Microglia are the resident immune cells of the central nervous system and play a crucial role in maintaining neuronal
health and function. Their dynamic behavior, that is, the constant extension and retraction of microglia processes, is
thought to be critical for communication between microglia and their cellular neighbors, such as neurons, astrocytes and
vascular endothelial cells.
Here, we investigated the morphology and dynamics of retinal microglia in vivo under normal conditions and in
response to focal laser injury of blood vessel endothelial wall, using a scanning laser ophthalmoscope (SLO) designed
specifically for imaging the retina of live mice. The multichannel confocal imaging system allows retinal microstructure,
such as the processes of microglia and retinal vasculature, to be visualized simultaneously. In order to generate focal
laser injury, a photocoagulator based on a continuous wave (cw) laser was coupled into the SLO. An acousto-optic
modulator chopped pulses from the cw laser. A tip-tilt-scanner was used to direct the laser beam into a blood vessel of
interest under SLO image guidance. Mild coagulation was produced using millisecond-long pulses.
Microglia react dynamically to focal laser injury of blood vessel endothelial walls. Under normal conditions,
microglia somas remain stationary and the processes probe a territory of their immediate environment. In response to
local injury, process movement velocity approximately doubles within minutes after injury. Moreover, the previously
unpolarized process movement assumes a distinct directionality towards the injury site, indicating signaling between the
injured tissue and the microglia. In vivo retinal imaging is a powerful tool for understanding the dynamic behavior of