Experience-dependent plasticity of dendritic spines in the developing rat barrel cortex in vivo

Do changes in neuronal structure underlie cortical plasticity? Here we used time-lapse two-photon microscopy of pyramidal neurons in layer 2/3 of developing rat barrel cortex to image the structural dynamics of dendritic spines and filopodia. We found that these protrusions were highly motile: spines and filopodia appeared, disappeared or changed shape over tens of minutes. To test whether sensory experience drives this motility we trimmed whiskers one to three days before imaging. Sensory deprivation markedly (approximately 40%) reduced protrusive motility in deprived regions of the barrel cortex during a critical period around postnatal days (P)11-13, but had no effect in younger (P8-10) or older (P14-16) animals. Unexpectedly, whisker trimming did not change the density, length or shape of spines and filopodia. However, sensory deprivation during the critical period degraded the tuning of layer 2/3 receptive fields. Thus sensory experience drives structural plasticity in dendrites, which may underlie the reorganization of neural circuits.     

Internal brain state regulates membrane potential synchrony in barrel cortex of behaving mice

Internal brain states form key determinants for sensory perception, sensorimotor coordination and learning. A prominent reflection of different brain states in the mammalian central nervous system is the presence of distinct patterns of cortical synchrony, as revealed by extracellular recordings of the electroencephalogram, local field potential and action potentials. Such temporal correlations of cortical activity are thought to be fundamental mechanisms of neuronal computation. However, it is unknown how cortical synchrony is reflected in the intracellular membrane potential (V(m)) dynamics of behaving animals. Here we show, using dual whole-cell recordings from layer 2/3 primary somatosensory barrel cortex in behaving mice, that the V(m) of nearby neurons is highly correlated during quiet wakefulness. However, when the mouse is whisking, an internally generated state change reduces the V(m) correlation, resulting in a desynchronized local field potential and electroencephalogram. Action potential activity was sparse during both quiet wakefulness and active whisking. Single action potentials were driven by a large, brief and specific excitatory input that was not present in the V(m) of neighbouring cells. Action potential initiation occurs with a higher signal-to-noise ratio during active whisking than during quiet periods. Therefore, we show that an internal brain state dynamically regulates cortical membrane potential synchrony during behaviour and defines different modes of cortical processing.     

Segmental patterns of neuronal development in the chick hindbrain

Identification of specific neuronal populations and their projections in the developing hindbrain reveals a segmental organization in which pairs of metameric epithelial units cooperate to generate the repeating sequence of cranial branchiomotor nerves. Neurogenesis also follows a two-segment repeat, suggesting parallels with insect pattern formation.     

Sparse optical microstimulation in barrel cortex drives learned behaviour in freely moving mice

Electrical microstimulation can establish causal links between the activity of groups of neurons and perceptual and cognitive functions. However, the number and identities of neurons microstimulated, as well as the number of action potentials evoked, are difficult to ascertain. To address these issues we introduced the light-gated algal channel channelrhodopsin-2 (ChR2) specifically into a small fraction of layer 2/3 neurons of the mouse primary somatosensory cortex. ChR2 photostimulation in vivo reliably generated stimulus-locked action potentials at frequencies up to 50 Hz. Here we show that naive mice readily learned to detect brief trains of action potentials (five light pulses, 1 ms, 20 Hz). After training, mice could detect a photostimulus firing a single action potential in approximately 300 neurons. Even fewer neurons (approximately 60) were required for longer stimuli (five action potentials, 250 ms). Our results show that perceptual decisions and learning can be driven by extremely brief epochs of cortical activity in a sparse subset of supragranular cortical pyramidal neurons.     

