連結核（nucleus reuniens, RE）與嗅緣皮質（perirhinal cortex, PRC）兩腦區和海馬迴（hippocampus, HPC）與內側前額葉皮質（medial prefrontal cortex, mPFC）之間有著直接且雙向的神經投射關係，是海馬迴與內側前額葉皮質之間重要的訊息傳遞中繼站。先前研究指出痕跡恐懼制約（trace fear conditioning）的學習需要海馬迴與內側前額葉皮質的參與，而連結核與嗅緣皮質也皆參與其中，然而我們對於此二腦區各自所扮演的角色還不甚瞭解，因此在本研究中，我們利用藥理學方法來比較在痕跡恐懼制約學習中，大鼠的連結核與嗅緣皮質之間的功能差異。
研究結果顯示，在痕跡恐懼制約的習得階段單獨抑制連結核或嗅緣皮質會部分影響記憶習得，而同時抑制兩腦區時，動物則完全無法習得恐懼記憶。接著我們測試在抑制連結核的狀態下增強嗅緣皮質的膽鹼性神經活性（cholinergic activity），是否能夠挽救抑制連結核所造成的恐懼記憶習得瑕疵；反之，在抑制嗅緣皮質的狀態下，增強連結核的膽鹼性神經活性，是否能夠挽救抑制嗅緣皮質所造成的恐懼記憶習得瑕疵。實驗結果與我們的假設有所不同，無論連結核在恐懼記憶的習得階段是否被抑制，增強嗅緣皮質的膽鹼性神經活性皆會造成動物在習得階段的恐懼行為表現異常，並且完全無法習得恐懼記憶；而當增強連結核的膽鹼性神經活性時，動物在記憶提取階段的恐懼反應出現整體下降的趨勢。我們的研究結果說明了連結核與嗅緣皮質在痕跡恐懼制約的習得階段皆扮演了不同的角色；而當改變嗅緣皮質中的膽鹼性神經活性時，動物的恐懼記憶習得瑕疵與改變連結核的膽鹼性神經活性相比較為嚴重，顯示出膽鹼性神經調控在此二腦區中重要性之差異。

The nucleus reuniens (RE) and the perirhinal cortex (PRC) are two major relay stations that interconnect the hippocampus (HPC) and the medial prefrontal cortex (mPFC). Previous studies have shown that both the RE and the PRC are involved in the acquisition of trace fear conditioning. However, the respective contribution of the two regions is unclear. In this study, we used pharmacological approach to compare their roles. Our data suggested that inactivation of the RE or the PRC during conditioning partially impaired, while inactivation of both areas totally abolished, the encoding of trace fear. We next examined whether the impaired encoding of trace fear under RE inactivation can be rescued with enhanced cholinergic tone in the PRC, and vice versa. Against our hypothesis, regardless of whether the RE was on-line or not, animals failed to encode trace fear when further engaging cholinergic activities in the PRC. Conversely, depending on PRC activation level during conditioning, further recruiting cholinergic activities in the RE led to a down-shift of fear response during retrieval. Our results revealed that the RE and the PRC were necessary for the encoding of trace fear. Moreover, there was differential importance of cholinergic modulation during the process.

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