Spine Ca2+ signaling in spike-timing-dependent plasticity.

Area of Science:

• Neuroscience
• Cellular Neuroscience
• Synaptic Plasticity

Background:

• Calcium ions (Ca2+) act as crucial second messengers in modifying synaptic efficacy.
• Understanding the precise role of postsynaptic Ca2+ in synaptic plasticity is essential for comprehending learning and memory mechanisms.

Purpose of the Study:

• To investigate if postsynaptic Ca2+ ([Ca2+]i) rise alone is sufficient to induce long-term potentiation (LTP) and long-term depression (LTD) in layer 2/3 pyramidal neurons.
• To elucidate the signaling pathways and Ca2+ sensors involved in spike-timing-dependent synaptic plasticity.

Main Methods:

• Measuring volume-averaged [Ca2+]i transients in dendritic spines during spike-timing-dependent plasticity induction protocols.
• Utilizing NMDA receptor activation and blocking metabotropic glutamate receptors (mGluRs) to differentiate plasticity induction mechanisms.

Main Results:

• Spine [Ca2+]i transients were uncorrelated with the direction of synaptic efficacy change (LTP vs. LTD).
• Metabotropic glutamate receptors (mGluRs) coupled with phospholipase C (PLC) acted as sequence-sensitive coincidence detectors for LTD induction.
• LTP induction required a large [Ca2+]i transient primarily via NMDA receptor activation.

Conclusions:

• The magnitude of long-term synaptic changes is determined by the peak elevation of postsynaptic [Ca2+]i.
• The direction of synaptic plasticity (LTP/LTD) is controlled by a mGluR-coupled signaling cascade, acting as a sequence-sensitive coincidence detector.
• Distinct Ca2+ sensors likely mediate spike-timing-dependent synaptic plasticity, differentiating between LTP and LTD induction.