Depotentiation depends on IP₃ receptor activation sustained by synaptic inputs after LTP induction

Area of Science:

• Neuroscience
• Synaptic Plasticity
• Cellular Electrophysiology

Background:

• Long-term potentiation (LTP) enhances synaptic strength, a key mechanism for learning and memory.
• Depotentiation reverses LTP, demonstrating the dynamic nature of synaptic plasticity.
• Understanding depotentiation mechanisms is crucial for comprehending neural circuit regulation.

Purpose of the Study:

• To investigate the molecular and cellular requirements for depotentiation in CA1 hippocampal neurons.
• To identify the signaling pathways involved in reversing established long-term potentiation.
• To elucidate the role of specific receptors and intracellular enzymes in synaptic plasticity modulation.

Main Methods:

• Induction of LTP and depotentiation in guinea pig hippocampal slices using high-frequency stimulation (HFS) and low-frequency stimulation (LFS).
• Electrophysiological recordings of field excitatory postsynaptic potentials (fEPSPs) and population spikes (PSs).
• Pharmacological manipulation using antagonists for N-methyl-D-aspartate receptors (NMDARs), group I metabotropic glutamate receptors (mGluRs), inositol 1,4,5-trisphosphate receptors (IP3Rs), Ca2+/calmodulin-dependent protein kinase II (CaMKII), and calcineurin.

Main Results:

• Depotentiation, the reversal of LTP, was inhibited by halting synaptic stimulation after HFS or LFS.
• NMDAR, group I mGluR, and IP3R antagonists blocked depotentiation.
• Inhibitors of CaMKII and calcineurin also prevented depotentiation when applied during specific post-HFS or post-LFS periods.

Conclusions:

• Sustained synaptic activity following LTP induction is necessary for depotentiation.
• Coactivation of NMDARs and group I mGluRs initiates a signaling cascade involving IP3Rs.
• This cascade activates CaMKII and calcineurin, ultimately leading to the depotentiation of CA1 synaptic responses.