Neural correlates of a magnetic sense

Many animals rely on Earth's magnetic field for spatial orientation and navigation. However, how the brain receives and interprets magnetic field information is unknown. Support for the existence of magnetic receptors in the vertebrate retina, beak, nose, and inner ear has been proposed, and immediate gene expression markers have identified several brain regions activated by magnetic stimulation, but the central neural mechanisms underlying magnetoreception remain unknown. Here we describe neuronal responses in the pigeon's brainstem that show how single cells encode magnetic field direction, intensity, and polarity; qualities that are necessary to derive an internal model representing directional heading and geosurface location. Our findings demonstrate that there is a neural substrate for a vertebrate magnetic sense.     

Electrical synapses control hippocampal contributions to fear learning and memory

The role of electrical synapses in synchronizing neuronal assemblies in the adult mammalian brain is well documented. However, their role in learning and memory processes remains unclear. By combining Pavlovian fear conditioning, activity-dependent immediate early gene expression, and in vivo electrophysiology, we discovered that blocking neuronal gap junctions within the dorsal hippocampus impaired context-dependent fear learning, memory, and extinction. Theta rhythms in freely moving rats were also disrupted. Our results show that gap junction-mediated neuronal transmission is a prominent feature underlying emotional memories.     

Jekyll and Hyde in the microbial world

Fungi are nonmotile organisms that obtain carbon from compounds in their immediate surroundings. Confronted with nutrient limitation, the yeast Saccharomyces cerevisiae undergoes a dimorphic transition, switching from spherical cells to filaments of adherent, elongated cells that can invade the substratum. A complex web of sensing mechanisms and cooperation among signaling networks (including a mitogen-activated protein kinase cascade, cyclic adenosine monophosphate-dependent protein kinase, and 5'-adenosine monophosphate-activated protein kinase) elicits the appropriate changes in physiology, cell cycle progression, cell polarity, and gene expression to achieve this differentiation. Highly related signaling processes control filamentation and virulence of many human fungal pathogens.     

柞蚕神经分泌细胞的研究 Ⅰ 脑神经分泌细胞

研究柞蚕(Antheraes pernyi G.)神经分泌细胞及其功能对于阐明柞蚕滞育机理,实现人为控制柞蚕化性具有重要意义。作者发现柞蚕脑内存在A、B两种神经分泌细胞,A细胞有三种类型,分布于脑间部的中央神经分泌细胞群由A、B两种细胞组成,此群细胞又可分为背、中、腹三区。侧群神经分泌细胞的主体在脑的侧背方,绝大多数为B细胞.中央群A细胞和侧群B细胞均发出轴突,前者的轴突在脑间部下方交叉后,分别进入另一个脑半球内;后者的轴突不交叉,直接进入本半球髓质部.自4龄第1天至蛹化第15天,A、B两种细胞大小无差异,但A细胞的染色性随蚕体发育而有一定变化,脑神经分泌细胞的相对数量以蛹化第1～3天为最多。     

Functional congruence: an index of neural homogeneity and a new measure of brain activity

Extremely high correlation between the probability that a single cell will fire and the amplitude of microelectrode electroencephalogram was established in on-line, real-time computer experiments. Such congruence between spike and wave shows orderly biological variation under sensory control. Congruence, as a measure of brain activity, provides an immediate estimate of regional neural homogeneity of function of cell populations in brain.     

Mammalian neural stem cells

Neural stem cells exist not only in the developing mammalian nervous system but also in the adult nervous system of all mammalian organisms, including humans. Neural stem cells can also be derived from more primitive embryonic stem cells. The location of the adult stem cells and the brain regions to which their progeny migrate in order to differentiate remain unresolved, although the number of viable locations is limited in the adult. The mechanisms that regulate endogenous stem cells are poorly understood. Potential uses of stem cells in repair include transplantation to repair missing cells and the activation of endogenous cells to provide "self-repair. " Before the full potential of neural stem cells can be realized, we need to learn what controls their proliferation, as well as the various pathways of differentiation available to their daughter cells.     

绒山羊关节炎-脑炎的病理组织学观察

2006年12月初,大庆某绒山羊养殖场发现,数只绒山羊羔出现跛足、运动失调和后肢麻痹、头痉挛,有时做转圈运动,确诊为山羊关节炎-脑炎。对脑组织、淋巴结和脾脏进行病理学观察发现:脑组织可见不对称性褐色-粉红色肿胀区并压迫邻近组织,有脑软化,淋巴结和脾脏稍肿大;同时,镜下可见脑脊髓炎,脑组织水肿神经细胞肿胀或萎缩,神经细胞与周围组织间隙增大;胞核肿胀或固缩;神经纤维有程度不等的脱髓鞘;毛细血管充血,有较多的淋巴细胞和巨噬细胞浸润;脾脏可见白髓萎缩,少量细胞坏死;淋巴结中淋巴组织增生,有小灶状坏死。     

Changing face of microglia

Microglia are resident brain cells that sense pathological tissue alterations. They can develop into brain macrophages and perform immunological functions. However, expression of immune proteins by microglia is not synonymous with inflammation, because these molecules can have central nervous system (CNS)-specific roles. Through their involvement in pain mechanisms, microglia also respond to external threats. Experimental studies support the idea that microglia have a role in the maintenance of synaptic integrity. Analogous to electricians, they are capable of removing defunct axon terminals, thereby helping neuronal connections to stay intact. Microglia in healthy CNS tissue do not qualify as macrophages, and their specific functions are beginning to be explored.     

