Biol. Pharm. Bull. 29(3) 557—559 (2006)

5-HT) plays an important role in the central nervous system and that 5-HT participates in neurological disorders such as depression, anxiety or schizophrenia. Several drugs affecting serotonergic neurons are administered as therapy of these diseases. 5-HT is also a significant factor of regulation of food intake. A serotonin-releasing drug fenfluramine and selective serotonin reuptake inhibitors (SSRIs) reduce food intake and modify bulimia in humans. Furthermore, the 5HT receptor agonists such as the 5-HT2A receptor agonist DOI or 5-HT2C receptor agonist mCPP can elicit hypophagia in rats and mice. Anorectic effects of 5-HT may involve both the central and peripheral nervous system, since central and peripheral injection of 5-HT or the peripheral 5-HT receptor agonist can decrease food intake. It has been reported that administration of the 5-HT precursor, 5-hydroxytryptophan (5-HTP) decreases food intake in rodents. It is considered that the anorectic effects of 5-HTP are caused by 5-HT formation. Supplementation of 5-HTP tablets for reducing body weights have been used in Europe and U.S.A. Leptin is an adipocytokine, released from adipose tissue. Leptin is a strong anorectic factor that affects the hypothalamus, which controls food intake. It is well known that mice deficient in leptin display marked hyperphagia and obesity. Leptin secretion is controlled by several hormones or peptides such as insulin, corticosterone or neuropeptide Y. We previously demonstrated that systemic injection of a 5-HT precursor, 5-HTP, increases serum leptin levels in mice. We further reported that hyperleptinemia elicited by 5-HTP is mediated by insulin but not corticosterone. Since both 5-HTP and leptin cause hypophagia, it is suggested that 5-HTP-induced anorexia may be related to its leptin-releasing effects. In this study, to clarify the involvement of leptin in 5-HTPinduced anorexia, we examined the correlation between serum leptin levels and food intake in normal mice and 5HTP-treated mice.