Effects of Breathing O 2 or O 2 + CO 2 and of the Injection of Neurohumors on the PO 2 of Cat Cerebral Cortex

Tissue PO2 was measured in the outer 1.7 mm of the brain of the lightly anesthetized cat by means of a micro O2 electrode introduced through a small hole in the skull. There was considerable variation from one location to another and from animal to animal. The interindividual variation was not related to the level of the arterial pressure or to rectal temperature. Individual values for the PO2 in 569 locations in the 11 cats ranged from 0 to 90 mm Hg with a mean of 25. There was a significant downward trend in PO2 from the surface layers inward. When the electrode was left in one location, the PO2 usually fluctuated, though not often rhythmically as seen in skeletal muscle. Breathing pure O2 (N=41) or 95% O2 – 5% CO2 (N = 33) caused an equal (50%) increase in PO2 . The intravenous injection of epinephrine or norepinephrine caused a primary rise in PO2 usually with a secondary decrease. Acetylcholine caused a primary decrease and usually a secondary increase.