Differing presynaptic contributions to LTP and associative learning in behaving mice.

Area of Science:

• Neuroscience
• Synaptic Plasticity
• Learning and Memory

Background:

• The hippocampal CA3-CA1 synapse models short- and long-term plasticity.
• High-frequency stimulation (HFS) and classical eyeblink conditioning induce synaptic changes.

Purpose of the Study:

• Investigate interactions between short- and long-term plasticity at the CA3-CA1 synapse.
• Determine how paired-pulse facilitation (PPF) is affected by HFS-induced long-term potentiation (LTP) and eyeblink conditioning.

Main Methods:

• Utilized input/output curves and paired-pulse studies to optimize stimulation for PPF and paired-pulse depression (PPD).
• Induced LTP with HFS and classical eyeblink conditioning in behaving mice.
• Measured field excitatory postsynaptic potentials (fEPSPs) during conditioning.

Main Results:

• HFS-induced LTP lasted approximately 10 days and initially depressed basal PPF.
• Recovery of PPF baseline took ~20 days, longer than LTP duration.
• During conditioning, basal PPF decreased steadily, reaching a minimum by the 10th session, opposite to LTP effects.

Conclusions:

• LTP and classical eyeblink conditioning share presynaptic mechanisms but exhibit opposite temporal dynamics.
• PPF and PPD may play a homeostatic role in regulating long-term synaptic plasticity at the CA3-CA1 synapse.