Fibre type composition of single motor units during synapse elimination in neonatal rat soleus muscle

Skeletal motor neurones innervate the specialized 'types' of fibres comprising most mammalian muscles in a characteristic fashion: each motor neurone forms a 'motor unit' by innervating a set of fibres all of the same type. Because the type expression of adult muscle fibres is plastic and apparently controlled by their innervation, each motor neurone is thought to impose a common type differentiation on all the fibres in its motor unit. However, the situation in developing muscles cannot be this simple. Muscle fibres in neonates receive synaptic input from several motor neurones and achieve the adult, single innervation only after a period of 'synapse elimination. Despite this polyneuronal innervation, differentiated fibre types are present in neonatal muscles. This means either that the motor neurones polyneuronally innervate fibres in a random fashion and type expression is not determined by innervation or that the polyneuronal innervation is ordered in such a way that each fibre could receive unambiguous instructions for type differentiation. We have investigated these possibilities here by determining the fibre type composition of motor units in neonatal rat soleus muscle. We find that even during the time of polyneuronal innervation each motor neurone confines its innervation to largely one of two fibre types present in the muscle. Therefore, some mechanism during early development segregates the synapses of two groups of soleus motor neurones onto two separate populations of soleus muscle fibres.     

The dead-end elimination theorem and its use in protein side-chain positioning

The prediction of a protein's tertiary structure is still a considerable problem because the huge amount of possible conformational space1 makes it computationally difficult. With regard to side-chain modelling, a solution has been attempted by the grouping of side-chain conformations into representative sets of rotamers2??. Nonetheless, an exhaustive combinatorial search is still limited to carefully indentified packing units?? containing a limited number of residues. For larger systems other strategies had to be developed, such as the Monte Carlo Procedure?? and the genetic algorithm and clustering approach?. Here we present a theorem, referred to as the 'dead-end elimination' theorem, which imposes a suitable condition to identify rotamers that cannot be members of the global minimum energy conformation. Application of this theorem effectively controls the computational explosion of the rotamer combinatorial problem, thereby allowing the determination of the global minimum energy conformation of a large collection of side chains.     

Increasing adult hippocampal neurogenesis is sufficient to improve pattern separation

Adult hippocampal neurogenesis is a unique form of neural circuit plasticity that results in the generation of new neurons in the dentate gyrus throughout life. Neurons that arise in adults (adult-born neurons) show heightened synaptic plasticity during their maturation and can account for up to ten per cent of the entire granule cell population. Moreover, levels of adult hippocampal neurogenesis are increased by interventions that are associated with beneficial effects on cognition and mood, such as learning, environmental enrichment, exercise and chronic treatment with antidepressants. Together, these properties of adult neurogenesis indicate that this process could be harnessed to improve hippocampal functions. However, despite a substantial number of studies demonstrating that adult-born neurons are necessary for mediating specific cognitive functions, as well as some of the behavioural effects of antidepressants, it is unknown whether an increase in adult hippocampal neurogenesis is sufficient to improve cognition and mood. Here we show that inducible genetic expansion of the population of adult-born neurons through enhancing their survival improves performance in a specific cognitive task in which two similar contexts need to be distinguished. Mice with increased adult hippocampal neurogenesis show normal object recognition, spatial learning, contextual fear conditioning and extinction learning but are more efficient in differentiating between overlapping contextual representations, which is indicative of enhanced pattern separation. Furthermore, stimulation of adult hippocampal neurogenesis, when combined with an intervention such as voluntary exercise, produces a robust increase in exploratory behaviour. However, increasing adult hippocampal neurogenesis alone does not produce a behavioural response like that induced by anxiolytic agents or antidepressants. Together, our findings suggest that strategies that are designed to increase adult hippocampal neurogenesis specifically, by targeting the cell death of adult-born neurons or by other mechanisms, may have therapeutic potential for reversing impairments in pattern separation and dentate gyrus dysfunction such as those seen during normal ageing.     

Synthesis of fast myosin induced by fast ectopic innervation of rat soleus muscle is restricted to the ectopic endplate region

Skeletal muscle fibres, long multinucleated cells, arise by fusion of mononucleated myoblasts to form a myotube that matures into the adult fibre. The two major types of mature fibre, fast and slow fibres, differ physiologically in their rate of isotonic shortening. At the molecular level these type-specific physiological properties are ascribed to different isoforms of myosin, a major protein involved in shortening. Differentiation of fast and slow fibres seems to be under the control of motoneurones, and mature fibres are innervated by only one motoneurone. When rat soleus muscle (SOL, a slow muscle) is dually innervated with a fast nerve, it acquires some properties of a fast muscle, that is, low sensitivity to caffeine and high glycogen content. We report here that in dually innervated soleus muscle the foreign fast nerve induces synthesis of fast isoforms of myosin, but only in the segment of the muscle fibre that is close to the foreign endplate. The localized influence of the nerve endplates suggest that factors controlling the phenotypic expression of the muscle fibre have a short range of activity.     

