Impact of the Central Histaminergic and Melanocortin Systems on Leptin-Induced Hypophagia in Neonatal Layer Chicken

The present study aimed to assess the probable impact of the central histaminergic and melanocortin systems on leptin-induced hypophagia in neonatal layer chickens. In experiment 1, the chickens received intracerebroventricular (ICV) injections of the control solution, 250 nmol of α-FMH, 10 µg of leptin, and α-FMH+leptin. Experimental groups 2-8 were injected the same as experiment 1. Nonetheless, the chickens in experiments 2-8 received ICV injections of 300 nmol of chlorpheniramine (H₁ receptor antagonist), 82 nmol of famotidine (H₂ receptor antagonist), 300 nmol of thioperamide (H₃ receptor antagonist), 0.5 nmol of SHU9119 (M₃/M₄ receptors antagonist), 0.5 nmol of MCL0020 (M₄ receptor antagonist), 30 µg of astressin-B (CRF₁/ CRF₂ receptors antagonist), and 30 µg of astressin2-B (CRF₂ receptor antagonist), instead of α-FMH, respectively. Food was provided for the birds immediately following the injection, and 30, 60, and 120 min after the injection, cumulative food intake (g) was measured. The findings pointed out that the ICV injection of leptin diminished food intake in neonatal chickens (P<0.05). The co-administration of M₃/M₄ receptor antagonist+leptin significantly decreased the hypophagic effect of leptin (P<0.05). A significant decrease was also detected in the hypophagic effect of leptin following the co-administration of the M₄ receptor antagonist and leptin (P<0.05). Moreover, the co-injection of the antagonists of CRF₁/CRF₂ receptors and leptin significantly mitigated the hypophagic effect of leptin (P<0.05). The co-injection of CRF₂ receptor antagonist and leptin led to a decrease in the hypophagic effect of leptin. As evidenced by the results of the current study the hypophagic effect of leptin is mediated by the receptors of H₁, H₃, M₃/M₄, and CRF₁/CRF₂ in neonatal layer chicken.