Journal of Neurophysiology, Vol 38, Issue 2 405-417, Copyright © 1975 by APS
NADH fluorescence and [K+]o changes during hippocampal electrical stimulation
D. V. Lewis and W. H. Schuette
1. Short (2 s) trains of stimuli were applied to the dorsal hippocampal
surface of cats, producing an increase in [K+]o and a decrease in NADH
fluorescence (the latter being indicative of an increase in tissue oxygen
utilization). 2. The [K+]o rose rapidly during stimulation (delta[K+]o
values from 1 to 6 mM) with larger stimulus currents producing larger
changes. The time course of the poststimulus decline of [K+]o was an
exponential decay function, with T 1/2 values varying from 1.3 to 6.9s, and
independent of the magnitude of the delta[K+]o. Consistent undershoots of
[K+]o occurred following stimuli causing less than 1 mM change in [K+]o. 3.
The maximum depression of fluorescence and the time integral of the
fluorescence changes following each stimulus train were both highly
correlated with the total increase of [K+]o occurring during the stimulus
train. 4. Application of several stimulus trains in close succession
resulted in more rapid potassium reuptake following the later trains and an
unusually large undershoot after the last train. Concomitantly, there was a
progressive decrease in the fluorescence level. 5. When afterdischarges
were induced by prolonged (less than 2 s) stimulation, larger and more
sustained increases in [K+]o and decreases of fluorescence were observed,
and there was some indication that afterdischarges were followed by
accelerated reuptake of extracellular potassium.
