Melatonin has many protective effects against
ischemic stroke, but the underlying neuroprotective mechanisms are not fully understood. Our aim was to explore the relationship between
melatonin's
neuroprotective effects and activation of the
MT2 melatonin receptor in a murine
ischemic-stroke model. Male ICR mice were subjected to a transient middle cerebral ischemic/reperfusional injury, and
melatonin (5 and 10 mg/kg, ip) was administrated once daily starting 2 h after
ischemia. More than 80% of the mice died within 5 days after
stroke without treatment.
Melatonin treatment significantly improved the survival rates and neural functioning with modestly prolonged life span of the
stroke mice by preserving blood-brain barrier (BBB) integrity via a reduction in the enormous amount of
stroke-induced
free radical production and significant gp91(
phox) cell infiltration. These protective effects of
melatonin were reversed by pretreatment with
MT2 melatonin receptor antagonists (4-phenyl-2-propionamidotetralin (4P-PDOT) and luzindole). Moreover, treatment with
melatonin after
stroke dramatically enhanced endogenous neurogenesis (doublecortin positive) and cell proliferation (ki67 positive) in the peri-
infarct regions. Most ki67-positive cells were
nestin-positive and NG2-positive neural stem/progenitor cells that coexpressed two neurodevelopmental
proteins (adam11 and adamts20) and the
MT2 melatonin receptor. RT-PCR revealed that the gene expression levels of doublecortin, ki67, adamts20, and adam11 are markedly reduced by
stroke, but are restored by
melatonin treatment; furthermore, pretreatment with
4P-PDOT and
luzindole antagonized
melatonin's restorative effect. Our results support the hypothesis that
melatonin is able to protect mice against
stroke by activating MT2
melatonin receptors, which reduces oxidative/inflammatory stress. This results in the preservation of BBB integrity and enhances endogenous neurogenesis by upregulating neurodevelopmental gene/
protein expression.