Decreased phosphorylation and protein expression of ERK1/2 in the brain of hypoxic preconditioned mice

Accumulated reports have suggested that activation of protein kinase C (PKC) isoforms may involve the activation of extracellular signal-regulated kinases 1/2 (ERK1/2) in the neuronal response to hypoxic stimuli. We have previously demonstrated that the membrane translocation or activation of conventional PKC (cPKC) betaII, gamma and novel PKC (nPKC) varepsilon are increased in the early phase of cerebral hypoxic preconditioning in mice. However, the role of ERK1/2 in the development of cerebral hypoxic preconditioning is unclear. In the current study, we used Western blot analysis to investigate the effects of repetitive hypoxic exposure (H0-H6, n=6 for each group) on the levels of phosphorylation and protein expression of ERK1/2 in the frontal cortex and the whole hippocampus of mice. We found that the levels of phosphorylated ERK1/2, not protein expression of ERK1/2, decreased significantly in both cortex and hippocampus of the early hypoxic preconditioned mice (H1-H4), when compared to that of the normoxic group (p<0.05). In addition, a significant decrease (p<0.05) in the ERK1/2 protein expression, not the phosphorylated form of ERK1/2, was found both in the frontal cortex and hippocampus of mice followed hypoxia with previous hypoxia (H5 and H6). These results suggest that the decreased phosphorylation and downregulation of protein expression of ERK1/2 might be involved in the development of hypoxic preconditioning.     

重复性低氧增高小鼠脑组织内CREB的磷酸化水平

为探讨cAMP反应元件结合蛋白(CREB)在小鼠脑低氧预适应形成过程中的作用,本研究应用Westernblot技术结合GelDoc凝胶成像系统,半定量检测了整体低氧预适应模型小鼠脑组织内CREB的磷酸化水平和非磷酸化水平的表达水平。结果显示:(1)随低氧暴露次数(H1H4)的增加,小鼠海马组织内CREB的磷酸化水平(激活程度)明显增高(P<0.05;n=7);同样,大脑皮层内CREB的磷酸化水平也随低氧暴露次数(H1H4)的增加而明显增高(P<0.05,n=7);(2)随低氧暴露次数(H1H4)的增加,CREB的蛋白表达量无论在小鼠海马组织还是皮层组织内均无明显变化。以上结果提示CREB磷酸化水平的增高(激活)可能参与了脑低氧预适应的形成过程。     

低氧预适应小鼠脑组织内CaMKⅡ磷酸化水平增高

目的探讨钙调蛋白依赖性蛋白激酶(CaMKⅡ)在小鼠脑低氧预适应(HPC)发生发展中的作用。方法成年雄性BALB/c小鼠随机分为正常对照(H0)、早期(H1～H4)和延迟性(H5～H6)低氧预适应等共计7组,制备小鼠HPC模型;用Western blot并结合GelDoc凝胶成像系统,检测小鼠脑组织内CaMKⅡ磷酸化水平和蛋白表达量;用免疫组化检测小鼠脑皮层和海马CaMKⅡ磷酸化水平。结果与H0组小鼠相比,H3～H5组海马和皮层的CaMKⅡ磷酸化水平明显升高(P<0.05);而H1～H6组的皮层和海马的CaMKⅡ蛋白表达量无明显变化;H3、H6组皮层和海马p-CaMKⅡ阳性细胞数目增多和灰度增强。结论CaMKⅡ磷酸化水平的升高可能参与了小鼠脑HPC的发生发展过程。     

低氧预适应鼠脑内核糖体S6激酶磷酸化水平和蛋白表达量的变化

探讨核糖体S6激酶(ribosomal S6kinase,RSK)Ser221(PDK1磷酸化位点)和Thr359/Ser363(ERK1/2磷酸化位点)的磷酸化水平以及总RSK蛋白表达量在小鼠脑低氧预适应发生发展过程中的变化。将成年雄性BALB/c小鼠(18～22g)随机分为正常对照(H0)和重复性低氧1～4次(H1～H4)等5组(每组n=6)。应用蛋白凝胶电泳(SDS-PAGE)和蛋白印迹(Western blot)技术,定量检测整体低氧预适应小鼠海马和皮层组织内Ser221位点(p-Ser221 RSK)和Thr359/Ser363位点(p-Thr359/Ser363 RSK)的磷酸化水平以及总RSK蛋白表达量。结果表明,随着低氧暴露次数增加,小鼠海马和皮层组织内p-Ser221 RSK磷酸化的水平显著增高(P<0.05,n=6),伴随着p-Thr359/Ser363 RSK磷酸化的水平明显降低(P<0.05,n=6);而RSK总蛋白的表达量则无明显改变。结果提示,Ser221 RSK磷酸化水平增高和Thr359/Ser363 RSK磷酸化水平降低可能参与了小鼠脑低氧预适应的发生发展过程。     

