We have previously shown that
cycloheximide significantly inhibited apoptosis, and reduced ensuing
cerebral infarction in a newborn rat model of cerebral hypoxiaischemia. This study was performed to determine the therapeutic window for
cycloheximide therapy. Seven day-old newborn rat pups were subjected to 100 min of 8%
oxygen following a unilateral carotid artery
ligation, and
cycloheximide was given at 0, 6, 12 and 24 hr after
hypoxia-
ischemia (HI). Apoptosis or
necrosis was identified by performing flow cytometry with a combination of fluorescinated
annexin V and
propidium iodide, and the extent of
cerebral infarction was evaluated with triphenyl tetrazolium
chloride (TTC) at 48 hr and 72 hr after HI, respectively. With
cycloheximide treatment at 0 hr after HI, both apoptotic and necrotic cells by flow cytometry were significantly reduced, only necrotic cells were significantly reduced at 6 and 12 hr, and no protective effect was seen if administration was delayed until 24 hr after HI compared to the HI control group.
Infarct volume, measured by TTC, was significantly reduced by 92% and 61% when
cycloheximide was given at 0 or 6 hr after HI respectively; however, there was an insignificant trend in
infarct reduction if
cycloheximide was administered 12 hr after HI, and no protective effect was observed when administration was delayed until 24 hr after HI. In summary,
cycloheximide was neuroprotective when given within 6 hr after HI in the developing newborn rat brain.