- 學位論文
短期睡眠剝奪增進雄性成年大鼠於Morris水迷宮空間學習之能力
Short-term Sleep Deprivation Enhances Spatial Learning in the Morris Water Maze in Male Adult Rats
摘要
許多研究顯示長期的睡眠剝奪會造成雄性成年大鼠海馬迴中齒狀回神經新生遭受到抑制，並損壞海馬迴依賴性的學習能力，然而對於短期的睡眠剝奪所造成的結果並不甚清楚。本研究之主要目的在觀察Long-Evans雄性大鼠進行12小時的短期睡眠剝奪後，對其海馬迴神經新生與空間學習之影響。 本實驗利用觸擾動物使其無法睡眠(觸擾組)，或置放動物於水中的小平台上(小平台組)作為睡眠剝奪之方式，於上午5時至下午5時給予大鼠12小時的睡眠剝奪；而對照組動物則是在鼠籠裡不受任何干擾。於下午1時及3時以腹腔注射方式給予所有大鼠劑量為100 mg/kg的5-bromo-2’-deoxyuridine (BrdU)之處理。睡眠剝奪結束後立刻或經過21天後將動物犧牲，並以免疫組織化學染色分別觀察其海馬迴背側齒狀回神經新生的細胞增生與細胞存活情況。結果發現觸擾組動物於12小時睡眠剝奪後，與小平台組或對照組者相比，其齒狀回中神經前驅細胞的增生有顯著的增加；而小平台組與對照組間彼此則無差異。但觀察睡眠剝奪21天後該腦區細胞存活之情形，發現三組動物之間並無顯著差異。當進行每週一次之12小時睡眠剝奪共四次後，觀察大鼠在Morris水迷宮之空間學習行為的表現，發現在給予每天四次試驗共連續3天的水迷宮訓練期中，隨著天數的增加各組之逃脫潛伏期(大鼠從置入水池到游至水下平台的時間)皆有明顯的縮短，但各組間並無差異，顯示三組動物記憶習得(acquisition)的情形隨著時間而有明顯的進步，並不受睡眠剝奪的影響。於水迷宮訓練結束後的1小時移走平台並進行探索試驗(probe test)，結果發現觸擾組在原置放平台之象限內(水迷宮被虛擬劃分為四個象限)停留的時間較其它二組為久，而小平台組與對照組之間並無差異。於水迷宮行為實驗結束之後將大鼠犧牲並採集血液，以酵素免疫法分析三組動物血清中皮質酮的含量，結果顯示三組間皆無差異。 綜合上述結果，睡眠剝奪可促進觸擾組齒狀回神經前驅細胞的增生，同時其空間記憶學習的能力會因12小時的睡眠剝奪而被增進。根據文獻報告，水迷宮行為實驗能增加6∼10天的新生細胞之存活。故推測本實驗中，雄性成年大鼠新生的神經前軀細胞的數量受到短期睡眠剝奪而明顯增加，並受到睡眠剝奪7日後的水迷宮空間記憶學習的影響，因此增進了新生細胞的存活並開始建立複雜的神經連結網路，進而提升海馬迴依賴性之學習能力，然而此能力的提升與皮質酮無關。
並列摘要
Several studies have shown that sleep deprivation (SD) of relatively long duration impaired hippocampal-dependent learning and neurogenesis in the hippocampal dentate gyrus (DG) of adult male rats. However, effects of the short-term SD on learning and neurogenesis were controversy and still not clear. The aim of the present study was to determine the effects of short-term SD for 12 h on spatial learning in young adult Long-Evans rats, using handling and small platform as models for SD, and leaving animals undisturbed in home cages as controls. During 12 h of SD (5:00 h - 17:00 h), 5-bromo-2’-deoxyuridine (BrdU) was given at a dose of 100 mg/kg to rats at 13:00 h and 15:00 h by intraperitoneal injection, respectively. Then we sacrificed animals immediately or 21 days of SD later, and the immunohistochemistry of BrdU was conducted to investigate cell proliferation (Day 0) and cell survival (Day 21) in the hippocampal DG of adult rats, respectively. Our results showed that handling-treated animals significantly increased cell proliferation in DG on Day 0 when compared to both small platform-treated ones and controls, while no difference in cell proliferation was found between platform-treated group and controls. But SD for 12 h did not have any effect on cell survival between these three groups at 21 days after BrdU injection. Furthermore, spatial learning in Morris water maze (MWM) was tested after 4 times of SD for 12 h at an interval of a week. Following the last MWM test, blood was collected and stored until analyzed by enzyme immunoassay for corticosterone. The escape latencies in MWM (the time taken to reach the platform) in all three groups were significantly decreased during 3 days of acquisition training, but no difference was seen between these groups on the same day, suggesting that the acquisition of memory in MWM training was not affected by SD. The performance of probe test (the time spent in target quadrant) in animals treated with handling was significantly enhanced when compared with control group 1 h after the last training test, On the contrary, there was no difference between small platform-treated rats and those of the control group. Taken together, 12 h of SD did not influence memory acquisition but memory retrieval in MWM task. However, no significant difference in the serum corticosterone concentrations was found between groups after MWM training. In summary, short-term (12 h) sleep deprivation by handling facilitates not only spatial memory but also cell proliferation in the DG. It has been documented that MWM tasks can enhance cell survival of newborn cells which are 6 - 10 days of age. These cells exhibit enhanced long-term potential with increased potential amplitude and decreased induction threshold, and start to extend neural fibers rapidly and thus facilitate synaptic plasticity, which may contribute to the enhancement of spatial tasks. Our results, therefore, indicated that the improvement of hippocampal-dependent learning and memory might be due to the enhancement of survival of 7-day-old newborn cells resulted from MWM tasks in the hippocampal dentate gyrus of adult rats. However, the enhanced spatial learning did not correlate with the serum corticosterone levels.