School of Biological Sciences, College of Natural Sciences, Seoul National University, Seoul 151-742, Republic of Korea.
Biochem Biophys Res Commun. 2011 Apr 8;407(2):339-42. doi: 10.1016/j.bbrc.2011.03.019. Epub 2011 Mar 6.
The retrieval of consolidated fear memory causes it to be labile or deconsolidated, and the deconsolidated fear memory is reconsolidated over time in a protein synthesis-dependent manner. We have recently developed an ex vivo model where during fear memory deconsolidation and reconsolidation the synaptic state can be monitored at thalamic input synapses onto the lateral amygdala (T-LA synapses), a storage site for auditory fear memory. In this ex vivo model, the deconsolidation and reconsolidation processes of auditory fear memory in the intact brain were prevented following brain slicing; therefore, we could monitor the synaptic state for memory deconsolidation and reconsolidation at the time of brain slicing. However, why the synaptic reconsolidation process stopped after brain slicing in the ex vivo model is not known. One possibility is that brain slicing severs neuromodulatory innervations, which are required for memory reconsolidation, from other brain regions (e.g., noradrenergic innervation). In the present study, we supplemented amygdala slices with exogenous norepinephrine as a substitute for the severed noradrenergic innervations. DHPG (a group I metabotropic glutamate receptor agonist)-induced depotentiation (mGluRI-depotentiation), a marker for consolidated synapses, was observed following norepinephrine application to slices prepared immediately after tone presentation (fear memory retrieval) to rats that had been pre-conditioned to a tone paired with a shock. These results suggest that noradrenergic activation initiates synaptic reconsolidation. In contrast, mGluRI-depotentiation was absent following norepinephrine application to slices that were prepared immediately after the tone presentation (no fear memory retrieval) to rats when a tone and a shock were unpaired, ruling out the possibility that noradrenergic activation somehow facilitates a subsequent synaptic depression induced by DHPG irrespective of synaptic reconsolidation. Furthermore, the restored mGluRI-depotentiation following application of exogenous norepinephrine was dependent on de novo protein synthesis, as is memory reconsolidation. Thus, our findings suggest that T-LA synapses from acute slice preparations can undergo a reconsolidation process, thereby providing an optimal preparation to study a fear memory reconsolidation process in vitro.
巩固的恐惧记忆的检索会导致其不稳定或去巩固，而去巩固的恐惧记忆会随着时间的推移以蛋白质合成依赖的方式重新巩固。我们最近开发了一种体外模型，在该模型中，在恐惧记忆去巩固和重新巩固期间，可以在丘脑输入到侧杏仁核（T-LA 突触）的突触状态进行监测，这是听觉恐惧记忆的存储位点。在这个体外模型中，在大脑切片后，完整大脑中的听觉恐惧记忆的去巩固和重新巩固过程被阻止；因此，我们可以在大脑切片时监测记忆去巩固和重新巩固的突触状态。然而，为什么在体外模型中大脑切片后突触重新巩固过程停止尚不清楚。一种可能性是，大脑切片切断了记忆重新巩固所需的神经调质传入神经，这些传入神经来自其他脑区（例如，去甲肾上腺素能传入神经）。在本研究中，我们用外源性去甲肾上腺素补充杏仁核切片，作为被切断的去甲肾上腺素能传入神经的替代物。在对已预先适应与电击配对的音调的大鼠进行的研究中，DHPG（I 型代谢型谷氨酸受体激动剂）诱导的去敏化（mGluRI 去敏化），作为巩固突触的标志物，在向立即在音调呈现后制备的切片中施加去甲肾上腺素（恐惧记忆检索）后观察到。这些结果表明，去甲肾上腺素的激活启动了突触的重新巩固。相反，当音调与电击未配对时，立即在音调呈现后制备的切片中施加去甲肾上腺素（无恐惧记忆检索）时，mGluRI 去敏化不存在，排除了去甲肾上腺素的激活以某种方式促进随后由 DHPG 诱导的突触抑制的可能性，而与突触重新巩固无关。此外，外源性去甲肾上腺素的应用恢复的 mGluRI 去敏化依赖于从头蛋白质合成，就像记忆重新巩固一样。因此，我们的发现表明，来自急性切片制备的 T-LA 突触可以经历重新巩固过程，从而为体外研究恐惧记忆重新巩固过程提供了最佳的制备方法。