Increased phosphorylation of neurogranin in the brain of hypoxic preconditioned mice

Neurogranin/RC3 (Ng/rodent cortex-enriched mRNA clone #3), a postsynaptic neuronal protein kinase C (PKC) substrate, binds calmodulin (CaM) at low Ca(2+) levels. Neurotransmitters triggering influx calcium induce neurogranin phosphorylation by PKC in physiological or pathophysiological conditions. Phosphorylated Ng reduces the affinity of Ng to bind CaM, which may affect the activities of calmodulin-dependent downstream enzymes, such as nitric oxide synthase (NOS), CaM-dependent protein kinase II (CaMKII) and adenylate cyclase (AC). These protein enzymes have been reported to play key roles in the development of ischemic/hypoxic preconditioning (I/HPC). We previously demonstrated that activation of cPKCbetaII and gamma isoforms may be involved in the early phase of cerebral hypoxic preconditioning. However, as a substrate of PKC, the role of Ng in the onset of cerebral hypoxic preconditioning is unknown. In this study, we examined the effects of repetitive hypoxic exposure on the status of Ng phosphorylation in the cortex and hippocampus of mice. Using Western blot analysis, we found that the levels of Ng phosphorylation in the cortex and hippocampus of the hypoxic group of mice increased significantly from that of the normoxic group (p<0.05). These results suggest that neurogranin protein may be involved in the development of cerebral hypoxic preconditioning.     

cPKCgamma参与低氧预适应对小鼠脑缺血皮层内CRMP2水解和磷酸化的调节

 摘要：目的 探讨经典型蛋白激酶Cgamma( cPKCgamma)在低氧预适应(HPC)调节小鼠脑缺血皮层内脑衰反应蛋白-2(CRMP2)水解和磷酸化中作用。方法 利用雄性BALB/c小鼠(18-22g) HPC和大脑中动脉阻塞(MCAO)模型,借助蛋白印迹、免疫共沉淀和免疫组化等生物化学技术,观察cPKCgamma激活对小鼠缺血脑皮层内CRMP2蛋白水解程度（BDP）和磷酸化水平（p-CRMP2）、cPKCgamma-CRMP2相互作用和皮层缺血半影区内p-CRMP2阳性细胞数的影响。结果　我们发现,HPC显著提高缺血脑皮层半影区内p-CRMP2水平,降低BDP产物形成,而侧脑室注射cPKCgamma抑制剂Go6983(6nM)可明显解除HPC对半影区内CRMP2蛋白水解和磷酸化的调节作用;免疫共沉淀结果提示,cPKCgamma激活程度参与HPC对缺血脑皮层半影区内cPKCgamma-CRMP2相互作用的调节;同时,免疫组化进一步证实,cPKCgamma激活与HPC提高脑缺血半影区内p-CRMP2阳性细胞数有关。结论 cPKCgamma参与HPC对小鼠缺血脑皮层内CRMP2水解与磷酸化的调节。     

Neuron-specific phosphorylation of c-Jun N-terminal kinase increased in the brain of hypoxic preconditioned mice

Accumulated studies have suggested that mitogen-activated protein kinase (MAPK) play a pivotal role in the development of cerebral hypoxic preconditioning (HPC). By using our “auto-hypoxia”-induced HPC mouse model, we have reported increased phosphorylation level of p38 MAPK, and decreased phosphorylation and protein expression levels of extracellular signal regulated kinases 1/2 (ERK1/2) in the brain of HPC mice. In the current study, we investigated the involvement of c-Jun N-terminal kinase (JNK) in the brain of HPC mice. By using Western blot analysis, we found that the phosphorylation levels of JNK at Thr183 and Tyr185 sites (phospho-Thr183/Tyr185 JNK), but not its protein expression, increased significantly (p < 0.05, n = 6 for each group) both in the hippocampus and frontal cortex of early (H1–H4) and delayed (H5 and H6) HPC mice than that of the normoxic group (H0, n = 6). Similarly, enhanced phospho-Thr183/Tyr185 JNK was also observed by immunostaining in the hippocampus and frontal cortex of mice following series of hypoxic exposures (H3 and H6). In addition, we found that phospho-Thr183/Tyr185 JNK predominantly co-localized with a neuron-specific protein, neurogranin, in both the hippocampus and frontal cortex of HPC mice (H3) by using double-labeled immunofluorescence. These results suggest that the increased neuron-specific phosphorylation of JNK at Thr183/Tyr185, not protein expression, might be involved in the development of cerebral HPC of mice.     

