於不同層次的神經系統的實驗指出，改變刺激和刺激間的間隔長度會對神經系統產生影響，如學習能力的改變，或是應激性(excitability)，但對於突觸的連結強度是否會產生影響，以及是透過什麼樣的機制來感測到不同的刺激和刺激間的間隔，仍不是十分清楚。本文以果蠅三齡幼蟲的神經-肌肉聯會(neuromuscular junction)作為研究系統，改變burst之間的間隔長度inter-burst interval (IBI)，來探討不同IBI的tetanus對於突觸連結強度所產生的影響。當生理食鹽水中的鈣離子濃度為0.2mM，給予IBI為0和3.25秒的tetanus後，Evoked junctional potential (EJP)的高度受到長時間的抑制；但當IBI的長度為1.25秒(介於0和3.25秒之間時)，EJP的高度反而沒受到抑制。改變tetanus的時間長度或burst的數目，並不會改變具有不同IBI的tetanus對於突觸連結強度所產生的影響。將生理食鹽水中的鈣離子濃度由0.2mM改成0.4mM後，IBI為3.25秒的刺激並不會抑制EJP的高度；相對於3.25秒，IBI為1.25秒的刺激反而會抑制EJP的高度。鈣離子濃度的增加似乎影響了IBI和不同突觸連結強度的形式之間的關係。給予cAMP cascade受到抑制的突變種rut2080不同長度的IBI tetanus，發現當鈣離子濃度為0.2mM時，IBI為3.25秒的抑制情形消失。除了長時間突觸連結強度的變化，不同IBI的刺激對於tetanus中短時間的突觸連結強度也會造成不同的影響。這些結果顯示，tetanus中IBI的長短對於NMJ的突觸連結強度是一個重要的因子，對於長時間或短時間的突觸連結強度變化都會產生影響。這些影響可能是透過鈣離子或是cAMP cascade的分子路徑來傳遞。

Experiments at different levels of neuronal system have shown that the interval between stimuli can affect neuronal system, for example, learning performance or neuronal excitability. However, the effect of different interval between stimuli is not clear in synaptic level. In the present study, we have used the neuromuscular junction (NMJ) of Drosophila third instar larvae and changed the interval between bursts to explore the role of inter-burst interval (IBI) in synaptic plasticity. When calcium concentration in buffer is 0.2mM, the amplitude of evoked junctional potential (EJP ) is suppressed after giving tetanus stimuli with IBI = 0 or 3.25 sec. When IBI is 1.25 sec, between 0 sec and 3.25 sec, the amplitude of EJP is not depressed after tetanus. The effects of different IBI on the synaptic plasticity are the same when the length of tetanus or the number of bursts is changed. Changing the calcium concentration in buffer from 0.2mM to 0.4mM affects the interval tuning at synaptic plasticity. At [Ca2+] = 0.4 mM, tetanus with IBI = 3.25 sec has no depression effect on EJP amplitude, but IBI = 1.25 sec suppresses EJP amplitude after tetanus. We have used rut2080, a mutant with reduced cAMP, to investigate the role of cAMP cascade in IBI tuning synaptic plasticity. At [Ca2+] = 0.2 mM, the suppressed effect on EJP amplitude when giving tetanus with IBI = 3.25 sec disappears. Besides the long term effect of synaptic plasticity, different IBI also affects the synaptic plasticity during tetanus. Thus, these results show that the length of IBI might be an important factor affecting synaptic plasticity at NMJ, and NMJ might discriminate different IBI through Ca2+ and cAMP cascade.

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