The Markey Scholars Conference Proceedings (2004) / Chapter Skim
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6 Electrophysiology of Synapses
6 Electrophysiology of Synapses
Pages 42-49
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From page 42... ...
The strength of the synaptic connection between two hippocampal pyramidal cells is fairly stable over a long period of time. If the input that is producing that synaptic response receives a high-frequency activation, 42
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From page 43... ...
In summary, AMPA receptors are not voltage-dependent, and NMDA receptors are voltage-dependent. The second important difference is that the AMPA receptor, when it carries current across the postsynaptic membrane, carries primarily sodium and potassium currents, but no calcium.
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From page 44... ...
When glutamate is released by a silent synapse there is no response in the resting membrane potential of the cell because the AMPA receptor is not there, and the NMDA receptor will not pass current at the resting potential. You can see a synaptic current at a silent synapse only if you depolarize the postsynaptic cell to unblock the NMDA receptor.
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From page 45... ...
For this particular application we simply picked two cells in the CA-3 region of hippocampus because these make synapses with each other and we recorded from the two cells simultaneously You can put your electrodes down on any two cells, and see if are they connected, and about half the time they are. If they are connected and if you depolarize one of the cells, it causes an action potential, and if it is synaptically connected it will cause a synaptic current to be produced in the postsynaptic cell.
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From page 46... ...
This means that in experiments we could treat a group of synapses as one, which gave us a great experimental advantage. In the hypothetical case where you have a mixture of silent synapses, those with no surface AMPA receptors, and active synapses, those with AMPA receptors in the cell membrane, the synaptic failure rates differ at different membrane potentials.
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From page 47... ...
This occurs by the postsynaptic increase in AMPA sensitivity and both silent and active connections can potentiate. Earlier we thought that only silent synapses could be potentiated and that active synapses already had AMPA receptors.
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From page 48... ...
This leads to the suggestion that a new memory trace may be protected in some way for at least some period of time over half an hour, which, interestingly enough, is sort of the time period over which memory consolidation is thought to occur. We knew that this recently silent state, which was protected from depression, was transitioning probably somewhere else in the model.
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From page 49... ...
Our working model is that active synapses have both NMDA and AMPA receptors, and they can potentiate, where they insert AMPA receptors into the membrane. The depotentiation from that state is now mGluR dependent, even though depression from this state is totally NMDA dependent.
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