磷酸二酯酶抑制剂与学习记忆相关信号转导通路研究进展

大量的研究表明,环磷酸腺苷反应元件结合蛋白(cAMP response element binding protein,CREB)直接或间接激活相关基因转录,进而表达c-fos、c-jun、BDNF等,在神经元应激损伤后的再生、存活及修复以及学习记忆等方面发挥重要作用。磷酸二酯酶可以水解环磷酸腺苷(cyclic AMP,cAMP)及环磷酸鸟苷(cyclic GMP,cGMP),进而影响其下游信号转导,发挥对CREB的调节作用。该文从磷酸二酯酶抑制剂与学习记忆相关信号通路的关系及在学习记忆障碍中发挥的作用予以综述,并由该通路入手对发现治疗神经退行性变疾病药物作用新靶点的可能性予以展望。     

Learning/memory and drug dependence

We investigated the possible mechanisms of development of latent learning and morphine dependence by the methods of behavioral pharmacology and confirmed them by using mutant mice. The heterozygous mice for the tyrosine hydroxylase (TH) gene and for the cyclic AMP (cAMP) response element binding protein (CREB) binding protein (CBP) gene showed the impairment of latent learning in the water finding task, and these mice did not develop morphine dependence. The spatial learning and hippocampal long-term potentiation (LTP) were normal in the both mutants. TH heterozygous mice showed a reduction of high K(+)-evoked noradrenaline release in the frontal cortex measured by the microdialysis technique and of cAMP content in the brain. In conclusion, the results of mutant mice suggest that the alternation of catecholamine biosynthesis and cAMP signal pathways may play a key role in development of latent learning and morphine dependence, and they furthermore show that the expression of genes mediated by phosphorylated CREB may be involved in the development of latent learning and morphine dependence.     

cAMP反应元件结合蛋白在药物依赖形成中的作用

反复应用成瘾性药物引起中枢神经系统特定部位cAMP信号系统出现适应性改变 ,cAMP反应元件结合蛋白(cyclicAMPresponseelementbindingprotein ,CREB)是受cAMP调节的主要转录因子 ,在动物产生药物依赖时脑内CREB含量及磷酸化程度发生变化 ,与动物躯体依赖和精神依赖有关。确定CERB在药物依赖中的作用有益于阐明药物依赖分子机制及采取相应的防治措施     

Neurobiology and treatment of anxiety: signal transduction and neural plasticity

The stress-dependence and chronic nature of anxiety disorders along with the anxiolytic effectiveness of antidepressant drugs suggests that neuronal plasticity may play a role in the pathophysiology of anxiety. Intracellular signaling pathways are known in many systems to be critical links in the cascades from surface signals to the molecular alterations that result in functional plasticity. Chronic antidepressant treatments can regulate intracellular signaling pathways and can induce molecular, cellular, and structural changes over time. These changes may be important to the anxiolytic effectiveness of these drugs. In addition, the signaling proteins implicated in the actions of chronic antidepressant action, such as cAMP response element binding protein (CREB), have also been implicated in conditioned fear and in anxiety. The cellular mechanisms underlying conditioned fear indicate roles for additional signaling pathways; however, less is known about such mechanisms in anxiety. The challenge to identify intracellular signaling pathways and related molecular and structural changes that are critical to the etiology and treatment of anxiety will further establish the importance of mechanisms of neuronal plasticity in functional outcome and improve treatment strategies.     

Possible mechanisms in latent learning formation investigated by using mutant mice

