伽瑪羥基丁酸對小鼠海馬回切片突觸塑性之影響

Abstract

Gamma-Hydroxybutyrate acid(GHB)是一種結構上與GABA相似的物質。因為GHB可以誘導睡眠，美國食品藥物管理局於2002年核可用於治療嗜睡症，除此之外，GHB也被建議用來治療戒斷症候群的治療。雖然GHB有其臨床用途，但是GHB目前常被濫用為約會強暴藥物。因為GHB的濫用趨勢，在美國列為第一級管制藥品，而在台灣則列管為第二級管制藥品。濫用GHB會導致依賴性以及數種中樞方面的毒理反應。雖然許多GHB濫用報告指出GHB會引起失憶，但機轉上不明確。本篇論文將討論GHB在小鼠海馬回Schaffer collateral–CA1突觸的基礎神經傳遞與神經突觸塑性。利用胞外紀錄評估GHB對小鼠基礎突觸傳導與突觸塑性影響。 在基礎突觸傳遞方面，我們使用兩群不同週齡老鼠，6-8與12-14週，使用0.05Hz的基礎刺激引發fEPSP用以評估GHB對基礎突觸傳遞影響。在兩群老鼠中，低濃度GHB(0.3~1 micro molar)刺激基礎突觸傳導增加，最高濃度GHB(10 micro molar)抑制突觸傳遞。在中間濃度GHB (3 micro molar)出現了雙向調控的趨勢，有增加也有抑制，但是只有在12-14周大的老鼠呈現有意義的增加，抑制的部份則不具統計意義。此外，10 micro molar的GHB受體拮抗劑(NCS-382)出現對抗GHB的傾向且零星地出現NCS-382加強10 micro molar GHB的抑制作用，但由於樣本數目不足難以判定NCS-382的拮抗效果。 在突觸傳導方面，使用6-8週大老鼠評估10 micro molar GHB對突觸塑性的影響。長期增益效應(LTP)引發是由三次相隔15秒的theta波刺激，每次theta波刺激由十個相隔200ms的100Hz波串；增強去增益效應(depotentiation)與長期抑制效應(LTD)由15分鐘的1Hz刺激引發。 10 micro molar GHB對LTP與強直性後增效應(Post-Tetanic Potentiation , PTP)有負向的影響，但這樣的影響不達統計意義。另外一方面，10 micro molar GHB增強depotentiation卻不影響LTD。NCS-382雖有表現出對抗GHB的趨勢，但可能因為樣本數而未達統計意義。 本實驗結論 (1)GHB的確會影響海馬回Schaffer collateral-CA1基礎神經傳導，也會增強depotentiation影響突觸塑性 ；(2)GHB在突觸傳導的作用是雙向，在GHB低濃度(0.3,1

Gamma-Hydroxybutyrate acid (GHB) is a compound structurally similar to the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). As GHB has the ability to induce sleep in humans, it was approved in 2002 by the U.S Food and Drug Administration (FDA) to treat narcolepsy. Previous publications have used this drug in alcohol addiction studies since GHB is believed to relieve withdrawal symptoms. Despite this beneficial application of GHB, it is an abused club drug that is often used in date rape cases. Due to the considerable abusive potential of GHB, it is classified as a Schedule I controlled substance in the United States, and is a Schedule II controlled substance in Taiwan. Long term use of GHB can lead to dependence, while multiple studies have reported its toxic effects in central nervous system. Although there is speculation that GHB causes amnesia, the underlying cellular mechanism(s) remain unclear. Therefore, this study investigates the effect of GHB on basal synaptic transmission and synaptic plasticity of field excitatory post synaptic potentials (fEPSP) at the Schaffer collateral–CA1 synapse of mouse brain hippocampus slices using an extracellular recording technique. In the basal synaptic transmission study, we used mice from two different age groups to evaluate the effect of GHB on fEPSP amplitudes evoked by a basal stimulation of 0.05Hz. In both groups, the lowest (0.3~1 micro molar) and highest (10 micro molar) GHB concentrations caused an increase and an obvious strong decrease of fEPSP amplitudes, respectively. At moderate concentrations (3 micro molar), there seemed to be a bi-directional effect on the fEPSP amplitudes; the increased effect was statistically significant while the decreased effect was not. In addition, 10 micro molar of the GHB receptor antagonist NCS-382 seemed to antagonize the effect of GHB, yet this could not be confirmed statistically due to an insufficient sample size. Interestingly, NCS-382 augmented the inhibitory effect of GHB in four slices. GHB (10 micro molar) was applied on six to eight week old murine hippocampus slices to evaluate synaptic plasticity at the Schaffer collateral–CA1 synapse. Long term depotentiation (LTP) was accomplished by using stimuli of three trains (with a 15 second interval) of 10 theta burst (100Hz for 0.04Hz); long term depression (LTD) and depotentiation were induced with a 1Hz stimulus for 15 minutes. Application of GHB (10 micro molar) had a negative effect on LTP and post titanic potentiation (PTP) with little significance; whereas there was a notably enhanced depotentiation but LTD was not affected. NCS-382 (10