Interconnection between Adrenergic and Dopaminergic Systems in Feeding Behavior in Neonatal Chicks

Central dopaminergic (DAergic) and adrenergic systems have a prominent role in appetite regulation; however, their interaction(s) have not been studied in neonatal layer chickens.Therefore, the current study aimed to determine the interaction of central DAergic and noradrenergic systems in food intake regulation in neonatal layer chickens. In the first experiment, chickens received the intracerebroventricular (ICV) injection of a control solution, prazosin (i.e., α1 adrenergic receptor antagonist; 10 nmol), dopamine (DA; 40 nmol), and prazosin plus DA. The second to fifth experiments were similar to the first experiment except that the birds were injected with yohimbine (i.e., α2 receptor antagonist; 13 nmol), metoprolol (i.e., β1 adrenergic receptor antagonist; 24 nmol), ICI 118,551 (i.e., β2 adrenergic receptor antagonist; 5 nmol), and SR59230R (i.e., β3 adrenergic receptor antagonist; 20 nmol) instead of prazosin. In the sixth experiment, the chickens received ICV injection with the control solution and noradrenaline (NA; 75, 150, and 300 nmol). In the seventh experiment, the birds were injected with the control solution, SCH23390 (i.e., D1 DAergic receptor antagonist; 5 nmol), NA (300 nmol), and SCH23390 plus NA In the eighth experiment, the control solution, AMI-193 (i.e., D2 DAergic receptor antagonist; 5 nmol), NA (300 nmol), and AMI-193 plus NA were injected. Then, cumulative food intake was recorded at 30, 60, and 120 min after the injection. According to the obtained results, the ICV injection of DA (40 nmol) significantly decreased food intake in comparison to that reported for the control group (p <0.05). The co-injection of yohimbine plus DA significantly amplified DA-induced hypophagia in the neonatal chickens (p <0.05). In addition, the co-administration of ICI 118,551 plus DA significantly inhibited the hypophagic effect of DA in the neonatal chickens (p <0.05). Furthermore, NA (75, 150, and 300 nmol) significantly reduced food intake in a dose-dependent manner (p <0.05). The co-injection of SCH23390 plus NA decreased the hypophagic effect of NA in the neonatal chickens, compared to that reported for the control group (p <0.05). The co-injection of AMI-193 plus NA diminished NA-induced hypophagia, compared to that reported for the control group (p <0.05). The aforementioned results suggested that there is an interconnection between central DAergic and noradrenergic systems through α2/β2 adrenergic and D1/D2 DAergic receptors in food intake regulation in neonatal chicks.