Transient morphological features of identified ganglion cells in living fetal and neonatal retina

The function and morphology of retinal ganglion cells in the adult mammalian visual system has been well studied, but little is known about how the adult state is achieved. To address this question, the morphological changes that retinal ganglion cells undergo during development were studied. Ganglion cells were first identified by retrograde labeling with rhodamine latex microspheres deposited in retinorecipient targets in fetal and early postnatal cats. The structure of ganglion cells was then revealed by intracellular injection of Lucifer yellow in living retinas removed and maintained in vitro. As early as 2 weeks before birth, a morphologically diverse assortment of ganglion cells is present, some of which resemble the alpha, beta, and gamma classes found in the adult. However, in contrast to the adult, developing ganglion cells exhibit several transient features, including excessive axonal and dendritic branching and exuberant somatic and dendritic spines. These morphological features indicate that there is a transient network of connectivity that could play an important role in the final determination of retinal ganglion cell form and function.     

Visual acuity and contrast sensitivity in patients with cerebral lesions

Spatial contrast sensitivity as a function of spatial frequency was measured in patients with cerebral lesions. In most of these patients visual acuity, as measured by the Snellen chart, was 20/30 or better, yet marked departures from normal contrast sensitivity were found. The greatest loss in contrast sensitivity occurred at high frequencies, but in one patient the loss was greatest in the midfrequency range. This finding lends support to the channel hypothesis of spatial contrast discrimination.     

Dynamic organization of developing Purkinje cells revealed by transgene expression

The cerebellum has many properties that make it a useful model for investigating neural development. Purkinje cells, the major output neurons of the cerebellar cortex, have drawn special attention because of the availability of biochemical markers and mutants that affect their development. The spatial expression of L7, a protein specific for Purkinje cells, and L7 beta Gal, a gene expressed in transgenic mice that was constructed from the L7 promoter and the marker beta-galactosidase, delineated bands of Purkinje cells that increased in number during early postnatal development. Expression of the transgene in adult reeler mutant mice, which show inverted cortical lamination, and in primary culture showed that the initial expression of L7 is intrinsic to Purkinje cells and does not depend on extracellular signals. This may reflect an underlying developmental map in cerebellum.     

Gene flow and population differentiation

There are many possible spatial patterns of selection and gene flow that can produce a given cline structure; the actual geography of natural selection and gene flow must be worked out before an attempt is made to explain a given natural cline in terms of a model. The results of experimental and theoretical models show that it is possible for local differentiation to evolve parapatrically in spite of considerable gene flow if the selection gradients are relatively uniform. Irregularities in environmental gradients increase the sensitivity of clines to the effects of gene flow in proportion to the increase in the differences in gene frequencies between the emigrants and the demes receiving the immigrants. It is not necessary for a sharp spatial environmental change to be present for distinct differentiation to occur. In some cases even a gentle environmental gradient can give rise to marked spatial differentiation along a genetically continuous series of demes; such environmental differences may be below the practical limits of resolution in field studies. Any asymmetry in gene flow does not lead to dedifferentiation if the environmental gradient is smooth; it merely shifts the position of the transition zone between the differentiated areas from that which would be expected if there were no asymmetry. Abrupt geographic differences in gene, genotype, or morph frequencies should not, therefore, be interpreted as evidence for environmental changes in the immediate vicinity of the steepest part of the cline; neither should they be interpreted as evidence for geographic barriers, sharp environmental differences, or sexual isolation among the differentiated groups of populations when there are no other sources of evidence for these phenomena. Gene flow may be unimportant in the differentiation of populations along environmental gradients.     

Steroscopic vision: cortical limitations and a disparity scaling effect

The spatial limitations of stereoscopic vision were studied by using vertical line stimuli containing sinusoidal disparity variations such that different parts of the line appeared at different depths. Stimuli with a finer grain than about 3 cycles per degree did not elicit depth perception, even though the sinusoidal curvature was clearly visible monocularly. At low spatial frequencies of curvature, stereoacuity was limited to the same extent as the monocular sensitivity. The limiting disparity for Panum's fusional region and the upper depth limit are subject to a scaling effect in proportion to stimulus dimensions. The disparity scaling can be characterized by a fixed maximum angular difference between the parts of the stereoscopic half-images.     

