Activity coregulates quantal AMPA and NMDA currents at neocortical synapses.

Area of Science:

• Neuroscience
• Synaptic Plasticity
• Receptor Biology

Background:

• AMPA and NMDA receptors are key excitatory neurotransmitter receptors coexpressed at central synapses.
• The precise regulation of AMPA/NMDA receptor ratios is critical for synaptic function but remains poorly understood.
• Understanding these ratios is essential for deciphering neural circuit function and dysfunction.

Purpose of the Study:

• To investigate the factors controlling the ratio of AMPA and NMDA receptors at synapses.
• To determine if synaptic activity influences the relative abundance of AMPA and NMDA receptors.
• To examine whether activity-dependent plasticity preserves the AMPA/NMDA receptor ratio.

Main Methods:

• Recording of mixed miniature and evoked synaptic currents from central neurons.
• Coactivation of postsynaptic AMPA and NMDA receptors.
• Analysis of synaptic currents before and after activity-dependent synaptic scaling protocols.

Main Results:

• Long-lasting changes in neuronal activity induced proportional scaling of both AMPA and NMDA receptor currents.
• Synaptic scaling occurred via alterations in the number of postsynaptic receptors.
• The ratio of NMDA to AMPA current was consistent across different synapses on the same neuron.
• This consistent receptor ratio was maintained even after activity-dependent synaptic scaling.

Conclusions:

• Synaptic activity tightly coregulates AMPA and NMDA receptors at synapses where both are expressed.
• A conserved mechanism actively maintains a constant ratio of AMPA and NMDA receptors across a neuron's synapses.
• This receptor ratio homeostasis is crucial for stable synaptic transmission and neuronal function.