Glucagon-like peptide-1, corticotropin-releasing hormone, and hypothalamic neuronal histamine interact in the leptin-signaling pathway to regulate feeding behavior

Glucagon-like peptide-1 (GLP-1), corticotropin-releasing hormone (CRH), and hypothalamic neuronal histamine suppress food intake,a target of leptin action in the brain. This study examined the interactions of GLP-1, CRH, and histamine downstream from the leptin-signaling pathway in regulating feeding behavior. Infusion of GLP-1 into the third cerebral ventricle (i3vt) at a dose of 1 mu g significantly decreased the initial 1 h cumulative food intake in rats as compared with phosphate-buffered saline (PBS) controls. The GLP-1-induced suppression of feeding was partially attenuated by intraperitoneal pretreatment with alpha-fluoromethylhistidine (FMH), a specific suicide inhibitor of histidine decarboxylase, which depletes hypothalamic neuronal histamine. Pretreatment with alpha-helical CRH (10 mu g/rat, i3vt), a nonselective CRH antagonist, abolished the GLP-1-induced suppression of feeding completely. I3vt infusion of GLP-1 increased the CRH content and histamine turnover assessed using the pargyline-induced accumulation of tele-methyl histamine(t-MH), a major metabolite of neuronal histamine,in the hypothalamus. The central infusion of CRH also induced the increase of histamine turnover and CRH receptor type 1 was localized on the cell body of histamine neuron. Pretreatment with exendin(9-39), a GLP-1 receptor ant agonist, attenuated the leptin-induced increase in CRH content of the hypothalamus. Finally,i3vt infusion of leptin also increased histamine turnover in the hypothalamus. Pretreatment with exendin(9-39), alpha-helical CRH or both antagonists attenuated the leptin-induced responses of t-MH levels in the hypothalamus. These results suggest that CRH or hypothalamic neuronal histamine mediates the GLP-1-induced suppression of feeding behavior, that CRH mediates GLP-1 signaling to neuronal histamine and that a functional link from GLP-1 to neuronal histamine via CRH constitutes the leptin-signaling pathway regulating feeding behavior.