In response to injury, the adult mammalian retina shows signs of structural remodeling, possibly in an attempt to preserve or regain some of its functional neural connections. In order to study the mechanisms involved in injury-induced plasticity, we have studied changes in
growth associated protein 43 (GAP-43) after
retinal ischemia/reperfusion in the rat.
GAP-43 is a marker for neuronal remodeling and is involved in synapse formation. Ischemic injury of the rat retina was induced by 60 min of
ischemia followed by reperfusion times varying from 2h up to 4 weeks.
GAP-43 mRNA levels were significantly increased between 12h and 72 h reperfusion with a peak around 24h.
GAP-43 specific
antibodies showed that the total amount of
GAP-43 labeling in the inner plexiform layer was diminished after 12h of reperfusion by approximately 35% and remained at this level up to 1 week postischemia despite the reduction in thickness of this layer during this period resulting from the
ischemia-induced cell loss. At 2 and 4 weeks reperfusion, the amount of labeling was reduced by 70%, simultaneously with a decrease of
GAP-43 transcript level. Between 72 h up to 2 weeks postischemia, the induction of intense
GAP-43 labeling was observed in NeuN- and
beta-tubulin-positive
ganglion cell somata and in horizontally and vertically oriented processes in the inner plexiform layer.
Ischemia also induced
GAP-43 expression in some GFAP-positive Müller cells. Double-labeling showed that in controls and after
ischemia GAP-43 was expressed by some amacrine cells of the glycinergic (
glycine transporter 1),
calretinin-positive, and dopaminergic (
tyrosine hydroxylase) subpopulations. No increase of
GAP-43 expression levels was found in these amacrine cells. The results demonstrate that
ganglion cells show an elevated expression of
GAP-43 after
ischemia-inflicted damage. These findings suggest a temporal window during which
ganglion cells may remodel their neuronal network in the damaged retina.