SD大鼠初级视皮层第Ⅱ/Ⅲ层兴奋性神经元在发育过程中内部侧向突触联系可塑性长时程增强效应（LTP）的研究

【作者】 金洲；

【导师】 石建；

【作者基本信息】 复旦大学 ， 生物物理学， 2009， 硕士

【摘要】 长期以来,哺乳动物中枢神经系统在发育过程中的可塑性变化一直都是大家非常感兴趣的问题,其中由于视觉经验很容易被控制,同时控制的结果可以在解剖,生理和分子的水平上进行测量,因此初级视皮层一直以来都是经验依赖性可塑性的研究材料和重要模型。LTP(长时程增强)就是神经系统突触联系可塑性的研究方向之一,被认为参与到了神经系统中神经回路整合以及学习和记忆过程的重要机制。在SD大鼠初级视皮层的发育过程中,兴奋性神经元第Ⅱ/Ⅲ层内部侧向突触可塑性变化的精确时间窗口以及这种侧向突触联系可塑性变化对于纵向(第Ⅳ层到第Ⅱ/Ⅲ层投射)突触联系可塑性的影响并未被完全了解。在本研究中,我们采用膜片钳全细胞记录的方法研究了SD大鼠初级视皮层第Ⅱ/Ⅲ层内部侧向突触联系可塑性发育变化的动态过程,揭示了SD大鼠初级视皮层第Ⅱ/Ⅲ层内部侧向突触联系可塑性从强到弱,从有到无的时间窗口,以及此过程中突触后膜上AMPA受体的自发反应变化情况。在了解内部侧向突触联系可塑性的变化情况后,我们采用双侧刺激的方法研究侧向输入对纵向突触发育可塑性的影响,并在这基础上,采用双侧强直刺激的方法研究了睁眼后侧向输入和纵向输入在纵向突触联系上的相互作用。实验结果表明:(1)SD大鼠初级视皮层第Ⅱ/Ⅲ层兴奋性神经元突触AMPA受体自发反应受发育调控。睁眼(P12-P13)后,AMPA受体自发反应频率大幅上升,幅度略有下降;(2)SD大鼠初级视皮层第Ⅱ/Ⅲ层之间的侧向联系的长时程突触可塑性(LTP)的时间窗口为到出生后第12天(未睁眼)为止。眼睁开后神经突触可塑性只呈现短时程增强(STP),而且强度较弱;(3)SD大鼠初级视皮层第Ⅱ/Ⅲ层兴奋性神经元在睁眼前,第Ⅱ/Ⅲ层内部突触联系LTP的表达不影响第Ⅳ层到第Ⅱ/Ⅲ层突触联系LTP的表达:(4)SD大鼠初级视皮层第Ⅱ/Ⅲ层兴奋性神经元睁眼后,水平方向的(第Ⅱ/Ⅲ层之间)强直刺激可诱导第Ⅳ层到第Ⅱ/Ⅲ层之间的突触联系LTP,但是幅度小于垂直方向强直刺激产生的LTP:当同时给予水平和垂直方向的强直刺激,其LTP的幅度为最小。根据我们的研究结果和以往的一些研究成果,我们认为在SD大鼠初级视皮层第Ⅱ/Ⅲ层的内部侧向相互作用起到了如下的作用:(1)通过可塑性时间窗口的关闭完成了兴奋性神经元间侧向突触联系的成熟化;(2)通过与纵向输入的相互作用修饰了来自于视网膜上行传导的信号处理,使之精细化:(3)这种侧向的抑制作用可能是神经网络中竞争机制的基础;可能在功能柱的形成过程中起到重要的调节作用:(4)这种侧向的相互抑制的基础很可能来源于神经突触后AMPA通道的联系强度的可塑性变化更多还原

【Abstract】 The development plasticity of the mammalian central nervous system (CNS) has been an attractive field in neuroscience for a long time. The visual cortex has long been a proving ground and model for the study of experience-dependent plasticity because visual experience can be easily manipulated and the consequences of manipulations can be readily measured at the anatomical, physiological and molecular levels. LTP (long-term potentiation) is one of the questions in the field of synaptic plasticity in nervous system which is thought to be one of the important mechanisms of information storage and neural circuit refinement in the brain. The precise ’time window’ of horizontal synaptic plasticity and the influence of this horizontal synaptic connection in the vertical synaptic plasticity during the development of primary visual cortex in SD rats has not been clearly understood. In our researches, we used whole-cell recording patch clamp to study the changes of the internal horizontal synaptic plasticity in LayerⅡ/Ⅲof the rats’ primary visual cortex and revealed the process of plasticity which is from strong to weak even loss at last which we called ’time windows’ and the changes of AMPA receptors (AMPARs) in the aspects of frequency and amplitude during this process. After that, we used both horizontal and vertical pairing stimulation to study influence of the horizontal inputs to the vertical synaptic plasticity. For further researches, we used both horizontal and vertical LTP stimulation at the same time to study the interaction between horizontal inputs and vertical inputs in the vertical synaptic plasticity.We finally found out that: (1) AMPARs in the LayerⅡ/Ⅲneuron synapses of rats’ primary visual cortex are influenced by the process of development. After eyes opening (Postnatal days 12-13), the frequency of AMPAR-mEPSCs(miniature postsynaptic spontaneous currents) obviously increases, meanwhile the amplification gently decreases. (2) the precious ’time windows’ of horizontal synaptic plasticity in LayerⅡ/Ⅲprimary visual cortex of rats is terminated in P12 before eyes opening. After it, the horizontal synaptic plasticity is short-term potentiation and weaker than before; (3) the generation of LTP in the horizontal synapses will not make a long term influence in the developing process of vertical synaptic connections before eyes opening (P10). (4)After eyes opening, the horizontal tetanic stimulation will make a long term influence in it and the amplification of it is weaker than the influence made by vertical tetanic stimulation; horizontal inputs and vertical inputs will have an inter-inhibited influence in the developing process of vertical synaptic plasticity to some extends.Based on our results and some former results, we think that the internal horizontal interactions in the LayerⅡ/Ⅲneurons of rats’ primary visual cortex play following roles: (1) finished the process of maturation in the horizontal synaptic connection by the closing of the plasticity ’time windows’; (2) finely modified the neuron signals from retina by interaction with the vertical inputs; (3) the horizontal inhibition may be the basis of competition mechanisms in the neuron network and the regulation mechanisms in the process of function columns development; (4) this inter-inhibition may be based on the changes of AMPARs in the neuron post-synapses.更多还原