神經新生遍及整個生命過程，目前認為大腦中仍然持續有神經新生的位置，主要在海馬迴與腦室下區。研究首先探討神經新生是否會發生在杏仁核，並且探究其與恐懼記憶維持與遺忘過程之相關性。為了測量新生神經細胞，進行恐懼記憶訓練(聲音與電刺激配對)前兩小時，小鼠皮下施予5-bromo-2'-deoxyuridine (BrdU)，隨後審視其神經新生情形。恐懼記憶訓練組，新生前驅神經細胞與新生神經細胞數目顯著變多，結果顯示聲音與電刺激配對訓練誘發神經新生。為了更加瞭解新生神經細胞與記憶之間的相關性，小鼠投予抗細胞有絲分裂期藥物，例如甲基氧化偶氮甲醇醋酸鹽。甲基氧化偶氮甲醇醋酸鹽降低神經新生與破壞恐懼記憶維持。同樣地，顱內杏仁核區給予阿糖胞苷干擾DNA合成，也可以降低恐懼行為反應。經歷恐懼記憶訓練後，Sonic hedgehog (Shh)，接收器patched1 (Ptc1) 和轉錄因子Gli1蛋白質個別表現自第一天漸增，第七天回復正常值。免疫螢光染色方式更加確認，增加Sonic hedgehog表達細胞數量，來自恐懼記憶學習。逆轉錄病毒載入小髮夾RNA，靜默當細胞處於有絲分裂時期Sonic hedgehog基因，顯示新生神經細胞數目與恐懼行為降低。上述結果得知，恐懼記憶性學習誘發杏仁核區Sonic hedgehog訊息活化，促使神經新生與恐懼記憶維持。研究接著探究杏仁核區神經新生與恐懼記憶遺忘相關性。小鼠經歷十五次聲音與電刺激配對，二十四小時後，小鼠又經歷每天共十五次單獨聲音出現試驗，一共七天的恐懼記憶遺忘訓練。遺忘訓練前兩小時，小鼠皮下施予BrdU，隨後審視神經新生情形。結果顯示，神經新生數目增加在經歷恐懼遺忘訓練組，相對於沒有經歷遺忘組與正常組別。個別投予抗細胞有絲分裂期或干擾DNA合成藥物後，能降低神經新生和阻礙遺忘訓練過程。逆轉錄病毒載入小髮夾RNA，靜默當細胞處於有絲分裂時期Sonic hedgehog基因，顯示降低新生細胞數目與阻礙遺忘訓練過程。相反地，逆轉錄病毒載入Sonic hedgehog cDNA，過度表達當細胞處於有絲分裂時期Sonic hedgehog基因，顯示增加新生神經細胞數目與加速遺忘訓練。上述結果得知，杏仁核區Sonic hedgehog訊息活化與神經新生，參與恐懼記憶遺忘過程。故, Sonic hedgehog訊息活化能促進杏仁核神經新生，並參與恐懼記憶形成與遺忘。

It is known that neurogenesis occurs throughout the life mostly in the subgranular zone (SGZ) of the hippocampus and the subventricular zone (SVZ) of the lateral ventricle. We investigated whether neurogenesis occurred in the amygdala and its function in fear memory formation. Mice were injected intraperitoneally with 5-bromo-2'-deoxyuridine (BrdU) 2 h before receiving 15 tone–footshock pairings. The number of BrdU+/DCX+ and BrdU+/NeuN+ cells was significantly higher in the conditioned mice suggesting that association of tone with footshock induced neurogenesis. To determine the relationship between neurogenesis and memory formation, mice were given cell proliferation inhibitor methylazoxymethanol acetate (MAM). MAM markedly reduced neurogenesis and impaired fear memory formation. Similarly, intra-amygdala infusion of cytosine arabinoside (Ara-C) which interferes with DNA synthesis decreased freezing responses. Sonic hedgehog (Shh), its receptor patched1 (Ptc1) and transcription factor Gli1 protein levels increased at 1 day and returned to baseline at 7 days after fear conditioning. Immunohistochemistry confirmed that Shh+ cells increased after conditioning. Silencing Shh gene expression with small hairpin interfering RNA (shRNA) by means of a retrovirus vector encoding Shh shRNA (Retro-Shh-shRNA) which allowed us to knockdown Shh specifically in the mitotic neurons reduced the number of BrdU+/NeuN+ cells and decreased freezing responses. These results suggest that fear learning induces Shh signaling activation in the amygdala which promotes neurogenesis and long-term memory formation. We next investigated the relationship between neurogenesis in the amygdala and extinction of fear memory. Mice received 15 tone-footshock pairings. Twenty-four hours after training, the mice were given 15 tone-alone trials (extinction training) once per day for 7 days. Two hours before extinction training, the mice were injected intraperitoneally with BrdU. BrdU+/NeuN+ cells were analyzed 52 days after training. A group of mice that received tone-footshock pairings but no extinction training served as controls (FC+No-Ext). The number of BrdU+/NeuN+ cells was significantly higher in the extinction (FC+Ext) than in the FC+No-Ext mice. MAM or Ara-C reduced neurogenesis and retarded extinction. Silencing Sonic hedgehog (Shh) gene with shRNA by means of a retrovirus expression system to knockdown Shh specifically in the mitotic neurons reduced neurogenesis and retarded extinction. By contrast, over-expression of Shh increased neurogenesis and facilitated extinction. These results suggest that amygdala neurogenesis and Shh signaling are involved in the extinction of fear memory. We conclude that activation of Shh signaling plays a critical role in promoting amygdalar neurogenesis, support of LTM formation and facilitating of extinction.

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