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標題: | 被動型躲避學習中之性別差異 Sex differences in passive avoidance learning |
作者: | Yi-Ya Fang 方怡雅 |
指導教授: | 蔡元奮(Yuan-Feen Tsai) |
關鍵字: | 被動型躲避學習,性別差異,品系,大鼠,extracellular signal-regulated kinase (ERK),海馬迴,杏仁核, passive avoidance learning,sex differences,strain,rat,extracellular signal-regulated kinase (ERK),hippocampus,amygdala, |
出版年 : | 2010 |
學位: | 碩士 |
摘要: | 第一部分:
被動型躲避學習 (passive avoidance learning) 是將動物自發性的趨暗行為與嫌惡性的電擊刺激配對,而引發該趨暗行為產生抑制性現象的一種學習作業。過去的研究指出在被動型躲避學習作業中,訓練與測試間隔超過15分鐘以上即可以觀察到雄鼠的學習表現顯著優於雌鼠的現象。根據與自發行為、制約學習與生殖相關的研究指出,大鼠的探索行為、躲避型學習與性行為都會隨著動物品系的差異而有所不同。為釐清大鼠品系對被動型躲避學習作業中性別差異現象的影響,我們比較鼠齡為8週的Wistar及Long-Evans兩種品系的大鼠在該學習作業中的行為表現。在被動型躲避學習的訓練中,先讓大鼠學習暗箱和足部電擊的配對關係,並在訓練後30分鐘的測試中以大鼠之步入暗箱時間 (step-through latency) 來評估其學習行為的良莠。研究結果顯示Wistar雄鼠在被動型躲避學習作業中的行為表現明顯較Wistar雌鼠為佳,但Long-Evans雄鼠和雌鼠間則沒有顯著的差異。換言之,我們可以在Wistar品系大鼠被動型躲避學習中觀察到性別差異的現象,卻無法在Long-Evans品系的大鼠中發現。故研究性別差異時所使用之實驗動物品系也將是影響實驗結果的重要因子之一。 第二部分: 雄鼠和雌鼠在與生殖相關的行為模式上存在著顯著的性別差異。然而,在與生殖非相關的行為方面,性別差異的現象則被研究得較少。在自發性反應 (如: 趨暗行為、飲水行為等) 與嫌惡型刺激配對的連結學習中,如在訓練後立即給予測試,雌鼠的自發性反應受到較強的抑制,然而,當訓練與測試的間隔較長時,雄鼠則表現出較強的抑制性自發反應。本研究以鼠齡為8週的Wistar大鼠作為實驗材料,觀察被動型躲避學習 (passive avoidance learning) 中訓練和測試的時距間隔改變,是否導致雄、雌鼠的行為表現有所差異。實驗組的動物在步入暗箱後會接受足部電擊,而控制組的動物在由亮箱步入暗箱後並不會接受足部的電擊。在此學習作業訓練後的立即測試中,雌鼠的學習行為表現顯著較雄鼠為佳。然而,在訓練後30分鐘給予測試,雄鼠的學習表現則顯著優於雌鼠。若訓練和測試的時距間隔延長至120分鐘,則雄、雌鼠之間沒有顯著的差異。Extracellular signal-regulated kinase (ERK) 的活化在神經可塑性與記憶處理的相關過程中扮演著重要的角色,且發現動物在接受被動型躲避學習訓練之後其會產生活化的現象。為釐清雄、雌鼠在被動型躲避學習作業中的行為差異,我們於動物完成測試之後進行斷頭犧牲,以西方點墨法分析背側海馬迴 (dorsal hippocampus)、腹側海馬迴 (ventral hippocampus)、中央杏仁核 (central nucleus of amygdala) 與基側杏仁核 (basolateral nucleus of amygdala) 等腦區中ERK的活性。結果顯示在訓練後立即測試並犧牲的雄鼠腦中,其背側海馬、腹側海馬中ERK的活性並沒有改變,但在中央杏仁核與基側杏仁核則觀察到ERK的活性有顯著提升的現象;而在訓練後立即測試並犧牲的雌鼠上述各腦區中則沒有觀察到ERK活性的改變。若訓練和測試的間隔延長為30分鐘,則雄、雌鼠在上述各腦區之ERK活性皆未觀察到有顯著的變化。訓練後120分鐘測試並犧牲的雄鼠腦中,其基側杏仁核中的ERK活化量有顯著提升的現象,但在雌鼠上述各腦區中則未觀察到ERK活性的變化。 綜合上述的結果,改變訓練與測試的時距間隔可以發現到雄、雌鼠有不同的學習表現。雄鼠在訓練後的立即測試中,其基側杏仁核會產生快速且短暫的ERK活化現象,而該現象並未在雌鼠腦中發現。因此,雄、雌鼠在被動型躲避學習行為上的差異以及ERK表現的不同可能顯示雄、雌鼠在記憶處理過程中有不同的機制。 First part: Passive avoidance learning is a one-trial fear-motivated avoidance task in which the animal learns to refrain from stepping through a door to an apparently safer but previously punished dark compartment. Male rats have been observed to be more efficient than females in a passive avoidance situation once the duration of the interval exceeds 15 min. According to previous studies on spontaneous behavior, reproductive behavior and conditioned learning, it appears that differences in the rat strains may influence exploratory behavior, sexual behavior, and learning behavior. To address this question, passive avoidance tasks were given to rats of two strains, albono (Wistar) and pigmented (Long-Evans) strains. During passive avoidance learning, rats had to learn from the training procedures that paired the dark compartment with a mild footshock. Step-through latencies were measured to infer the animal’s memory for the fearful experience. The passive avoidance behavior of Wistar male rats were superior