探討D-cycloserine 促進條件化恐懼消減作用中即始基因zif268之表現

邱貞瑜(Zhen-Yu Qiu)

指導教授 ： 呂國棟博士

國立臺灣師範大學/理學院/生命科學研究所/碩士(2006年)

摘要

條件化恐懼記憶消減作用（extinction of conditioned fear）的神經分子作用機制，是近年來許多神經科學研究者所關心的研究課題，希望能夠藉由釐清其作用機制，以增加對於神經可塑性的瞭解，並且能對於臨床上治療恐懼失調之相關疾病有所助益。
於前人的研究指出，由腹腔或直接於中樞杏仁核投予麩胺酸NMDA型受器致效劑D-cycloserine（DCS），可藉由活化mitogen activated protein kinase（MAPK）訊息傳遞路徑，促進條件化恐懼之消減作用，然而其下游之基因調控機制，迄今尚未完全明瞭。即始基因zif268為可被誘發之轉錄因子（inducible transcription factors）之一，能被多種刺激所活化，其蛋白質產物一旦被轉譯後，會立即進入細胞核內，調節其他基因之表現，造成神經可塑性之改變，近期的研究結果顯示zif268參與了條件化恐懼記憶的形成。
本研究利用恐懼所促進之動物驚跳反應（fear-potentiated startle）行為模式，及投予zif268反意義股之寡去氧核?酸（antisense oligodeoxynucleotide）於杏仁核內，探討DCS所促進之條件化恐懼記憶消減作用是否與即始基因zif268的表現有關。本實驗結果顯示：(1)於條件化恐懼消減作用訓練前30分鐘，經由腹腔注射投予30 mg/ kg之DCS，可以有效促進消減作用的表現。(2)於條件化恐懼消減作用訓練前90分鐘，於杏仁核直接投予zif268 反意義股之寡去氧核?酸，可以有效抑制DCS對消減作用之促進效果。(3)於條件化恐懼消減作用訓練前90分鐘，於杏仁核直接投予zif268 反意義股之寡去氧核?酸，可以有效抑制Zif268蛋白質的表現，而使DCS對消減作用之促進效果降低。
本研究結果初步證實，DCS所促進之條件化恐懼消減作用，極可能是透過zif268之調節機制，啟動更下游之基因表現，造成神經可塑性之改變。期盼本研究能夠對於恐懼的學習與記憶之神經分子機制的研究，及未來對於恐懼失調疾病之治療有所貢獻。

關鍵字

條件化恐懼 ； 消減作用 ； 杏仁核

並列摘要

In recent years, many neuroscience scientists concern about the neural mechanisms of the extinction of conditioned fear. They hope to investigate the mechanisms to know more about the neural plasticity, and can use to treat the clinical anxiety disorders.
Recent results suggest that the amygdala plays a key role in fear extinction, and an important component of extinction is activation of glutamatergic NMDA receptors in amygdala. Scientists used systemic administration and direct amygdalar infusion of D-cycloserine (DCS), one of partial NMDA receptor agonists, into rats can facilitate extinction. And the facilitation is activated by the mitogen activated protein kinase (MAPK) signal transduction pathway. However, the mechanisms of downstream regulation are unknown. zif268 belongs to the category of immediate early genes (IEG), act as a transcription factor, zif268 protein, Zif268, can be activated by many stimulus. When once it is translated, it transports into nucleus immediately, controls expression of other genes, and associates synaptic plasticity. Recent studies suggest that zif268 plays a critical role in formation of conditioned fear memory.
In this study, we used fear-potentiated startle and direct amygdalar infusion of zif268 antisense oligodeoxynucleotide to investigate whether facilitating extinction of fear memory by DCS is related to the expression of zif268. Our results shown that administration of DCS 30 minutes prior to the extinction training can facilitate the expression of extinction. Direct amygdalar infusion of zif268 antisense oligodeoxynucleotide 90 minutes prior to the extinction training can block the expression of extinction facilitated by DCS and also decrease the expression of Zif268 protein.
Our study provide evidence that the facilitation of DCS effect on the extinction of conditioned fear is meditated by zif268. It starts downstream signal transduction pathway and alters synaptic plasticity. We expect that the study will contribute to the development of new treatment for anxiety disorders.

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