Dynamic Gain Analysis Reveals Encoding Deficiencies in Cortical Neurons That Recover from Hypoxia-Induced Spreading...

Area of Science:

• Neuroscience
• Cellular Electrophysiology

Background:

• Spreading depolarization (SD) is a common neuronal response to insults like hypoxia and trauma.
• SD causes a transient breakdown of ionic gradients in cortical neurons.
• The long-term functional consequences of SD on neuronal excitability remain unclear.

Purpose of the Study:

• To investigate the lasting electrophysiological changes in cortical neurons following hypoxia-induced SD.
• To assess neuronal function beyond standard excitability measures, focusing on information processing capacity.

Main Methods:

• Electrophysiological recordings from mouse cortical slices after hypoxia-induced SD.
• Introduction of 'dynamic gain' as a measure of action potential encoding bandwidth.
• Pharmacological inhibition of calpain to investigate its role in SD-induced changes.
• Ankyrin G staining to assess axon initial segment integrity.

Main Results:

• Neurons recovering from SD showed normal excitability but a marked reduction in dynamic gain, impairing high-frequency input encoding.
• Hypoxia alone, without SD, did not cause this encoding deficit.
• A significant decrease in intact axon initial segments was observed post-SD.
• Both the encoding deficit and axon damage were prevented by calpain inhibition, implicating Ca2+-dependent calpain activation.

Conclusions:

• Hypoxia-induced SD causes lasting impairments in neuronal information processing capacity, specifically affecting the ability to encode high-frequency inputs.
• The observed functional deficits and structural changes (axon initial segment integrity) are mediated by SD-induced intracellular calcium rise and subsequent calpain activation.
• Neurons surviving SD may have limited effectiveness in cortical circuits due to these impairments.