视网膜杆细胞圆盘膜的结构

眼睛的功能之一是把光刺激转换为神经脉冲信号,这一功能是由视网膜上光感受器细胞完成的。在大部分脊椎动物中,光感受器细胞分为二类:视杆细胞和视锥细胞。从形态学上看,光感受器细胞可以分为内段和外段。视杆细胞的外段呈圆柱形。在电子显微镜视野中,杆细胞外段内部,有一叠为数约从500至2,000个有规则堆积的圆盘。和其他膜一样,圆盘膜也是镶嵌有包括吸收光子的视紫红质分子等蛋白的磷脂     

眼睛的新奥秘

科学家们发现了眼睛所具有的一些非视觉功能 ,例如瞳孔见光收缩和设定生物钟。他们发现 ,视网膜系统除了与视觉相关的杆状和圆锥细胞外 ,还有 1个全新的光感受器—— melanopsin。R.J.Lucas和英国、美国的研究小组发现 ,缺少光感受器 melanopsin的小鼠 ,瞳孔见光时没有正常的收缩反应 ,所以 ,正常的瞳孔收缩反应除了需要杆状和圆锥细胞外 ,还需要melanopsin参与。另外 ,Russell Van Gelder和同事发现 ,缺少感光色素—— cryptochrome的小鼠也没有正常的瞳孔收缩反应。两篇近期的论文详细叙述了这些发现 (《科学》,2 0 0 2年 11月 13日 ) …     

钙离子和光感受器适应

Ｃａ＾２＋并非是视网膜光感受器光电换能过程中的第二信使,但近年的工作表明,光感受器在明适应时,Ｃａ＾２＋内流的降低使光感受器外段中鸟苷酸环化酶活力增加,促进ｃＧＭＰ的形成,与光导致ｃＧＭＰ的水解作用相对抗,这种反馈机制可能的光感受器明适应中起重要作用。     

10眼菌紫质光感受器及其对运动边的检测

铜（或不锈钢）／保护膜／紫膜薄膜／氧化铟锡型菌紫质光电池（有时也叫做光感受器）具有微分光电流特性和方波型光电压特性。用该种光电池仿昆虫复眼的小眼结构构制了１０眼菌紫质光感受器,用其模拟动物神经节细胞的ＯＮ中心感受野并用于运动边的检测     

大熊猫的昼夜活动节律

本文采用无线电遥测、跟踪和直接观察等方法,研究了四川卧龙自然保护区野外5只大熊猫1981-1982年的昼夜活动。大熊猫昼夜有两个活动高峰,最高是18:00时,次高是04:00时;有两个低谷,最低是09:00时,次低是24:00时;年平均昼夜活动率为57-66%。     

四川梅花鹿的昼夜活动节律与时间分配

1987 年2 月至2000 年9 月, 用直接观察法在四川省铁布自然保护区中先后对287 只四川梅花鹿的昼夜活动节律和时间分配进行了2 934 h 的观察。四川梅花鹿的昼夜活动具有明显的活动与休息相间出现的节律, 晨昏和午夜是其活动的高峰期, 白昼活动强度较低以休息反刍为主。不同季节其昼夜活动节律有较大的变化。春、夏、秋、冬4 季每天单位时间的平均活动频率分别为: 55.29 ±32.97 %、46.42 ±37.24 %、48.21 ±35.80 %、47.75±32.21 % , 季节差异不明显( F = 0.32 < F_o.o1 ) 。昼夜年平均每天约有52.07 %的时间在活动, 其中白昼活动仅占5.28 % , 而晨昏和夜晚的活动占46.79 %。影响时间分配比例的因素为: 鹿的年龄、性别、繁殖状态、食物资源、天气状况、人为干扰等。     

鲫鱼松果体的显微和超微结构研究

本文作者发现鲫鱼的松果体与一般硬骨鱼不同,它除由背囊和背囊内褶中松果管所组成的松果体外,还有退化的旁突体和副松果体.背囊是单层柱状纤毛上皮,其腔与第3脑室相通,松果管由光感觉细胞、支持细胞、节细胞、丰富的血管和无髓神经纤维构成.松果体既是光感受器又有内分泌的功能.       

