Synaptic plasticity at the endbulb of Held
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Synaptic plasticity is the activity dependent change in synaptic transmission. Short-term plasticity (STP) is a form of synaptic plasticity that affects the synaptic strength for a very short time period (few milliseconds to second) and is found at all synapses. However the functional role of STP is not well-understood. Using voltage-clamp and current-clamp experiments, I studied the mechanism and functional importance of different forms of STP at a mammalian synapse called the endbulb of Held. This synapse plays an important role in the auditory pathway by relaying auditory information from the auditory nerve to higher auditory centers. I found that the presynaptic protein Complexin I is necessary to maintain the initial probability of neurotransmitter release at the endbulb, which in turn is required for the fidelity of synaptic transmission at this synapse. I also found that postsynaptic receptor desensitization is present even in the mature form of the endbulb and it decreases the probability of action potential firing during a long period of activity. Finally, I found gamma-aminobutyric acid (GABA)-mediated neuromodulation inhibits the relay property of this synapse and turns it into a coincidence detector for multiple auditory nerve fiber activity. Thus different forms of STP and neuromodulation dependent plasticities are present at the endbulb and they play important roles for maintaining the functional properties of this synapse.