We examined possible mechanisms in the development of latent learning by methods of behavioral pharmacology and confirmed them by using mutant mice. Mice that received dopamine agonists, a noradrenergic neurotoxin or a traumatic brain injury showed impairment of latent learning. This impairment was suggested to be mediated by imbalance of dopaminergic and noradrenergic systems since the impairment was attenuated by a noradrenaline uptake inhibitor or a dopamine-D2 antagonist. The heterozygous mice for the tyrosine hydroxylase (TH) gene and for the cyclic AMP (cAMP) response element binding protein (CREB) binding protein (CBP) gene showed impairment of latent learning in the water finding task. The spatial learning and hippocampal long-term potentiation (LTP) were normal in both the mutants. TH heterozygous mice showed a reduction of high K(+)-evoked noradrenaline release in the frontal cortex by the microdialysis technique and a reduction of cAMP of the brain cAMP content. The central noradrenergic systems and/or cAMP signal pathways play an important role in latent learning, but not spatial memory. In contrast with TH and CBP mutant mice, nociceptin-knockout mice showed an enhanced retention of latent learning in the water finding task, greater learning ability in the water maze task and larger LTP than wild-type mice. Such mice showed hyperfunction of dopaminergic systems in the cortex. Nociceptin itself induced latent learning impairment in wild-type mice. These results suggest that the nociceptin system seems to play negative roles in learning and memory. In conclusion, the results of mutant mice further supported our previous results of behavioral pharmacology and suggest that the alternation of catecholamine biosynthesis and cAMP signal pathways may play a key role in development of latent learning. They further suggest that the expression of genes mediated by phosphorylated CREB may be involved in the development of latent learning.     

Improving memory: a role for phosphodiesterases

During the last decennia, our understanding of the neurobiological processes underlying learning and memory has continuously improved, leading to the identification of targets for the development of memory-enhancing drugs. Here we review a class of drugs which has more recently been identified: the phosphodiesterase (PDE) inhibitors. An overview is given of the different PDEs that are known and we focus on three PDEs which have been identified as possible relevant targets for memory improvement: PDE2, PDE4 and PDE5. PDEs differ in the substrate, i.e. cyclic adenosine monophosphate (cAMP) and/or cyclic guanosine monophosphate (cGMP), being hydrolyzed. Since these cyclic nucleotides have been suggested to play distinct roles in processes of memory, selective PDE inhibitors preventing the breakdown of cAMP and/or cGMP could improve memory. The present data suggest that PDE4 (cAMP) is involved in acquisition processes, although a possible role in late consolidation processes cannot be excluded. PDE5 (cGMP) is involved in early consolidation processes. Since PDE2 inhibition affects both cAMP and cGMP, PDE2 inhibitors may improve both memory processes. The field of PDEs is highly dynamic and new isoforms of PDEs are still being described. This may lead to the discovery and development of new memory enhancing drugs that selectively inhibit such isoforms. Such drugs may exert their effects only in specific brain areas and hence possess an improved side effect profile.     

Tanshinone I enhances learning and memory,and ameliorates memory impairment in mice via the extracellular signal-regulated kinase signalling pathway

Background and purpose:

The intracellular signalling kinase, extracellular signal-regulated kinase 1/2 (ERK1/2) is required for new memory formation, suggesting that control of ERK signalling might be a target for the treatment of cognitive dysfunction. Previously, we reported that tanshinone congeners have ameliorating effects on drug-induced memory impairment in mice. Here, we have investigated possible modes of action of tanshinone I on learning and memory, associated with ERK phosphorylation.

Experimental approach:

Using immunohistochemical, Western blot techniques, and behavioural testing, we studied the effect of tanshinone I on memory impairment induced by diazepam or dizocilpine (MK-801) in mice.

Key results:

Tanshinone I (2 or 4 mg·kg⁻¹, p.o.) increased latency times versus vehicle-treated control group in the passive avoidance task. Western blot analysis and immunohistochemical data showed that tanshinone I (4 mg·kg⁻¹) increased levels of phosphorylated cAMP response element binding protein (pCREB) and phosphorylated ERK (pERK) in the hippocampus. These increases in pCREB and pERK were blocked by U0126 (inhibitor of ERK1/2), which also prevented the increase in passive avoidance task latency time after tanshinone I. In models of learning and memory impairment induced by diazepam and MK-801, tanshinone I (4 mg·kg⁻¹) reversed learning and memory impairments detected by the passive avoidance test. Western blot analysis showed that tanshinone I reversed the diazepam- and MK-801-induced inhibitions of ERK and CREB activation in hippocampal tissues. These effects were also blocked by U0126.

Conclusions and implications:

Tanshinone I ameliorates the learning and memory impairments induced by diazepam and MK-801 through activation of ERK signalling.     