猪眼视紫红质膜液晶态结构特征

光敏色素视紫红质(Rhodopsin)是一种以生色团为辅基的色素蛋白。近年来的研究表明视紫红质分子是在脊椎动物视网膜光感受器的片层膜内或膜上,它在光-电转换机能中起着重要作用。光感受器膜类似于一般生物膜,也处于有序、多变的液晶态。在自我有序的液晶相-片层结构中,分子的长轴基本平行,形成分子层。这种表面可用于简单的有机反应,如异构化、酶的氧化、还原以及脱氢作用等。这些结构对能量的变化也很容易发生反应。因此研究视紫红质在片层膜上的液晶态结构,对进一步探索光感受器功能是有重要意义。     

计算机三维重建华虻复眼性特异小网膜细胞结构

本文在计算机三维重建的基础上讨论了华虻复眼小网膜性特异结构与功能的关系,三维模型展示了中央小网膜细胞和部分外周小网膜细胞的空间构型及相互关系.在生物组织连续切片三维重建的对位技术方面,摸索了一套方法.保证了在Cromemco微机系统上实现对华虻复眼小网膜细胞的三维重建.证实了复眼光感受器性特化区R_7和R_8为并行排列的形式,并与非性特化区的R_7、R_8进行了比较.     

脊椎动物和无脊椎动物的光感受器结构

光感受器是感光细胞一个特化部分。动物通过视觉来感知外界多变的环境,首先由光感受器将光能转变为化学能。对感光器官结构研究,始于上世纪后叶。随着科学技术的高速发展,透射电镜、扫描电镜和冰冻蚀刻复型等新技术的广泛应用,对感光细胞结构的研究,     

Circadian rhythm entrainment in flies and mammals

Circadian rhythms are a fundamental adaptation of living cells to the daily and seasonal fluctuation in light and temperature. Circadian oscillations persist in constant conditions; however, they are also phase-adjusted (entrained) by day-night cycles. It is this entrainability that provides for the proper phasing of the program, to the sequence of external changes that it has evolved to exploit. Synchronization of circadian oscillators with the outside world is achieved because light, temperature, or other external temporal cues, have acute effects on the levels of one or more of the clock's components. The consequences are ripples through the interconnected molecular loops, leading to a stable phase realignment of the endogenous rhythm generator and the external conditions. This review summarized the evolving knowledge of the different types, modes, and molecular processes of entrainment in flies and mammals.     

Circadian photoreception in humans and mice

Circadian rhythms are the endogenous oscillations, occurring with a periodicity of approximately twenty-four hours, in the biochemical and behavioral functions of organisms. In mammals, the phase and period of the rhythm are synchronized to the daily light-dark cycle by light input through the eye. Certain retinal degenerative diseases affecting the photoreceptor cells, both rods and cones, in the outer retina reveal that classical opsins (i.e., rhodopsin and color opsins located in these cells) are essential for vision, but are not required for circadian photoreception. The mammalian cryptochromes and melanopsin (and possibly other opsin family pigments) have been proposed as circadian photoreceptor pigments that exist in the inner retina. Genetic analysis indicates that the cryptochromes, which contain flavin and folate as the light-absorbing cofactors, are the primary circadian photoreceptors. The classical photoreceptors in the outer retina, and melanopsin or other minor opsins in the inner retina, may perform redundant functions in circadian rhythmicity.     

昼夜节律钟调控代谢的研究进展

生理和行为的昼夜节律性调控对健康生活是必需的。越来越多的流行病学和遗传学证据显示昼夜节律的破坏与代谢紊乱性疾病相关联。在分子水平上,昼夜节律受到时钟蛋白组成的转录一翻译负反馈环的调控。时钟蛋白通过以下两种途径调节代谢：首先,时钟蛋白作为转录因子直接调节一些代谢关键步骤的限速酶和代谢相关核受体的表达,其次作为代谢相关核受体的辅调节因子来激活或抑制其转录活性。虽然时钟蛋白对代谢途径的调节导致代谢物水平呈昼夜节律振荡,但是产生的代谢物反过来又可以影响昼夜节律钟基因的表达,进而影响昼夜节律钟。深入研究昼夜节律钟与代谢的交互调节可能为治疗某些代谢紊乱性疾病提供新的治疗方案。     

