KiSS-1 neurones are direct targets for leptin in the ob/ob mouse

Leptin is an adipocyte-derived hormone that acts on the hypothalamus to influence feeding, metabolism and reproduction, but the cellular and molecular targets for the action of leptin in the brain have yet to be fully elucidated. Kisspeptins are encoded by the Kiss1 gene, which is expressed in the hypothalamus and has been implicated in the neuroendocrine regulation of gonadotrophin-releasing hormone secretion. We tested the hypothesis that kisspeptin-expressing neurones are targets for leptin. First, we examined whether leptin regulates the expression of Kiss1 by comparing levels of KiSS-1 mRNA in the arcuate nucleus among groups of mice having different circulating levels of leptin: (i) wild-type (WT); (ii) leptin-deficient ob/ob; and (iii) ob/ob mice treated with leptin. All mice were castrated to control for endogenous concentrations of gonadal steroids. KiSS-1 mRNA was significantly reduced in ob/ob compared to WT mice and levels of KiSS-1 mRNA in ob/ob mice treated with leptin were increased, but not fully restored to that found in WT animals. Second, we performed double-label in situ hybridisation for KiSS-1 mRNA and the leptin receptor (Ob-Rb) mRNA and found that almost one-half (approximately 40%) of KiSS-1 mRNA-expressing cells in the arcuate nucleus expressed Ob-Rb mRNA. These results demonstrate that KiSS-1 neurones are direct targets for regulation by leptin and suggest that the reproductive deficits associated with leptin-deficient states may be attributable, in part, to diminished expression of Kiss1.