title: Ghrelin-induced hippocampal neurogenesis and enhancement of cognitive function are mediated independently of GH/IGF-1 axis: lessons from the spontaneous dwarf rats.
abstract: We recently have reported that ghrelin modulates adult hippocampal neurogenesis. However, there is a possibility that the action of ghrelin on hippocampal neurogenesis could be, in part, due to the ability of ghrelin to stimulate the GH/insulin-like growth factor (IGF)-1 axis, where both GH and IGF-1 infusions are known to increase hippocampal neurogenesis. To explore this possibility, we assessed the impact of ghrelin on progenitor cell proliferation and differentiation in the dentate gyrus (DG) of spontaneous dwarf rats (SDRs), a dwarf strain with a mutation of the GH gene resulting in total loss of GH. Double immunohistochemical staining revealed that Ki-67-positive progenitor cells and doublecortin (DCX)-positive neuroblasts in the DG of the SDRs expressed ghrelin receptors. We found that ghrelin treatment in the SDRs significantly increased the number of proliferating cell nuclear antigen- and BrdU-labeled cells in the DG. The number of DCX-labeled cells in the DG of ghrelin-treated SDRs was also significantly increased compared with the vehicle-treated controls. To test whether ghrelin has a direct effect on cognitive performance independently of somatotropic axis, hippocampus-dependent learning and memory were assessed using the Y-maze and novel object recognition (NOR) test in the SDRs. Ghrelin treatment for 4 weeks by subcutaneous osmotic pump significantly increased alternation rates in the Y-maze and exploration time for novel object in the NOR test compared to vehicle-treated controls. Our results indicate that ghrelin-induced adult hippocampal neurogenesis and enhancement of cognitive function are mediated independently of somatotropic axis.
authors.affiliation: Department of Pharmacology and Medical Research Center for Bioreaction to ROS and Biomedical Science Institute, School of Medicine, Kyung Hee University, Seoul, Korea.
authors.forename: Endan
authors.initials: E
authors.lastname: Li
authors.forename: Yumi
authors.initials: Y
authors.lastname: Kim
authors.forename: Sehee
authors.initials: S
authors.lastname: Kim
authors.forename: Seungjoon
authors.initials: S
authors.lastname: Park
mesh_terms: D000215:Acylation; D000818:Animals; D001522:Behavior, Animal; D015415:Biomarkers / Q000378:metabolism; D049109:Cell Proliferation; D003071:Cognition; D018891:Dentate Gyrus / Q000166:cytology / Q000378:metabolism; D000089662:Doublecortin Protein; D054439:Ghrelin / Q000378:metabolism*; D013006:Growth Hormone / Q000235:genetics / Q000378:metabolism*; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D018782:Maze Learning; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D058953:Neural Stem Cells / Q000166:cytology / Q000378:metabolism; D055495:Neurogenesis; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D011922:Rats, Mutant Strains; D021641:Recognition, Psychology
chemical_list: D015415:Biomarkers; C000714848:Dcx protein, rat; D000089662:Doublecortin Protein; D054439:Ghrelin; D009419:Nerve Tissue Proteins; C548904:insulin-like growth factor-1, rat; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone