Effects of naloxone on tissue oxygen supply and somatosensory evoked potentials in cat brain during focal cerebral ischemia

The effects of naloxone on local tissue oxygen partial pressure (pO2) and on the somatosensory evoked potentials (SEP) were studied in the brain of cat during focal cerebral ischemia. Ischemia, produced by clamping of the middle cerebral artery (MCA) by a transorbital approach, was performed in two series of cats for 3 h. In one group of cats (n = 5), naloxone 5 mg.kg-1 was injected i.v. 0.5 h after clamping. The pO2 was continuously recorded on different depths (0-5000 microns) of the median gyrus by a polarographic oxygen microelectrode. After MCA clamping, pO2 (depth of 0-1000 microns) decreased markedly and hypoxia occurred in the ischemic area. But in the deeper brain (1001-5000 microns) pO2 did not change significantly. The amplitude of SEP decreased after MCA clamping, while the conduction time of SEP did not significantly decrease. The mean pO2 values in the ischemic area were increased as compared to the control group after naloxone, especially at the depths of 0-1000 microns, and the hypoxia was improved. The amplitude of SEP was increased after naloxone in comparison to the situation of ischemia without naloxone. The conduction time of SEP was not improved significantly. We conclude that naloxone can improve the oxygen supply and the electrical activity of neurons in the ischemic region of the brain.