Subcellular Distribution of Persistent Sodium Conductance in Cortical Pyramidal Neurons

Area of Science:

• Neuroscience
• Cellular Electrophysiology
• Molecular Biology

Background:

• Cortical pyramidal neurons utilize a persistent sodium current (INaP) for subthreshold voltage processing.
• The subcellular localization and voltage-dependent properties of INaP channels remain largely unknown.
• Understanding INaP is critical for deciphering neuronal excitability and information processing.

Purpose of the Study:

• To investigate the subcellular distribution and voltage-dependent properties of INaP in cortical pyramidal neurons.
• To elucidate the mechanisms underlying INaP generation and its contribution to neuronal activity.
• To determine the role of endogenous polyamines in regulating INaP.

Main Methods:

• High-speed fluorescence sodium imaging in mouse cortical brain slices.
• Whole-cell electrophysiological recordings.
• Analysis of INaP activation using voltage ramps and Boltzmann function fitting.

Main Results:

• INaP conductance follows a Boltzmann function across neuronal compartments (soma and processes).
• The axon initial segment (AIS) exhibits lower INaP channel density but faster activation compared to the soma.
• Most functionally relevant INaP at subthreshold voltages originates from the AIS due to its distinct voltage dependence.
• Endogenous polyamines were found to significantly constrain INaP availability in both somatodendritic and axonal compartments.

Conclusions:

• The AIS is a primary source of INaP at functionally relevant subthreshold voltages, driven by specific channel voltage dependence.
• Endogenous polyamines act as a significant modulator of INaP across the entire neuron.
• These findings provide crucial insights into the spatial and molecular regulation of neuronal excitability.