Increasing expression of microglia in the retina after optic nerve transection in rats

Objective To investigate the expression of microglia after optic nerve transection in rats.Method Thirty healthy adult female SD rats were randomly grouped to experimental and control groups according to the random number table.The experimental group received an optic nerve transection (ONT) on their right eyes.ONT was performed 1.5 mm from the eye ball.The control group received a surgery on day 5. Rats were killed 7 days after the first operation. Retinal ganglion cells (RGC) were retrograde labeled by placing fluorogold dye on the stump of the optic nerve. Microglia was immunohistochemically stained in the retinas of normal and 7-day injury groups using ionized calcium adaptive molecular 1 ( Iba-1 ) as the marker.The protein levels of Iba-1 in the retinas were also examined using Western blotting.The number of RGCs was quantified using flatmount of retinas in the two groups.Results There were some resting microglia (Iba-1 positive cells) in the nerve fiber layer and inner plexiform layer in the normal control retina.However,microglia showed a moderately activated morphology with increased Iba-1 immunoreactivity in the stroma and processes up to outer plexiform layer. Western blotting showed that the levels of Iba-1 was lower in the normal retina and increased to 2.3-fold 7 days after injury (t =7.669,P =0.001 ).The number of RGCs after injury was ( 1182 ± 64 ) per mm2,decreased to 51％ in the normal groups (t =23.85,P ＜ 0.0001 ).Conclusions The results implicated that microglia was increased and partially activated after the optic nerve transection.This may be a manifestation of the self-protection mechanism of RGCs against the injury insult. Key words: Optic nerve injuries;  Microglia;  Retinal ganglion cells;  Rats