| Summary: | 碩士 === 國立清華大學 === 分子醫學研究所 === 95 === 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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