贵州省玉屏县2000—2015年土地利用与景观格局变化研究

采用土地利用综合动态度模型、土地利用转移矩阵及景观格局指数对玉屏县2000-2015年土地利用数据进行分析处理.结果表明:整个研究时期内土地利用变化的核心是建设用地、耕地、林地、草地及水域用地.建设用地和水域用地呈现逐年增加的趋势,耕地呈现逐年减少的趋势;土地利用综合动态度呈先缓后快增加的趋势.景观破碎化程度呈现上升发展趋势,景观多样性指数先增加后降低;均匀度指数在研究时段内有波动,总体上有所提高;蔓延度指数和优势度指数呈现下降趋势;耕地、林地、草地及建设用地的分离度、破碎度、分维数指数呈现递增趋势发展.     

岷江上游茂县土地利用格局

以地理信息系统为技术手段,分析了岷江上游茂县近30年的土地利用变化.结果表明,研究区内最主要的土地利用类型是有林地,四个时期面积比例均在55%以上,其面积在逐年减小,且减小的速度也在逐年减小,是其它土地利用面积增加的唯一来源.在面积增加的土地利用类型中,灌木林地面积增加最为明显,且其增加的速度在逐年的减小.而各土地利用类型面积相互间转化主要发生在耕地、草地、有林地、灌木林地、经济林地和居民用地之间.由于各土地利用类型间的相互转化,导致该区的土地利用类型偏离原来的程度在增加,到2000年时偏离程度有所减小,这也说明由于一系列相关政策的实施,使该区生态环境恶化趋势有所改变.     

茵栀黄注射液对新生大鼠胆红素脑损伤的保护作用

目的:探讨茵栀黄注射液对新生大鼠胆红素脑损伤的保护作用.方法:175只7日龄SD大鼠随机分成正常对照组、脑损伤组、治疗组Ⅰ、Ⅱ、Ⅲ,腹腔注射质量分数为120 mg/kg的胆红素溶液诱发新生大鼠脑损伤,治疗组Ⅰ、Ⅱ和Ⅲ新生大鼠建模同时每天分别腹腔注射质量分数分别为513.2、265.5和132.8mg/kg的茵栀黄注射液...     

Selective collateral elimination in early postnatal development restricts cortical distribution of rat pyramidal tract neurones

The pyramidal tract, comprising those axons which pass from the neocortex to the medulla and spinal cord, is among the most thoroughly studied projections of the mammalian cortex. Recent studies using anterograde axon tracing techniques have provided information concerning the time course of the growth of pyramidal tract fibres, yet much remains to be learned about its development. We have now begun to study the distribution of the neurones of origin of the pyramidal tract during the postnatal development of the rat neocortex using the recently introduced retrogradely transported fluorescent marker, True blue. During the first postnatal week, injections of True blue into the pyramidal decussation result inthe labelling of pyramidal tract neurones which are distributed virtually throughout the tangential extent of layer V of the neocortex, whereas after comparable injections during the fourth postnatal week the distribution of such cells is much more restricted and remains restricted into adult life. This developmental restriction is most dramatic in the occipital cortex: during the first postnatal week many pyramidal tract neurones are found throughout the visual cortex while none is seen in this area of the adult. When True blue is injected into the pyramidal decussation during the first postnatal week and the animals are allowed to survive until the fourth postnatal week, the distribution of pyramidal tract neurones is as widespread as in the immediate postnatal period and includes the entire visual cortex. This implies that many of the neurones in the occipital cortex initially send a collateral into the pyramidal tract which is later eliminated, although the neurones themselves persist. These findings, together with similar recent observations on the development of the callosal connections, indicate that the elimination of axon collaterals may be a general feature of the development of cortical projection systems, and that such transitory collaterals may traverse considerable distances.     

槲皮素对大鼠骨骼肌脂质过氧化影响研究

目的研究抗氧化剂槲皮素对大鼠运动能力的影响。方法以跑台训练建立动物模型,测定了大鼠运动力竭时间和肌糖原含量、骨骼肌组织超氧化物歧化酶(SOD)、谷胱甘肽过氧化物酶(GSH-Px)、丙二醛(MDA)含量及血清肌酸激酶(CK)的活性。结果服用槲皮素后大鼠力竭时间明显延长;肌糖原含量升高;力竭即刻骨骼肌组织SOD,GSH-Px活性升高,MDA含量显著降低,血清酶CK活性的上升幅度显著降低。结论槲皮素能通过增加肌糖原含量,减轻骨骼肌自由基损伤来提高大鼠的运动能力,可作为一种运动保健品开发利用。