Inhibition of PKCgamma membrane translocation mediated morphine preconditioning-induced neuroprotection against oxygen-glucose deprivation in the hippocampus slices of mice

We previously reported that novel protein kinase C (nPKC) varepsilon and N-methyl-d-aspartic acid (NMDA) receptors participated in morphine preconditioning (MP)-induced neuroprotection. In this study, we used Western blot analysis, 2,3,5-triphenyltetrazolium chloride (TTC) staining and lactate dehydrogenase (LDH) leakage assay to determine the involvement of conventional PKC isoforms (cPKC) in MP-induced neuroprotection against oxygen-glucose deprivation (OGD). Hippocampus slices (400-mum thickness) from healthy male BALB/c mice exposed to OGD for 5-45min to mimic mild, moderate and severe ischemia in the presence of MP pretreatment. We found that OGD-induced damage in neuronal cell survival rate and LDH leakage could be improved by MP pretreatment (3muM) within 20min of OGD, which was abolished by concomitant incubation with non-selective opioid receptor antagonist naloxone (Nal, 50muM). The results of Western blot analysis showed that only cPKCgamma membrane translocation, not alpha, betaI and betaII, increased under the condition of OGD 10min and 2h reperfusion (OGD/2h), and this increment of cPKCgamma membrane translocation was inhibited by MP pretreatment. To further elucidate the role of cPKCgamma in MP-induced neuroprotection, we found that cPKCgamma membrane translocation inhibitor, Go6983 (6nM) did not affect MP-induced neuroprotection while Go6983 alone exhibited a significant inhibition on OGD-induced increment in LDH leakage and decrease in cell survival rate. These phenomena were defined by the results that Go6983 could restore OGD-induced cPKCgamma membrane translocation, but had no further effect on MP-induced inhibition of cPKCgamma membrane translocation. These results demonstrated that MP can reduce OGD-induced neuronal injuries, and the down-regulation of cPKCgamma membrane translocation might be involved in the neuroprotection.     

Differential expression of ADAM15 and ADAM17 metalloproteases in the rat brain after severe hypobaric hypoxia and hypoxic preconditioning

The ADAMs (a disintegrin and metalloprotease) are a family of membrane-anchored glycoproteins capable of shedding a multitude of proteins from the cell surface. Although ADAMs are being considered as crucial modulators of physiological and pathophysiological processes, their roles in neuronal death/survival are largely unexplored. In the present study, changes in brain expression of ADAM15 and ADAM17 (TACE) have been quantitatively examined in rats in response to injurious severe hypoxia (SH) and in animals which acquired hypoxic tolerance through preconditioning to mild hypoxia prior SH. SH persistently up-regulated ADAM15 mRNA and protein levels in hippocampus and neocortex but not in thalamus or hypothalamus. This effect was not observed in the preconditioned rats tolerant to SH. In contrast, hippocampal levels of ADAM17 mRNA and neocortical levels of ADAM17 mRNA and protein were largely reduced following SH in non-preconditioned rats. Hypoxic preconditioning prevented down-regulation of the adam17 gene and considerably enhanced ADAM17 protein expression in hippocampus and neocortex in response to SH. The present findings implicate ADAM15 in the processes of neuronal hypoxic injury. On the other hand, these results also provide evidence for a pro-survival neuroprotective role of ADAM17 and its engagement in the process of preconditioning-induced hypoxic tolerance. The analysis of the protein levels of soluble and membrane-bound forms of APP in the neocortex and hippocampus of rats subjected to SH and SH with preconditioning has demonstrated that an increased ADAM17 expression in preconditioned animals 24h after hypoxia corresponded to a higher level of soluble form of APP and a reduction of the membrane bound fraction which reflects the role of ADAM17 in APP shedding.     

