Interrupted blow flow in the brain, or cerebral ischemia, results in a lesion comprised of dying cells surrounded by the penumbra, a band of tissue containing cells at risk of dying. Biochemical elements, such as glutamate and glycogen, are vital to brain cells and play an important role in cell survival post-stroke. Spatially mapping these biochemical elements, using Fourier Transform Infrared (FTIR), at several time points in the post-stroke brain allows how us to gain a more complete biochemical picture of the recovering the stroke lesion and penumbra, to provide insights into potential therapeutic targets. 

We induced a permanent stroke in adult mice using the photothrombotic stroke model and collected brain sections at several time points post-stroke, ranging from 1h to 4 weeks. FTIR imaging was performed on the sections to map the distribution of biochemical elements, such as lipids, proteins, aggregated proteins, glycogen, lactate and glutamate. We then measured the concentration of these elements in different areas of the post-stroke brain at each time point. Immunohistochemistry was performed on adjacent tissues to correlate brain cell distribution (astrocytes, myelin, activated macrophage, etc.) with changes revealed by FTIR.

Significant biochemical and cellular distribution changes were observed in the ischemic lesion and penumbra at all time points study. During the first week post-stroke, the lesion shows decreased lipid and protein content. Loss of myelin is noticeable starting at 1h post stroke while astrocytes and activated macrophage appear around 24h and 48h post stroke, respectively, in the penumbra.

Looking at acute and chronic biochemical changes using FTIR imaging in an animal model of stroke