Ghrelin promotes neurologic recovery and neurogenesis in the chronic phase after experimental stroke

The neuroprotective and proangiogenic potential of ghrelin in acute ischemic stroke has been demonstrated in experimental studies. However, the transferability of these results is limited as ghrelin was administered either before or very early after stroke onset and follow-up was limited to the first days after stroke. The aim of this study was therefore to close and extend this knowledge gap. To this end, we investigated the effect of ghrelin in two different translational animal models, one investigating acute and one investigating long-term structural and functional recovery after experimental stroke.

Middle cerebral artery occlusion (MCAO) or photothrombotic stroke was induced in 65 adult male Wistar rats. Eleven sham-operated animals served as controls. The rats were treated with either ghrelin, the ghrelin receptor antagonist [D-Lys]-GHRP-6 or a control substance. Up to four weeks after ischemia, behavioral tests such as the cylinder test, the tape removal test, and the rotarod test were performed to examine sensorimotor deficits, and the Morris water maze was performed to examine effects on the acquisition and consolidation of new memories. The structural outcome was determined by a differential analysis of neurogenesis in relation to survival and proliferation of newborn neurons in the post-ischemic brain, angiogenesis and determination of infarct size.

Ghrelin treatment improved motor and somatosensory functions and preserved the consolidation of new memories after photothrombotic stroke. As a structural correlate, long-term survival and sustained proliferation of neuronal cells after stroke was significantly increased in ghrelin-treated rats, while angiogenesis remained unaffected. In contrast to these neuroregenerative mechanisms, ghrelin did not induce immediate neuroprotective effects after MCAO.

Our results suggest that ghrelin has a significant pro-neuroregenerative effect by enhancing long-term survival and sustained proliferation of neurons in the dentate gyrus and peri-infarct area, thus promoting functional recovery. Overall, ghrelin represents a promising target in the subacute and chronic phase after ischemic stroke.