Melatonin's protective action against ischemic neuronal damage is associated with up-regulation of the MT2 melatonin receptor.

Melatonin is a potent free radical scavenger and antioxidant and has protective effects against ischemic damage. In the present study, we examined the relationship between the neuroprotective effects of melatonin and the activation of MT2 melatonin receptor in the hippocampal CA1 region (CA1) after transient cerebral ischemia. MT2 immunoreactivity and protein levels were increased in the CA1 after ischemic damage. Most of MT2-immunoreactive cells were colocalized with astrocytes, not microglia, in the ischemic CA1. In the melatonin-sham group, MT2 immunoreaction and protein levels were increased compared with the sham group, and MT2 immunoreactivity and its protein levels in the melatonin-ischemia group were similar to those in the melatonin-sham group. In addition, melatonin treatment attenuated the activation of astrocytes and microglia. These results indicate that MT2 are increased and expressed in astrocytes in the ischemic region after an ischemic insult. The activation of MT2 melatonin receptor in the CA1 after melatonin treatment may be involved in the neuroprotective effect associated with melatonin after ischemic injury.