Protective effect of melatonin against hippocampal DNA damage induced by intraperitoneal administration of kainate to rats.

The pineal hormone melatonin protects neurons in vitro from excitotoxicity mediated by kainate-sensitive glutamate receptors and from oxidative stress-induced DNA damage and apoptosis. Intraperitoneal injection on kainate into experimental animals triggers DNA damage in several brain areas, including the hippocampus. It is not clear whether melatonin is neuroprotective in vivo. In this study, we tested the in vivo efficacy of melatonin in preventing kainate-induced DNA damage in the hippocampus of adult male Wistar rats. Melatonin and kainate were injected i.p. Rats were killed six to 72 h later and their hippocampi were examined for evidence of DNA damage (in situ dUTP-end-labeling, i.e. TUNEL staining) and for cell viability (Nissl staining). Quantitative assay was performed using computerized image analysis. At 48 and 72 h after kainate we found TUNEL-positive cells in the CA1 region of the hippocampus; in the adjacent sections that were Nissl-stained, we found evidence of cell loss. Both the number of TUNEL-positive cells and the loss of Nissl staining were reduced by i.p. administration of melatonin (4 x 2.5 mg/kg; i.e. 20 min before kainate, immediately after, and 1 and 2 h after the kainate). Our results suggest that melatonin might reduce the extent of cell damage associated with pathologies such as epilepsy that involve the activation of kainate-sensitive glutamate receptors.