FOXO3a蛋白在缺氧小鼠脑组织中的表达

目的:探讨叉头框蛋白O3a(FOXO3a)在缺氧小鼠大脑组织中的表达.方法:16只SPF级3月龄C57小鼠随机分为对照组(control)和缺氧组(hypoxia).两组小鼠分别接受常氧浓度环境及低氧环境处理1 h,应用Western Blot法定量检测FOXO3a蛋白的表达水平;应用免疫荧光染色技术检测FOXO3a蛋...     

脑衰蛋白反应调节蛋白-2参与低氧预适应减轻小鼠脑缺血损伤

目的 研究参与低氧预适应(HPC)的经典型蛋白激酶C II(cPKC II)相互作用的脑衰蛋白反应调节蛋白-2(CRMP-2) 对缺血脑是否有保护作用。方法 成年雄性BALB/c小鼠随机分为常氧(Nor)、HPC、常氧假手术(Nor+sham)、HPC假手术(HPC+sham)、常氧缺血(Nor+I)和HPC缺血(HPC+I)等6组(每组n=6)。应用小鼠整体HPC和脑中动脉梗死(MCAO)致脑局部缺血模型,结合免疫沉淀、双向凝胶电泳和质谱等技术,分离和鉴定与cPKC II相互作用蛋白;利用聚丙烯酰胺凝胶电泳(SDS-PAGE)和蛋白印迹(Western blot)技术,分析CRMP-2磷酸化和蛋白降解水平在脑HPC和缺血中的变化。结果 与Nor组比,HPC鼠脑皮层组织内有10种与cPKC? II相互作用蛋白的表达发生了明显变化,其中CRMP-2在膜相关蛋白组分中的表达量升高,而在胞质蛋白组分中的表达量降低。在脑缺血模型中,与Nor+Sham组相比,Nor+I组小鼠脑皮层缺血核心区(Ic)CRMP-2磷酸化水平明显降低(p<0.05, n=6);与Nor+I组相比,HPC+I组小鼠脑皮层Ic区内CRMP-2磷酸化水平明显增高(p<0.05, n=6)。脑缺血可导致CRMP-2发生水解并伴随着大量55-ku水解片段(BDP)的出现,但与Nor+I组相比,HPC+I组小鼠脑皮层缺血半影区(P)内CRMP-2水解片段减少,水解率明显降低(p<0.05, n=6)。结论 CRMP-2参与了 HPC缓解小鼠脑缺血Ic区内CRMP-2磷酸化水平的降低和减少P区内CRMP-2水解片段从而减轻缺血脑组织的损伤。     

缺氧预处理大鼠心肌组织蛋白质组双向凝胶电泳分析

目的 :分析缺氧预处理诱导的大鼠心肌组织与正常心肌组织蛋白质的差异表达。方法 :采用双向凝胶电泳技术和计算机辅助的图像分析方法 ,对缺氧预处理大鼠心肌组织与正常大鼠心肌组织胞浆蛋白质进行分离和比较分析。结果 :正常心肌组织可分离 2 71± 2 3 个蛋白点 ,蛋白点匹配率为 75 .2 3 %± 3 .5 4%。有 5种蛋白质在缺氧处理后发生了明显和稳定的量的改变 ,其中 2种 (Mr/ pI :18.1KD/ 3 .86,5 1.43KD/ 4.67)在缺氧预处理后表达增高 ,3种 (Mr/pI :3 3 .14KD/ 9.11,3 1.89KD/ 8.5 8,15 .85KD/ 8.2 4)在缺氧预处理后表达降低。结论 :缺氧预处理大鼠心肌组织双向电泳后蛋白表达与正常心肌组织有明显差异 ,有 2种蛋白表达明显增高 ,3种明显降低。这些差异表达的蛋白质可能参与了心肌缺氧预处理的保护机制     

