Requirements for LTP induction by pairing in hippocampal CA1 pyramidal cells

Area of Science:

• Neuroscience
• Cellular and Molecular Neuroscience

Background:

• Long-term potentiation (LTP) in the hippocampal CA1 region is crucial for learning and memory.
• LTP induction necessitates presynaptic activity and significant postsynaptic depolarization.
• Standard protocols use low-frequency stimulation paired with prolonged depolarization (1-3 min) and cesium-based internal solutions.

Purpose of the Study:

• To investigate methods for more rapid LTP induction.
• To determine the role of depolarization duration and internal solution composition in LTP induction.

Main Methods:

• Whole-cell recording in the hippocampal CA1 region.
• Pairing high-frequency stimulation (HFS) with short (15s) or long (3min) depolarizing pulses.
• Utilizing both cesium (Cs+)-based and potassium (K+)-based internal solutions.

Main Results:

• HFS paired with short depolarization failed to induce LTP with Cs+ internal solution.
• LTP was successfully induced with Cs+ internal solution when HFS was applied at the end of prolonged depolarization.
• HFS paired with short depolarization successfully induced LTP with K+ internal solution.
• Subsequent standard protocol successfully induced LTP after the failed rapid induction protocol.

Conclusions:

• The requirement for prolonged depolarization for LTP induction is dependent on the use of Cs+ internal solutions.
• Cesium may interfere with N-methyl-D-aspartate (NMDA)-dependent LTP when applied early during depolarization.
• This inhibitory effect appears to dissipate over time, allowing LTP induction with prolonged depolarization.