Heterogeneity of ventricular fibrillation dominant frequency during global ischemia in isolated rabbit hearts

Introduction: Ventricular fibrillation (VF) studies show that ECG-dominant frequency (DF) decreases as ischernia develops. This study investigates the contribution of the principle ischernic metabolic components to this decline. Methods and Results: Rabbit hearts were Langendorff-perfused at 40 mL/min with Tyrode's solution and loaded with RH237. Epicardial optical action potentials were recorded with a photodiode array (256 sites, 15 x 15 mm). After 60 seconds of VF (induced by burst pacing), global ischernia was produced by low flow (6 mL/min), or the solution changed to impose hypoxia (95 % N-2/5% CO2), low pH(o) (6.7, 80 % O-2/20% CO2), or raised [K+](o) (8 mM). DF of the optical signals was determined at each site. Conduction velocity (CV), action potential duration (APD90), effective refractory period (ERP), activation threshold, dV/dt(max) and membrane potential were measured in separate experiments during ventricular pacing. During VF, ischernia decreased DF in the left ventricle (LV) (to [58 6] %, P < 0.001), but not the right (RV) ([93 5]%). Raised [K+]o reproduced this DF pattern (LV: [67 +/- 12]%, P < 0.001; RV: [95 91%). LV DF remained elevated in hypoxia or low pH,,. During ventricular pacing, ischernia decreased CV in LV but not RV. Raised [K+](o) did not change CV in either ventricle. Ischernia and raised [K+](o) shortened APD90 without altering ERP. LV activation threshold increased in both ischernia and raised [K+](o) and was associated with diastolic depolarization and decreased dV/dt(max),Conclusions: These results suggest that during VF, decreased ECG DF in global ischemia is largely due to elevated [K+](o) affecting the activation thresholds in the LV rather than RV

A cross-species judgement bias task: integrating active trial initiation into a spatial Go/No-go task

Abstract Judgement bias tasks are promising tools to assess emotional valence in animals, however current designs are often time-consuming and lack aspects of validity. This study aimed to establish an improved design that addresses these issues and can be used across species. Horses, rats, and mice were trained on a spatial Go/No-go task where animals could initiate each trial. The location of an open goal-box, at either end of a row of five goal-boxes, signalled either reward (positive trial) or non-reward (negative trial). Animals first learned to approach the goal-box in positive trials (Go) and to re-initiate/not approach in negative trials (No-go). Animals were then tested for responses to ambiguous trials where goal-boxes at intermediate locations were opened. The Go:No-go response ratio was used as a measure of judgement bias. Most animals quickly learned the Go/No-go discrimination and performed trials at a high rate compared to previous studies. Subjects of all species reliably discriminated between reference cues and ambiguous cues, demonstrating a monotonic graded response across the different cue locations, with no evidence of learning about the outcome of ambiguous trials. This novel test protocol is an important step towards a practical task for comparative studies on judgement biases in animals

Non-lattice surface oxygen species implicated in the catalytic partial oxidation of decane to oxygenated aromatics

The one-step transformation of C7–C12 linear alkanes into more valuable oxygenates provides heterogeneous catalysis with a major challenge. In evaluating the potential of a classic mixed-metal-oxide catalyst, we demonstrate new insights into the reactivity of adsorbed oxygen species. During the aerobic gas-phase conversion of n-decane over iron molybdate, the product distribution correlates with the condition of the catalyst. Selectivity to oxygenated aromatics peaks at 350 °C while the catalyst is in a fully oxidized state, whereas decene and aromatic hydrocarbons dominate at higher temperatures. The high-temperature performance is consistent with an underlying redox mechanism in which lattice oxide ions abstract hydrogen from decane. At lower temperatures, the formation of oxygenated aromatics competes with the formation of CO2, implying that electrophilic adsorbed oxygen is involved in both reactions. We suggest, therefore, that so-called non-selective oxygen is capable of insertion into carbon-rich surface intermediates to generate aromatic partial oxidation products