Oxygen measurements in brain stem slices exposed to normobaric hyperoxia and hyperbaric oxygen

We previously reported (J Appl Physiol 89: 807-822, 2000) that less than or equal to 10 min of hyperbaric oxygen (HBO2; less than or equal to2,468 Torr) stimulates solitary complex neurons. To better define the hyperoxic stimulus, we measured PO2 in the solitary complex of 300-mum-thick rat medullary slices, using polarographic carbon fiber microelectrodes, during perfusion with media having PO2 values ranging from 156 to 2,468 Torr. Under control conditions, slices equilibrated with 95% O-2 at barometric pressure of 1 atmospheres absolute had minimum PO2 values at their centers (291 +/- 20 Torr) that were similar to 10-fold greater than PO2 values measured in the intact central nervous system (10-34 Torr). During HBO2, PO2 increased at the center of the slice from 616 +/- 16 to 1,517 +/- 15 Torr. Tissue oxygen consumption tended to decrease at medium PO2 greater than or equal to 1,675 Torr to levels not different from values measured at PO2 found in all media in metabolically poisoned slices (2-deoxy-D-glucose and antimycin A). We conclude that control medium used in most brain slice studies is hyperoxic at normobaric pressure. During HBO2, slice PO2 increases to levels that appear to reduce metabolism.