Geniculate neural plasticity in kittens after exposure to periodic gratings

Kittens were exposed for 2 hours a day to a periodic vertical grating during the first 10 weeks after birth, and otherwise kept in darkness. The spatial frequency of the grating fell in the range of highest contrast sensitivity of normal cats. After the 10-week exposure period, cortical evoked potentials and lateral geniculate mass responses to alternating gratings showed a reduced amplitude for the spatial frequency of exposure. This reduction was independent of grating orientation. An analysis of orientational sensitivity of cortical units did not show any bias in favor of the vertical orientation.     

HMGCS1基因对猪肌肉生长发育的影响及 miRNA-18a/b对HMGCS1基因的调控

【目的】研究HMGCS1基因对猪骨骼肌生长发育的影响及其靶标的验证。【方法】采用real-time PCR对通城猪不同组织以及背最长肌不同发育时间点的HMGCS1基因的表达变化进行检测。【结果】①HMGCS1基因在成年猪肺组织中的表达量最高;②在背最长肌发育中,该基因分别在胚胎期33 和65 d高表达,出生后20、30、40和60 d低表达;③双荧光素酶试验显示,转染miR-18a/b minics组荧光素酶活性低于对照组。【结论】HMGCS1参与了猪骨骼肌生长发育过程,并受miR-18a/b的调控,是猪的产肉性状的潜在候选基因。     

Force detection of nuclear magnetic resonance

Micromechanical sensing of magnetic force was used to detect nuclear magnetic resonance with exceptional sensitivity and spatial resolution. With a 900 angstrom thick silicon nitride cantilever capable of detecting subfemtonewton forces, a single shot sensitivity of 1.6 x 10(13) protons was achieved for an ammonium nitrate sample mounted on the cantilever. A nearby millimeter-size iron particle produced a 600 tesla per meter magnetic field gradient, resulting in a spatial resolution of 2.6 micrometers in one dimension. These results suggest that magnetic force sensing is a viable approach for enhancing the sensitivity and spatial resolution of nuclear magnetic resonance microimaging.     

Fate mapping analysis reveals that adult microglia derive from primitive macrophages

Microglia are the resident macrophages of the central nervous system and are associated with the pathogenesis of many neurodegenerative and brain inflammatory diseases; however, the origin of adult microglia remains controversial. We show that postnatal hematopoietic progenitors do not significantly contribute to microglia homeostasis in the adult brain. In contrast to many macrophage populations, we show that microglia develop in mice that lack colony stimulating factor-1 (CSF-1) but are absent in CSF-1 receptor-deficient mice. In vivo lineage tracing studies established that adult microglia derive from primitive myeloid progenitors that arise before embryonic day 8. These results identify microglia as an ontogenically distinct population in the mononuclear phagocyte system and have implications for the use of embryonically derived microglial progenitors for the treatment of various brain disorders.     

Induction of cachexia in mice by systemically administered myostatin

Mice and cattle with genetic deficiencies in myostatin exhibit dramatic increases in skeletal muscle mass, suggesting that myostatin normally suppresses muscle growth. Whether this increased muscling results from prenatal or postnatal lack of myostatin activity is unknown. Here we show that myostatin circulates in the blood of adult mice in a latent form that can be activated by acid treatment. Systemic overexpression of myostatin in adult mice was found to induce profound muscle and fat loss analogous to that seen in human cachexia syndromes. These data indicate that myostatin acts systemically in adult animals and may be a useful pharmacologic target in clinical settings such as cachexia, where muscle growth is desired.     

