Roberts E B, Meredith M A, Ramoa A S
Department of Anatomy, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298-0709, USA.
J Neurophysiol. 1998 Sep;80(3):1021-32. doi: 10.1152/jn.1998.80.3.1021.
Pioneering work has shown that pharmacological blockade of the N-methyl-D-aspartate (NMDA) receptor channel reduces ocular dominance plasticity. However, the results also show that doses of NMDA receptor antagonists that have an effect on ocular dominance plasticity profoundly reduce sensory responses and disrupt stimulus selectivity of cortical cells. It is, therefore, not possible to determine whether effects of NMDA receptor blockade on visual plasticity result from a specific role of NMDA receptors or from the reduction in sensory response. We have used an alternate approach to examine this question. We performed knockdown experiments using antisense oligodeoxynucleotides (ODNs) complementary to mRNA coding the NR1 subunit of the NMDA receptor. After 5 days of antisense, but not sense, ODN treatment NMDA receptor-mediated synaptic transmission was reduced markedly relative to the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor response, as indicated by whole cell patch-clamp recordings in the cortical slice preparation. This suppression of NMDA receptor-mediated currents was due to a selective reduction in the NR1 protein near the injection site relative to the untreated hemisphere in the same animal, as indicated by immunocytochemistry and Western blotting. In contrast, AMPA receptors were not affected by the antisense ODN treatment indicating specificity of effects. Another major effect of this treatment was to decrease ocular dominance plasticity. Ferrets that were monocularly deprived 1 wk during the antisense ODN treatment had ocular dominance histograms similar to those found in untreated, nondeprived animals. In contrast, ferrets treated with sense ODN and monocularly deprived had ocular dominance histograms resembling those of untreated, monocularly deprived animals. The effects on ocular dominance plasticity did not result from a disruption of sensory responses because maximum responses as well as orientation and direction selectivity of cortical cells were not affected by the treatment. In conclusion, the present results show that antisense techniques can accomplish more selective manipulations of cortical function than is possible with traditional pharmacological agents. Use of this approach also provides unambiguous evidence for a specific role of NMDA receptors in visual plasticity.
开创性研究表明，对N-甲基-D-天冬氨酸（NMDA）受体通道进行药物阻断可降低眼优势可塑性。然而，结果还显示，对眼优势可塑性有影响的NMDA受体拮抗剂剂量会显著降低感觉反应并破坏皮层细胞的刺激选择性。因此，无法确定NMDA受体阻断对视觉可塑性的影响是源于NMDA受体的特定作用还是感觉反应的降低。我们采用了另一种方法来研究这个问题。我们使用与编码NMDA受体NR1亚基的mRNA互补的反义寡脱氧核苷酸（ODN）进行敲低实验。反义ODN处理5天后，相对于α-氨基-3-羟基-5-甲基-4-异恶唑丙酸（AMPA）受体反应，NMDA受体介导的突触传递明显减少，这在皮层切片制备中的全细胞膜片钳记录中得到了体现。免疫细胞化学和蛋白质印迹表明，这种对NMDA受体介导电流的抑制是由于同一动物注射部位附近的NR1蛋白相对于未处理的半球选择性减少所致。相比之下，AMPA受体不受反义ODN处理的影响，表明其作用具有特异性。这种处理的另一个主要作用是降低眼优势可塑性。在反义ODN处理期间单眼剥夺1周的雪貂，其眼优势直方图与未处理的非剥夺动物相似。相比之下，用正义ODN处理并单眼剥夺的雪貂，其眼优势直方图与未处理的单眼剥夺动物相似。对眼优势可塑性的影响并非源于感觉反应的破坏，因为皮层细胞的最大反应以及方向和方向选择性不受该处理的影响。总之，目前的结果表明，与传统药物相比，反义技术可以更有选择性地操纵皮层功能。使用这种方法还为NMDA受体在视觉可塑性中的特定作用提供了明确的证据。
