72 research outputs found
Two-dimensional wave patterns of spreading depolarization: retracting, re-entrant, and stationary waves
We present spatio-temporal characteristics of spreading depolarizations (SD)
in two experimental systems: retracting SD wave segments observed with
intrinsic optical signals in chicken retina, and spontaneously occurring
re-entrant SD waves that repeatedly spread across gyrencephalic feline cortex
observed by laser speckle flowmetry. A mathematical framework of
reaction-diffusion systems with augmented transmission capabilities is
developed to explain the emergence and transitions between these patterns. Our
prediction is that the observed patterns are reaction-diffusion patterns
controlled and modulated by weak nonlocal coupling. The described
spatio-temporal characteristics of SD are of important clinical relevance under
conditions of migraine and stroke. In stroke, the emergence of re-entrant SD
waves is believed to worsen outcome. In migraine, retracting SD wave segments
cause neurological symptoms and transitions to stationary SD wave patterns may
cause persistent symptoms without evidence from noninvasive imaging of
infarction
Significance of Local Tissue PO2 and of Extracellular Cations for Functional and Reactive Hyperemia of Microcirculation in the Brain
Variation of functional MRI signal in response to frequency of somatosensory stimulation in α-chloralose anesthetized rats
Effects of increases in the inspired oxygen fraction on brain surface oxygen pressure fields in pig and man
Simultaneous monitoring of tissue P2 and NADH fluorescence during synaptic stimulation and spreading depression reveals a transient dissociation between oxygen utilization and mitochondrial redox state in rat hippocampal slices
Nicotinamide adenine dinucleotide (NADH) imaging can be used to monitor neuronal activation and ascertain mitochondrial dysfunction, for example during hypoxia. During neuronal stimulation in vitro, NADH normally becomes more oxidized, indicating enhanced oxygen utilization. A subsequent NADH overshoot during activation or on recovery remains controversial and reflects either increased metabolic activity or limited oxygen availability. Tissue P2 measurements, obtained simultaneously with NADH imaging in area CA1 in hippocampal slices, reveal that during prolonged train stimulation (ST) in 95% O2, a persistent NADH oxidation is coupled with increased metabolic demand and oxygen utilization, for the duration of the stimulation. However, under conditions of either decreased oxygen supply (ST-50% O2) or enhanced metabolic demand (K+-induced spreading depression (K+-SD) 95% O2) the NADH oxidation is brief and the redox balance shifts early toward reduction, leading to a prolonged NADH overshoot. Yet, oxygen utilization remains elevated and is correlated with metabolic demand. Under these conditions, it appears that the rate of NAD+ reduction may transiently exceed oxidation, to maintain an adequate oxygen flux and ATP production. In contrast, during SD in 50% O2, the oxygen levels dropped to a point at which oxidative metabolism in the electron transport chain is limited and the rate of utilization declined
- …