Journal: International Journal of Molecular Sciences

Article Title: Event-Associated Oxygen Consumption Rate Increases ca. Five-Fold When Interictal Activity Transforms into Seizure-Like Events In Vitro

doi: 10.3390/ijms18091925

Figure Lengend Snippet: Variations in basal pO 2 under bicuculline and bicuculline + XE-991: ( A ) Left: Picture and scheme of typical electrode placement in acute hippocampal slice. Double-barreled ion-sensitive microelectrodes (with field potential and ion-sensitive recording side) and Clark-style oxygen electrodes were placed ~80 µm below the slice surface in the pyramidal layer of area CA3. Acute brain slices receive oxygen from surface and bottom and the partial oxygen pressure (pO 2 ) decreases with the distance to the source of oxygen (i.e., distance to the slice bottom and surface) providing typical depth profiles (see right, numbers in trace—distance to slice surface). The oxygen gradient along the slice depends on oxygen supply and solubility, which are both constant under experimental conditions. Hence, changes in pO 2 depth profiles reflect activity-dependent O 2 consumption; and ( B ) Using an established reaction-diffusion model, peak pO 2 -levels at each vertical step in the pO 2 profile ( left ) were fitted ( right ) to calculate oxygen consumption rates (OCR). OCRs increased from control (spontaneous activity, gray , 31.2 mmHg·s −1 ) to induced ILEs ( black , 33.8 mmHg·s −1 ) and SLEs ( red , 39.5 mmHg·s −1 ) in this example. The quantitative analysis (inset) revealed a significant OCR increase during SLEs ( red ) compared with control conditions ( gray , * p = 0.008, n.s. not significant, n = 8, paired t -test with Bonferroni post-hoc correction).

Article Snippet: Basal and event-associated pO 2 were measured using Clark-style oxygen sensors (tip: 10 μm; Unisense, Aarhus, Denmark) placed near the ion-sensitive microelectrode.

Techniques: Solubility, Activity Assay, Diffusion-based Assay

Journal: International Journal of Molecular Sciences

Article Title: Event-Associated Oxygen Consumption Rate Increases ca. Five-Fold When Interictal Activity Transforms into Seizure-Like Events In Vitro

doi: 10.3390/ijms18091925

Figure Lengend Snippet: Locality of activity and modeling of local oxygen consumption rates associated with ILEs and SLEs in brain slices: ( A ) Typical f.p., extracellular potassium ([K + ] o ) and oxygen recordings of ILEs ( black ) and SLEs ( red ). Event-associated oxygen baseline drops were larger in SLEs compared with ILEs; ( B ) Local oxygen drops during ILEs and SLEs at 80 µm from the slice surface. Event-related pO 2 drops during SLEs ( red ) were significantly larger compared with ILEs ( black ) ( p = 0.011, n = 8 and 15 for ILEs and SLEs respectively, independent t -test); ( C ) Scheme of brain slice recordings under interface conditions with two pairs of double-barreled potassium-sensitive microelectrodes and Clark-style oxygen electrodes. One pair of electrodes was moved in vertical steps through the pyramidal layer in area CA3 (moving electrode). A second stationary pair of electrodes was placed in close vicinity at ~80 µm below the slice surface (fixed electrode) to control for signal stability; ( D ) Overlay of the recording signals from the two pairs of electrodes ( black : moving electrode, grey: fixed electrode) during bicuculline-induced ILEs. F.p., [K + ] o and oxygen drops remained stable at the fixed electrode, while f.p. amplitudes and [K + ] o peaks were larger at 100 µm compared with 0 and 200 µm at the moving electrode. Oxygen dips increased from 0 to 100 µm and remained large at a depth of 200 µm in the moving electrode; ( E ) ILE-associated amplitudes, event-related peak potassium levels and pO 2 -drops at different depths along the slice. Field potential and potassium levels showed a very similar amplitude distribution with a peak around 100 µm. Oxygen drops were smaller near the surface, but remained stable after 60–80 µm ( gray —fixed electrode, black—moving electrode); ( F ) Fitted basal pO 2 -depth profiles ( left , solid line) and event-associated depth profiles ( left , dashed line) for bicuculline ( black ) and bicuculline + XE-991 ( red ). Basal OCRs (solid line, right graph) and depth-dependent event-associated OCRs (EAOCR, dotted line, right graph, EAOCR = OCR/event (mmHg·s −1 )). Bar plots show EAOCRs for ten individual events; and ( G ) EAOCR ( top ) and ratio of EAOCR to basal OCR ( bottom ) during ILEs and SLEs. During SLEs ( red ) EAOCRs were significantly higher compared with EAOCRs during ILEs (black; p = 0.016, n = 8 and 15 for ILEs and SLEs; independent t -test). The ratio comparing EAOCRs to the basal OCR was significantly higher under SLEs compared with ILEs ( p = 0.035, n = 8 and 15 for ILEs and SLEs, respectively, independent t -test).

Article Snippet: Basal and event-associated pO 2 were measured using Clark-style oxygen sensors (tip: 10 μm; Unisense, Aarhus, Denmark) placed near the ion-sensitive microelectrode.

Techniques: Activity Assay, Slice Preparation