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Retinal spreading depression and the extracellular milieu.
Canadian Journal of Physiology and Pharmacology
|May 1, 1987
Summary
Extracellular milieu influences spreading depression in chick retinas. Ionic changes and chemical balance affect wave propagation velocity, impacting retinal susceptibility.
Area of Science:
- Neuroscience
- Ophthalmology
- Biophysics
Background:
- Spreading depression (SD) is a wave of neuronal depolarization.
- The extracellular milieu's role in SD occurrence and propagation remains incompletely understood.
Purpose of the Study:
- To investigate the extracellular milieu's participation in spreading depression (SD) in isolated chick retina.
- To elucidate the ionic and chemical factors influencing SD propagation velocity and susceptibility.
Main Methods:
- Isolated chick retina preparations were used for in vitro studies.
- Spreading depression propagation was monitored via visual observation and microphotometry.
- Extracellular ionic changes (Cl-, Na+, Ca2+, K+) and voltage shifts were recorded using ion-selective microelectrodes.
Main Results:
- The SD wave front exhibited increased light scattering and significant ionic shifts in the extracellular space.
- Extracellular K+ increased, while Cl-, Na+, and Ca2+ decreased, accompanied by an alkaline-acid shift.
- SD propagation velocity was modulated by extracellular constituents (K+, HCO-3, glucose facilitating; Cl-, Mg2+ hindering) and physical factors (temperature, superfusate flow).
Conclusions:
- Spreading depression is a chemical diffusion reaction, primarily in the inner plexiform layer.
- The extracellular milieu's chemical steady-state is critical for SD occurrence and propagation.
- Altering extracellular conditions can modify SD velocity and increase retinal susceptibility.