Tuned responses of astrocytes and their influence on hemodynamic signals in the visual cortex

Astrocytes have long been thought to act as a support network for neurons, with little role in information representation or processing. We used two-photon imaging of calcium signals in the ferret visual cortex in vivo to discover that astrocytes, like neurons, respond to visual stimuli, with distinct spatial receptive fields and sharp tuning to visual stimulus features including orientation and spatial frequency. The stimulus-feature preferences of astrocytes were exquisitely mapped across the cortical surface, in close register with neuronal maps. The spatially restricted stimulus-specific component of the intrinsic hemodynamic mapping signal was highly sensitive to astrocyte activation, indicating that astrocytes have a key role in coupling neuronal organization to mapping signals critical for noninvasive brain imaging. Furthermore, blocking astrocyte glutamate transporters influenced the magnitude and duration of adjacent visually driven neuronal responses.     

Single-neuron activity and tissue oxygenation in the cerebral cortex

Blood oxygen level-dependent functional magnetic resonance imaging uses alterations in brain hemodynamics to infer changes in neural activity. Are these hemodynamic changes regulated at a spatial scale capable of resolving functional columns within the cerebral cortex? To address this question, we made simultaneous measurements of tissue oxygenation and single-cell neural activity within the visual cortex. Results showed that increases in neuronal spike rate were accompanied by immediate decreases in tissue oxygenation. We used this decrease in tissue oxygenation to predict the orientation selectivity and ocular dominance of neighboring neurons. Our results establish a coupling between neural activity and oxidative metabolism and suggest that high-resolution functional magnetic resonance imaging may be used to localize neural activity at a columnar level.     

Specification and morphogenesis of astrocytes

Astrocytes are the most abundant cell type in the mammalian brain. Interest in astrocyte function has increased dramatically in recent years because of their newly discovered roles in synapse formation, maturation, efficacy, and plasticity. However, our understanding of astrocyte development has lagged behind that of other brain cell types. We do not know the molecular mechanism by which astrocytes are specified, how they grow to assume their complex morphologies, and how they interact with and sculpt developing neuronal circuits. Recent work has provided a basic understanding of how intrinsic and extrinsic mechanisms govern the production of astrocytes from precursor cells and the generation of astrocyte diversity. Moreover, new studies of astrocyte morphology have revealed that mature astrocytes are extraordinarily complex, interact with many thousands of synapses, and tile with other astrocytes to occupy unique spatial domains in the brain. A major challenge for the field is to understand how astrocytes talk to each other, and to neurons, during development to establish appropriate astrocytic and neuronal network architectures.     

Control of synapse number by glia

Although astrocytes constitute nearly half of the cells in our brain, their function is a long-standing neurobiological mystery. Here we show by quantal analyses, FM1-43 imaging, immunostaining, and electron microscopy that few synapses form in the absence of glial cells and that the few synapses that do form are functionally immature. Astrocytes increase the number of mature, functional synapses on central nervous system (CNS) neurons by sevenfold and are required for synaptic maintenance in vitro. We also show that most synapses are generated concurrently with the development of glia in vivo. These data demonstrate a previously unknown function for glia in inducing and stabilizing CNS synapses, show that CNS synapse number can be profoundly regulated by nonneuronal signals, and raise the possibility that glia may actively participate in synaptic plasticity.     

Astrocytes synthesize angiotensinogen in brain

Cell types associated with angiotensinogen mRNA in rat brain were identified in individual brain sections by in situ hybridization with tritiated RNA probes or with a sulfur-35--labeled oligonucleotide combined with immunocytochemical detection of either glial fibrillary acidic protein (GFAP) for astrocytes or microtubule-associated protein (MAP-2) for neurons. Autoradiography revealed silver grains clustered primarily over GFAP-reactive soma and processes; most grain clusters were not associated with MAP-2--reactive cells. These results demonstrate that, in contrast to other known neuropeptide precursors, angiotensinogen is synthesized by glia.     

