PtiO2 and CMRO2 changes in cortex and hippocampus of aging gerbil brain

Tissue O2 partial pressure (PtiO2) and O2 disappearance rates (dPO2/dt) after bilateral carotid artery occlusion were measured with recessed cathode O2 microelectrodes (tips < 3 microns) in gerbil brains (n = 38) from three age groups: young (Y, 3-6 mo), mature (M, 10-12 mo), and older (O, 18-21 mo). Mean PtiO2 values were 18.4 +/- 1.2 (SE), 14.0 +/- 0.8 (P < 0.005), and 21.2 +/- 1.0 (NS) Torr for Y, M, and O groups, respectively, in the cortex and 14.1 +/- 0.8, 15.6 +/- 0.8 (NS), and 16.1 +/- 0.8 (NS) Torr in the hippocampus (Mann-Whitney comparisons with Y). In the cortex, mean dPO2/dt declined significantly with age: -19.2 +/- 1.1, -14.2 +/- 0.9 (P < 0.001), and -12.4 +/- 0.5 (P < 0.001) Torr/s for Y, M, and O, respectively (ANOVA comparisons with Y). In the hippocampus, the respective mean dPO2/dt values were -16.4 +/- 0.8, -15.6 +/- 1.9, and -13.9 +/- 2.2 Torr/s. Although the time trend for dPO2/dt was significant (P < 0.05), mean hippocampal differences compared by ANOVA were not. In Y, mean PtiO2 and dPO2/dt were lower in the hippocampus than in the cortex (P < 0.05). Apparent Michaelis-Menten constants for O2 were estimated from the O2 disappearance curves. These constants were significantly higher for the O group in the hippocampus (5.1 +/- 0.8 Torr) than in the cortex (2.7 +/- 0.6 Torr, P < 0.05).