In vitro study of rat visual cortical plasticity

大鼠视皮层可塑性的体外研究出生前与出生后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，即层组织和柱状组织，分别取决于基因和学习。本研究采用离体方法研究了大鼠视皮层柱状组织在学习过程中的可塑性，探讨了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LTP。快速（fLTP）几乎立即（在5分钟内）发展。在θ-爆发刺激白色物质后，缓慢LTP（sLTP）逐渐发展（1小时内）。两种LTP表现出以下不同的性质。首先，fLTP发生在成年以及年轻的大鼠切片，而sLTP优先发生在年轻的切片。第二，fLTP的诱导被NMDA受体（APV）阻断剂阻断，而sLTP的诱导被电压门控Ca通道阻断剂以及蛋白质和RNA合成的阻断剂阻断。第三，sLTP在第一和第二级膝状皮质突触中表达，而fLTP在第5和第6层的轴突侧支突触中表达。这些结果表明，sLTP是基础的柱状结构，如眼优势和方向柱的形成，而fLTP是成人可塑性的基础学习现象，如适应性的发展可塑性的基板。

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.