Interaction of the dopaminergic and Nociceptin/Orphanin FQ on central feed intake regulation in chicken

1. The aim of the current study was to determine the effects of the central dopaminergic system on N/OFQ-induced feed intake in 3-h feed-deprived neonatal broilers.

2. In experiment 1, chicken received intracerebroventricular (ICV) injections of a control solution, SCH 23 390 (D₁ receptors antagonist, 5 nmol), N/OFQ (16 nmol) or their combination (SCH23 390 + N/OFQ). In experiment 2, a control solution, AMI-193 (D₂ receptors antagonist, 5 nmol), N/OFQ (16 nmol) or their combination (AMI-193 + N/OFQ) were ICV injected into chickens. In experiment 3, birds received ICV injections of a control solution, NGB2904 (D₃ receptors antagonist, 6.4 nmol), N/OFQ (16 nmol) and co-injection of NGB2904 + N/OFQ. In experiment 4, ICV injections of the control solution, L-741,742 (D₄ receptors antagonist, 6 nmol), N/OFQ (16 nmol) or their combination (L-741,742 + N/OFQ) were applied to broilers. In experiment 5, birds were ICV injected with control solution, L-DOPA (dopamine precursor, 125 nmol), N/OFQ (16 nmol) and L-DOPA + N/OFQ. Cumulative feed intake was recorded until 120 min after injection.

3. According to the results, ICV injection of N/OFQ significantly increased feed intake (P < 0.05). Co-injection of N/OFQ and D₁ receptor antagonist (SCH 23390) amplified hyperphagic effect of N/OFQ (P < 0.05). The N/OFQ-induced feed intake was increased by the D₂ receptor antagonist (P < 0.05). The hyperphagic effect of N/PFQ was weakened by co-injection of L-DOPA + N/OFQ (P < 0.05).

4. These results suggested that an interaction exists between dopamine and N/OFQ via D₁ and D₂ receptors on central feed intake in neonatal broiler chickens.