2018 Volume 39 Pages 121-130
Ghrelin is involved in the brain reward circuits via dopamine neurons related to motivational properties. Here, we showed the relevance of ghrelin as an initiator of voluntary exercise in ghrelin knockout (GKO) mice. The plasma ghrelin concentration showed a bimodal diurnal rhythm with peaks at the beginning and end of the dark phase in the wild type (WT) mice. Although predominant increases in wheel running activity were observed accordant to both peaks of plasma ghrelin in the WT mice, those were severely attenuated in the GKO mice. A single injection of ghrelin receptor agonist brought about marked enhancement of wheel running activity, in contrast to no effect by the continuous administration. The brain dopamine level was attenuated in GKO mice compared to that in WT mice. These findings suggested that the surge in ghrelin should play a crucial role in the motivation for voluntary exercise via the central hedonic dopamine system.