cPKCγ-HSP60信号通路参与小鼠脑低氧预适应

目的: 鉴定参与低氧预适应(HPC)的常规型蛋白激酶Cγ (cPKCγ)相互作用蛋白,探讨与cPKCγ相互作用的热休克蛋白60(HSP60)表达水平在小鼠脑低氧预适应和脑缺血中的变化。方法: 健康雄性BALB/c小鼠,随机分为: 常氧组(Norm)和HPC组,结合是否进行大脑中动脉阻塞(MCAO)分为常氧假手术组(Norm+sham)、常氧缺血组(Norm + I)、HPC假手术组(HPC+sham)和HPC缺血组(HPC+I)。应用整体低氧预适应和MCAO缺血模型,结合免疫沉淀、双向凝胶电泳、质谱等技术分离、鉴定与cPKCγ相互作用的蛋白;利用蛋白印迹技术分析HSP60蛋白表达量在脑HPC和缺血中的变化。结果: 与常氧组比较,HPC小鼠脑皮层膜相关成分中与cPKCγ相互作用的HSP60蛋白表达量升高,经免疫共沉淀证明cPKCγ与HSP60存在相互作用。在MCAO缺血模型中,与Norm+sham组小鼠相比,Norm+I组及HPC+I组小鼠皮层缺血核心区、半影区HSP60表达水平明显升高(P<0.05)。HPC+I组小鼠缺血核心区HSP60表达水平低于Norm+I组(P<0.05)。结论: 研究结果表明,cPKCγ-HSP60信号通路可能参与了低氧预适应的发生发展过程。     

Sevoflurane stimulates MAP kinase signal transduction through the activation of PKC alpha and betaII in fetal rat cerebral cortex cultured neuron

Protein kinase C (PKC) is a key enzyme that participates in various neuronal functions. PKC has also been identified as a target molecule for general anesthetic actions. Raf, mitogen-activated protein kinase (MEK) and extracellular signal-regulated kinase (ERK1/2) have been thought to be target effectors of PKC. In the present study, we attempted to evaluate the effect of sevoflurane on PKC/MAPK cascade signaling in cultured fetal rat cerebral -cortex neurons, prepared from embryonic day 18 fetuses. The effects of sevoflurane on the translocation of 7 PKC isoforms (alpha, betaI, betaII, gamma, delta, varepsilon and zeta) were observed by immunoblotting using isoform-selective antibodies to PKCs. The treatment of neurons with sevoflurane induced the translocation of PKC alpha and PKC betaII species from the cytosol to the membrane fraction, which indicated the activation of these PKC isoforms. In contrast, there was no clear change in the distribution of other PKC isoforms. We next examined whether the specific activation of PKC alpha and betaII by sevoflurane could stimulate the MAP kinase signaling pathway in cultured neurons. Raf phosphorylation was increased by the administration of 0.25 mM sevoflurane. The phosphorylation of Raf proteins reached a maximum at 5-10 min. Subsequently, the phosphorylation of MEK proteins was increased at 10-15 min after sevoflurane treatments. That of ERK proteins was induced at 15-60 min. Moreover, the phosphorylation of ERK induced by sevoflurane was significantly decreased by the treatment of PKC inhibitor (staurosporine) and MEK inhibitor (PD98059). On the other hand, the contents of total Raf, MEK and ERK proteins were relatively constant at all times examined. To examine the -localization of phosphorylated-ERK protein, immunohistochemical staining of sevoflurane-treated cultured neurons was performed. The phosphorylated-ERK proteins were markedly accumulated in both the cytosol of the cell body and the neurites in the neuronal cells with time after 0.25 mM sevoflurane-treatment. These results demonstrated that sevoflurane induced the phosphorylation of the MAP kinase cascade through the activation of the PKC alpha and PKC betaII species.     

核转录因子-κB在缺氧预处理抑制心肌细胞凋亡中的作用

目的 :研究缺氧预处理 (hypoxicpreconditioning ,HPC)对于心肌细胞蛋白激酶C(PKC)和核转录因子κB (NF κB)表达的影响 ,及其在缺氧复氧诱导心肌细胞凋亡中的作用。方法 :在培养的SD乳鼠心肌细胞制作缺氧 /复氧 (H/R)模型 ,以荧光素染料Hoechst3 3 2 5 8测定心肌细胞凋亡率 ;制备心肌细胞蛋白提取物 ,以新PKCε亚型 (nPKCε)特异性抗体测定nPKCε相对蛋白含量 ;以抗NF κB抗体检测NF κB的表达 ;并以PKC抑制剂H7与心肌细胞预孵育后 ,观察H7对于HPC诱导的PKC和NF κB表达上调以及心肌细胞保护作用的影响。结果 :缺氧复氧造成心肌细胞凋亡 ,HPC可以降低心肌细胞H/R后凋亡率 ,并诱导nPKCε和NF κB表达上调 ;PKC抑制剂H7可以消除HPC诱导的PKC、NF κB表达上调和心肌细胞保护作用。结论 :HPC可以提高乳鼠心肌细胞对于H/R的耐受性 ,其机制涉及PKC介导的NF κB表达上调。     

