCG组和盐酸多奈哌齐组突触界面曲率变化不明显;突触间隙宽度变窄,突触后致密物厚度增加（P＜0.05）。免疫荧光结果显示,海马CA1区NCAM、ST8Sia Ⅱ蛋白表达在神经元的胞体内,EGCG组和盐酸多奈哌齐组NCAM、ST8Sia Ⅱ蛋白表达明显增加 (P＜0.05),免疫印迹实验发现其含量亦呈高表达水平(P＜0.05)。结论 EGCG对 APP/PS1 转基因小鼠的空间学习记忆功能具有改善作用,其机制可能与影响小鼠海马突触结构,提高小鼠海马神经黏附分子表达有关。     

Simvastatin enhances hippocampal long-term potentiation in C57BL/6 mice

Statins inhibit 3-hydroxy-3-methylglutaryl CoA reductase, the rate-limiting enzyme in the cholesterol biosynthetic pathway, and they are widely used to control plasma cholesterol levels and prevent cardiovascular disease. However, emerging evidence indicates that the beneficial effects of statins extend to the CNS. Statins have been shown to improve the outcome of stroke and traumatic brain injury, and statin use has been associated with a reduced prevalence of Alzheimer's disease (AD) and dementia. However, prospective studies with statins in AD have produced mixed results. Recently, we reported that simvastatin, a widely used statin in humans, enhances learning and memory in non-transgenic mice as well as in transgenic mice with AD-like pathology on a mixed genetic background. However, the cellular and molecular mechanisms underlying the beneficial effects of simvastatin on learning and memory remain elusive. The present study was undertaken to investigate the effect of acute simvastatin treatment on hippocampal long-term potentiation (LTP), a cellular model of learning and memory, in brain slices from C57BL/6 mice. Our results demonstrate that a prolonged in vitro simvastatin treatment for 2–4 h, but not a short-term 20-min exposure, significantly increases the magnitude of LTP at CA3–CA1 synapses without altering basal synaptic transmission or the paired-pulse facilitation ratio in hippocampal slices. Furthermore, we show that phosphorylation of Akt (protein kinase B) is increased significantly in the CA1 region following 2-hour treatment with simvastatin, and that inhibition of Akt phosphorylation suppresses the simvastatin-induced enhancement of LTP. These findings suggest activation of Akt as a molecular pathway for augmented hippocampal LTP by simvastatin treatment, and implicate enhancement of hippocampal LTP as a potential cellular mechanism underlying the beneficial effects of simvastatin on cognitive function.     

Electrophysiological analysis of the hippocampal-septal projections: I. Response and topographical characteristics

Summary The hippocampal input to the septal region was studied, in rats, by electrophysiological methods. The major observations were: 1. the hippocampal fibers are excitatory with respect to their target cells in the lateral septal nucleus (LSN); 2. the distribution of the subcallosal fornix is restricted to the dorsomedial regions of the LSN; 3. the fimbria contains fibers terminating throughout the dorsal aspect of the ipsilateral and contralateral septum; 4. there is an extensive overlapping in the distribution of the ipsi-and contra-lateral fimbria components with convergence upon single septal cells frequently seen; 5. the posterior part of hippocampal region CA1 contributes fibers to the fimbria as well as to the fornix.Abbreviations ACB Bed nucleus of the anterior commissure - AP Ref 0 The anterior-posterior and midline reference zero - CA Anterior commissure - CC Corpus callosum - CCA 3–4 Contralateral hippocampal fields CA-3–4 - Cd Pt Caudate putamen complex - CFim Contralateral fimbria - CMA Corticomedial maygdaloid division - GP Globus pallidus - Hipp Hippocampus - ICA1 (a) Anterior part of the ipsilateral hippocampal field CA1 - ICA1 (p) Posterior part of the ipsilateral hippocampal field CA1 - ICA3–4 Ipsilateral hippocampal field CA3–4 - IFim Ipsilateral fimbria - IFx Ipsilateral fornix - LSN Lateral septal nucleus - ME Microelectrode - MSN Medial septal nucleus - POA Pre-optic area This study was supported by U.S. Public Health Service Grants RR 5384 and NB 00405.