This PhD fellowship focuses on the assessment of astrocytic reactivity induced by tauopathy, associated with Alzheimer's disease, using PET imaging or 3D-autoradiography using the radioligand [11C]BU99008 or [3H]BU99008 specific for I2-BS receptors, target of astrocytic reactivity. The main objectives of this research project are: 1- to validate the specificity of the [11C]/[3H]BU99008 ligand binding in different models of tauopathy; 2- to characterise the signature of reactive astrocytes detected by BU99008; and 3- to assess the specific binding of [11C]/[3H]BU99008 as well as gene expression following a therapeutic strategy targeting I2-BS receptors in one of the tauopathy models. Our methodological approach adopts a multiscale perspective, combining PET imaging with microscopic and transcriptomic analyses, thus enabling a multiscale analysis ranging from macro (in vivo) to micro (in vitro). These studies not only provide a fundamental understanding of astrocytic reactivity, but also open important perspectives for the development of therapeutic strategies targeting astrocytic reactivity in the context of neurodegenerative diseases.