Hypoxic tolerance induction in rat brain slices following hypoxic preconditioning due to expression of neuroprotective proteins as revealed by dynamic changes in glucose metabolism

We prepared rat brain slices following sublethal hypoxic pretreatment (preconditioning) and untreated (control) rats, and measured the cerebral glucose metabolic rate (CMRglc) by dynamic positron autoradiography with [18F]2-fluoro-2-deoxy-D-glucose before and after originally lethal 20-min hypoxic loading. In the regions of interest such as the frontal cortex, the CMRglc before hypoxic loading did not differ between the preconditioning and control groups. The CMRglc after reoxygenation was markedly lower than that before hypoxic loading in the control group but did not significantly differ from the preloading value in the preconditioning group. Thus, hypoxic tolerance induction by preconditioning was demonstrated using the maintenance of CMRglc as a neuronal viability index. In addition, profiling of gene expression using an Atlas Rat Stress Array suggested the involvement of the expression of genes such as stress protein in hypoxic tolerance induction.     

吗啡长时程作用对小鼠脑组织蛋白激酶A及C活性的影响

本文通过复制小鼠吗啡耐受依赖模型，观察了吗啡长时程作用对小鼠脑组织ＰＫＡ及ＰＫＣ活性的影响。结果发现：（１）吗啡耐受依赖小鼠纹状体、海马、大脑皮层神经细胞胞浆ＰＫＡ活性显著升高，而小脑胞浆及以上各部位膜相ＰＫＡ活性变化不明显；（２）不同脑组织中ＰＫＣ活性变化不同，吗啡耐受依赖小鼠大脑皮层及小脑胞浆ＰＫＣ活性明显升高，在纹状体胞浆则显著下降，但纹状体膜相ＰＫＣ活性却显著增加，海马及小脑膜相ＰＫＣ活性则明显降低；（３）纳洛酮可拮抗吗啡引起的上述变化。结果提示：一些脑组织胞浆ＰＫＡ活性的升高、ＰＫＣ活性的变化以及可能存在的ＰＫＣ于胞浆和膜相之间的移位可能是吗啡耐受依赖的重要生化基础，且此变化可能由阿片受体所介导。     

The effects of aging on N-methyl-d-aspartate receptor subunits in the synaptic membrane and relationships to long-term spatial memory

There are declines in the protein expression of the NR2B (mouse ε2) and NR1 (mouse ζ1) subunits of the N-methyl-d-aspartate (NMDA) receptor in the cerebral cortex and hippocampus during aging in C57BL/6 mice. This study was designed to determine if there is a greater effect of aging on subunit expression and a stronger relationship between long-term spatial memory and subunit expression within the synaptic membrane than in the cell as a whole. Male, C57BL/6JNIA mice (4, 11 and 26 months old) were tested for long-term spatial memory in the Morris water maze. Frontal cortex, including prefrontal regions, and hippocampus were homogenized and fractionated into light and synaptosomal membrane fractions. Western blots were used to analyze protein expression of NR2B and NR1 subunits of the NMDA receptor. Old mice performed significantly worse than other ages in the spatial task. In the frontal cortex, the protein levels of the NR2B subunit showed a greater decline with aging in the synaptic membrane fraction than in the whole homogenate, while in the hippocampus a similar age-related decline was observed in both fractions. There were no significant effects of aging on the expression of the NR1 subunit. Within the middle-aged mouse group, higher expression of both NR2B and NR1 subunits in the synaptic membrane of the hippocampus was associated with better memory. In the aged mice, however, higher expression of both subunits was associated with poorer memory. These results indicate that aging could be altering the localization of the NR2B subunit to the synaptic membrane within the frontal cortex. The correlational results suggest that NMDA receptor functions, receptor subunit composition, and/or the environment in which the receptor interacted in the hippocampus were not the same in the old animals as in younger mice and this may have contributed to memory declines during aging.