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

Abstract

We previously reported (J Appl Physiol 89: 807-822, 2000) that < or =10 min of hyperbaric oxygen (HBO(2); < or = 2,468 Torr) stimulates solitary complex neurons. To better define the hyperoxic stimulus, we measured PO(2) in the solitary complex of 300-microm-thick rat medullary slices, using polarographic carbon fiber microelectrodes, during perfusion with media having PO(2) 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 PO(2) values at their centers (291 +/- 20 Torr) that were approximately 10-fold greater than PO(2) values measured in the intact central nervous system (10-34 Torr). During HBO(2), PO(2) increased at the center of the slice from 616 +/- 16 to 1,517 +/- 15 Torr. Tissue oxygen consumption tended to decrease at medium PO(2) or = 1,675 Torr to levels not different from values measured at PO(2) 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 HBO(2), slice PO(2) increases to levels that appear to reduce metabolism.

Modulation of 4-aminopyridine-induced neuronal activity and local pO2 in rat hippocampal slices by changing the flow rate of the superfusion medium

“…Our data shows that normobaric hyperoxygenated ASCF (95% O2/5% CO 2 at normal atmospheric pressure) at flow rate 2 ml/min provides constant normoxic conditions at 100-150 μm depth of slice. These results are close to previous studies investigating the oxygen profile in the brain slice tissue under various perfusion rate and oxygen concentrations [7,13]. In contrast, in the conditions of the absence of medium flow in the recording chamber we observed progressive reduction in the pO 2 as well as decrease in the power of 4-AP-induced synchronous neuronal activity.…”

Graded Reductions in Oxygenation Evoke Graded Reconfiguration of the Isolated Respiratory Network

“…Neural tissue O 2 -depth profiles have been previously reported in vivo (for summary see Garcia 3rd et al 2010), in situ in the working heart-brain stem preparation (Wilson et al 2001), as well as in vitro in both isolated brain stem-spinal cord preparations (Brockhaus et al 1993;Okada et al 1993) and brain slices (Bingmann and Kolde 1982;Garcia 3rd et al 2010;Mulkey et al 2001). Several factors influence the degree of in vitro tissue oxygenation within a brain slice.…”

“…Although only a handful of brain slice studies have shown that neuronal activity is affected throughout a broad range of O 2 tensions outside of hypoxia (0% O 2 ) and the conventional control condition (95% O 2 ), these studies have shown that graded changes in O 2 , and not only hypoxia, can influence biochemical activity (D'Agostino 2007;Fowler 1993) and excitability of neurons within local networks (Fowler 1993;Garcia 3rd et al 2010;Hoffmann et al 2006;Mulkey et al 2001). Similarly, in invertebrate systems, small changes in oxygenation also have been shown to influence network activity (Clemens et al 2001).…”

“…In the CNS, it is essential that the partial pressure of O 2 (PO 2 ) remains tightly regulated over a fine range because hyperoxia can be as detrimental as hypoxia (D'Agostino et al 2007;Haddad and Jiang 1993). Tissue PO 2 in the CNS is maintained in a narrow range between 10 and 34 Torr (corresponding to a range of 1 to 4% O 2 ; Mulkey et al 2001). Thus neurons, which are very metabolically active, exist in a microenvironment with an O 2 tension only slightly higher than the threshold for aerobic metabolism (ϳ1% O 2 ; Clemens et al 2001).…”

Effects of Hyperoxia on Brain Tissue Oxygen Tension in Non-Sedated, Non- Anesthetized Arctic Ground Squirrels: An Animal Model of Hyperoxic Stress

“…Therefore, hyperoxic gas mixtures are routinely used for chemical denervation of peripheral O 2 receptors in in-vivo studies of respiratory control. The response mechanisms under hyperoxic inhalation conditions are commonly considered to be regulated by oxygen-chemosensitive neurons of the central nerve system, which are distributed throughout the brain stem from the thalamus to the medulla (Neubauer and Sunderram, 2004;Dean et al, 2003Dean et al, , 2004Mulkey et al, 2001). Therefore, the higher response level of P t O 2 during 100% O 2 inhalation in AGS compared to rat is accounted by the regulation mechanism controlled by oxygen-chemosensitive neurons of the central nerve system.…”