Limiting section thickness of guinea pig olfactory cortical slices studied from tissue pO2 values and electrical activities.

The relationship between tissue oxygen partial pressure (pO2) values and electrical activities of guinea pig olfactory cortical slices were investigated as the slices were superfused with Krebs-Ringer's solution equilibrated with different gas mixtures. The pO2 values were measured in the slices with oxygen microelectrodes (tip diameter less than 1 micrometer). 1. Studies of pO2 measurements showed the variability of minimum pO2 value of oxygen profiles in the tissue slice. The profile depends on the pO2 value of the superfusate and on the thickness and the oxygen consumption of the slice. With our experimental conditions an anoxic area developed in the middle layers of the slice when the thickness of the slice exceeded ca. 430 micrometers; in thinner slices there was no anoxic area. In our case the limiting section thickness of the slice was ca.430 micrometers from the viewpoint of tissue pO2 value. 2. The N potential (extra-cellularly recorded EPSP) showed a tendency to decrease in amplitude, for slices being thicker than ca 430 micrometers. It would seem reasonable to think that the decrement of the N potential was brought about by the existence of the anoxic area. 3. When the slice was bubbled with 25, 45 or 95% O2, the tissue pO2 value changed, and the N potential height also changed. The N potential was higher in amplitude when bubbled with 95% O2 than with 25% O2. On the other hand, the amplitude of the IS potential (the lateral olfactory tract potential) was not influenced as much as that of the N potential by the change of tissue pO2 value in the slice. 4. The tissue pO2 value was continuously measured during the electrical stimulation of the lateral olfactory tract. The steady state level of tissue pO2 value obtained during the stimulation diminished as the frequency of stimulation increased from 5-30 Hz.