牛精原干细胞研究进展

精原干细胞(spermatogonial stem cells,SSCs)是雄性生殖系干细胞,位于睾丸曲细精管基膜上,既具有自我更新潜能,又具有定向分化潜能,是自然状态下出生后动物体内在整个生命过程中进行自我更新并能将基因传递至子代的惟一成体干细胞。根据国内外最新相关进展,系统评述了牛SSCs的生物学特性、分离纯化、冷冻保存、体外培养、永生细胞系的建立及移植等方面的现状及问题。     

东北地区亚洲飞蝗的生物学特性

采用室内饲养与野外调查相结合的方法对东北地区亚洲飞蝗的生活史及主要的生物学特性进行了研究.结果表明:亚洲飞蝗在东北地区1年发生1代,以卵在土中越冬,越冬蝗卵6月上中旬开始孵化,6月中旬为孵化盛期,蝗蝻发育历期为28～35 d,每个龄期历时5～7d,7月上旬末期开始羽化为成虫,7月中旬为羽化盛期,成虫羽化后约7d雌雄两性开始交尾,7月下旬为交尾盛期,交尾约14 d后雌性开始产卵,产卵一直延续到9月末.生态环境条件对亚洲飞蝗的取食、蜕皮、羽化、交尾、产卵等生长发育及繁殖活动具有重要影响.     

精原干细胞的体外增殖与分化

最近,由于干细胞研究普遍取得的令人鼓舞的进展以及干细胞分离、培养、移植等新技术方法的出现和发展,出生后雄性个体的生殖系干细胞———精原干细胞(spermatogonialstemcell,SSC)已成为一个愈加引人瞩目的课题。SSC位于睾丸曲细精管基膜上,既具有自增殖(self-renewal)潜能和定向分化潜能,又是自然状态下出生后个体内在整个生命期间能够进行自增殖并能将基因传递至子代的惟一成体干细胞。了解干细胞增殖与分化的调节机制,获得足够数量的种子细胞一直是所有干细胞研究共同面临的迫切问题之一。近年来,借助于SSCs移植技术这一功能性检测方法,国内外学者就SSCs体外培养的条件进行了深入探讨,取得了可喜进展。结合自己的前期工作,参考相关最新进展,就影响哺乳类SSCs体外存活、增殖、分化的因素及未来需要解决的问题进行了评述。     

精原干细胞的体外增殖与分化

最近，由于干细胞研究普遍取得的令人鼓舞的进展以及干细胞分离、培养、移植等新技术方法的出现和发展，出生后雄性个体的生殖系干细胞——精原干细胞(spermatogonial stem cell, SSC)已成为一个愈加引人瞩目的课题。SSC位于睾丸曲细精管基膜上，既具有自增殖(self-renewal)潜能和定向分化潜能，又是自然状态下出生后个体内在整个生命期间能够进行自增殖并能将基因传递至子代的惟一成体干细胞。了解干细胞增殖与分化的调节机制，获得足够数量的种子细胞一直是所有干细胞研究共同面临的迫切问题之一。近年来，借助于SSCs移植技术这一功能性检测方法，国内外学者就SSCs体外培养的条件进行了深入探讨，取得了可喜进展。结合自己的前期工作，参考相关最新进展，就影响哺乳类SSCs体外存活、增殖、分化的因素及未来需要解决的问题进行了评述。     

妊娠后期胎儿宫内生长受限对出生后羔羊内脏器官的影响

【目的】研究妊娠后期胎儿宫内生长受限对出生后羔羊内脏器官的影响。【方法】选择健康的蒙古绵    羊45只（经同期发情且同期受孕）,妊娠（90±1） d分为自由采食组（CG）、0.33 MJ ME•kgw-0.75•d-1（RG1）以及0.175 MJ ME•kgw-0.75•d-1（RG2）3个营养水平处理组,进行不同营养水平的限饲饲养。各组分别于羔羊初生及28周龄时选择4只屠宰,取出内脏。【结果】妊娠后期不同营养水平限饲母羊,严重限制了RG1（P＜0.05）、RG2（P＜0.01）组羔羊的平均初生体重：①初生时,RG1组羔羊仅肺脏重和肺脏组织总DNA含量显著低于CG组（P＜0.05）,脾脏重及脾脏组织总DNA含量极显著低于CG组（P＜0.01）;而 RG2组羔羊肺脏和脾脏均显著低于CG组（P＜0.01）,心脏、肝脏、肾脏、总胃及小肠重均显著低于CG组（P＜0.05）;其中,心脏和肾脏总DNA含量、肺脏总DNA含量和蛋白与DNA含量比、肝脏组织蛋白和DNA含量比均显著低于CG组（P＜0.05）。②28周龄时,RG1组胎儿期生长受限的肺脏、脾脏重及其总DNA含量与对照组差异不显著（P＞0.05）;除心脏外,RG2组胎儿期生长受限的肝脏、肺脏及脾脏重出生后经过28周的生长与CG组差异不显著（P＞0.05）;RG2组胎儿期降低的肾脏、脾脏细胞总DNA含量,肝脏细胞蛋白和DNA比,在试验结束羔羊28周龄时与CG组差异不显著（P＞0.05）,并且肺脏细胞蛋白和DNA比显著高于CG组（P＜0.05）,而心脏和肺脏组织总DNA含量仍显著低于CG组（P＜0.05）。【结论】妊娠后期胎儿宫内生长受限通过对其胎儿内脏器官细胞增殖与增肥不同程度的影响而改变了出生后羔羊内脏器官的生长发育轨迹。     

