In vitro study of rat visual cortical plasticity

大鼠视皮质可塑性的体外研究出生前和出生后的理论之间的争论一直是神经科学的中心问题之一。最近的研究表明，大脑皮层的两种基本结构--层组织和柱状组织--分别依赖于基因和学习。我们一直在用体外方法研究负责学习视皮层柱状组织的可塑性，研究大鼠视皮层脑片突触传递的长时程增强(LTP)可塑性。我们发现了两种LTPS。FAST(Fltp)几乎立即出现(5分钟内)刺激白质后，慢LTP(SLTP)逐渐发展(1小时内)。这两种LTP表现出以下不同的特性。首先，Fltp既存在于成年大鼠脑片，也存在于幼年大鼠脑片，而sLTP优先出现在幼年大鼠脑片。第二，NMDA受体(APV)阻断剂阻断Fltp的诱导，电压门控性钙通道阻断剂以及蛋白质和RNA合成阻断剂阻断sLTP的诱导。SLTP在一级和二级膝状皮质突触中表达，而Fltp在第5层和第6层轴突侧支突触中表达。这些结果表明，sLTP是形成柱状结构(如眼优势和定向柱)的发育可塑性的底物，而Fltp是成人可塑性的底物，是学习现象(如适应)的底物。

In vitro study of rat visual cortical plasticityA debate between the prenatal vs. postnatal theory has long been one of the central issues in neuroscience. Recently, it has been shown that two basic structures in the cerebral cortex, the layer and columnar organizations, depend on the gene and learning, respectively. We have been studying the plasticity responsible for learning of the columnar organization in the visual cortex by in vitro approach, investigating the plasticity as long term potentiation (LTP) of synaptic transmission in the rat visual cortical slices. We found two types of LTPs. Fast (fLTP) developed almost immediately (in 5 min.) after theta-burst stimulation of the white matter while slow LTP (sLTP) developed gradually (in one hour). The two LTPs exhibited the following distinct properties. First, the fLTP occurred in the adult as well as young rat slices, while the sLTP preferentially occurred in the young slices. Second, the induction of the fLTP was blocked by blockers of the NMDA receptors (APV) while that of the sLTP was blocked by blockers of the voltage-gated Ca channels as well as those of the protein and RNA syntheses. Third, sLTP expressed in the first and second order geniculo-cortical synapses while fLTP expressed in the axon collateral synapses in layers 5 and 6. These findings indicate that the sLTP is the substrate for the developmental plasticity underlying formation of columnar structures such as the ocular dominance and orientation columns while the fLTP is that for the adult plasticity underlying learning phenomena such as adaptation.