Retinal spreading depression induced by photoactivation: involvement of free radicals and potassium.

The threshold for spreading depression (SD) in chicken retina elicited by rose bengal photoactivation was raised by Trolox (water soluble vitamin E) suggesting the participation of reactive oxygen species in SD. The typical increases in K+ concentration associated with SD were preceded by small K+ oscillations that were more sensitive to photoactivation than was SD. It is hypothesised that all these phenomena could be accounted for by a free-radical mediated transient increase in membrane permeability and that this may be relevant to ischemic brain damage.

Threshold determination of spreading depression evoking substances in the retina in vitro.

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.

Threshold determination of spreading depression evoking substances in the retina in vitro

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

Effects of local anaesthetics on retinal spreading depression.

This study examines the effect of two local anaesthetics, benzocaine and lidocaine, on propagation, amplitude and duration of the slow potential change of spreading depression. The experiments were performed in isolated chick retina superfused with Ringer's solution. We observed, for both drugs, a dose-related decrease in all parameters analysed. The maximal effect on propagation was blockade of the reaction.

Phenytoin and retinal spreading depression.

Several studies indicate that spreading depression is fundamentally related to seizure marches and to the aura of classical migraine. Moreover, recent investigations call attention to its possible relevance in clinical disturbances associated with brain ischemia, trauma, and hypoglycemia. The anticonvulsant phenytoin has been shown to protect the nervous tissue from the effects of anoxia and ischemia. These properties suggest that phenytoin should be able to counteract spreading depression. Therefore, we investigated its effect on spreading depression elicited by mechanical or chemical (KCl) stimulation, in isolated chick retinas. The results showed that phenytoin: (1) increases the threshold concentration of KCl to initiate the phenomenon; (2) decreases the velocity of propagation of spreading depression; (3) shortens considerably the duration of the slow potential, ionic (K+, Ca2+, Cl-), and volume changes of the extracellular compartment during spreading depression. Possible mechanisms underlying the observed effects are discussed.

The effect of diphenylhydantoin on spreading depression

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

Extracellular Ca2+ and retinal spreading depression

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

The effect of diphenylhydantoin on spreading depression.

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 Cl- 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 diphenylhydantoin.

Extracellular Ca2+ and retinal spreading depression.

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 effect is more pronounced for variations occurring 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.

Retinal spreading depression and the extracellular milieu.

We used isolated chick retina in vitro to study the participation of the extracellular milieu in the occurrence and propagation of spreading depression. The propagation was followed by visual observation or microphotometry and the ionic changes in the extracellular compartment were recorded with double-barreled ion-selective microelectrodes. The front of the spreading wave is accompanied by increased light scattering in the tissue and by decrease of Cl-, Na+, and Ca2+, increase of K+, and an alkaline-acid shift in the extracellular space, concomitant with the slow voltage changes characteristic of the wave. As the spread is related to the chemical steady-state of the extracellular milieu, the velocity of propagation is influenced by a balanced interplay of the chemical constituents of the superfusing solution, e.g., K+, HCO-3, and glucose facilitate, while Cl- and Mg2+ hinder the wave. Steady-state alterations induced by physical factors (temperature) or related to experimental conditions (speed and direction of superfusate flow) change markedly the velocity of propagation. Generally the procedures that cause increase of velocity augment the susceptibility of the preparation to the reaction and eventually may trigger it. Propagated spreading depression is considered as a chemical diffusion reaction pervading more intensively the inner plexiform layer of the retina.

Glutamate and spreading depression in chick retina.

This work is centered on the involvement of glutamate in spreading depression. Chick eye cup preparations bathed with Ringer solution at 28 degrees C were used. For chemical stimulation KCl was increased and glutamate was added to the Ringer solution. The occurrence of spreading depression was detected by visual observation of the optical changes accompanying the phenomenon. Enzymatic method based on the fluorescence of the reduced form of nicotinamide adenine dinucleotide was used for glutamate dosage in the Ringer's samples. The investigations proceeded under six different experimental conditions, and the results were analysed by nonparametric statistical methods. No correlation was found between spreading depression and glutamate outflux. The glutamate hypothesis to account for spreading depression was discussed, and experimental situations involving glutamate, K+ and Cl- were indicated that proved unfavorable to the incidence of the reaction.

Influence of ionic disturbances produced by gastric washing on cortical spreading depression.

The ionic composition of the internal environment was altered in rabbits by means of gastric washing, combined with intramuscular administration of 3-Beta-aminoethylpyrazole. The effects of this treatment on cortical spreading depression (SD) were studied. Cl- and Na+ concentrations decreased significantly in serum and in cerebrospinal fluid after the treatment. This made the animals much more susceptible to SD, as established by the high incidence of "spontaneous" SD, increased SD velocity of propagation and facilitated its interhemispheric transfer. An intensification of the epileptiform activity associated with SD was also observed. Intravenous replacement of NaCl abolished the above effects of SD. When the intravenous replacement was done with Na-Isethionate, those effects were enhanced. It is concluded that chloride deficiency was the main factor responsible for the observed facilitating effects.