To stereotactically inject lysolecithin and generate two in vivo lesions at different stages of myelination in the contralateral internal capsules (ICs). To conduct histological characterization and ex vivo MRI validation of the generated lesions.

 

Therapeutic interventions capable of halting demyelination and promoting remyelination are topics of intense research in demyelinating disorders of the central nervous system. A major hindrance to translating basic science to clinical practice is the lack of in vivo measures that are truly indicative of myelin changes and not due to other structural changes. In particular, establishing neuroimaging protocols requires live animals with multiple controlled lesions.

For establishing coordinates of the injection site, 4 mice underwent stereotactic surgery for injecting visible dye into the IC and were sacrificed post-surgery for analysis. For histological validation, stereotactic surgery was conducted in 5 mice to inject lysolecithin. 17 days later, a second stereotactic surgery was conducted to inject lysolecithin into the contralateral IC. Animals were sacrificed for histology 5 days post-surgery. An additional, 4 animals underwent a stereotactic surgery for ex vivo MRI scanning validation.

Position of the dye confirmed that the stereotactic coordinates of 3.55mm ML, -0.9 mm AP and 2.9 mm DV at 30° approach angle, targeted the dorsal tip of IC. Solochrome staining showed higher area fraction stained for myelin at first lesion site compared to very low staining at the second lesion site. Ex vivo MRI scanning confirmed that the targeted ICs were hypo-intense in T2 weighted high resolution images. 

The results validate the methodology to generate multiple lesions in live mice at different stages of remyelination. This will allow comparing signal generated by two lesions at different stages of repair within the same image using different MRI modalities. Additionally, the model has application in testing novel therapies aimed at promoting myelin repair.