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Temperature dependence of extracellular ionic changes evoked by anoxia in hippocampal slices

Temperature dependence of extracellular ionic changes evoked by anoxia in hippocampal slices Abstract 1. Extracellular K and Ca were measured with ion-selective microelectrodes in CA1 pyramidal cell layer of rat hippocampal slices in an interface chamber. 2. Near room temperature (21-22 degrees C), brief periods of anoxia (3- to 4-min substitution of 95% N2-5% CO2 for 95% O2-5% CO2) produced very small changes in Ko -0.022 +/- 0.10 (SE) mM or Cao (-0.030 +/- 0.0029 mM) and were associated with only minor depression of population spikes (-22.5 +/- 11%). 3. Stratum radiatum (SR) stimulation (0.2-5 Hz) could evoke substantial increases in Ko (by 0.2-2 mM); although variable, they were consistent in any one slice. The same stimulation regularly caused only small depressions of Cao (by less than 0.1 mM, typically). 4. Also at 21-22 degrees neither stimulation nor anoxia generated more than minimal reductions in extracellular space by 2.3 +/- 0.94%, as measured by the tetramethylammonium (TMA) method, and spreading depression (SD) occurred in only 1 out of 20 slices. 5. At 33-34 degrees C, anoxia (also for 3-4 min) consistently produced more substantial increases in Ko (0.83 +/- 0.18 mM); but the apparent changes in Cao at 33 degrees C (0.058 +/- 0.12 mM) could not with certainty be distinguished from thermoelectric artifacts. There was a severe depression of population spikes (-76 +/- 10%). 6. Although electrical stimulation evoked greater reductions in Cao, increases in Ko were 50% smaller. 7. During anoxia at 33-34 degrees C, the extracellular space was significantly reduced, by 6.1 +/- 0.9%. Moreover, in 37% of the slices, either stimulation or anoxia triggered massive increases in Ko (greater than 10 mM) and large reductions in Cao (less than 1 mM), associated with SD-like swings in focal potential. 8. It is concluded that the extracellular ionic changes evoked by brief anoxia do not contribute in a major way to the depression of synaptic transmission. Copyright © 1991 the American Physiological Society http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Neurophysiology The American Physiological Society

Temperature dependence of extracellular ionic changes evoked by anoxia in hippocampal slices

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Publisher
The American Physiological Society
Copyright
Copyright © 1991 the American Physiological Society
ISSN
0022-3077
eISSN
1522-1598
Publisher site
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Abstract

Abstract 1. Extracellular K and Ca were measured with ion-selective microelectrodes in CA1 pyramidal cell layer of rat hippocampal slices in an interface chamber. 2. Near room temperature (21-22 degrees C), brief periods of anoxia (3- to 4-min substitution of 95% N2-5% CO2 for 95% O2-5% CO2) produced very small changes in Ko -0.022 +/- 0.10 (SE) mM or Cao (-0.030 +/- 0.0029 mM) and were associated with only minor depression of population spikes (-22.5 +/- 11%). 3. Stratum radiatum (SR) stimulation (0.2-5 Hz) could evoke substantial increases in Ko (by 0.2-2 mM); although variable, they were consistent in any one slice. The same stimulation regularly caused only small depressions of Cao (by less than 0.1 mM, typically). 4. Also at 21-22 degrees neither stimulation nor anoxia generated more than minimal reductions in extracellular space by 2.3 +/- 0.94%, as measured by the tetramethylammonium (TMA) method, and spreading depression (SD) occurred in only 1 out of 20 slices. 5. At 33-34 degrees C, anoxia (also for 3-4 min) consistently produced more substantial increases in Ko (0.83 +/- 0.18 mM); but the apparent changes in Cao at 33 degrees C (0.058 +/- 0.12 mM) could not with certainty be distinguished from thermoelectric artifacts. There was a severe depression of population spikes (-76 +/- 10%). 6. Although electrical stimulation evoked greater reductions in Cao, increases in Ko were 50% smaller. 7. During anoxia at 33-34 degrees C, the extracellular space was significantly reduced, by 6.1 +/- 0.9%. Moreover, in 37% of the slices, either stimulation or anoxia triggered massive increases in Ko (greater than 10 mM) and large reductions in Cao (less than 1 mM), associated with SD-like swings in focal potential. 8. It is concluded that the extracellular ionic changes evoked by brief anoxia do not contribute in a major way to the depression of synaptic transmission. Copyright © 1991 the American Physiological Society

Journal

Journal of Neurophysiology – The American Physiological Society

Published: Feb 1, 1991

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