Voltage Gated Calcium Channel Activation by Backpropagating Action Potentials Downregulates NMDAR Function

Area of Science:

• Neuroscience
• Cellular Neuroscience
• Synaptic Plasticity

Background:

• Excitatory synapses on cortical glutamatergic neurons are primarily located on dendritic spines.
• Compartmentalized calcium (Ca2+) signals in spines translate electrical activity into lasting biochemical and structural changes.
• Backpropagating action potentials (bAPs) activate voltage-gated calcium channels (VGCCs) in spines, serving as a biochemical feedback of neuronal activity.

Purpose of the Study:

• To investigate the impact of spine VGCCs on glutamatergic synaptic transmission.
• To understand how activity-dependent VGCC plasticity influences Ca2+ influx and synaptic function.

Main Methods:

• Electrophysiology
• Two-photon Ca2+ imaging
• Two-photon glutamate uncaging in acute rat brain slices
• Analysis of T- and R-type VGCCs in layer 2 neurons

Main Results:

• T- and R-type VGCCs are the primary Ca2+ conductances in dendritic spines but do not affect somatic excitatory postsynaptic potentials (EPSPs).
• While VGCCs contribute to Ca2+ influx during EPSPs, their expression level does not determine the total EPSP-mediated Ca2+ influx.
• Activation of VGCCs by bAP bursts leads to a long-term downregulation of spine NMDAR function.

Conclusions:

• Spine VGCCs play a role in modulating synaptic transmission, particularly through their influence on NMDAR function following bAP bursts.
• Activity-dependent plasticity of VGCCs contributes to interspine variability in Ca2+ signaling.
• The findings highlight a mechanism by which neuronal activity shapes synaptic strength and plasticity.