Investigating white matter alterations and secondary neurodegeneration with MRI imaging and pathology in a mouse model of ischaemic stroke

Abstract

Advances in acute ischaemic stroke treatment have increased survival rates, yet many individuals experience long-term complications such as post-stroke cognitive impairment and dementia. While the primary infarct is well characterised, the mechanisms driving chronic degenerative changes in remote but anatomically connected brain regions remain unclear, despite their importance for brain function and recovery after stroke. Emerging clinical imaging evidence suggests that white matter degeneration, secondary neurodegeneration and inflammation in areas like the corpus callosum and thalamus after a middle cerebral artery stroke may contribute to cognitive decline.

The aim of the current study was to examine remote grey and white matter alterations in anatomically connected brain regions following experimental cortical ischaemic stroke, with a particular focus on changes in cerebral perfusion, glial responses, and structural integrity.

This study is based on the hypothesis that stroke involves disturbances of the neurogliovascular unit in remote, anatomically connected brain regions, and that these disturbances are associated with degenerative changes affecting both grey and white matter.

We used in vivo MRI imaging and immunohistochemistry to investigate remote brain changes pre-surgery and one month after cortical ischemic stroke induced by distal middle cerebral artery occlusion in male C57BL/6J mice (stroke: n=5, sham: n=4). Cerebral blood flow (CBF) was measured using arterial spin labelling (ASL) MRI in the white and grey matter regions.

Diffusion tensor imaging (DTI) assessed white matter integrity via fractional anisotropy (FA) and mean diffusivity (MD). Immunohistochemistry evaluated astrocyte (GFAP) and microglia (Iba1) reactivity, axonal damage (APP), myelin integrity (MAG), and secondary neurodegeneration (NeuN).

Diffusion tensor imaging (DTI) assessed white matter integrity via fractional anisotropy (FA) and mean diffusivity (MD). Immunohistochemistry evaluated astrocyte (GFAP) and microglia (Iba1) reactivity, axonal damage (APP), myelin integrity (MAG), and secondary neurodegeneration (NeuN).

Immunohistochemistry revealed axonal damage, gliosis, and axon-myelin alterations in the connected grey and white matter regions, as well as secondary neurodegeneration in the thalamus. Our findings indicate that cortical stroke triggers chronic, region-specific alterations in anatomically connected brain areas, with distinct patterns of hypoperfusion, hyperperfusion, inflammation, and structural degeneration. This work provides a foundation for future studies using spatial transcriptomic approaches to define the molecular correlates of these remote neuroimaging and pathophysiological changes.