Louloudis, G. | bioRxiv Science

bioRxiv2022

Imaging increased metabolism in the spinal cord in mice after middle cerebral artery occlusion

Emerging evidence indicates crosstalk between the brain and the hematopoietic system following cerebral ischemia. Here, we investigated metabolism and oxygenation in the spleen and spinal cord in a transient middle cerebral artery occlusion (tMCAO) mouse model that is widely used in focal cerebral ischemia research. Naive, sham and tMCAO mice underwent positron emission tomography (PET) using [18F]fluorodeoxyglucose (FDG) for assessing glucose metabolism and multispectral optoacoustic tomography (MSOT) assisted with quantitative model-based reconstruction and unmixing algorithms for accurate mapping of oxygenation patterns in the peripheral tissues at 24 h after reperfusion. We found increased levels of [18F]FDG uptake and reduced MSOT oxygen saturation, indicating hypoxia in the thoracic spinal cord of tMCAO mice compared with sham-operated mice but not in the spleen. A positive correlation was observed between splenic and ipsilateral striatal [18F]FDG uptake. Reduced spleen size was observed in tMCAO mice compared with sham-operated mice ex vivo. tMCAO led to a significant increase in the numbers of mature T cells (CD4 and CD8) in femoral bone marrow tissues, concomitant with a stark reduction in these cell subsets in the spleen and their decrease in peripheral blood. The numbers of mature granulocytes (determined as CD11b+Gr1hi cells) decreased in bone marrow tissues and blood but increased in the spleen. The combination of quantitative PET and MSOT thus enabled the observation of hypoxia and increased metabolic activity in the spinal cord of tMCAO mice at 24 h after occlusion compared to sham-operated mice.

neuroscience↗

bioRxiv2021

In vivo imaging of cannabinoid type 2 receptors, functional and structural alterations in mouse model of cerebral ischemia by PET and MRI

Background and purposeBrain ischemia is one of the most important pathologies of the central nervous system. Non-invasive molecular imaging methods have the potential to provide critical insights into the temporal dynamics and follow alterations of receptor expression and metabolism in ischemic stroke. The aim of this study was to assess the cannabinoid type 2 receptors (CB2R) levels in transient middle cerebral artery occlusion (tMCAO) mouse models at subacute stage using positron emission tomography (PET) with our novel tracer [18F]RoSMA-18-d6, and structural imaging by magnetic resonance imaging (MRI). MethodsOur recently developed CB2R PET tracer [18F]RoSMA-18-d6 was used for imaging the neuroinflammation at 24 h after reperfusion in tMCAO mice. The RNA expression levels of CB2R and other inflammatory markers were analyzed by quantitative real-time polymerase chain reaction using brain tissues from tMCAO (1 h occlusion) and sham-operated mice. [18F]fluorodeoxyglucose (FDG) was included for evaluation of the cerebral metabolic rate of glucose (CMRglc). In addition, diffusion-weighted imaging and T2-weighted imaging were performed for anatomical reference and delineating the lesion in tMCAO mice. ResultsmRNA expressions of inflammatory markers TNF-, Iba1, MMP9 and GFAP, CNR2 were increased at 24 h after reperfusion in the ipsilateral compared to contralateral hemisphere of tMCAO mice, while mRNA expression of the neuronal marker MAP-2 was markedly reduced. Reduced [18F]FDG uptake was observed in the ischemic striatum of tMCAO mouse brain at 24 h after reperfusion. Although higher activity of [18F]RoSMA-18-d6 in ex-vivo biodistribution studies and higher standard uptake value ratio (SUVR) were detected in the ischemic ipsilateral compared to contralateral striatum in tMCAO mice, the in-vivo specificity of [18F]RoSMA-18-d6 was confirmed only in the CB2R-rich spleen. ConclusionsThis study revealed an increased [18F]RoSMA-18-d6 measure of CB2R and a reduced [18F]FDG measure of CMRglc in ischemic striatum of tMCAO mice at subacute stage. [18F]RoSMA-18-d6 might be a promising PET tracer for detecting CB2R alterations in animal models of neuroinflammation without neuronal loss.

neuroscience↗