Résumé
A technique for the determination of the threshold concentrations of chemical substances for elicitation of spreading depression is described. The technique minimizes the interference of mechanical stimulating effects and alterations in the susceptibility of the retina to spreading depression due to changes in unstirred layers at the liquid-tissue interphase. The following threshold concentrations were shown to elicit the wave: 8000-10000 microM KCl, 100-200 microM sodium glutamate, 5-10 microM sodium kainate, 10-20 microM sodium N-methyl-aspartate, 600-1200 microM (NH4)2SO4 and 400-600 microM BaCl2. Variations of K+ or Mg2+ concentration in the standard Ringer solution that may cause an increase or decrease of spreading depression velocity have an inverse effect on the threshold for elicitation of the reaction
Sujets)
Animaux , Dépression corticale envahissante , Rétine/physiologie , Embryon de poulet , Limite admissible des risques professionnels , Solution isotonique/administration et posologie , Facteurs tempsRésumé
The chick retina in vitro preparation was used to quantify the effect of Na+ and Cl- on the velocity of propagation of spreading depression (SD). The progressive reduction of chloride concentration in the superfusing Ringer solution, solution, either by partial removal of NaCl or by its partial substitution with isethionate, caused a logarithmic increase in the velocity of propagation of SD. Substituting Tris for Na+ had no appreciable effect on propagation velocity, suggesting that the propagation of the reaction is not necessarily dependent con Na+. Howeverm choline did not substitute for Na+ because it decreased propagation velocity and, at higher concentration, even blocked the spread of the reaction
Sujets)
Animaux , Chlore/pharmacologie , Dépression corticale envahissante , Techniques in vitro , Rétine/effets des médicaments et des substances chimiques , Sodium/pharmacologie , Poulets , Solution isotonique , Chlorure de sodium/métabolismeRésumé
The present study examines the effect of diphenylhydantoin on the elicitation by K+ and propagation of spreading depression in chick retina preparations in vitro. A dose-related decrease in the velocity of propagation was observed, this effect being lessened by increasing the pH of the Ringer bathing the preparation. Changes in Ringer C1- concentration also altered the efficacy of the drug, higher concentrations enhancing and lower concentrations reducing efficacy. The threshold concentration of K+ necessary to elicit the reaction was elevated by dyphenylhydantoin
Sujets)
Animaux , Dépression corticale envahissante/effets des médicaments et des substances chimiques , Techniques in vitro , Phénytoïne/pharmacologie , Potassium/métabolisme , Rétine/métabolisme , PouletsRésumé
The present study focuses on the influence of changes in extracellular Ca2+ on retinal spreading depression in vitro. It shows that changes in Ca2+ concentration alter the speed of the reaction. This effects is more pronounced for variations occuring within limits close to the physiological concentration level. The experiments also indicate that if the tissue is initially exposed to a lowered extracellular Ca2+ concentration, then the effects of transient variation in Ca2+ are significantly enhanced. Finally, a synergistic action of Ca2+ and K+ is observed with respect to the spreading of the reaction