《自然》杂志两篇文章揭示控制果蝇睡眠大脑区域

　　

生物通报道：美国西北大学的研究人员确定出了果蝇的一个对睡眠至关重要的大脑区域，从而使研究人员得到了有关睡觉目的和它与学习、记忆可能联系的一个非常有趣的推测。这项研究的结果发表在6月8日的Nature杂志上。

由Ravi Allada领导的研究组证明所谓的蘑菇体（mushroom bodies）对果蝇的睡眠调节至关重要。在同期的Nature杂志上，还有一篇由霍华德休斯医学院的Amita Sehgal进行的一项研究利用了与该研究组不同的方法，也获得了相同的结果。

虽然目前还不清楚蘑菇体如何控制睡眠，但是Allada和同事已经证明如果这个区域被化学物质破坏了，那么果蝇就很少会睡觉。

已经知道蘑菇体在学习和基因中起到一定的作用，因此使研究人员自然而然地想到睡觉和学习可能在果蝇的大脑中以我们还不知道的方式联系着。这些发现支持了睡觉可能巩固果蝇白天形成的记忆的观点——这种情况与脊椎动物很相似。

睡着的果蝇与睡眠中的人很相似，两者在被突然叫醒时都会头晕眼花的，而且睡眠不足时都需要补充上才行。文章的作者认为调节睡眠和学习的一个机制可能在进化上具有保守性。因此，研究蘑菇体可能有助于人们了解控制脊椎动物和非脊椎动物睡眠机制。（生物通记者杨遥）

以下附上本期Nature上的这两篇相关文章的摘要

A dynamic role for the mushroom bodies in promoting sleep in Drosophila

Jena L. Pitman¹, Jermaine J. McGill¹, Kevin P. Keegan¹ and Ravi Allada¹

 

The fruitfly, Drosophila melanogaster, exhibits many of the cardinal features of sleep, yet little is known about the neural circuits governing its sleep¹. Here we have performed a screen of GAL4 lines expressing a temperature-sensitive synaptic blocker shibire^ts1 (ref. 2) in a range of discrete neural circuits, and assayed the amount of sleep at different temperatures. We identified three short-sleep lines at the restrictive temperature with shared expression in the mushroom bodies, a neural locus central to learning and memory³. Chemical ablation of the mushroom bodies also resulted in reduced sleep. These studies highlight a central role for the mushroom bodies in sleep regulation.

Modulation of intracortical synaptic potentials by presynaptic somatic membrane potential

Yousheng Shu¹, Andrea Hasenstaub¹, Alvaro Duque¹, Yuguo Yu¹ and David A. McCormick¹

Traditionally, neuronal operations in the cerebral cortex have been viewed as occurring through the interaction of synaptic potentials in the dendrite and soma, followed by the initiation of an action potential, typically in the axon^{1, 2}. Propagation of this action potential to the synaptic terminals is widely believed to be the only form of rapid communication of information between the soma and axonal synapses, and hence to postsynaptic neurons. Here we show that the voltage fluctuations associated with dendrosomatic synaptic activity propagate significant distances along the axon, and that modest changes in the somatic membrane potential of the presynaptic neuron modulate the amplitude and duration of axonal action potentials and, through a Ca²⁺-dependent mechanism, the average amplitude of the postsynaptic potential evoked by these spikes. These results indicate that synaptic activity in the dendrite and soma controls not only the pattern of action potentials generated, but also the amplitude of the synaptic potentials that these action potentials initiate in local cortical circuits, resulting in synaptic transmission that is a mixture of triggered and graded (analogue) signals.