The neuronal representation of pitch in primate auditory cortex

Pitch perception is critical for identifying and segregating auditory objects, especially in the context of music and speech. The perception of pitch is not unique to humans and has been experimentally demonstrated in several animal species. Pitch is the subjective attribute of a sound's fundamental frequency (f(0)) that is determined by both the temporal regularity and average repetition rate of its acoustic waveform. Spectrally dissimilar sounds can have the same pitch if they share a common f(0). Even when the acoustic energy at f(0) is removed ('missing fundamental') the same pitch is still perceived. Despite its importance for hearing, how pitch is represented in the cerebral cortex is unknown. Here we show the existence of neurons in the auditory cortex of marmoset monkeys that respond to both pure tones and missing fundamental harmonic complex sounds with the same f(0), providing a neural correlate for pitch constancy. These pitch-selective neurons are located in a restricted low-frequency cortical region near the anterolateral border of the primary auditory cortex, and is consistent with the location of a pitch-selective area identified in recent imaging studies in humans.     

ClC-5 Cl- -channel disruption impairs endocytosis in a mouse model for Dent's disease

Dent's disease is an X-linked disorder associated with the urinary loss of low-molecular-weight proteins, phosphate and calcium, which often leads to kidney stones. It is caused by mutations in ClC-5, a renal chloride channel that is expressed in endosomes of the proximal tubule. Here we show that disruption of the mouse clcn5 gene causes proteinuria by strongly reducing apical proximal tubular endocytosis. Both receptor-mediated and fluid-phase endocytosis are affected, and the internalization of the apical transporters NaPi-2 and NHE3 is slowed. At steady state, however, both proteins are redistributed from the plasma membrane to intracellular vesicles. This may be caused by an increased stimulation of luminal parathyroid hormone (PTH) receptors owing to the observed decreased tubular endocytosis of PTH. The rise in luminal PTH concentration should also stimulate the hydroxylation of 25(OH) vitamin D3 to the active hormone. However, this is counteracted by a urinary loss of the precursor 25(OH) vitamin D3. The balance between these opposing effects, both of which are secondary to the defect in proximal tubular endocytosis, probably determines whether there will be hypercalciuria and kidney stones.     

Attention modulates synchronized neuronal firing in primate somatosensory cortex

A potentially powerful information processing strategy in the brain is to take advantage of the temporal structure of neuronal spike trains. An increase in synchrony within the neural representation of an object or location increases the efficacy of that neural representation at the next synaptic stage in the brain; thus, increasing synchrony is a candidate for the neural correlate of attentional selection. We investigated the synchronous firing of pairs of neurons in the secondary somatosensory cortex (SII) of three monkeys trained to switch attention between a visual task and a tactile discrimination task. We found that most neuron pairs in SII cortex fired synchronously and, furthermore, that the degree of synchrony was affected by the monkey's attentional state. In the monkey performing the most difficult task, 35% of neuron pairs that fired synchronously changed their degree of synchrony when the monkey switched attention between the tactile and visual tasks. Synchrony increased in 80% and decreased in 20% of neuron pairs affected by attention.     

Iso-orientation domains in cat visual cortex are arranged in pinwheel-like patterns

The mammalian cortex is organized in a columnar fashion: neurons lying below each other from the pia to the white matter usually share many functional properties. Across the cortical surface, cells with similar response properties are also clustered together, forming elongated bands or patches. Some response properties, such as orientation preference in the visual cortex, change gradually across the cortical surface forming 'orientation maps'. To determine the precise layout of iso-orientation domains, knowledge of responses not only to one but to many stimulus orientations is essential. Therefore, the exact depiction of orientation maps has been hampered by technical difficulties and remained controversial for almost thirty years. Here we use in vivo optical imaging based on intrinsic signals to gather information on the responses of a piece of cortex to gratings in many different orientations. This complete set of responses then provides detailed information on the structure of the orientation map in a large patch of cortex from area 18 of the cat. We find that cortical regions that respond best to one orientation form highly ordered patches rather than elongated bands. These iso-orientation patches are organized around 'orientation centres', producing pinwheel-like patterns in which the orientation preference of cells is changing continuously across the cortex. We have also analysed our data for fast changes in orientation preference and find that these 'fractures' are limited to the orientation centres. The pinwheels and orientation centres are such a prominent organizational feature that it should be important to understand their development as well as their function in the processing of visual information.     

