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161 p., Brain stroke is the second cause of death worldwide. Among the cerebrovascular accidents, ischemic stroke is the most common. It is caused by an interruption of blood flow, and it is characterized by sudden neuronal death (necrosis in the core) and apoptotic neuronal loss in the penumbra. After the generation of the glial scar surrounding the penumbra, ischemia in animal model can activate the neurogenic machinery in the subventricular zone (SVZ). However, the rapid formation of the glial scar after brain ischemia represents a double edged sword for brain survival. On one side, the ischemic scar isolates the healthy tissues from deadly factors released in the ischemic core but on the other hand, it impedes the neuronal regeneration from the SVZ. Previous results in our laboratory demonstrated that high levels of extracellular adenosine, one of the factors released after brain ischemia, could activate theSVZ and generate new astrocytes. In this PhD project, we used a mice model of transient brain ischemia by middle cerebral artery occlusion (MCAO) to accomplish the following objectives:1) To characterize the SVZ activation and astrogliogenesis following brain ischemia;2) To investigate the role of newborn astrocytes generated from the SVZ.By combining immunofluorescence with genetic cellular tracing (in vivo electroporation of neural progenitor cells) we demonstrated that brain ischemia induced the generation of newborn astrocytes from the SVZ. Newborn astrocytes expressed the specific marker Thbs4 and were derived from the activated Type B cells at the dorsal SVZ. The neural stem cells and the Thbs4 astrocytes generated from the SVZ, deviated their physiological route to the olfactory bulb and reached the ischemic scar. Here, astrocytes generated after brain ischemia could degrade and synthetize the hyaluronic acid of the extracellular matrix suggesting a dual role in the modulation of the ischemic glial scar. We demonstrated for the first time that astrocytes deriv

161 p., Brain stroke is the second cause of death worldwide. Among the cerebrovascular accidents, ischemic stroke is the most common. It is caused by an interruption of blood flow, and it is characterized by sudden neuronal death (necrosis in the core) and apoptotic neuronal loss in the penumbra. After the generation of the glial scar surrounding the penumbra, ischemia in animal model can activate the neurogenic machinery in the subventricular zone (SVZ). However, the rapid formation of the glial scar after brain ischemia represents a double edged sword for brain survival. On one side, the ischemic scar isolates the healthy tissues from deadly factors released in the ischemic core but on the other hand, it impedes the neuronal regeneration from the SVZ. Previous results in our laboratory demonstrated that high levels of extracellular adenosine, one of the factors released after brain ischemia, could activate theSVZ and generate new astrocytes. In this PhD project, we used a mice model of transient brain ischemia by middle cerebral artery occlusion (MCAO) to accomplish the following objectives:1) To characterize the SVZ activation and astrogliogenesis following brain ischemia;2) To investigate the role of newborn astrocytes generated from the SVZ.By combining immunofluorescence with genetic cellular tracing (in vivo electroporation of neural progenitor cells) we demonstrated that brain ischemia induced the generation of newborn astrocytes from the SVZ. Newborn astrocytes expressed the specific marker Thbs4 and were derived from the activated Type B cells at the dorsal SVZ. The neural stem cells and the Thbs4 astrocytes generated from the SVZ, deviated their physiological route to the olfactory bulb and reached the ischemic scar. Here, astrocytes generated after brain ischemia could degrade and synthetize the hyaluronic acid of the extracellular matrix suggesting a dual role in the modulation of the ischemic glial scar. We demonstrated for the first time that astrocytes deriv

Adenosine A(l) receptors (A(l)ARs) are promising imaging biomarkers and targets for the treatment of stroke. Nevertheless, the role of A(l)ARs on ischemic damage and its subsequent neuroinflammatory response has been scarcely explored so far. Methods: In this study, the expression of A(1)ARs after transient middle cerebral artery occlusion (MCAO) was evaluated by positron emission tomography (PET) with [F-18]CPFPX and immunohistochemistry (IHC). In addition, the role of AIARs on stroke inflammation using pharmacological modulation was assessed with magnetic resonance imaging (MRI), PET imaging with [F-18]DPA-714 (TSPO) and [F-18]FLT (cellular proliferation), as well as IHC and neurofunctional studies. Results: In the ischemic territory, [F-18]CPFPX signal and IHC showed the overexpression of A(l)ARs in microglia and infiltrated leukocytes after cerebral ischemia. Ischemic rats treated with the AAR agonist ENBA showed a significant decrease in both [F-18]DPA-714 and [F-18]FLT signal intensities at day 7 after cerebral ischemia, a feature that was confirmed by IHC results. Besides, the activation of A(l)AR promoted the reduction of the brain lesion, as measured with T2W-MRI, and the improvement of neurological outcome including motor, sensory and reflex responses. These results show for the first time the in vivo PET imaging of A(l)AR expression after cerebral ischemia in rats and the application of [F-18]FLT to evaluate glial proliferation in response to treatment. Conclusion: Notably, these data provide evidence for A(l)AR playing a key role in the control of both the activation of resident glia and the de novo proliferation of microglia and macrophages after experimental stroke in rats.

In vivopositron emission tomography of neuroinflammation has mainly focused on the evaluation of glial cell activation using radiolabeled ligands. However, the non-invasive imaging of neuroinflammatory cell proliferation has been scarcely evaluated so far.In vivoandex vivoassessment of gliogenesis after transient middle cerebral artery occlusion (MCAO) in rats was carried out using PET imaging with the marker of cell proliferation 3 '-Deoxy-3 '-[18F] fluorothymidine ([F-18]FLT), magnetic resonance imaging (MRI) and fluorescence immunohistochemistry. MRI-T2W studies showed the presence of the brain infarction at 24 h after MCAO affecting cerebral cortex and striatum.In vivoPET imaging showed a significant increase in [F-18]FLT uptake in the ischemic territory at day 7 followed by a progressive decline from day 14 to day 28 after ischemia onset. In addition, immunohistochemistry studies using Ki67, CD11b, and GFAP to evaluate proliferation of microglia and astrocytes confirmed the PET findings showing the increase of glial proliferation at day 7 after ischemia followed by decrease later on. Hence, these results show that [F-18]FLT provides accurate quantitative information on the time course of glial proliferation in experimental stroke. Finally, this novel brain imaging method might guide on the imaging evaluation of the role of gliogenesis after stroke.