Following transient
retinal ischemia, there is neuronal cell death, breakdown of the blood-retinal barrier, activation of microglia and infiltration by hematogenous cells. The early appearance of
cyclooxygenase-2 (COX-2) following an ischemic event may be responsible for signaling some of the responses that lead to neurodegeneration. We have determined the time courses of changes in
protein levels and cellular localizations of COX-2 in the rat retina after transient
ischemia. In the normal rat retina, COX-2 immunoreactivity was present in neurons in the INL and
ganglion cell layer (GCL). Six to 12 hr after
ischemia, COX-2 immunoreactivity was upregulated/induced in horizontal cells, amacrine cells, retinal ganglion cells, displaced amacrine cells of the INL and GCL, and Müller cells. The
NMDA-receptor antagonist,
MK801, blocked the increased COX-2
protein level and COX-2 immunoreactivity in neurons of the INL and GCL, but did not affect the induction of COX-2 in Müller cells after
ischemia. The selective
COX-2 inhibitor,
SC-58236, prevented apoptotic cell death and was neuroprotective against loss of retinal ganglion cells after
ischemia. Following transient
ischemia, the selective
COX-2 inhibitor did not prevent breakdown of the blood-retinal barrier or activation of microglia. However, the selective
COX-2 inhibitor reduced infiltration of hematogenous cells into the retina. These results suggest that the early, increased activity of COX-2 signals neurodegenerative events following
retinal ischemia.