Astrocyte‐driven plasticity contributes to environment‐related changes of hippocampal oscillations
Astrocyte‐driven plasticity contributes to environment‐related changes of hippocampal oscillations
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星形胶质细胞驱动的可塑性有助于海马振荡的环境相关变化
DOI：
10.1113/jp275055
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
L. Wittner
中科院分区：
文献类型：
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作者：
L. Wittner
环境对情绪和行为的影响是当前大脑研究的焦点。当然，我们所有人都对这个话题有自己的看法，比如孩子们有多喜欢有许多五颜六色的玩具的地方，或者人们通常在明亮和风景如画的环境中比在黑暗和沉闷的地方感觉更好。在丰富的环境中饲养的实验动物似乎是探索经验对行为相关脑功能影响的有价值的模型。已经进行了系统和详细的研究，以揭示丰富的环境与负责学习和记忆能力的解剖学，电生理学和分子变化之间的联系。动物居住在一个丰富的环境中表现出增强的神经发生，和各种树突和轴突的变化，涉及兴奋性和抑制性神经元回路。因此，初级视觉，听觉和体感皮层表达其诱发电位和感受野的经验依赖性修饰，此外，在生活在丰富环境中的动物的海马体中观察到增加的突触传递和可塑性（综述参见Hirase & Shinohara，2014）。海马突触可塑性被认为是学习和记忆的细胞基础。突触连接的功效通过两个主要途径响应于神经元活动的变化而改变。谷氨酸通道的开放和细胞内Ca2+水平的增加与长时程增强（一种暂时的突触修饰）有关，而持久的记忆储存涉及调节基因表达的第二信使途径（Kreutz & Sala，2012）。突触可塑性归因于神经元及其分子机制，但最近的研究引起了对神经胶质钙信号传导以及某些形式的突触可塑性的作用的关注（例如参见Takata et al. 2011）。海马振荡已被证明在学习和记忆过程以及空间导航中至关重要。Theta和gamma振荡出现在主动探索和快速眼动睡眠期间，并且在导航和记忆检索中至关重要，而在行为不动和慢波睡眠期间可以观察到尖波涟漪复合体，并且被证明在记忆巩固中具有重要作用（综述参见Colgin，2016）。在本期《生理学杂志》上，Tanaka et al.（2017）的研究是首批研究环境如何影响海马网络振荡的研究之一。他们证明，与标准条件下饲养的动物相比，在丰富环境中饲养的小鼠具有更大的海马γ振荡和增加的涟漪活动。他们更进一步，在转基因小鼠品系中测试神经胶质钙信号是否参与了这些效应的改变。他们无法将星形胶质细胞Ca2+水平的增加与伽马振荡的经验依赖性增强联系起来，但有趣的是，他们发现星形胶质细胞Ca2+缺乏的动物中波纹减少。他们的结果表明，丰富的居住环境对与记忆过程相关的海马振荡有显着影响。它们显示了神经胶质细胞活性在涟漪事件的产生中的贡献，但在伽马振荡中没有。由于星形胶质细胞Ca2+升高减少的小鼠品系表达抑郁表型，他们还得出结论，涟漪和动物的情绪可能相关。除了它所描述的事实，我们还能从这项令人兴奋的研究中学到什么？我们的环境对我们的大脑功能有影响，包括我们的学习和记忆能力以及情绪调节。虽然实验室动物无疑与人类不同，但刺激的环境和社会互动对两个物种来说都具有相似的重要性。看来，一个丰富的物质和社会刺激的环境有助于保持我们的神经元活跃，并保持海马振荡在一个高水平，促进学习条件，并防止出现与抑郁表型相关的电生理模式。Tanaka et al.（2017）的工作引起了人们对另一个主要与研究人员有关的问题的注意。虽然丰富的环境越来越受到关注，但为科学目的饲养的啮齿动物仍然主要被隔离在笼子里，只提供食物和饮料。我们关于大脑皮层的基本解剖学和生理学、细胞和网络特性的大多数数据主要是在生活在物质和社会剥夺中的动物身上获得的。我们应该重新考虑我们的模型动物的居住条件，使它们更接近人类的环境，以更好地描述人类的生理皮层功能。另一个观点来自Tanaka et al.（2017）的研究：神经胶质细胞在突触可塑性中的作用。这项开创性的工作表明，星形胶质细胞有助于与记忆巩固相关的复杂振荡现象，它开辟了一条新的研究途径，专注于学习和记忆过程中神经元和神经胶质细胞的联合和对齐活动。
The effect of the environment on mood and behaviour is the focus of current brain research. All of us certainly have personal observations on this topic, such as how much children love places with numerous colourful toys, or that people usually feel better in a bright and picturesque milieu compared to dark and dull places. Laboratory animals reared in an enriched environment seem to be a valuable model for exploring the effects of experience on behaviour-related brain functions. Systematic and detailed studies have been performed to reveal the link between an enriched environment and anatomical, electrophysiological and molecular changes responsible for learning and memory capacities. Animals housed in an enriched environment show enhanced neurogenesis, and a variety of dendritic and axonal changes involving both excitatory and inhibitory neuronal circuits. Consequently, primary visual, auditory and somatosensory cortices express an experience-dependent modification of their evoked potentials and receptive fields, and furthermore, increased synaptic transmission and plasticity have been observed in the hippocampus of animals living in an enriched environment (for review see Hirase & Shinohara, 2014). Hippocampal synaptic plasticity is considered to be the cellular basis of learning and memory. The efficacy of synaptic connections is altered in response to changes in neuronal activity through two main pathways. Opening of glutamate channels and increase in intracellular Ca2+ levels are linked to long-term potentiation (a temporary synaptic modification), whereas long-lasting memory storage involves a second messenger pathway regulating gene expression (Kreutz & Sala, 2012). Synaptic plasticity is attributed to neurons and their