Synaptic strength at excitatory synapses influences whether a neuron reaches threshold at the axon initial segment following synaptic input.

Which ONE of the following changes would be most likely to increase synaptic strength at an excitatory glutamatergic synapse in the hippocampus?

Question

Synaptic strength at excitatory synapses influences whether a neuron reaches threshold at the axon initial segment following synaptic input.

Which ONE of the following changes would be most likely to increase synaptic strength at an excitatory glutamatergic synapse in the hippocampus?

BlackTom AI · Accepted Answer

Synaptic strength is determined by how much excitatory current the postsynaptic neuron receives for a given presynaptic action potential. Key determinants include presynaptic release probability and amount of transmitter released, the number and sensitivity of postsynaptic AMPA/NMDA receptors, and transmitter clearance/desensitization mechanisms.

1) Relevant knowledge points and concepts
- Quantal model: EPSC (or EPSP) ≈ n × p × q, where n = number of release sites, p = probability of release, q = quantal size (postsynaptic response to one vesicle).  
- At hippocampal glutamatergic synapses, fast excitatory transmission is primarily mediated by AMPA receptors; more glutamate in the cleft increases AMPA receptor occupancy and current.  
- Greater postsynaptic current produces a larger EPSP at the dendrite and a larger depolarization arriving at the axon initial segment, increasing likelihood of reaching spike threshold.

2) Step-by-step reasoning
- Increasing the amount of glutamate released per vesicle (increasing q) or increasing the number of vesicles released (increasing p or effective n) raises the total postsynaptic current: EPSC_new = n × p × q_new > EPSC_old.  
- Larger EPSC → larger EPSP amplitude at the soma/axon initial segment (less attenuation leads to greater depolarization).  
- If that depolarization crosses threshold at the axon initial segment, an action potential is triggered more readily.

3) Calculation/representation
- If initial EPSC = n·p·q and q is increased by 50%, EPSC_new = n·p·(1.5q) = 1.5·EPSC_old, a 50% larger synaptic current and corresponding larger EPSP.

4) Why the correct answer is correct
- The stated change (increase in amount of glutamate released) directly increases quantal size and/or effective release, producing a larger postsynaptic current and stronger synaptic strength, making threshold attainment more likely.

5) Why other options would be incorrect (brief)
- Reductions in postsynaptic AMPA receptors, increased inhibition, enhanced Mg2+ block of NMDA, or mechanisms that reduce release or accelerate clearance would decrease, not increase, synaptic strength. While insertion of more AMPA receptors or increased release probability would also strengthen the synapse, the option explicitly given — increased glutamate release — is the most direct way to increase synaptic strength.

6) Conclusion
The best choice is an increase in the amount of glutamate release from the presynaptic terminal, which matches the provided correct answer.

Synaptic strength at excitatory synapses influences whether a neuron reaches threshold at the axon initial segment following synaptic input. Which ONE of the following changes would be most likely to increase synaptic strength at an excitatory glutamatergic synapse in the hippocampus?单项选择题

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