Hyperphagia and Decreases of Brain Serotonin in Rats Fed Freely on Sugar Rich Diet for Three Weeks

Abstract

In view of evidence linking obesity and hyperphagia with high intake of sugar and a role of brain serotonin in the regulation of appetite, the present study concerns the effects of consumption of sugar-rich diet for three weeks on food intake, growth rate and brain serotonin metabolism in rats. Sugar-rich diet was prepared by mixing standard rodent diet and table sugar in the ratio of 3:1 (w/w) and rats were fed freely on this diet for three weeks. Control rats were fed freely on standard rodent diet. Cumulative food intakes of 2nd and 3rd week but not of 1st week were greater in rats fed on sugar rich diet. Rats consuming sugar rich diet exhibited higher growth rates than controls after one week of the treatment but not after 2nd and 3rd week of the treatment Three weeks of sugar-rich diet consumption did not alter plasma levels of glucose and tryptophan and brain levels of tryptophan. 5-Hydroxytryptamine (5-HT; serotonin) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) concentrations decreased in the hypothalamus and in the whole brain. Dopamine (DA) turnover decreased in the hypothalamus but not in the whole brain. Metabolism of NA (noradrenaline) monitored in the hypothalamus was not altered. The results suggest that decreases of brain serotonin following prolonged consumption of sugar rich diet may be involved in the precipitation of hyperphagia.