Postsynaptic NMDA receptor-mediated calcium accumulation in hippocampal CA1 pyramidal cell dendrites

Area of Science:

• Neuroscience
• Cellular Biology
• Synaptic Plasticity

Background:

• Intracellular calcium acts as a second messenger for long-term potentiation (LTP) induction in the CA1 hippocampus.
• N-methyl-D-aspartate (NMDA) receptor antagonists like AP5 block LTP, and their magnesium block influences calcium permeability, suggesting a model for LTP induction.

Purpose of the Study:

• To investigate the spatial and temporal dynamics of intracellular calcium changes during LTP induction in CA1 pyramidal cells.
• To test the hypothesis that NMDA receptor-mediated calcium influx is the biophysical basis for LTP induction.

Main Methods:

• Microfluorometric measurements were performed on individual CA1 pyramidal cells.
• Cells were subjected to high-frequency stimulus trains known to induce LTP.
• The effect of the NMDA receptor antagonist AP5 on calcium transients was assessed.

Main Results:

• High-frequency stimulation induced a widespread postsynaptic calcium accumulation.
• A novel, transient calcium component was observed, localized to dendritic areas near activated afferents.
• This localized calcium transient was blocked by the NMDA receptor antagonist AP5.

Conclusions:

• The findings directly confirm the predicted calcium rise through NMDA receptor-coupled ion channels during LTP induction.
• This localized, transient calcium influx is a critical biophysical event underlying LTP in the CA1 hippocampus.
• The results support NMDA receptor models of synaptic plasticity and LTP induction.