Dynamics of Ionic Shifts in Cortical Spreading Depression

Area of Science:

• Neuroscience
• Neurophysiology
• Brain Electrophysiology

Background:

• Cortical spreading depression (CSD) is a wave of brain cell depolarization linked to migraine aura, stroke, and brain trauma.
• CSD involves neuronal swelling, ion shifts (K+, glutamate), altered blood flow, and reduced oxygen.
• The exact mechanism and chemical mediator driving CSD propagation remain unclear, with proposed roles for intercellular signaling or interstitial diffusion.

Purpose of the Study:

• To investigate the spatiotemporal dynamics of ionic shifts during CSD propagation in the mouse visual cortex.
• To determine the primary chemical substance and pathway mediating CSD wavefronts.

Main Methods:

• Extracellular direct current potential recordings.
• Potassium (K+)-sensitive microelectrode recordings.
• Two-photon imaging using ultrasensitive calcium (Ca2+) and glutamate fluorescent probes in vivo.

Main Results:

• CSD propagation was characterized by significant extracellular K+ elevation.
• Intercellular Ca2+ spread was not observed to drive the CSD wavefront.
• Data support interstitial K+ diffusion as the primary mechanism, rather than glutamate diffusion.

Conclusions:

• Interstitial K+ diffusion is the leading event in cortical spreading depression propagation.
• This finding clarifies the mechanism of CSD and has implications for understanding migraine aura and brain injury.