Preferential localization of effector memory cells in nonlymphoid tissue

Many intracellular pathogens infect a broad range of host tissues, but the importance of T cells for immunity in these sites is unclear because most of our understanding of antimicrobial T cell responses comes from analyses of lymphoid tissue. Here, we show that in response to viral or bacterial infection, antigen-specific CD8 T cells migrated to nonlymphoid tissues and were present as long-lived memory cells. Strikingly, CD8 memory T cells isolated from nonlymphoid tissues exhibited effector levels of lytic activity directly ex vivo, in contrast to their splenic counterparts. These results point to the existence of a population of extralymphoid effector memory T cells poised for immediate response to infection.     

Brave new world?

Recent developments in biology and medicine are raising new problems in the prevention and treatment of birth defects, and in research on these diseases. The problems include immediate issues such as genetic counseling, abortion for birth defects, the withholding of complex treatments from individuals in some situations, screening for genetic and other diseases, artificial insemination, and fertilization in vitro. Other problems, such as the dysgenic effects of modern medicine and the possibilities of cloning and gene therapy, are more remote. Each of these issues should be considered on its own merits and by its immediate and remote consequences rather than by a priori absolute criteria. Ways must be found to deal with these issues in a manner acceptable to most human beings. Open discussions and freedom from coercion are the best guarantees for ultimate success. The ethical human brain is the highest accomplishment of biologic evolution. By harmonizing our scientific, cultural, and ethical capabilities, the potentially achievable results can place us at the threshold of a new era of better health and less human suffering.     

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.     

Expression and properties of two types of protein kinase C: alternative splicing from a single gene

Two complementary DNA's, encoding the complete sequences of 671 and 673 amino acids for subspecies of rat brain protein kinase C, were expressed in COS 7 cells. The complementary DNA sequence analysis predicted that the two enzymes are derived from different ways of splicing and differ from each other only in the short ranges of their carboxyl-terminal regions. Both enzymes showed typical characteristics of protein kinase C that responded to Ca2+, phospholipid, and diacylglycerol. The enzymes showed practically identical physical and kinetic properties and were indistinguishable from one of the several subspecies of protein kinase C that occurs in rat brain but not in untransfected COS 7 cells. Partial analysis of the genomic structure confirmed that these two subspecies of protein kinase C resulted indeed from alternative splicing of a single gene.     

Neuronal soma and whole neuroglia of rat brain: a new isolation technique

Minced rat brain softened by treatment with trypsin is disrupted by filtration through nylon and steel meshes to produce a suspension of free-floating cells and debris. The cells are separated and purified by centrifugation on discontinuous sucrose gradients. Preparations of neuronal perikarya, retaining stumps of processes, so obtained are 90 percent pure and yield 33.6 x 10(6) cells per brain (3 milligrams, dry weight). The glial cells, apparently intact with extensive branched processess, are about 70 percent pure by weight and are obtained in a yield of 6.6 x 10(6) cells per brain (2 milligrams dry weight). The neurons are smaller and have less lipid than the glial cells.     

Mosaic organization of neural stem cells in the adult brain

The in vivo potential of neural stem cells in the postnatal mouse brain is not known, but because they produce many different types of neurons, they must be either very versatile or very diverse. By specifically targeting stem cells and following their progeny in vivo, we showed that postnatal stem cells in different regions produce different types of neurons, even when heterotopically grafted or grown in culture. This suggests that rather than being plastic and homogeneous, neural stem cells are a restricted and diverse population of progenitors.     

LOW DOSE RADIATION OF THE DEVELOPING BRAIN

X-irradiation administered in single doses of 10 to 40 r has a widespread effect on the developing rat brain. It first diminishes the formation of cytoplasmic basophilic material in the nerve cells and inhibits their growth. Single doses of 20 to 40 r cause permanent alterations of individual nerve cells, and interfere with their organization into neuronal assemblies, such as layers of the cerebral cortex.     

Electroencephalographic responses to ionizing radiation

Electroencephalographic recordings made from chronically implanted cortical electrodes indicate that ionizing radiation has an immediate effect upon brain wave patterns. X-rays delivered at the rate of 0.2 roentgen per second produce an arousal effect resembling that which occurs as a result of stimulation through peripheral receptor systems.     

Neurobiology. Heretical view of visual development

For decades, neurobiologists have believed that so-called ocular dominance columns--neat columns of brain cells that respond to visual activity from one eye or the other--form as a result of visual activity. Now, in work described on page 1321, neuroscientists report that ocular dominance columns in ferrets appear long before the columns can be modified by visual experience. They propose instead that innate molecules that guide growing axons to their locations in the developing brain may be primarily responsible for building these columns. But others contest the conclusion that neural activity is not required for constructing the columns, arguing that there are other explanations for the researchers' findings.     

Neuroglia: biophysical properties and physiologic function

The membrane time constant of neocortical glial cells is abolut 385 microseconds, less than one-twentieth the known value for the Betz cell. Glial membrane specific resistance is low (approximately 200 to 500 ohm centimeters squared. Neuroglial cells are ideally suited to buffer the immediate extraneuronal space at areas of synaptic contact against the increases in external potassium ion concentration that accompany postsynaptic and spike activity and to minimize the spread of potassium ions to other pre- and postsynaptic regions.     

Noncytotoxic lytic granule-mediated CD8+ T cell inhibition of HSV-1 reactivation from neuronal latency

Reactivation of herpes simplex virus type 1 (HSV-1) from neuronal latency is a common and potentially devastating cause of disease worldwide. CD8+ T cells can completely inhibit HSV reactivation in mice, with interferon-gamma affording a portion of this protection. We found that CD8+ T cell lytic granules are also required for the maintenance of neuronal latency both in vivo and in ex vivo ganglia cultures and that their directed release to the junction with neurons in latently infected ganglia did not induce neuronal apoptosis. Here, we describe a nonlethal mechanism of viral inactivation in which the lytic granule component, granzyme B, degrades the HSV-1 immediate early protein, ICP4, which is essential for further viral gene expression.