Presence of nonoxidative ethanol metabolism in human organs commonly damaged by ethanol abuse

Acetaldehyde, the end product of oxidative ethanol metabolism, contributes to alcohol-induced disease in the liver, but cannot account for damage in organs such as the pancreas, heart, or brain, where oxidative metabolism is minimal or absent; nor can it account for the varied patterns of organ damage found in chronic alcoholics. Thus other biochemical mediators may be important in the pathogenesis of alcohol-induced organ damage. Many human organs were found to metabolize ethanol through a recently described nonoxidative pathway to form fatty acid ethyl esters. Organs lacking oxidative alcohol metabolism yet frequently damaged by ethanol abuse have high fatty acid ethyl ester synthetic activities and show substantial transient accumulations of fatty acid ethyl esters. Thus nonoxidative ethanol metabolism in addition to the oxidative pathway may be important in the pathophysiology of ethanol-induced disease in humans.     

Age-associated changes in the DNA of mouse tissue

The template activity of DNA with calf thymus DNA polymerase has been studied in sections of fixed brain, liver, and heart tissues from young and senescent mice. The enzyme catalyzed greater incorporation of deoxyribonucleotide monophosphates into nuclei of old mouse neurons, astrocytes, Kupffer cells, and heart muscle fibers. The results are interpreted as the accumulation of DNA strand breaks with aging.     

骨髓间充质干细胞移植治疗脑缺血的动物实验研究

    探讨骨髓间充质干细胞(MSCs)移植对大鼠脑缺血的修复和治疗.体外分离培养大鼠MSCs,以Hoeschst33342标记,移植到大脑中动脉梗塞(MCAO)模型的大鼠体内,分别设立缺血1 d和缺血7 dMSCs移植组与缺血对照组,对各组大鼠进行神经功能损害严重程度评分(NSS)及大脑组织切片观察比较.结果发现,缺血1 d MSCs移植组大鼠NSS评分低于另外两组,差异显著(P＜0.05),大脑组织结构清晰、完整,胶质瘢痕少;缺血7 d MSCs移植组与对照组无明显差异(P＞0.05).故缺血早期进行MSCs移植,大鼠神经功能恢复情况明显.MSCs在损伤后的脑组织内能够存活并且分化为神经元、胶质细胞等,对动物神经损伤后组织重建及功能恢复有一定的治疗作用.     

The brain in AIDS: central nervous system HIV-1 infection and AIDS dementia complex

Infection with human immunodeficiency virus type 1 (HIV-1) is frequently complicated in its late stages by the AIDS dementia complex, a neurological syndrome characterized by abnormalities in cognition, motor performance, and behavior. This dementia is due partially or wholly to a direct effect of the virus on the brain rather than to opportunistic infection, but its pathogenesis is not well understood. Productive HIV-1 brain infection is detected only in a subset of patients and is confined largely or exclusively to macrophages, microglia, and derivative multinucleated cells that are formed by virus-induced cell fusion. Absence of cytolytic infection of neurons, oligodentrocytes, and astrocytes has focused attention on the possible role of indirect mechanisms of brain dysfunction related to either virus or cell-coded toxins. Delayed development of the AIDS dementia complex, despite both early exposure of the nervous system to HIV-1 and chronic leptomeningeal infection, indicates that although this virus is "neurotropic," it is relatively nonpathogenic for the brain in the absence of immunosuppression. Within the context of the permissive effect of immunosuppression, genetic changes in HIV-1 may underlie the neuropathological heterogeneity of the AIDS dementia complex and its relatively independent course in relation to the systemic manifestations of AIDS noted in some patients.     

Thyroxine: effects on amino acid incorporation into protein in vivo

Treatment of rats with L-thyroxine increases the incorporation in vivo of radioactive amino acids into protein of liver, kidney, and heart, but not of spleen, testis, or brain. The distribution of the effect among the organs is the same as that observed in thyroxine stimulation of oxidative metabolism. Thus, stimulation of protein synthesis seems to be a physiological action of the thyroid hormone.     

