Weeks Andrew C W, Ivanco Tammy L, Leboutillier Janelle C, Marrone Diano F, Racine Ronald J, Petit Ted L
Department of Psychology, Nipissing University, North Bay, Ontario, Canada.
Synapse. 2003 Jan;47(1):77-86. doi: 10.1002/syn.10113.
Long-term potentiation (LTP) in the hippocampus has been associated with changes in synaptic morphology. Whether these changes are LTP-dependent or simply a result of electrophysiological stimulation has not yet been fully determined. This study involved an examination of synaptic morphology in the rat dentate gyrus 24 h after electrophysiological stimulation sufficient to induce LTP. In one group, ketamine, a competitive NMDA antagonist, was injected prior to stimulation to block the formation of LTP. Synaptic morphological quantification included estimating the total number of synapses per neuron, determining synaptic curvature and the presence of synaptic perforations, and measuring the maximal PSD profile length of the synapses. The results indicated that most of the changes observed following the induction of LTP (increases in the proportion of concave-shaped synapses, increases in perforated concave synapses, and a decrease in the length of nonperforated concave synapses) are not observed under ketamine blockade, suggesting that they are LTP-specific and not simply the result of tetanic stimulation. Ketamine was associated, however, with several novel structural changes including a decrease in the length of the perforations in the concave perforated synapses, a reduction in the number of convex perforated synapses, and a nonlayer-specific increase in synaptic length compared to controls. Based on previous research, this combination of morphological characteristics is potentially less efficacious, which suggests that synapses that are tetanized but not potentiated, due to pharmacological blockade, appear to undergo opposing, compensatory, or homeostatic changes. These results support the suggestion that synaptic morphology changes are both stimulation- and area-specific, are highly complex, and depend on the specific local physiology.
海马体中的长时程增强（LTP）与突触形态的变化有关。这些变化是依赖于LTP还是仅仅是电生理刺激的结果尚未完全确定。本研究对大鼠齿状回在足以诱导LTP的电生理刺激后24小时的突触形态进行了检查。在一组中，在刺激前注射竞争性NMDA拮抗剂氯胺酮以阻断LTP的形成。突触形态定量包括估计每个神经元的突触总数、确定突触曲率和突触穿孔的存在以及测量突触的最大突触后致密部（PSD）轮廓长度。结果表明，在氯胺酮阻断下未观察到诱导LTP后观察到的大多数变化（凹形突触比例增加、穿孔凹形突触增加以及非穿孔凹形突触长度减少），这表明它们是LTP特异性的，而不仅仅是强直刺激的结果。然而，氯胺酮与几种新的结构变化有关，包括凹形穿孔突触中穿孔长度的减少、凸形穿孔突触数量的减少以及与对照组相比突触长度的非层特异性增加。基于先前的研究，这种形态特征的组合可能效率较低，这表明由于药理学阻断而被强直刺激但未增强的突触似乎经历了相反、补偿或稳态变化。这些结果支持了突触形态变化具有刺激特异性和区域特异性、高度复杂且依赖于特定局部生理学的观点。
