Vascular Response to Spreading Depolarization Predicts Stroke Outcome

Background: Cortical spreading depolarization (CSD) is a massive neuro-glial depolarization wave, which propagates across the cerebral cortex. In stroke, CSD is a necessary and ubiquitous mechanism for the development of neuronal lesions that initiates in the ischemic core and propagates through the penumbra extending the tissue injury. Although CSD propagation induces dramatic changes in cerebral blood flow, the vascular responses in different ischemic regions and their consequences on reperfusion and recovery remain to be defined. Methods: Ischemia was performed using the thrombin model of stroke and reperfusion was induced by r-tPA (recombinant tissue-type plasminogen activator) administration in mice. We used in vivo electrophysiology and laser speckle contrast imaging simultaneously to assess both electrophysiological and hemodynamic characteristics of CSD after ischemia onset. Neurological deficits were assessed on day 1, 3, and 7. Furthermore, infarct sizes were quantified using 2,3,5-triphenyltetrazolium chloride on day 7. Results: After ischemia, CSDs were evidenced by the characteristic propagating DC shift extending far beyond the ischemic area. On the vascular level, we observed 2 types of responses: some mice showed spreading hyperemia confined to the penumbra area (penumbral spreading hyperemia) while other showed spreading hyperemia propagating in the full hemisphere (full hemisphere spreading hyperemia). Penumbral spreading hyperemia was associated with severe stroke-induced damage, while full hemisphere spreading hyperemia indicated beneficial infarct outcome and potential viability of the infarct core. In all animals, thrombolysis with r-tPA modified the shape of the vascular response to CSD and reduced lesion volume. Conclusions: Our results show that different types of spreading hyperemia occur spontaneously after the onset of ischemia. Depending on their shape and distribution, they predict severity of injury and outcome. Furthermore, our data show that modulating the hemodynamic response to CSD may be a promising therapeutic strategy to attenuate stroke outcome

Leptomeningeal collaterals regulate reperfusion in ischemic stroke and rescue the brain from futile recanalization.

Recanalization is the mainstay of ischemic stroke treatment. However, even with timely clot removal, many stroke patients recover poorly. Leptomeningeal collaterals (LMCs) are pial anastomotic vessels with yet-unknown functions. We applied laser speckle imaging, ultrafast ultrasound, and two-photon microscopy in a thrombin-based mouse model of stroke and fibrinolytic treatment to show that LMCs maintain cerebral autoregulation and allow for gradual reperfusion, resulting in small infarcts. In mice with poor LMCs, distal arterial segments collapse, and deleterious hyperemia causes hemorrhage and mortality after recanalization. In silico analyses confirm the relevance of LMCs for preserving perfusion in the ischemic region. Accordingly, in stroke patients with poor collaterals undergoing thrombectomy, rapid reperfusion resulted in hemorrhagic transformation and unfavorable recovery. Thus, we identify LMCs as key components regulating reperfusion and preventing futile recanalization after stroke. Future therapeutic interventions should aim to enhance collateral function, allowing for beneficial reperfusion after stroke

Compartmental investigation of brain energy metabolism using radiotracer kinetics

The measurement of metabolism-related processes in vivo is a critical prerequisite for a better understanding of brain metabolism and its relationship to the brain at work. For a long time it was supposed that blood-borne glucose was the sole energy substrate of brain cells and that it was metabolized by the neurons and the astrocytes more or less independently. Only during the last few decades did one begin to appreciate the compartmentalization of energy metabolism between neurons and astrocytes. The finding of an activity-dependent glutamate mediated activation of the astrocytic glycolysis to generate and release lactate has led to the idea of an astrocyte neuron lactate shuttle (ANLS). The ANLS hypothesis claims that neurons take up the astrocytic lactate and use it for oxidation. This hypothesis has provoked a vivid debate about lactate use of neurons as an energy substrate. This project aimed at measuring the kinetics of positron emitter labeled tracers for the investigation of specific metabolic compartments of the neuron-astrocyte unit. In vivo radiotracer studies are useful tools to estimate the exchange of specific substances between different compartments. They can be performed both in animals and humans. The project was divided into three main parts: First, astrocytic oxidative metabolism was investigated using 1-11C-acetate. It turned out that this is a promising tracer to investigate astrocytic oxidative metabolism in rats and humans. An increased radioactivity washout was found during brain activation pointing to an increase in astrocytic oxidative metabolism during increased synaptic activity. Different pharmacological interventions supported the hypothesis that the measured acetate turnover is indeed related to oxidative metabolism. In a second part, we focused on neuronal oxidative metabolism. Inspired by previous reports demonstrating preferential lactate uptake by neurons, we evaluated the newly synthesized radiotracer 1-11C-L-lactate with respect to its kinetic properties in the rodent brain and were able to Summary 2 demonstrate its feasibility to quantify cerebral lactate oxidation in vivo. We could show increased cerebral - most probably neuronal - lactate oxidation during increased brain activity. We further hypothesize, that the kinetics of 1-11C-L-lactate is not only measuring lactate metabolism, but is in addition an indicator of total neuronal oxidative metabolism. In a final method-oriented part of the project, we introduced a novel high-sensitivity surface probe for the measurement of radiotracer concentration through the intact although thinned skull. We demonstrated its ability to measure glucose utilization and blood flow in the rat cerebral cortex. This new development potentially broadens the field of applications for beta probes compared to conventional intracortical beta scintillators. Due to its decreased invasiveness it was successfully applied in the conscious animal. In summary, we demonstrated the usefulness of radiotracer methods for the investigation of specific aspects of cerebral energy metabolism and improved the methodology of beta probes

Vascular Response to Spreading Depolarization Predicts Stroke Outcome

International audienceBackground: Cortical spreading depolarization (CSD) is a massive neuro-glial depolarization wave, which propagates across the cerebral cortex. In stroke, CSD is a necessary and ubiquitous mechanism for the development of neuronal lesions that initiates in the ischemic core and propagates through the penumbra extending the tissue injury. Although CSD propagation induces dramatic changes in cerebral blood flow, the vascular responses in different ischemic regions and their consequences on reperfusion and recovery remain to be defined. Methods: Ischemia was performed using the thrombin model of stroke and reperfusion was induced by r-tPA (recombinant tissue-type plasminogen activator) administration in mice. We used in vivo electrophysiology and laser speckle contrast imaging simultaneously to assess both electrophysiological and hemodynamic characteristics of CSD after ischemia onset. Neurological deficits were assessed on day 1, 3, and 7. Furthermore, infarct sizes were quantified using 2,3,5-triphenyltetrazolium chloride on day 7. Results: After ischemia, CSDs were evidenced by the characteristic propagating DC shift extending far beyond the ischemic area. On the vascular level, we observed 2 types of responses: some mice showed spreading hyperemia confined to the penumbra area (penumbral spreading hyperemia) while other showed spreading hyperemia propagating in the full hemisphere (full hemisphere spreading hyperemia). Penumbral spreading hyperemia was associated with severe stroke-induced damage, while full hemisphere spreading hyperemia indicated beneficial infarct outcome and potential viability of the infarct core. In all animals, thrombolysis with r-tPA modified the shape of the vascular response to CSD and reduced lesion volume. Conclusions: Our results show that different types of spreading hyperemia occur spontaneously after the onset of ischemia. Depending on their shape and distribution, they predict severity of injury and outcome. Furthermore, our data show that modulating the hemodynamic response to CSD may be a promising therapeutic strategy to attenuate stroke outcome