Melatonin has been widely studied as a
protective agent against oxidative stress. However, the molecular mechanisms underlying neuroprotection in neurodegeneration and
ischemic stroke are not yet well understood. In this study, we evaluated the neuroprotective/
antioxidant mechanism of action of
melatonin in organotypic hippocampal cultures (OHCs) as well as in photothrombotic
stroke model in vivo.
Melatonin (0.1, 1, and 10 μM) incubated postoxygen and
glucose deprivation (OGD) showed a concentration-dependent protection; maximum protection was achieved
at 10 μM (90% protection). Next, OHCs were exposed to 10 μM
melatonin at different post-OGD times; the protective effect of
melatonin was maintained at 0, 1, and 2 hr post-OGD treatment, but it was lost at 6 hr post-OGD. The protective effect of
melatonin and the reduction in OGD-induced ROS were prevented by
luzindole (
melatonin antagonist) and α-bungarotoxin (α-Bgt, a selective α7 nAChR antagonist). In Nrf2 knockout mice, the protective effect of
melatonin was reduced by 40% compared with controls.
Melatonin, incubated 0, 1, and 2 hr post-OGD, increased the expression of
heme oxygenase-1 (HO-1), and this overexpression was prevented by
luzindole and α-bungarotoxin. Finally, administration of 15 mg/kg
melatonin following the induction of photothrombotic
stroke in vivo, reduced
infarct size (50%), and improved motor skills; this effect was partially lost in 0.1 mg/kg
methyllycaconitine (MLA, selective α7 nAChR antagonist)-treated mice. Taken together, these results demonstrate that postincubation of
melatonin provides a protective effect that, at least in part, depends on
nicotinic receptor activation and overexpression of HO-1.