Involvement of Hypothalamic Histamine H1 Receptor in the Regulation of Feeding Rhythm and Obesity

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Abstract
Histamine H1 receptors (H1-Rs) are found in peripheral tissues and in regions of the hypothalamus that are concerned with regulating body composition. In the present study, we investigated the detailed mechanisms of histamine H1-Rs in the development of obesity. Histamine H1-R knockout (H1KO) mice gradually developed mature-onset obesity, which was accompanied by hyperphagia and decreased expression of uncoupling protein-1 (UCP-1) mRNA. Both younger nonobese (12-week-old) and older obese (48-week-old) H1KO mice exhibited impairment of the responsiveness to the leptin. In addition, disruption of the diurnal rhythm of feeding occurred before the onset of obesity in H1KO mice. Correction of these abnormal feeding rhythms by means of scheduled feeding caused a reduction in obesity and associated metabolic disorders in H1KO mice. Furthermore, central administration of a histamine H1-R agonist affected feeding behavior, body weight, and c-fos-like immunoreactivity in the hypothalamus. Taken together, these findings suggest that histamine H1-Rs are crucial for the regulation of feeding rhythm and in mediating the effects of leptin. Early disruption of H1-R-mediated functions in H1KO mice may lead to hyperphagia and decreased expression of UCP-1 mRNA, which may contribute to the development of obesity in these animals. In addition, centrally acting histamine H1-R may be a novel therapeutic target for the treatment of obesity and related metabolic disorders.