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 Tor r) stimulates solitary complex neurons. To better define the hyperoxic stim ulus, we measured PO2 in the solitary complex of 300-mum-thick rat medullar y slices, using polarographic carbon fiber microelectrodes, during perfusio n with media having PO2 values ranging from 156 to 2,468 Torr. Under contro l conditions, slices equilibrated with 95% O-2 at barometric pressure of 1 atmospheres absolute had minimum PO2 values at their centers (291 +/- 20 To rr) that were similar to 10-fold greater than PO2 values measured in the in tact 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 co nsumption tended to decrease at medium PO2 greater than or equal to 1,675 T orr 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 co nclude that control medium used in most brain slice studies is hyperoxic at normobaric pressure. During HBO2, slice PO2 increases to levels that appea r to reduce metabolism.