TY - JOUR
T1 - Superoxide Production Increases in Nucleus Tractus Solitarius (NTS) Neurons in Rat Brain Slices during Acute Normobaric Hyperoxia and Hypoxia
AU - Dean, Jay B.
AU - D'Agostino, Dominic P.
AU - Landon, Carol S.
AU - Matott, Michael P.
AU - Hartzler, Lynn K.
AU - Putnam, Robert W.
PY - 2008/11/17
Y1 - 2008/11/17
N2 - We previously reported that hyperbaric hyperoxia stimulates firing rate of putative CO 2 -chemoreceptors in the solitary complex of the dorsocaudal medulla oblongata in rat brain slices ( JAP 95: 910-921, 2003). We next reported that the typical control level of 95%O 2 is a greater source of redox stress than ≤ 40%O 2 leading to increased cell death in brain slices ( J. Neurophysiol. 98:1030-1041, 2007). In the present study we used 20-40%O 2 as the control to test the hypothesis that normobaric hyperoxia and hypoxia increase the rate of superoxide production (·O 2 - ) in NTS neurons. Brain slices (400μm, 36-37 o C) were maintained using 1- or 2-sided superfusion. Brainstem neurons maintained in 20-40%O 2 (5%CO 2 , balance N 2 ) exhibited i) whole-cell/intracellular activity for many hours, ii) CO 2 chemosensitivity (10-15%CO 2 ) and iii) were stimulated by hyperoxia (60-95%O 2 ). ·O 2 - production was measured (3 min intervals) using the fluorogenic probe, dihydroethidium (2.5μM), continuously loaded via the superfusate. The rate of ·O 2 - production (slope of fluorescence intensity units/min, FIU/min) increased during acute hyperoxia (20 to 95%O 2 , 15-20min). Likewise, FIU/min increased during hypoxia (40/20% to 0%O 2 , 10-20min). ·O 2 - production during hypoxia was dependent on a lower threshold tissue pO 2 that is estimated to be well below 20 Torr based on measurements of tissue slice pO 2 . ·O 2 - production during hypoxia was repeatedly induced using 95%N 2 -5%CO 2 during either 1) 1-sided slice superfusion or 2) in combination with an O 2 -scavenger (1mM Na 2 SO 3 ) during 2-sided slice superfusion. Myxothiazol (10μM; an inhibitor of Complex III) decreased ·O 2 - production during hypoxia but had little effect during hyperoxia. This suggests that mitochondrial Complex III is the primary source of ·O 2 - during hypoxia but not hyperoxia in NTS neurons. Preliminary experiments in CA1 hippocampus and Inferior olive indicate that these neurons do not increase their rate of ·O 2 - production during hypoxia/Na 2 SO 3 . We posit that the similar pattern of ·O 2 - production in NTS neurons activated by hypoxia and hyperoxia renders these cardio-respiratory neurons vulnerable to redox stimulation and/or stress during sleep disordered breathing (episodic hypoxia, reoxygenation and rebound hyperoxia) and during exposure to normobaric and hyperbaric hyperoxia
AB - We previously reported that hyperbaric hyperoxia stimulates firing rate of putative CO 2 -chemoreceptors in the solitary complex of the dorsocaudal medulla oblongata in rat brain slices ( JAP 95: 910-921, 2003). We next reported that the typical control level of 95%O 2 is a greater source of redox stress than ≤ 40%O 2 leading to increased cell death in brain slices ( J. Neurophysiol. 98:1030-1041, 2007). In the present study we used 20-40%O 2 as the control to test the hypothesis that normobaric hyperoxia and hypoxia increase the rate of superoxide production (·O 2 - ) in NTS neurons. Brain slices (400μm, 36-37 o C) were maintained using 1- or 2-sided superfusion. Brainstem neurons maintained in 20-40%O 2 (5%CO 2 , balance N 2 ) exhibited i) whole-cell/intracellular activity for many hours, ii) CO 2 chemosensitivity (10-15%CO 2 ) and iii) were stimulated by hyperoxia (60-95%O 2 ). ·O 2 - production was measured (3 min intervals) using the fluorogenic probe, dihydroethidium (2.5μM), continuously loaded via the superfusate. The rate of ·O 2 - production (slope of fluorescence intensity units/min, FIU/min) increased during acute hyperoxia (20 to 95%O 2 , 15-20min). Likewise, FIU/min increased during hypoxia (40/20% to 0%O 2 , 10-20min). ·O 2 - production during hypoxia was dependent on a lower threshold tissue pO 2 that is estimated to be well below 20 Torr based on measurements of tissue slice pO 2 . ·O 2 - production during hypoxia was repeatedly induced using 95%N 2 -5%CO 2 during either 1) 1-sided slice superfusion or 2) in combination with an O 2 -scavenger (1mM Na 2 SO 3 ) during 2-sided slice superfusion. Myxothiazol (10μM; an inhibitor of Complex III) decreased ·O 2 - production during hypoxia but had little effect during hyperoxia. This suggests that mitochondrial Complex III is the primary source of ·O 2 - during hypoxia but not hyperoxia in NTS neurons. Preliminary experiments in CA1 hippocampus and Inferior olive indicate that these neurons do not increase their rate of ·O 2 - production during hypoxia/Na 2 SO 3 . We posit that the similar pattern of ·O 2 - production in NTS neurons activated by hypoxia and hyperoxia renders these cardio-respiratory neurons vulnerable to redox stimulation and/or stress during sleep disordered breathing (episodic hypoxia, reoxygenation and rebound hyperoxia) and during exposure to normobaric and hyperbaric hyperoxia
UR - https://corescholar.libraries.wright.edu/biology/205
M3 - Article
JO - Society for Neuroscience Abstracts
JF - Society for Neuroscience Abstracts
T2 - 2008 Society for Neuroscience Annual Meeting
Y2 - 15 November 2008 through 19 November 2008
ER -