Regulatory mechanism of synaptic plasticity in the abnormally developed visual cortex

我们用柯林注射液诱导的实验性脑积水研究了大脑皮层的功能重组。我们通过多种成像方法证实脑室增大，皮层变薄，并通过脑室-腹腔分流术维持模型动物良好的状态。利用本征光学成像方法，我们发现这些模型动物在17区和18区几乎以正常的方式形成了定向图。通过在异常薄的视觉皮层中引入微电极，我们成功地记录了单个单元的活动，并发现一些神经元表现出正常的感受野特性。然而，它们大多数是单眼的，这表明这些动物双眼视觉所需的神经回路发育不全。体外切片实验表明，脑积水猫的视皮质神经元在去极化电流的作用下能够产生正常的动作电位。这些细胞的树突结构发育不全。我们利用正电子发射断层扫描进一步研究了脑积水猫视觉皮层的代谢活动。f18标记脱氧葡萄糖PET成像显示，视觉皮层内侧库对示踪剂的摄取活性相对较高，但视觉皮层的一般代谢活性明显较低。这些结果表明，在发育过程中诱导了功能重组，以补偿结构和代谢异常。

We have used experimental hydrocephalus induced by Keolin injection to study the functional reorganization of the cerebral cortex. We confirmed enlargement of cerebral ventricles and thinner cortical layers by several imaging methods and maintained model animals in good conditions by performing cerebral ventricular-peritoneal cavity shunting operation. By using an intrinsic optical imaging method, we found that the orientation maps in areas 17 and 18 were formed almost in normal manner in these model animals. By introducing a microelectrode in the abnormally thinner visual cortex, we succeeded to record single unit activities and found that some neurons showed normal receptive field properties. However, most of them were monocular, indicating the neuronal circuits required for binocular vision were poorly developed in these animals. In vitro slice experiments showed that visuocortical neurons in hydrocephalus cats could generate normal action potentials responding to the depolarizing currents injected into the cells. Their dendritic structures were poorly developed in these cells. We further examined metabolic activity of the visual cortex of hydrocephalus cats by use of positron emission tomography. PET imaging using F18-labelled deoxyglucose showed that medial bank of the visual cortex has relatively higher uptake activity of the tracer, however general metabolic activity in the visual cortex was clearly lower in these animals. These results indicate that the functional reorganization was induced during development to compensate the structural and metabolic abnormality.