to that of Wistar female rats, but there was no significant difference in this behavior between the retenion of Long-Evans male and female rats. In conclusion, our data demonstrate that sex differences in passive avoidance learning exist in Wistar rats, but not in Long-Evans rats. Thus, choice of animal strains for studies on sex differences may be an important variable. Second part: Although there is extensive literature demonstrating that male and female rats differ in many behavioral patterns related to reproductive behavior, sex differences in non-reproductive behaviors have been investigated less. Female rats show more response suppression in aversively motivated learning when the effect of presentation of an aversive stimulus upon subsequent responding is measured immediately, whereas males show more suppression in procedures in which the effect of an aversive stimulus is measured after longer intervals. In the present study, we used both male and female Wistar rats aged 8 weeks which have been through passive avoidance learning to examine whether sexual divergence can indeed be attributed to temporal parameters. The step-through latencies were studied using various intervals between footshock and retention interval. During training, male and female rats received a footshock in the dark section of a conditioning chamber while control rats received the same training procedures but without the footshock. Female rats were superior to males in the retention of a step-through type passive avoidance response immediately after training. However, males performed better in the acquisition of a passive avoidance response 30 min after training. Males and females showed no sex differences in behavioral performance when they were tested 120 min after training. In order to examine whether the sex difference in the performance of passive avoidance conditioning is associated with a change in the activation of extracellular signal-regulated kinase (ERK), animals were decapitated immediately after testing, and we used western blot analysis to examine the activation of ERK in the dorsal hippocampus, ventral hippocampus, central nucleus of amygdale (CeA), and basolateral nucleus of amygdala (BLA). Our data demonstrated that phosphorylated ERK levels in the BLA and CeA, but not dorsal hippocampus, or ventral hippocampus, were higher in males than in females, relative to same sex controls, immediately after training. In both males and females, phosphorylation of ERK was not found in any brain regions at 30 min after training. When a shock-retest interval was 120 min, ERK activation in the BLA was observed only in males, but not in females. In summary, sex differences in passive avoidance learning depend on the time intervals between training and retention trial. ERK would be activated in the BLA only in males, immediately after training. Together, these findings suggest that there may be the existence of sexual dimorphism in memory process. |
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