The research team want to induce long-term potentiation (LTP) in synapses onto AgRP neurons, following Hebbian principles. Which of the following stimulation protocols would be most appropriate

Note: 1 Hz = 1 cycle / second, or 1 stimulus per second.

Question

The research team want to induce long-term potentiation (LTP) in synapses onto AgRP neurons, following Hebbian principles. Which of the following stimulation protocols would be most appropriate

Note: 1 Hz = 1 cycle / second, or 1 stimulus per second.

BlackTom AI · Accepted Answer

Spike-timing-dependent plasticity (STDP) dictates that a presynaptic action potential that reliably precedes a postsynaptic action potential within a narrow time window (typically ~5–20 ms) produces LTP because it produces coincident glutamate release and postsynaptic depolarization that relieves the NMDA receptor Mg2+ block and permits large Ca2+ influx.

1) Relevant knowledge points and concepts
- Hebbian principle: “cells that fire together wire together” — coincident pre- and postsynaptic activity strengthens the synapse.
- NMDA receptor as a coincidence detector: requires glutamate (presynaptic release) and postsynaptic depolarization to relieve Mg2+ block.
- STDP time window: presynaptic-before-postsynaptic spikes within ~5–20 ms → LTP; the reverse order or longer delays → no LTP or LTD.
- Other induction protocols (tetanic high-frequency stimulation, continuous ChR2 activation, low-frequency stimulation) have different outcomes or require particular postsynaptic conditions.

2) Step-by-step reasoning
- To induce Hebbian LTP you must ensure presynaptic glutamate release occurs just before the postsynaptic spike so the NMDA channel is open when glutamate binds.
- If the postsynaptic spike occurs ~5–10 ms after the presynaptic spike, depolarization coincides with receptor activation, allowing Ca2+ influx sufficient for LTP signaling cascades (e.g., CaMKII activation).
- If timing is wrong (post before pre or a long delay), Ca2+ signals are smaller or differently timed, producing no potentiation or producing LTD.

3) Calculations / timing detail
- Example window: presynaptic spike at t = 0 ms, postsynaptic spike at t = +5–10 ms → optimal overlap of glutamate presence and relieved Mg2+ block; outside this, efficacy drops steeply.

4) Why the correct answer is correct
- Paired pre→post stimulation with the postsynaptic spike 5–10 ms after the presynaptic spike directly implements STDP and the Hebbian requirement for coincidence, maximizes NMDA-mediated Ca2+ entry, and reliably induces LTP.

5) Why other options are incorrect
- High-frequency 100 Hz with postsynaptic at resting potential: tetanic presynaptic firing can induce LTP but only if postsynaptic depolarization occurs; at rest NMDA channels remain blocked.
- Continuous ChR2 stimulation for 30 min: prolonged depolarization causes inactivation/adaptation and is not the precise timing-dependent pairing required for Hebbian LTP.
- Low-frequency (1 Hz) for 15 min: this protocol typically induces LTD, not LTP.

6) Conclusion
The paired pre‑ and postsynaptic stimulation with the postsynaptic spike 5–10 ms after the presynaptic spike is the correct Hebbian protocol to induce LTP, matching the provided answer.

The research team want to induce long-term potentiation (LTP) in synapses onto AgRP neurons, following Hebbian principles. Which of the following stimulation protocols would be most appropriate Note: 1 Hz = 1 cycle / second, or 1 stimulus per second.Single choice

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