Treatment of cerebral ischemia with melanocortins acting at MC sub(4) receptors induces marked neurogenesis and long-lasting functional recovery

Melanocortins produce neuroprotection against ischemic stroke with subsequent long-lasting functional recovery, through melanocortin MC sub(4) receptor activation. Here we investigated whether the long-lasting beneficial effect of melanocortins in stroke conditions is associated with a stimulation of neurogenesis. Gerbils were subjected to transient global cerebral ischemia by occluding both common carotid arteries for 10 min; then, they were prepared for 5-bromo-2'-deoxyuridine (BrdU) labeling of proliferating cells. Delayed treatment (up to 9 h after the ischemic injury) for 11 days with the melanocortin analog [Nle super(4),d-Phe super(7)] alpha -melanocyte-stimulati ng hormone (NDP- alpha -MSH) improved learning and memory throughout the 50-day observation period. Immunohistochemical examination of the hippocampus on day 50 showed, in the dentate gyrus, an elevated number of BrdU immunoreactive cells colocalized with NeuN (used as indicator of mature neurons) and Zif268 (used as indicator of functionally integrated neurons). Retrospective analysis during the early stage of neural stem/progenitor cell development (days 3 and 4 after stroke) showed, in NDP- alpha -MSH-treated gerbils, a high degree of daily cell proliferation and revealed that NDP- alpha -MSH favorably affects Wnt-3A signaling pathways and doublecortin expression. Pharmacologic blockade of MC sub(4) receptors prevented all effects of NDP- alpha -MSH. These data indicate that treatment of cerebral ischemia with MC sub(4) receptor agonists induces, with a broad window of therapeutic opportunity, long-lasting functional recovery associated with a large number of mature and likely functional newborn neurons in brain injured areas. Our findings reveal previously undescribed effects of melanocortins which might have major clinical implications.