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FRIMEDBIO-Fri prosj.st. med.,helse,biol

Does the gut hormone ghrelin act as a general reward enhancer?

Alternative title: Øker bukhormonet ghrelin belønningens verdi?

Awarded: NOK 6.6 mill.

Project Manager:

Project Number:

275316

Application Type:

Project Period:

2018 - 2023

Location:

Partner countries:

Ghrelin is a gut hormone that affects appetite and food intake. However, rat and human studies suggest that it does more than that. It increases intake of particularly fats and sugars, affects cocaine and alcohol usage, and alters sexual motivation in rats. Therefore, we propose that ghrelin generally increases the attractiveness of different types of rewards. In this project, we will investigate 1) how ghrelin influences the experience of gentle touch, sweet taste and social rewards in humans by collecting subjective ratings and measuring brain activity with functional magnetic resonance imaging (fMRI); 2) if ghrelin enhances positive reactions to tickling in rats, particularly the emission of ultrasonic vocalisations (USV). USV are sounds that express the rat?s emotional state. To investigate this, ghrelin or saline solution will be injected before the behavioural and brain reactions to the different pleasant stimuli are assessed. This study can deliver causal evidence for ghrelin?s influence on the experienced pleasantness of food and non-food stimuli. The results would further develop theories about ghrelin's function and help to better understand the various factors which make experiences rewarding, as well as the underlying biological systems. The results could also be relevant for therapeutic purposes because blunted pleasantness experiences can reduce well-being. Also, various psychiatric disorders such as depression and schizophrenia are characterized by anhedonia, a reduced ability to feel pleasure. If experienced reward can be increased through ghrelin, it may be used to treat anhedonia.

- our results contribute to our understanding of ghrelin's role in enhancing the subjective value of pleasant odours, gentle touch, sweet taste and social rewards - we found no evidence for ghrelin to target neurobiological pathways involved in touch and social reward in humans - and therefore, no support for our theory that ghrelin acts as a general amplifier of rewards in humans. However, some support for such a role in rats, at least with respect to social rewards. These results increase our understanding of ghrelin's role in rewards beyond food reward and can therefore contribute to theory development. They can be expected to stimulate research on the involvement of ghrelin in social reward.

Ghrelin is a hormone that affects appetite and food intake, but also increases intake of drugs such as cocaine and alcohol. This effect has been attributed to ghrelin activating the reward system in the brain. Because the reward system is stimulated in the same way by different kinds of rewards (food, alcohol, music, pleasant touch, etc.), we assume that ghrelin generally increase the positive experience and the attractiveness of different types of rewards. The goal of this project is to examine how ghrelin contributes to the positive experience of gentle touch, sweet taste and social rewards in humans, and whether it also enhances the reward value of tickling in rats. In order to obtain as comprehensive a picture of ghrelin's function as possible, psychophyscial measurements, subjective estimates and measurement of brain activation using functional magnetic resonance imaging (fMRI), and a behavioural study in rats will be combined. Ghrelin or saline solution will be injected, after which the behavioural and brain reaction to the different pleasant stimuli is assessed. This would be the first time to deliver causal evidence for a connection between the ghrelin system and the experience of pleasantness in the reaction to different food and non-food stimuli. The results would contribute to theory development about ghrelin's function and to the understanding of factors contributing to rewarding experiences. The project can thus provide insight into the biological systems that support our emotional reactions to pleasant primary and secondary rewards. The results would also be relevant for therapeutic purposes because numbed pleasantness experiences can reduce well-being. An increase of experienced reward through ghrelin would therefore pave the way to treat anhedonia, a reduced ability to feel pleasure, which characterises various psychiatric disorders such as depression and schizophrenia.

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Funding scheme:

FRIMEDBIO-Fri prosj.st. med.,helse,biol

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