Firing patterns of long-term cultured neuronal network on multi-electrode array

Spontaneous neuronal activity plays an important role in the development and plasticity of brain. To explore the developmental changes in the firing pattern of the neuronal networks in vitro, the hippocampal neurons were cultured on the multi-microelectrode array dish for over 14 weeks and the spontaneous activity was recorded. The results showed that random firing was observed in the 1st week and transformed into synchronized activity after two weeks, then tightly synchronized activity appeared in week 2 to 7 and finally the activities transformed into the random firing pattern. These results suggested three stages in the long-term development of neuronal network in vitro: the stage for connection, the stage of synchronized activity and the mature stage. Synchronized firing shown by spontaneous activity was an important phenomenon in high density cultured neuronal network and transformed patterns during development.     

Formation of target-specific neuronal projections in organotypic slice cultures from rat visual cortex.

A characteristic feature of the mammalian cortex is that projection neurons located in distinct cortical layers send their axons to different targets. In visual cortex, cells in layers 2 and 3 project to other cortical areas, whereas cells in layers 5 and 6 project to subcortical targets such as the lateral geniculate nucleus. The proper development of these projections is crucial for correct functioning of the visual system. Here we show that specific connections are established in an organotypic culture system in which rat visual cortex slices are co-cultured with another slice of the visual cortex or with a thalamic slice. The laminar origin and cellular morphology in vitro of cortical projections to other cortical regions or to subcortical targets are remarkably similar to those seen in vivo. In addition, axons of projecting cells are not restricted to particular pathways, but appear instead to grow directly towards their appropriate target. These observations raise the possibility that chemotropic attraction from the target areas may play an important part in the development of the cortical projection pattern.     

Fluorescent latex microspheres as a retrograde neuronal marker for in vivo and in vitro studies of visual cortex

The use of retrograde axonal transport of various substances (for example, enzymes, lectins, synthetic fluorescent compounds) has yielded much information on the organization of neuronal pathways. Each type of retrograde tracer has its own set of attributes which define the scope of problems it can address. We describe here a new class of retrograde tracer, rhodamine-labelled fluorescent latex microspheres (0.02-0.2 micron diameter), which have distinct advantages over other available tracers for in vivo and in vitro applications. When injected into brain tissue, these microspheres show little diffusion and consequently produce small, sharply defined injection sites. Once transported back to neuronal somata, the label persists for at least 10 weeks in vivo and 1 yr after fixation. Microspheres have no obvious cytotoxicity or phototoxicity as assessed by intracellular recording and staining of retrogradely labelled cells in a cortical brain slice preparation. This approach was further used to visualize and compare, in cat visual cortex slices, neurones with different projection patterns, and revealed significant differences in patterns of intrinsic axons and dendrites. These properties of microspheres open new avenues for anatomical and physiological studies of identified projection neurones in slices as well as in dissociated cell cultures.     

双管板换热器设计探讨

讨论了实际设计中双管板换热器管板的计算以及双管板管板间距的计算,并提出在设计中注意的问题。     

Targeted disruption of the murine int-1 proto-oncogene resulting in severe abnormalities in midbrain and cerebellar development

The int-1 proto-oncogene was first identified as a gene activated in virally induced mouse mammary tumours. Expression studies, however, suggest that the normal function of this gene may be in spermatogenesis and in the development of the central nervous system. Genes sharing sequence similarity with int-1 have been found throughout the animal kingdom. For example, int-1 has 54% amino-acid identity to the Drosophila segment polarity gene wingless (wg). Both the int-1 and wg gene products seem to be secreted proteins, presumably involved in cell-cell signalling. We have now explored the function of int-1 in the mouse by disrupting one of the two int-1 alleles in mouse embryo-derived stem cells using positive-negative selection. This cell line was used to generate a chimaeric mouse that transmitted the mutant allele to its progeny. Mice heterozygous for the int-1 null mutation are normal and fertile, whereas mice homozygous for the mutation may exhibit a range of phenotypes from death before birth to survival with severe ataxia. The latter pathology in mice and humans is often associated with defects in the cerebellum. Examination of int-1-/int-1- mice at several stages of embryogenesis revealed severe abnormalities in the development of the mesencephalon and metencephalon indicating a prominent role for the int-1 protein is in the induction of the mesencephalon and cerebellum.     

