Melatonin reduces infarction volume in a photothrombotic stroke model in the wild-type but not cyclooxygenase-1-gene knockout mice

Cyclooxygenase (COX)-2 plays a harmful role in cerebral ischemic/reperfusion injury, but the role of COX-1 is uncertain. In the present study, cerebral infarct was induced by photothrombosis. Intraperitoneal injections of melatonin at 15 g/kg or its vehicle were made at 0.5 hr before stroke and 24 and 48 hr after stroke. Cerebral blood flow (CBF) in the penumbra was monitored during stroke using a laser Doppler flowmeter. Sensorimotor behavior was evaluated using the turning in an alley and falling from a pole tests at 1 hr before stroke and 24 and 48 hr after stroke. Infarct volume was determined from the T2-weighted magnetic resonance images at 72 hr after stroke. During the first 15 min of stroke, CBF decreased in the penumbra in both homozygous COX-1-gene knockout and wild-type mice. Melatonin treatment improved the penumbral CBF in the wild-type mice. Mild poststroke impairment in sensorimotor behavior was detected by the turning in an alley test in which the COX-1-gene knockout mice performed better. Melatonin treatment did not affect the poststroke sensorimotor behavior. The relative infarct volume at 72 hr after stroke was 8.1% and 8.4% in the COX-1-gene knockout and wild-type mice, respectively. Melatonin treatment reduced the relative infarct volume to 6.3% in the latter but not in the former (8.2%). Thus, COX-1-gene knockout does not affect the brain's susceptibility to photothrombotic stroke. Melatonin treatment reduces infarct size in the wild-type mice following photothrombotic stroke partly via maintenance of penumbral CBF in which the COX-1-gene may play a role.