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M. Paques, M. Simonutti, B. El Mathari, J.-A. Sahel; In vivo Observation of the Locomotion of Microglial Cells in the Retina of Wild-Type Rodents. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5347.
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Microglial cells (MCs) are active sensors and reactive phagocytes of neural tissues. They are known to migrate and accumulate in areas of neuronal damage. Yet, there have been no direct observation of targeted microglial locomotion in vivo. Here, we observed noninvasively the migrating behaviour of individual MCs using a novel labeling procedure in wild-type rodents.
Cyanine dyes (indocyanine green, DiO or DiI) were intravitreally injected in Long Evans rats and C57 mice. In the following weeks, the fundus was observed by confocal scanning laser ophthalmoscopy (cSLO).
Immunohistochemistry showed that intravitreally injected cyanine dyes were sequestrated in MCs. High-contrast in vivo images of DiO or ICG-labelled MCs could be obtained by confocal scanning laser ophthalmoscopy up to several months after a single administration. Time-lapse observations showed that, in the basal state, cyanine+ MCs had intermittent, slow (1-10µm/h) locomotion accounting for progressive and extensive remodeling of the distribution of MCs. Following focal laser damage, MCs promptly (i.e. within 30-45 mn) initiated convergent, centripetal migration. There was a progressive extension of the recruitment area consistent with a centrifugal diffusion of chemoattractants. MCs up to 400 microns distant migrated into the scar at velocities up to 7µm/mn. Twenty-four hours later, while centripetal migration had ceased, persistent, nontargeted locomotion around and within injured sites was observed. At day 5 and thereafter, basal locomotion had resumed.
Activated MCs are prompt and mobile effectors of the acute inflammatory response in the retina. The locomotor response of MCs includes successively translocation into damaged areas and nontargeted, perilesional locomotion around the developing scar. To our knowledge, this is the first in vivo observation of MC locomotion.
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