Development of Circadian Oscillators in Neurosphere Cultures during Adult Neurogenesis

Circadian rhythms are common in many cell types but are reported to be lacking in embryonic stem cells. Recent studies have described possible interactions between the molecular mechanism of circadian clocks and the signaling pathways that regulate stem cell differentiation. Circadian rhythms have not been examined well in neural stem cells and progenitor cells that produce new neurons and glial cells during adult neurogenesis. To evaluate circadian timing abilities of cells undergoing neural differentiation, neurospheres were prepared from the mouse subventricular zone (SVZ), a rich source of adult neural stem cells. Circadian rhythms in mPer1 gene expression were recorded in individual spheres, and cell types were characterized by confocal immunofluorescence microscopy at early and late developmental stages in vitro. Circadian rhythms were observed in neurospheres induced to differentiate into neurons or glia, and rhythms emerged within 3–4 days as differentiation proceeded, suggesting that the neural stem cell state suppresses the functioning of the circadian clock. Evidence was also provided that neural stem progenitor cells derived from the SVZ of adult mice are self-sufficient clock cells capable of producing a circadian rhythm without input from known circadian pacemakers of the organism. Expression of mPer1 occurred in high frequency oscillations before circadian rhythms were detected, which may represent a role for this circadian clock gene in the fast cycling of gene expression responsible for early cell differentiation.     

Environmental Circadian Disruption Worsens Neurologic Impairment and Inhibits Hippocampal Neurogenesis in Adult Rats After Traumatic Brain Injury

Circadian rhythms modulate many physiologic processes and behaviors. Therefore, their disruption causes a variety of potential adverse effects in humans and animals. Circadian disruption induced by constant light exposure has been discovered to produce pathophysiologic consequences after brain injury. However, the underlying mechanisms that lead to more severe impairment and disruption of neurophysiologic processes are not well understood. Here, we evaluated the effect of constant light exposure on the neurobehavioral impairment and survival of neurons in rats after traumatic brain injury (TBI). Sixty adult male Sprague–Dawley rats were subjected to a weight-drop model of TBI and then exposed to either a standard 12-/12-h light/dark cycle or a constant 24-h light/light cycle for 14 days. Our results showed that 14 days of constant light exposure after TBI significantly worsened the sensorimotor and cognitive deficits, which were associated with decreased body weight, impaired water and food intake, increased cortical lesion volume, and decreased neuronal survival. Furthermore, environmental circadian disruption inhibited cell proliferation and newborn cell survival and decreased immature cell production in rats subjected to the TBI model. We conclude that circadian disruption induced by constant light exposure worsens histologic and neurobehavioral impairment and inhibits neurogenesis in adult TBI rats. Our novel findings suggest that light exposure should be decreased and circadian rhythm reestablished in hospitalized TBI patients and that drugs and strategies that maintain circadian rhythm would offer a novel therapeutic option.     

周期节律与肿瘤关系的分子机理

周期节律是由内在时钟系统介导的多重生物过程的周期循环.周期节律系统是由位于大脑的视神经交叉上核的中央时钟系统和位于外周的几乎存在于所有细胞的外周时钟系统组成的.中央时钟与外周时钟都能够对生物体的生理过程进行调控,如激素的分泌、能量代谢、细胞增殖、DNA损伤修复等.而周期节律基因的表达失调,对其下游靶基因包括细胞周期相关基因的表达,以及细胞抗凋亡能力等产生重要的影响.而这一结果会导致细胞增殖加速及基因组不稳定,并可能促进肿瘤的发生.许多实验证据表明,肿瘤是一种节律相关的生理失调,在许多肿瘤中都发现周期节律遭到破坏,如乳腺癌、前列腺癌、子宫内膜癌等.本文将从周期节律对细胞周期进程及对细胞DNA损伤修复的影响来讨论分子水平上细胞的周期节律与肿瘤发生发展的关系.