Targeted disruption of the mouse transforming growth factor-beta 1 gene results in multifocal inflammatory disease.

Transforming growth factor-beta 1 (TGF-beta 1) is a multifunctional growth factor that has profound regulatory effects on many developmental and physiological processes. Disruption of the TGF-beta 1 gene by homologous recombination in murine embryonic stem cells enables mice to be generated that carry the disrupted allele. Animals homozygous for the mutated TGF-beta 1 allele show no gross developmental abnormalities, but about 20 days after birth they succumb to a wasting syndrome accompanied by a multifocal, mixed inflammatory cell response and tissue necrosis, leading to organ failure and death. TGF-beta 1-deficient mice may be valuable models for human immune and inflammatory disorders, including autoimmune diseases, transplant rejection and graft versus host reactions.     

Long-term potentiation of prefrontal cortex in NR1 knockout mice

利用前脑特异性NR1基因敲除小鼠,采用离体脑片场电位技术,研究了NR1亚基在前额叶脑区突触可塑性中的作用.刺激强度—反应( input-output curve)和双脉冲抑制反应(paired pulse depression,PPD)的结果表明,与同窝对照组小鼠相比,NR1基因敲除小鼠前额叶脑区的基本突触传递无明显变化.采用高频刺激(100 Hz,1 000 ms×2,间隔30 s)在小鼠的前额叶脑区诱导长时程增强( long-term potentiation,LTP),与对照组小鼠相比,NR1基因敲除小鼠前额叶脑区的LTP明显受损.以上数据提示,NR1亚基在前额叶脑区LTP的诱导中起着重要的作用.     

装甲车辆模拟射击中身管角度采集装置设计

设计并实现了装甲车辆实装模拟射击训练中通用型身管角度采集装置。该装置是通用型实装模拟射击训练系统的一个测量部件。详细阐述了该装置的实现原理和方法。装置在倾斜角和俯仰角的采集中采用ADXL345三轴加速度计来达到高精度的要求,在方位角采集中采用槽光耦和光栅盘为核心的计数单元进行角度测量。装置对采集到的身管各个角度数据进行了角度解算,最终通过串行接口和LCD等多种形式实现数据传输和显示。     

Impairment of angiogenesis and cell migration by targeted aquaporin-1 gene disruption

Aquaporin-1 (AQP1) is a water channel protein expressed widely in vascular endothelia, where it increases cell membrane water permeability. The role of AQP1 in endothelial cell function is unknown. Here we show remarkably impaired tumour growth in AQP1-null mice after subcutaneous or intracranial tumour cell implantation, with reduced tumour vascularity and extensive necrosis. A new mechanism for the impaired angiogenesis was established from cell culture studies. Although adhesion and proliferation were similar in primary cultures of aortic endothelia from wild-type and from AQP1-null mice, cell migration was greatly impaired in AQP1-deficient cells, with abnormal vessel formation in vitro. Stable transfection of non-endothelial cells with AQP1 or with a structurally different water-selective transporter (AQP4) accelerated cell migration and wound healing in vitro. Motile AQP1-expressing cells had prominent membrane ruffles at the leading edge with polarization of AQP1 protein to lamellipodia, where rapid water fluxes occur. Our findings support a fundamental role of water channels in cell migration, which is central to diverse biological phenomena including angiogenesis, wound healing, tumour spread and organ regeneration.     

宁德核电站1号机组堆芯吊篮梁型振动特性研究

核电站反应堆堆芯吊篮的振动在一定范围内是允许的;但其异常振动可能会导致故障甚至事故的发生。掌握核电站堆芯吊篮振动特性能够对核电站的安全运行提供保障。运用中子噪声分析技术,对宁德核电站1号机组多个燃料循环周期内的堆外中子噪声信号的自功率谱、互功率谱和相干、相位进行了分析,得到了吊篮梁型振动频率和中子噪声信号峰功率均方根值变化趋势。对核电站堆芯吊篮梁型振动特性的研究成果,为堆芯吊篮早期故障诊断奠定了基础。