What role do AMPA receptors play at synapses that exhibit NMDA mediated long-term potentiation?

Question

BlackTom AI · Accepted Answer

AMPA receptors primarily conduct a depolarizing sodium (Na+) current, so they provide the fast excitatory drive that triggers NMDA receptor activation during NMDA-mediated LTP.

1) Relevant knowledge points and concepts
- AMPA and NMDA are ionotropic glutamate receptors located postsynaptically. AMPA receptors mediate fast excitatory postsynaptic currents mainly by allowing Na+ influx (and K+ efflux), producing rapid depolarization. NMDA receptors are voltage- and ligand-gated, are blocked by Mg2+ at resting membrane potentials, and permit Ca2+ entry when the Mg2+ block is relieved. Ca2+ influx through NMDA receptors is the critical trigger for intracellular signaling that induces long-term potentiation (LTP).

2) Step-by-step reasoning process
- Presynaptic terminal releases glutamate into the synaptic cleft.
- Glutamate binds AMPA receptors, which open quickly and allow Na+ to flow into the postsynaptic neuron, producing an excitatory postsynaptic potential (EPSP).
- The EPSP depolarizes the postsynaptic membrane enough to relieve the Mg2+ block from NMDA receptors.
- With Mg2+ relieved and glutamate bound, NMDA receptors open and allow Ca2+ influx.
- The Ca2+ signal activates kinases and molecular pathways that lead to LTP (e.g., insertion of additional AMPA receptors), increasing synaptic strength.

3) Calculations
- No numerical calculations are required; the sequence of ionic events is the key.

4) Why the correct answer is correct
- The chosen option states that AMPA receptors conduct a significant depolarizing sodium current, which is exactly their principal biophysical role at excitatory synapses and essential for the voltage change that unblocks NMDA receptors during LTP induction.

5) Why the other options are incorrect
- "They conduct a significant part of the depolarizing calcium ion current": Ca2+ entry is mainly through NMDA receptors during LTP induction; AMPARs typically are not a major Ca2+ pathway (only some GluA2-lacking AMPARs are Ca2+ permeable, but this is not the general mechanism).
- "After LTP they conduct cation currents that depolarize the post-synaptic neuron": While AMPAR currents are cationic and are increased after LTP, this answer is vague and not as specific as the correct description of Na+ conductance.
- "They are the main mechanism for glutamate reuptake into the presynaptic terminal": Glutamate reuptake is accomplished by transporters (EAATs) on glia and presynaptic terminals, not by AMPA receptors.

6) Conclusion
This explanation confirms the correct answer: They conduct a significant depolarizing sodium current.

What role do AMPA receptors play at synapses that exhibit NMDA mediated long-term potentiation?单项选择题

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What role do AMPA receptors play at synapses that exhibit NMDA mediated long-term potentiation? AMPA 受体在表现出 NMDA 介导的长时程增强作用的突触中发挥什么作用？

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