The neural control of coactivation during fatiguing contractions revisited

In addition to the role of muscle coactivation, a major question in the field is how antagonist activation is controlled to minimize its opposing effect on agonist muscle performance. Muscle fatigue is an interesting condition to analyze the neural adjustments in antagonist muscle activity and to gain more insights into the control mechanisms of coactivation. In that context, previous studies have reported that although the EMG activity of agonists and antagonists increase in parallel, the ratio between EMG activities in the two sets of muscles during a fatiguing submaximal contraction decreased progressively and contributed to a reduction in the time to task failure. In contrast, more recent studies using a novel normalization procedure indicated that the agonist/antagonist ratio remained relatively constant, suggesting that the fatigue-related increase in coactivation does not impede performance. Current knowledge also indicates that peripheral mechanisms cannot by themselves mediate the intensity of antagonist coactivation during fatiguing contractions, implying that supraspinal mechanisms are involved. The unique modulation of the synaptic input from Ia afferents to the antagonist motor neurones during a fatiguing contraction of the agonist muscles further suggests a separate control of the two sets of muscles.     

An outline of functional self-organization in V1: synchrony, STLR and Hebb rules

A model of self-organization of synapses in the striate cortex is described, and its functional implications discussed. Principal assumptions are: (a) covariance of cell firing declines with distance in cortex, (b) covariance of stimulus characteristics declines with distance in the visual field, and (c) metabolic rates are approximately uniform in all small axonal segments. Under these constraints, Hebbian learning implies a maximally stable synaptic configuration corresponding to anatomically and physiologically realistic ‘‘local maps’’, each of macro-columnar size, and each organized as Möbius projections of a “global map” of retinotopic form. Convergence to the maximally stable configuration is facilitated by the spatio-temporal learning rule. A tiling of V1, constructed of approximately mirror-image reflections of each local map by its neighbors, is formed. The model supplements standard concepts of feed-forward visual processing by introducing a new basis for contextual modulation and neural network identifications of visual signals, as perturbation of the synaptic configuration by rapid stimulus transients. On a long time-scale, synaptic development could overwrite the Möbius configuration, while LTP and LTD could mediate synaptic gain on intermediate time-scales.     

Characterizing the functional significance of the neonatal rat vibrissae prior to the onset of whisking

The present series of experiments assessed how information from the whiskers controls and modulates infant rat behavior during early learning and attachment. Passive vibrissal stimulation can elicit behavioral activity in pups throughout the first two postnatal weeks, although orienting to the source of stimulation is evident only after ontogenetic emergence of whisking. In addition, while pups were capable of demonstrating learning in a classical conditioning paradigm pairing vibrissa stimulation with electric shock, no corresponding changes were detected in the anatomy of the barrel cortex as determined by cytochrome oxidase (CO) staining. Finally, the role of whiskers in a more naturalistic setting was determined in postnatal day (PN)3-5 and PN11-12 pups. Our results showed that both nipple attachment and huddling were disrupted in whisker-clipped PN3-5 pups but only marginally altered in PN11-12 pups. Together, these results suggest that the neonatal whisker system is behaviorally functional and relevant for normal mother-infant interactions, though it lacks the sophistication of a mature whisker system that evokes very specific and directed responses.     

不同含湿率及加载条件对人皮质骨纳米压痕测试的影响

目的:探讨不同含湿率及加载条件对人皮质骨纳米压痕测试的影响。方法:采用美国Hysitron纳米压痕仪,设定不同加载模式(高峰载荷分别为300、400、500 nm;加载速度分别为6、8、10 nm/s)对不同含湿率(20‰、30‰、40‰、50‰、60‰)人皮质骨进行弹性模量及硬度测量。结果:在同一加载模式下,不同含湿率标本的测试值随着含湿率增高,弹性模量及硬度值均显著降低(P0.01);三种不同加载模式对含湿率为20‰标本测试值无明显变化;对含湿率60‰标本测试值有显著性影响(P0.02)。结论:纳米压痕仪测试骨微观力学特性时,测试值不仅受标本本身含湿率的影响,当测试条件改变,对湿润标本测试结果也完全不同。当使用纳米压痕技术时,通常采用脱水包埋处理的标本测试出的机械性能,对我们在微观层面认识人体骨在湿润的生理环境下的机械性能是不够全面的。     

