探利用大白鼠模式探討新生期投予 Dexamethasone 對杏仁核中麩胺酸突觸傳遞的影響

Abstract

Dexamethasone（DEX）是一種人工合成的糖皮質激素，目前廣泛的作為消炎藥劑，及用於治療早產兒的呼吸窘迫症。前人的研究結果顯示，新生時期DEX的投藥，會影響海馬迴的功能，導致青少年期的記憶障礙。但是否會對杏仁核之功能造成影響？及其詳細機制，則仍有待進一步探討。因此，本研究將探討新生時期的DEX投藥，對青春期大鼠杏仁核功能的可能影響。對出生後第一至三天的Wistar大鼠以皮下注射方式，投予遞減劑量之DEX (0.5 mg/kg, 0.3 mg/kg和0.1mg/kg)。於6週齡時，以電生理紀錄來評估杏仁核的功能。結果顯示，DEX處理過的大鼠於出生第三天至六週齡時的體重有顯著降低。新生期經DEX處理的大鼠，不僅損害杏仁核處之長效增益（LTP）的反應，也增強了在急性壓力曝露後的類憂鬱行為。而給予NMDA受體促進劑D-cycloserine後的這些初步結果顯示，新生時期的DEX投藥，會對大鼠的杏仁核功能產生長期的影響，其機轉可能與影響杏仁核中麩胺酸的傳遞有關。本研究想闡明對新生時期給予DEX，對大鼠青春期杏仁核中麩胺酸神經傳遞影響的機制。為了證實這一目標，以DCS進行實驗發現可以改善新生期投予DEX的大鼠LTP誘發障礙的現象。此外，使用西方墨漬法，發現杏仁核細胞中麩胺酸NMDA受體的表現量並無顯著差異，但是新生期投予DEX的大鼠杏仁核細胞中NKCC1受體的表現量顯著低於 saline組。Dexamethasone (DEX) is a synthetic glucocorticoid and has been widely used as an anti-inflammatory agent and also used to treat respiratory distress syndrome in preterm infants. Although numerous reports indicated that neonatal DEX exposure may altered neural plasticity in hippocampus leading to memory impairment, the possible long-term adverse effect of neonatal DEX treatment on amygdale have not yet been examine properly. Therefore, we completed a series of pilot experiments to investigate the possible effect of neonatal DEX treatment on amygdale function in adult rats. In brief, Wistar rats were subjected for subcutaneous injection with tapering dose of DEX (0.5 mg/kg, 0.3 mg/kg and 0.1mg/kg) from postnatal day 1 to 3, PN1~PN3. Electrophysiological recording and forced swimming test were employed to evaluate the amygdale function at the age of 6 weeks. Results showed that DEX-treated rats exhibited a significant reduction in somatic weights during adolescence, but did not affect in adult stage. Neonatal DEX treatment not only impaired long-term potentiation (LTP) response in amygdale but also enhance the depression-like behavior after acute stress exposure. Our results also found that superfusion partially with either NMDA agonist D-cycloserine could restore the formation of LTP in amygdala. These results suggested that neonatal DEX treatment has long-term adverse effect on amygdale function and probably via receptor level mechanism especially a glutamatergic transmission might be involved. The present study is aimed to elucidate the detail mechanism of neonatal DEX treatment effects on the amygdaloid glutamatergic neurotransmission. To achieve this goal, an antagonistic design will be proceed to verify our preliminary results. In addition, western blotting was applied to evaluate the expression level and cellular distribution of glutamate NMDA receptor within amygdale after neonatal DEX treatment. No significant difference on the expression of amygdaloid NMDA receptors among groups had been found.