molecular machinery, but recent studies draw attention to the role of glial calcium signalling as well in certain forms of synaptic plasticity (for example see Takata et al. 2011). Hippocampal oscillations have been demonstrated to be crucial in learning and memory processes as well as in spatial navigation. Theta and gamma oscillations emerge during active exploration and rapid-eye-movement sleep and are essential in navigation and memory retrieval, whereas sharp-wave ripple complexes can be observed during behavioural immobility and slow wave sleep, and were shown to have an important role in memory consolidation (for review see Colgin, 2016). In the current issue of The Journal of Physiology, the study by Tanaka et al. (2017) is one of the first to investigate how the environment affects hippocampal network oscillations. They demonstrate that mice reared in an enriched environment have larger hippocampal gamma oscillation and increased ripple activity compared to animals housed in standard conditions. They go one step further and test in a genetically modified mouse strain whether glial calcium signalling participates in the modification of these effects. They could not relate the increase of astrocytic Ca2+ levels to the experience-dependent enhancement of gamma oscillation, but interestingly, they found reduced ripples in animals with astrocytic Ca2+ deficiency. Their results demonstrate that an enriched housing environment has a significant effect on hippocampal oscillations linked to memory processes. They show the contribution of glial cell activity in the generation of ripple events but not in gamma oscillation. Since the mouse strain with reduced astrocytic Ca2+ elevations expresses depression phenotypes, they also conclude that ripples and the animal’s mood might be correlated. What can we learn from this exciting study, beside the facts it describes? Our environment has an influence on our brain functions, including our learning and memory abilities and mood regulation. Although laboratory animals are undoubtedly different from humans, a stimulating milieu and social interactions are of similar importance for both species. It seems that an environment rich in material and social stimuli helps to keep our neurons active and to maintain hippocampal oscillations at a high level, facilitating learning conditions and preventing the emergence of electrophysiological patterns correlated to depressive phenotypes. The work of Tanaka et al. (2017) draws attention to another question primarily concerning researchers. Although an enriched environment is gaining more and more attention, rodents reared for scientific purposes are still kept mainly in isolation, in cages where only food and drink are provided. Most of our data concerning basic anatomical and physiological, cellular and network properties of the cortex are largely obtained in animals living in material and social deprivation. We should reconsider the housing conditions of our model animals and make them closer to human circumstances to describe physiological cortical functions with better implications for humans. Another perspective emerges from the study of Tanaka et al. (2017): the role of glial cells in synaptic plasticity. This groundbreaking work shows that astrocytes contribute to a complex oscillatory phenomenon connected to memory consolidation, and it opens a new research pathway focusing on joint and aligned activity of neurons and glial cells in learning and memory processes.
DOI：
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发表时间：
2012
期刊：
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影响因子：
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作者：
M. Kreutz;C. Sala
通讯作者：
M. Kreutz;C. Sala