Neurotransmitter plasticity at the molecular level

Contrary to long-held assumptions, recent work indicates that neurons may profoundly change transmitter status during development and maturity. For example, sympathetic neurons, classically regarded as exclusively noradrenergic or cholinergic, can also express putative peptide transmitters such as substance P. This neuronal plasticity is directly related to membrane depolarization and sodium ion influx. The same molecular mechanisms and plastic responses occur in mature as well as developing neurons. Further, contrary to traditional teaching, adult primary sensory neurons may express the catecholaminergic phenotype in vivo. Transmitter plasticity is not restricted to the peripheral nervous system: ongoing studies of the brain nucleus locus ceruleus in culture indicate that specific extracellular factors elicit marked transmitter changes. Consequently, neurotransmitter expression and metabolism are dynamic, changing processes, regulated by a variety of defined factors. Transmitter plasticity adds a newly recognized dimension of flexibility to nervous system function.     

Micro-optical sectioning tomography to obtain a high-resolution atlas of the mouse brain

The neuroanatomical architecture is considered to be the basis for understanding brain function and dysfunction. However, existing imaging tools have limitations for brainwide mapping of neural circuits at a mesoscale level. We developed a micro-optical sectioning tomography (MOST) system that can provide micrometer-scale tomography of a centimeter-sized whole mouse brain. Using MOST, we obtained a three-dimensional structural data set of a Golgi-stained whole mouse brain at the neurite level. The morphology and spatial locations of neurons and traces of neurites could be clearly distinguished. We found that neighboring Purkinje cells stick to each other.     

Glutamate induces calcium waves in cultured astrocytes: long-range glial signaling

The finding that astrocytes possess glutamate-sensitive ion channels hinted at a previously unrecognized signaling role for these cells. Now it is reported that cultured hippocampal astrocytes can respond to glutamate with a prompt and oscillatory elevation of cytoplasmic free calcium, visible through use of the fluorescent calcium indicator fluo-3. Two types of glutamate receptor--one preferring quisqualate and releasing calcium from intracellular stores and the other preferring kainate and promoting surface-membrane calcium influx--appear to be involved. Moreover, glutamate-induced increases in cytoplasmic free calcium frequently propagate as waves within the cytoplasm of individual astrocytes and between adjacent astrocytes in confluent cultures. These propagating waves of calcium suggest that networks of astrocytes may constitute a long-range signaling system within the brain.     

Brain region and gene specificity of neuropeptide gene expression in cultured astrocytes

Astrocytes have many neuronal characteristics, such as neurotransmitter receptors, ion channels, and neurotransmitter uptake systems. Cultured astrocytes were shown to express certain neuropeptide genes, with specificity for both the gene expressed and the brain region from which the cells were prepared. Somatostatin messenger RNA and peptides were detected only in cerebellar astrocytes, whereas proenkephalin messenger RNA and enkephalin peptides were present in astrocytes of cortex, cerebellum, and striatum. Cholecystokinin was not expressed in any of the cells. These results support the hypothesis that peptides synthesized in astrocytes may play a role in the development of the central nervous system.     

Regional astrocyte allocation regulates CNS synaptogenesis and repair

Astrocytes, the most abundant cell population in the central nervous system (CNS), are essential for normal neurological function. We show that astrocytes are allocated to spatial domains in mouse spinal cord and brain in accordance with their embryonic sites of origin in the ventricular zone. These domains remain stable throughout life without evidence of secondary tangential migration, even after acute CNS injury. Domain-specific depletion of astrocytes in ventral spinal cord resulted in abnormal motor neuron synaptogenesis, which was not rescued by immigration of astrocytes from adjoining regions. Our findings demonstrate that region-restricted astrocyte allocation is a general CNS phenomenon and reveal intrinsic limitations of the astroglial response to injury.     

