Time-dependent influence of glial cell line-derived neurotrophic factor (GDNF) was examined after 90 min of transient middle cerebral artery occlusion (MCAO) in rats. Treatment with GDNF significantly reduced the infarct volume stained with 2,3,5-triphenyltetrazolium chloride (TTC) when GDNF was topically applied at 0 and 1 h of reperfusion, but became insignificant at 3 h as compared to vehicle group. The protective effect of GDNF was closely related to the significant reduction of the number of TUNEL positive cells as well as immunofluorescently positive cells for active forms of caspases, especially active caspase-3 but not -9. Thus, the present study showed that topical application of GDNF significantly reduced infarct size in a time-dependent manner, while the therapeutic time window was shorter than other chemical compounds such as an NMDA receptor antagonist (MK-801) and a free radical scavenger (PBN). The effect of GDNF was stronger in suppressing active caspase-3 than active caspase-9.
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