甘草萤叶甲空间分布型初步研究

对甘草萤叶甲成虫和幼虫的空间分布型进行了测定,结果表明,成虫符合核心分布和负二项分布,幼虫符合负二项分布;聚集度指标检验成虫、幼虫均为聚集分布。并分析拟合了成虫和幼虫在大田中的理论抽样数学模型。     

Dependence of olfactory bulb neurogenesis on prokineticin 2 signaling

Neurogenesis persists in the olfactory bulb (OB) of the adult mammalian brain. New interneurons are continually added to the OB from the subventricular zone (SVZ) via the rostral migratory stream (RMS). Here we show that secreted prokineticin 2 (PK2) functions as a chemoattractant for SVZ-derived neuronal progenitors. Within the OB, PK2 may also act as a detachment signal for chain-migrating progenitors arriving from the RMS. PK2 deficiency in mice leads to a marked reduction in OB size, loss of normal OB architecture, and the accumulation of neuronal progenitors in the RMS. These findings define an essential role for G protein-coupled PK2 signaling in postnatal and adult OB neurogenesis.     

Adult neural function requires MeCP2

Rett syndrome (RTT) is a postnatal neurological disorder caused by mutations in MECP2, encoding the epigenetic regulator methyl-CpG-binding protein 2 (MeCP2). The onset of RTT symptoms during early life together with findings suggesting neurodevelopmental abnormalities in RTT and mouse models of RTT raised the question of whether maintaining MeCP2 function exclusively during early life might protect against disease. We show by using an inducible model of RTT that deletion of Mecp2 in adult mice recapitulates the germline knock-out phenotype, underscoring the ongoing role of MeCP2 in adult neurological function. Moreover, unlike the effects of other epigenetic instructions programmed during early life, the effects of early MeCP2 function are lost soon after its deletion. These findings suggest that therapies for RTT must be maintained throughout life.     

长白山针阔混交林乔木幼苗组成与空间分布

目的了解长白山地区针阔混交林森林群落中乔木树种天然更新幼苗的组成及空间分布情况,为进一步科学经营奠定理论基础。方法以长白山光明林场针阔混交林固定样地为研究平台,通过对连续1 hm2面积内乔木幼苗和大树进行定位调查,分析了该森林群落中乔木幼苗的物种组成;运用点格局分析法,对样地内典型阔叶乔木(水曲柳、紫椴)和针叶乔木(红松、臭冷杉)幼苗的空间分布及幼苗与大树空间分布之间的关系进行研究。结果(1) 样地内乔木幼苗树种组成丰富,共调查到幼苗10 865株,隶属于17个乔木树种,且幼苗全部来自样地内大树树种,未发现样地外其他树种的幼苗;(2)从幼苗的空间分布格局来看,在较小的研究尺度上,水曲柳、紫椴、红松和臭冷杉的幼苗均呈现聚集性空间分布;(3)从幼苗与大树空间分布的关系来看,在一定的研究尺度范围内,水曲柳、紫椴幼苗与其大树表现出正相关关系,而红松、臭冷杉幼苗与其大树则表现为负相关关系。结论长白山针阔混交林中主要阔叶乔木和针叶乔木的幼苗在较小尺度上多表现为聚集分布,主要阔叶乔木幼苗与大树在空间上呈正相关,主要针叶乔木幼苗与大树在空间上呈负相关。