Astrocytes potentiate transmitter release at single hippocampal synapses

Astrocytes play active roles in brain physiology. They respond to neurotransmitters and modulate neuronal excitability and synaptic function. However, the influence of astrocytes on synaptic transmission and plasticity at the single synapse level is unknown. Ca(2+) elevation in astrocytes transiently increased the probability of transmitter release at hippocampal area CA3-CA1 synapses, without affecting the amplitude of synaptic events. This form of short-term plasticity was due to the release of glutamate from astrocytes, a process that depended on Ca(2+) and soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein and that activated metabotropic glutamate receptors (mGluRs). The transient potentiation of transmitter release became persistent when the astrocytic signal was temporally coincident with postsynaptic depolarization. This persistent plasticity was mGluR-mediated but N-methyl-d-aspartate receptor-independent. These results indicate that astrocytes are actively involved in the transfer and storage of synaptic information.     

Astrocytes block axonal regeneration in mammals by activating the physiological stop pathway

Regenerating sensory axons in the dorsal roots of adult mammals are stopped at the junction between the root and spinal cord by reactive astrocytes. Do these cells stop axonal elongation by activating the physiological mechanisms that normally operate to stop axons during development, or do they physically obstruct the elongating axons? In order to distinguish these possibilities, the cytology of the axon tips of regenerating axons that were stopped by astrocytes was compared with the axon tips that were physically obstructed at a cul-de-sac produced by ligating a peripheral nerve. The terminals of the physically obstructed axon tips were distended with neurofilaments and other axonally transported structures that had accumulated when the axons stopped elongating. By contrast, neurofilaments did not accumulate in the tips of regenerating axons that were stopped by spinal cord astrocytes at the dorsal root transitional zone. These axo-glial terminals resembled the terminals that axons make on target neurons during normal development. On the basis of these observations, astrocytes appear to stop axons from regenerating in the mammalian spinal cord by activating the physiological stop pathway that is built into the axon and that normally operates when axons form stable terminals on target cells.     

Three-dimensional representation and analysis of brain energy metabolism

Quantitative autoradiography of brain glucose metabolism has been combined with digital image processing to represent the brain as a three-dimensional (3-D) reconstruction of brain energy use. Autoradiographs contain enormous amounts of potentially useful data, but conventional analyses, based on tedious manual methods, can sample and analyze only a small portion of this information. Computer 3-D reconstruction provides a mechanism for observing and analyzing all the data; therefore, a system of computer programs was developed for this purpose. The programs use digital imaging methods for image registration, superimpose whole brain data sets, and allow resampling of the 3-D data in arbitrary planes for pixel-by-pixel comparisons among multiple 3-D sets. These programs operate on the mathematical properties of the images alone, obviating the need for manual image alignment. Various statistical analyses can be applied to the data directly to study the patterns of metabolic changes in different experiments. The system is applied to data from experiments on the influence of injectable anesthetics on cerebral glucose metabolism.     

转录组学分析意大利蜜蜂脑部哺育行为相关基因

【目的】意大利蜜蜂(Apis mellifera ligustica)哺育行为在维护蜂群稳定和生产蜂王浆方面发挥重要作用。本研究通过人工组建蜂群获得相同日龄的哺育蜂和采集蜂,筛选出排除日龄因素干扰后哺育蜂脑部与哺育行为密切相关的差异表达基因,揭示哺育蜂脑部调控哺育行为的分子网络。【方法】通过人工组建蜂群的方法获得3日龄工蜂、10日龄哺育蜂和采集蜂、21日龄哺育蜂和采集蜂,解剖各组工蜂头部获得脑组织样本,应用RNA-seq技术对5组脑部样本(3日龄工蜂、10日龄哺育蜂、10日龄采集蜂、21日龄哺育蜂、21日龄采集蜂)中基因表达量进行转录组测序的全面分析,筛选出哺育蜂脑部哺育行为密切相关的差异表达基因,并对这些差异表达基因进行GO和KEGG富集分析。同时利用实时荧光定量PCR(qPCR)对随机选取的4个差异表达基因的表达模式进行验证。【结果】RNA-seq分析筛选得到32个与哺育蜂哺育行为密切相关的差异表达基因,这些基因在10日龄哺育蜂脑中表达量均显著高于3日龄工蜂、10日龄采集蜂、21日龄采集蜂,且在21日龄哺育蜂脑中的表达量也显著高于21日龄采集蜂。GO富集分析发现上调差异表达基因主要...