Vinogradova O S
Institute of Theoretic and Experimental Biophysics, Russian Academy of Sciences, Pushchino.
Zh Vyssh Nerv Deiat Im I P Pavlova. 2000 Sep-Oct;50(5):743-74.
The new neuroscience data rapidly accumulating by the end of the second millennium calls for radical revision of many long-established and widely accepted postulates. This paper reviews some data leading to new concepts of life and work of neurons. The adult brain contains stem cells which are the source of the precursors for all main types of the brain cells: neurons, astrocytes, and oligodendroglia. These cells can substitute the deteriorating elements in the adult and even old brain. The neurons occur to be highly resistant to lesion of their processes as well to anoxia, and inhibitory neurons are shown to be especially stable in some pathological conditions. Changes in the afferent inputs result in various types of rapid compensatory morphological and functional reorganizations at different levels. Thus, the previous fatalistic view of the nervous system is substituted now for an optimistic one regarding various possibilities of prolongation and restoration of normal functioning of the brain. Simultaneously, our concepts of the neurons changed drastically. An unitary neuron may operate by several neurotransmitting substances; their synaptic influences upon the dendrites may evoke the active propagation of calcium and sodium spikes, their axons may differentially release transmitter substances depending on parameters of excitation. All neuronal functions are helped and controlled by astroglia, which participates in the synthesis of transmitters and protects the neurons from the excitotoxic death. Besides the synaptic interactions between the neurons, there exist other types of communications, such as volume conduction of transmitters after their spillover from the excited synapses and non-synaptic (varicose) zones, as well as exchange of molecules and ions through the gap junctions. A complex picture of interneuronal communications with multiple synaptic, presynaptic, and parasynaptic interactions is further complicated by the intimate participation of neurotrophic substances and "mediators of the immune system"--cytokines in these processes. The mutual regulatory influences between neurotransmitters, neurotrophic, and neuroimmune systems show that in normal conditions all they are working in concert. This increase in number of factors determining the final result of interaction between the neurons contributes new difficulties to the development of theoretical concepts or simulation of brain functions. In this context it is possible to speak about a certain crisis of theoretical neurobiology at present, because multiplicity of fine details obtained by molecular neurobiology and neurogenetics cannot be integrated in a coherent view of the brain functions. Overcoming the present gap between the analytic and synthetic approaches to understanding the brain work will be the main aim for the neurobiologists of the third millennium.
到第二个千年末迅速积累的新神经科学数据，要求对许多长期确立且被广泛接受的假设进行彻底修订。本文回顾了一些导致神经元生命和功能新概念的数据。成人大脑中含有干细胞，这些干细胞是所有主要类型脑细胞（神经元、星形胶质细胞和少突胶质细胞）前体的来源。这些细胞可以替代成体甚至老年大脑中不断退化的成分。神经元被发现对其突起的损伤以及缺氧具有高度抗性，并且在某些病理条件下，抑制性神经元表现得尤其稳定。传入输入的变化会在不同水平导致各种类型的快速代偿性形态和功能重组。因此，以前对神经系统的宿命论观点现在已被关于大脑正常功能延长和恢复的各种可能性的乐观观点所取代。同时，我们对神经元的概念也发生了巨大变化。单个神经元可能通过几种神经递质起作用；它们对树突的突触影响可能引发钙和钠峰电位的主动传播，其轴突可能根据兴奋参数差异释放递质物质。所有神经元功能都受到星形胶质细胞的辅助和控制，星形胶质细胞参与递质的合成并保护神经元免受兴奋毒性死亡。除了神经元之间的突触相互作用外，还存在其他类型的通讯方式，例如递质从兴奋突触溢出后在非突触（曲张）区域的容积传导，以及通过缝隙连接进行分子和离子的交换。神经营养物质和“免疫系统介质”——细胞因子在这些过程中的密切参与，使得具有多种突触、突触前和旁突触相互作用的神经元间通讯的复杂图景更加复杂。神经递质、神经营养和神经免疫系统之间的相互调节影响表明，在正常情况下它们都协同工作。决定神经元间相互作用最终结果的因素数量增加，给理论概念的发展或大脑功能的模拟带来了新的困难。在这种情况下，可以说目前理论神经生物学存在一定的危机，因为分子神经生物学和神经遗传学获得的大量精细细节无法整合为对大脑功能的连贯看法。克服目前在理解大脑工作的分析方法和综合方法之间的差距，将是第三个千年神经生物学家的主要目标。
