Role of Dopaminergic and Cannabinoidergic Receptors on Ghrelin-Induced Hypophagia in 5-Day-Old Broiler Chicken

The present study aimed to identify the role of dopaminergic and cannabinoidergic systems in the ghrelin-induced hypophagia among meat-type chickens. In the first experiment, intracerebroventricular (ICV) injection was applied to birds with control solution, D1 receptor antagonist (5 nmol), ghrelin (6 nmol), and D1 receptor antagonist plus ghrelin. The second to sixth experiments were similar to the first one, with the difference that D2 receptor antagonist (5 nmol), D3 receptor antagonist (6.4 nmol), D4 receptor antagonist (6 nmol), the precursor of dopamine (125 nmol), and 6-hydroxy dopamine (150 nmol) instead of D1 antagonist were injected into the broiler chickens. In experiment 7, control solution and different levels of ghrelin antagonists (5, 10, and 20 nmol) were injected. In experiment 8, the chickens were ICV injected with control solution, ghrelin antagonist (10 nmol), dopamine (40 nmol), and ghrelin antagonist plus dopamine. In experiments 9 and 10, CB1 and CB2 receptors antagonist (6.25µg and 5µg) were co-injected with ghrelin (6 nmol), respectively, measuring the food intake for 120 min after the injection. It was observed that ghrelin ICV injection considerably reduced food intake, whereas ghrelin antagonist increased food intake, depending on the dose (P<0.05). In addition, ghrelin-induced hypophagia was significantly attenuated by D1 receptor antagonist and 6-hydroxy dopamine (P<0.05), while the dopamine precursor considerably elevated the ghrelin-induced food intake (P<0.05). The dopamine-induced feeding behavior was diminished by the co-administration of [D-Lys-3]-GHRP-6 (10 nmol)+dopamine (40 nmol) (P<0.05). In addition, CB1 receptor antagonists enhanced the ghrelin influence on food intake (P<0.05). The results implied that the hypophagic impact of ghrelin was probably mediated by D1 and CB1 receptors within neonatal broilers.