Cilostazol improves hippocampus-dependent long-term memory in mice

Rationale

Phosphodiesterases (PDEs) play an important role in the regulation of intracellular signaling mediated by cyclic adenosine monophosphate (cAMP). Recently, several PDE inhibitors were assessed for their possible cognitive enhancing properties. However, little is known about the effect of PDE3 inhibitors on memory function.

Objectives

We examined how the PDE3 inhibitor cilostazol affects C57BL/6 J mice as they perform various behavioral tasks. After behavioral assessment, brains of the mice were analyzed immunohistochemically to quantify the phosphorylation of cAMP-responsive element binding protein (CREB), a downstream component of the cAMP pathway.

Results

Oral administration of cilostazol significantly enhanced recollection of the exact platform location in the Morris water maze probe test. Cilostazol also improved context-dependent long-term fear memory, without affecting short-term memory. No apparent effect was observed in cue-dependent fear memory. The results suggest that cilostazol selectively improves hippocampus-dependent long-term memory in these tasks. Cilostazol also significantly increased the number of phosphorylated-CREB-positive cells in hippocampal dentate gyrus.

Conclusions

These results suggest that cilostazol may exert its beneficial effects on learning and memory by enhancing the cAMP system in hippocampus, where it increases intracellular cAMP activity.     

Effect of pretreatment with intracerebroventricular injection of minocycline on morphine‐induced memory impairment in passive avoidance test: Role of P‐CREB and c‐Fos expression in the dorsal hippocampus and basolateral amygdala regions

Minocycline as a member of the tetracycline family is a lipophilic broad‐spectrum antibiotic, which can display some non‐antibiotic properties such as antioxidant, antiapoptosis, neuroprotection and modulation of pharmacological traits of drugs of abuse (ie, reward, sensitization and/or analgesia). Thus, the aim of the present study was to investigate the effect of intracerebroventricular (ICV) injection of minocycline on morphine‐induced memory impairment and motor function in male Wistar rats. The behavioural responses were measured by a passive avoidance test for evaluating memory, and in the open field for studying motor function. Furthermore, the expression of Phospho‐cAMP response element‐binding protein (P‐CREB) and c‐Fos were assessed using immunohistochemistry in the dorsal hippocampus and basolateral amygdala (BLA). Our results showed that morphine dose‐dependently impairs memory consolidation, but not motor function. Maximum effect was achieved with morphine at dose of 5 mg/kg. Pretreatment with ICV injection of minocycline (50 μg/rat) prevented morphine‐induced memory impairment, but there was no effect on motor function. The results of immunohistochemistry analysis demonstrated that morphine decreased expression of P‐CREB positive cells compared to saline control group in the BLA, but not in the dorsal hippocampus. On the other hand, pretreatment of animals with ICV injection of minocycline increased the expression of P‐CREB in both brain areas. Moreover, there was no significant change in the expression of c‐Fos positive cells in above‐mentioned regions. In summary, our results indicated that pretreatment with ICV injection of minocycline prevented morphine‐induced memory impairment and increased P‐CREB expression in the dorsal hippocampus and BLA, which may explain its memory improvement property.     

中枢认知功能有关基因

中枢学习记忆功能障碍是衰老及老年性痴呆病人的典型特征之一。大量研究初步表明中枢学习记忆的生理和病理过程受基因调控,已发现多种基因及其产物与中枢学习记忆的生理及病理过程有密切的关系。即刻早期基因家族作为“第三信使”参与调节神经细胞内信号转导而与学习记忆密切相关,其中ｃ ｆｏｓ的表达与学习记忆功能的变化具有密切关系。神经细胞粘附分子、ｅｐｅｎｄｙｍｉｎ及ＧＡＰ ４３基因参与和影响突触的可塑性与重建及细胞间粘附连接。ＣＲＥＢ能激活与学习记忆密切相关的基因,在长时记忆（ＬＴＭ）过程中起重要作用。此外,ｂｃｌ ２、ＩＣＥ、ｐ５３、及ｈｓｐ等基因参与了神经元的信号转导及凋亡等过程,与学习记忆过程也有一定的联系。因此,寻找和研究学习记忆功能有关基因对从基因水平阐明中枢学习记忆功能的调控机制具有重要意义。     

