Hypothalamic gastrin-releasing peptide receptor mediates an antidepressant-like effect in a mouse model of stress

Evidence has shown that gastrin-releasing peptide receptor (GRPR) is involved in responses to stress and anxiety. The primary role of GRPR is to stimulate corticotrophin-releasing hormone (CRH) or adrenocorticotropic hormone (ACTH) secretion. Thus, the mechanisms of GRPR signaling should be elucidated to discover novel therapeutic targets for treating depression. This study aimed to investigate GRPR alterations in the C57 mouse hypothalamus after the animals were subjected to stress and fluoxetine treatments. Specifically, we subjected the mice to isolation and chronic unpredictable mild stress (CUMS) for three weeks to establish an experimental model of depression. These mice were subsequently treated with fluoxetine for three weeks. Then, we performed the sucrose preference test and the open field test and measured food intake and body weight to explore the effects of stress and fluoxetine on activity and anhedonia. After fluoxetine treatment, we also assessed changes in the levels of GRPR expression in the hypothalamus using immunohistochemistry, western blotting, and real-time quantitative PCR (RT-PCR). We found that stressed mice showed significant reductions in locomotion, food intake/body weight, and sucrose preference; these reduced parameters indicated a state of anhedonia. Marked increases in mRNA and protein expression of GRPR in the hypothalamus of CUMS-exposed mice were also observed, although treatment with fluoxetine reversed these stress-induced changes. Our results also demonstrated the feasibility and effectiveness of the C57 mouse model of depression established by CUMS and isolation. After fluoxetine treatment was administered, the animals' depression symptoms were alleviated, and these behavioral alterations were accompanied by specific changes in mRNA and protein expression of GRPR in the hypothalamus. These results suggest that GRPR may be implicated in depression; therefore, new therapeutic targets of depression focused on GRPR signaling should be explored.