原生动物伪红色双轴虫细胞纤毛器微管胞器的直接荧光标记

应用荧光紫杉醇直接荧光标记法显示,原生动物纤毛虫伪红色双轴虫(Diaxonellapseudorubra)细胞纤毛器微管中,口围带基部含小膜托架及与托架相联系的肋壁微管;额腹横棘毛基部含前纵微管束、后纵微管束、横微管束和周围微管束,其微管在不同棘毛基部的定向和发达程度不一;缘棘毛基部含前纵微管束、后纵微管束。细胞形态发生过程中,前仔虫口纤毛器微管独立发生于老口围带内侧,在细胞形态发生末期新纤毛器微管形成时,尚有部分老额棘毛、横棘毛和缘棘毛残存,此后老结构逐渐被吸收。结果表明,伪红色双轴虫的纤毛器基部微管的分化很可能具有种属级的特异性,新纤毛器微管分化过程中老结构可能具有定位和物质贡献作用。     

Divergent effects of peripheral and global neuropeptide Y deletion

Objectives:Neuropeptide Y (NPY) is involved in the coordination of bone mass and adiposity. However, multiple NPY sources exist and their individual contribution to the skeleton and adiposity not known. The objectives of our study were to evaluate the effects of peripheral mesenchymal derived NPY to the skeleton and adiposity and to compare them to the global NPY^KO model.Methods:To study the role of mesenchymal-derived NPY, we crossed conditional NPY (NPY^fl/fl) mice with Prx1cre to generate PrxNPY^KO mice. The bone phenotype was assessed using micro-CT. The skeletal phenotype of PrxNPY^KO mice was subsequently compared to global NPY^KO model. We evaluated body weight, adiposity and functionally assessed the feeding response of NPY neurons to determine whether central NPY signaling was altered by Prx1cre.Results:We identified the increase in cortical parameters in PrxNPY^KO mice with no changes to cancellous bone. This was the opposite phenotype to global NPY^KO mice generated from the same conditional allele. Male NPY^KO mice have increased adiposity, while PrxNPY^KO mice showed no difference, demonstrating that local mesenchymal-derived NPY does not influence adiposity.Conclusion:NPY mediates both positive and negative effects on bone mass via separate regulatory pathways. Deletion of mesenchymal-derived NPY had a positive effect on bone mass.     

腹毛目纤毛虫鬃棘尾虫纤毛器基部微管的荧光标记

腹毛目纤毛虫鬃棘尾虫的纤毛器微管骨架由口围带、波动膜、额腹横尾棘毛、左右缘棘毛和背触毛等纤毛器微管和纤毛器基部附属微管等组成,其中口围带基部含小膜托架、小膜后微管、小膜托架微管及小膜托架间的倒"V"形微管连接;波动膜基部形成微管骨架网;额腹横棘毛和左、右缘棘毛基部含前纵微管束、后纵微管束和横微管束,但不同位置的棘毛基部微管发达程度不一样;背触毛基部以纤毛基体为中心向前、后皮层发出前纵微管和后纵微管,形成背皮层微管网.     

Stability and structural constraints of random brain networks with excitatory and inhibitory neural populations

The stability of brain networks with randomly connected excitatory and inhibitory neural populations is investigated using a simplified physiological model of brain electrical activity. Neural populations are randomly assigned to be excitatory or inhibitory and the stability of a brain network is determined by the spectrum of the network’s matrix of connection strengths. The probability that a network is stable is determined from its spectral density which is numerically determined and is approximated by a spectral distribution recently derived by Rajan and Abbott. The probability that a brain network is stable is maximum when the total connection strength into a population is approximately zero and is shown to depend on the arrangement of the excitatory and inhibitory connections and the parameters of the network. The maximum excitatory and inhibitory input into a structure allowed by stability occurs when the net input equals zero and, in contrast to networks with randomly distributed excitatory and inhibitory connections, substantially increases as the number of connections increases. Networks with the largest excitatory and inhibitory input allowed by stability have multiple marginally stable modes, are highly responsive and adaptable to external stimuli, have the same total input into each structure with minimal variance in the excitatory and inhibitory connection strengths, and have a wide range of flexible, adaptable, and complex behavior.