Melatonin Potentiates Cells Proliferation in the Dentate Gyrus Following Ischemic Brain Injury in Adult Rats

Melatonin, a potent free radical scavenger with neuroprotective property is thought to play some role in adult neurogenesis. The researchers investigated the influence of melatonin. on cell proliferations in the adult dentate gyrus of the hippocampus in transient ischemia. About 36 adult male sprague-dawley rats were assigned into either the 72 h or the 7 days post ischemic duration groups. The pre-ischemic melatonin groups received 5 mg kg(-1) melatonin intraperitoneally prior to induction of ischemia. Rats were anaesthetised with ketamine and perfusion fixed with saline followed by 4% paraformaldehyde. Brains were removed with one hemisphere sectioned at 50 mu m for Ki-67 immunohistochemical staining and the other hemisphere processed by plastic embedding, sectioned at 20 mu m and stained with Giemsa stain. Ki-67 positive cells and pyknotic cells were counted in all stained sections with 100x oil-immersion objective to obtain the estimated total cell number. In the 72 h post-ischemic duration, the estimated total Ki-67 cells was 5964 +/- 1894 for the pre-ischemic melatonin group and lowest (201 6 +/- 566) in the ischemic group. In the 7 day post-ischemic duration, the Ki-67 positive cells were 6900 +/- 2011 in the pre-ischemic melatonin and 2268 +/- 591 in the ischemic group. Pyknotic cell were highest in the ischemic group 462 +/- 52 and 486 +/- 46 in both the 72 h and 7 days durations, respectively. The results show that melatonin administration prior to ischemia enhances adult neurogenesis in the dentate gurus of the hippocampus in adult sprague-dawley rat brain.