長期增益現象(LTP)是當突觸前神經纖維受到高頻電刺激後，突觸間興奮性訊息傳遞持續性增強的一種現象。有實驗證據指出，在杏仁體側核高頻電刺激所誘發的LTP (LA-LTP)是恐懼記憶形成的一種細胞模式。此外，先前的研究顯示，在老鼠海馬迴的LTP以及與海馬迴相關的學習與記憶都有性別差異。但是LA-LTP及與杏仁體側核相關的恐懼記憶是否也有性別差異，目前則不十分清楚。因此在本研究中，我們利用胞外電生理紀錄的技術及藥理學的方法，探討在大白鼠腦薄片中，高頻電刺激所誘發的LA-LTP是否有性別上的差異及其機制。我們的結果顯示，高頻電刺激在雌鼠所誘發的LA-LTP較雄鼠為大。此外，雄鼠較小的LA-LTP可以被電生理紀錄五週前的睪丸切除手術所完全反轉。而且，在切除睪丸的雄鼠的腦薄片中給予睪固酮，可抑制LA-LTP，且其抑制作用呈現濃度依賴效應，此結果顯示，睪固酮有參與在雄鼠LA-LTP比較小的現象中。此外，我們發現在切除睪丸的雄鼠腦薄片中，睪固酮係透過活化去磷酸酶來抑制LA-LTP，且此抑制作用不需要依賴新蛋白質的合成。相同地，雌鼠較大的LA-LTP也可以被電生理紀錄五週前的卵巢切除手術所完全反轉。值得注意的是，在切除卵巢的雌鼠腦薄片中給予雌激素，可增強LA-LTP，且其增強作用呈現濃度依賴效應，但是給予助孕酮，則無增強作用。另外，我們發現在切除卵巢的雌鼠腦薄片中，雌激素係透過活化蛋白激酶A來增強LA-LTP，且此增強作用不需要依賴新蛋白質的合成。有趣的是，在切除卵巢的雌鼠腦薄片中，雌激素係透過活化型雌激素受體來增強LA-LTP。綜合以上結果可知，我們第一次發現大白鼠之LA-LTP是有性別上的差異，且睪固酮與雌激素皆有參與在這種性別差異之中。睪固酮係透過活化去磷酸酶來抑制LA-LTP，而雌激素則透過活化β型雌激素受體及蛋白激酶A，來增強LA-LTP，且二者的作用皆不需要依賴新蛋白質的合成。

Long-term potentiation (LTP) is a phenomenon in which brief high-frequency stimulation (HFS) of a synaptic pathway results in long-term enhancement of the efficacy of connections made by that pathway. LTP in the lateral nucleus of amygdala (LA) has been shown to be intimately involved in the cellular changes that underlie fear memory formation. Previous studies have indicated that there are sex differences in hippocampus LTP and hippocampus-dependent learning tasks. However, it is unclear whether sex differences also occur in LA-LTP and amygdala-dependent fear memory. In the present study, we used the extracellular electrophysiological recording technique and pharmacological methods to characterize the sex difference in HFS-induced LTP at cortico-LA synapses in rat slices. Our results revealed that LA-LTP was significantly greater in female rats than in male rats. In addition, the male’s reduced LA-LTP was completely reversed by testectomy (TX) 5 weeks before electrophysiological recordings. Furthermore, bath application of testosterone concentration-dependently suppressed LA-LTP in TX rats, indicating that testosterone was involved in the male’s reduced LA-LTP. Moreover, testosterone suppressed LA-LTP through a calcineurin-dependent and translation-independent mechanism in TX rats. Similarly, the female’s enhanced LA-LTP was completely reversed by ovariectomy (OVX) 5 weeks before recordings. It is noteworthy that bath application of 17β-estradiol but not progesterone concentration-dependently potentiated LA-LTP in OVX rats. Moreover, 17β-estradiol potentiated LA-LTP through a protein kinase A (PKA)-dependent and translation-independent mechanism in OVX rats. Interestingly, 17β-estradiol acts through estrogen receptor β(ERβ) to potentiate LA-LTP in OVX rats. In conclusion, we demonstrate, for the first time, that there is a sex difference in rat LA-LTP and that both testosterone and 17β-estradiol are involved in this sex difference. In addition, testosterone and 17β-estradiol act through calcineurin and ERβ-PKA, respectively, to modulate rat LA-LTP in a translation-independent manner.

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