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J. Lee, K. J. Liang, W. T. Wong; Dynamic Imaging of Retinal Microglia in Explant Tissue Using Time-Lapse Confocal Microscopy. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4260. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Microglia in the retina, like those in other parts of the central nervous system (CNS), are the resident immune cells of the neural parenchyma. In intact mouse cerebral cortex, resting microglia exhibit prominent structural dynamism. Similar findings in the retina have not yet been demonstrated. We aim to characterize the behavior of resting retinal microglia using time-lapse confocal microscopy and determine the nature of microglial response to focal laser injury.
Retinal explants were acutely isolated from transgenic CX3CR1+/GFP mice in which microglia are specifically labeled with green fluorescent protein. Live tissue time-lapse confocal imaging was used to follow the morphology of retina microglia over time. Recordings were performed in CX3CR1+/GFP and CX3CR1GFP/GFP animals aged postnatal day 12 to 6 month. Observations of microglia following focal argon laser injury were also made.
Retinal microglia demonstrated marked structural dynamism in their processes. These movements consist of constant and repeated extensions and retractions of processes, and generation and elimination of processes. The average terminal process displayed a velocity of 5.17 ± 4.62 microns/min. Global cell process movement was balanced between extensions and retractions. These movements were directed around the soma in no preferential direction. Movements appear qualitatively similar in all animals studied, regardless of age or genotype, and in deep as well as superficial layers of the retina. In response to argon laser injury, nearby microglia preferentially reoriented their processes toward the injury site, maintained constant surveying movements, and at times migrated towards the injury site by a slow translocation of its soma and processes.
Retinal microglia, like other CNS microglia, exhibit marked structural motility in their processes that are well adapted to a constant and rapidly sampling of their environment. This phenomenon, while uniformly distributed in the resting state, can be redirected in cases of a focal injury, a finding that may have implications in the endogenous role of microglia in the retina and the underlying retinal tissue response to therapeutic laser treatment.
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