Comparative Aspects of Microglia Reaction in White and Gray Matter

Objectives: Microglia are considered as the primary immune effector cells in the brain and have a critical role in all brain lesions. We wanted to find out if there is any difference in the way that white and gray matter microglia react to the same type of lesion. Material and Method: We used 14-16 weeks old single transgenic CX3CR1-EGFP mice, whereon microglia were labeled by expression of the green fluorescent protein EGFP and the L1-L2 dorsal spinal columns were exposed. After 10 min of continuous base line image acquisition, we made a micro-lesion by focusing and raising the power of the laser and, than, we monitored it for an additional hour. Laser-lesion and image recording were also made in the right somato-sensory cortex. We quantified microglial response and compared white vs. grey matter. Results: 5-10 min after the lesion, microglia already showed signs of polarization by extending their processes both in white and gray matter. Processes were sent by the microglial bodies situated at a distance of 50 to 100 µm, depending on the lesion size. Microglial processes did not display a preferred target site from the lesion; in contrast, they formed a uniform “shielding” ring around the lesion. Conclusions: Microglia showed targeted responses to acute injuries in grey and white matter also; no major differences were observed besides the speed of the process, due probably to particular cortex and spine architecture.