The need to eat is initiated, in part, by a hormone known as ghrelin. Although ghrelin is known to be produced in the gut and to trigger the brain to promote eating, it remains to be determined precisely how ghrelin affects different parts of the brain. Now, in a study appearing online on October 19, in advance of publication in the December print issue of the Journal of Clinical Investigation, researchers from Yale University, have shown that in mice and rats ghrelin triggers the same neurons as delicious food, sexual experience, and many recreational drugs; that is, neurons that provide the sensation of pleasure and the expectation of reward. These neurons produce dopamine and are located in a region of the brain known as the ventral tegmental area (VTA). Tamas Horvath and colleagues showed that ghrelin bound its receptor on neurons of the VTA and triggered their production of dopamine. Importantly, infusion of ghrelin into the VTA of rats increased their food intake. Conversely, infusion of inhibitors of the ghrelin receptor into the VTA of rats decreased the amount they consumed after a 24-hour fast. This study identifies the VTA as a site of action for ghrelin to induce food intake. As this region of the brain is also triggered by many recreational drugs and is known to be produce the expectation of reward, the authors suggest that ghrelin stimulation of the VTA might be involved in diseases of food abuse.
TITLE: Ghrelin modulates the activity and synaptic input organization of midbrain dopamine neurons while promoting appetite
Tamas L. Horvath
Yale University School of Medicine, New Haven, Connecticut, USA.
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