ISSN:
1432-1106
Keywords:
Spreading depression
;
Slow potentials
;
Diffusion in brain tissue
;
Potassium chloride
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary Cortical spreading depression (CSD) was evoked in anaesthetized rats by intracortical microinjection of 3.4·10−8 mol KCl (the single injection threshold T1). With two simultaneous injections at 1 mm tip separation 59% T1 had to be applied to each point to elicit CSD. For interfocal distances 2, 3 and 4 mm the double injection thresholds T1,2 were 65%, 74% and 97% of T1 respectively. The spatial summation effect was still significant at 3 mm and undetectable at 4 mm tip separation. Recording electrodes placed 1–3 mm from the point of injection detected local slow potential changes which attained with subthreshold KCl injections 16% of the maximum CSD negativity at the 1.5 mm distance. The threshold amount of KCl required to trigger CSD at different intervals (30–480 sec) after initial injection of 0.8 T1, exponentially increased with time from 28.2% t1 at 30 sec to 88.9% at 480 sec with the slope 16.8% T1 for a twofold increase of the interinjection interval. Quantitative analysis of results based on equations describing diffusion from an instantaneous point source indicates that the critical volume of depolarization is reached 61 sec after injection. According to the value of the diffusion coefficient of potassium the critical K+ concentration lies between 45 and 12 mequ/l and is reached at a distance of 600–950 μ from the injection.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00237916
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