A possible mechanism for improvement by a cognition-enhancer nefiracetam of spatial memory function and cAMP-mediated signal transduction system in sustained cerebral ischaemia in rats

1. Accumulated evidence indicates that the adenylyl cyclase (AC)/cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)/cAMP-responsive element binding protein (CREB) signal transduction system may be linked to learning and memory function. 2. The effects of nefiracetam, which has been developed as a cognition enhancer, on spatial memory function and the AC/cAMP/PKA/CREB signal transduction system in rats with sustained cerebral ischaemia were examined. 3. Microsphere embolism (ME)-induced sustained cerebral ischaemia was produced by injection of 700 microspheres (48 micro m in diameter) into the right hemisphere of rats. Daily oral administration of nefiracetam (10 mg kg(-1) day(-1)) was started from 15 h after the operation. 4. The delayed treatment with nefiracetam attenuated the ME-induced prolongation of the escape latency in the water maze task that was examined on day 7 to 9 after ME, but it did not reduce the infarct size. 5. ME decreased Ca(2+)/calmodulin (CaM)-stimulated AC (AC-I) activity, cAMP content, cytosolic PKA Cbeta level, nuclear PKA Calpha and Cbeta levels, and reduced the phosphorylation and DNA-binding activity of CREB in the nucleus in the right parietal cortex and hippocampus on day 3 after ME. The ME-induced changes in these variables did not occur by the delayed treatment with nefiracetam. 6. These results suggest that nefiracetam preserved cognitive function, or prevented cognitive dysfunction, after sustained cerebral ischaemia and that the effect is, in part, attributable to the prevention of the ischaemia-induced impairment of the AC/cAMP/PKA/CREB signal transduction pathway.     

抑郁症信号转导通路研究

长期给予抗抑郁剂可以增加脑内cAMP依赖性PKA的表达水平,继而激活cAMP反应元件结合蛋白。CREB可以调节脑源性神经生长因子的表达。大量的研究表明cAMP和BDNF是多种抗抑郁剂的共同通路,现就此进行综述,探讨其与抗抑郁剂之间的关系,为精神药理和新药研发提供依据。     

Liquiritigenin ameliorates memory and cognitive impairment through cholinergic and BDNF pathways in the mouse hippocampus

Liquiritigenin (LQ), a flavonoid extracted from the radix of Glycyrrhiza, has anti-inflammatory and neuroprotective properties. In this study, we evaluated the cognitive enhancing effects of LQ on learning and memory impairments induced by scopolamine (0.5 mg/kg, i.p.), a muscarinic antagonist, using the Y-maze, passive avoidance, and novel object recognition tests. A single administration of LQ significantly improved scopolamine-induced cognitive impairments in these behavioral tests. In addition, LQ dramatically inhibited acetylcholinesterase and thiobarbituric acid reactive substance activities in the hippocampus of scopolamine-induced mice in a dose-dependent manner. Furthermore, LQ markedly increased the protein level of brain-derived neurotrophic factor (BDNF) and phosphorylation of extracellular signal-regulated kinase (ERK) and cAMP response element binding (CREB) in the hippocampus of scopolamine-induced mice. Taken together, our results indicate that LQ may be useful for the treatment of learning and memory impairments, and that the beneficial effects of LQ are mediated, in part, by cholinergic and BDNF/ERK/CREB signaling enhancement and/or protection.     

cAMP/PKA/CREB信号通路调控组织器官细胞纤维化及中医药干预作用的研究进展

环磷酸腺苷（cAMP）通过活化cAMP依赖的蛋白激酶A（PKA）,使cAMP反元件结合蛋白（CREB）磷酸化,从而调节基因转录,广泛参与神经系统的学习记忆过程,而近年来研究显示cAMP/PKA/CREB信号通路参与组织器官细胞的纤维化过程。机体损伤后在其组织器官细胞修复过程中,细胞外基质异常增生谓之纤维化,纤维化可使肝、肺、肾及心等脏器组织功能下降。中医药在治疗纤维化等慢性复杂疾病过程中有独特的优势,而调节cAMP/PKA/CREB信号通路是其防治组织器官细胞纤维化的机制之一。