Actavia 0 Shojaei, M. Zendehdel, M. Babapour, V. Charkhkar, S. Hassanpour, S. 2015 2015-9-30 400-410 Opioidergic and serotonergic (5-HTergic) systems have crucial role in central regulation of food intake. This study was designed to investigate the role of the opioidergic system and the interaction with the 5-HTergic system in opioid-induced feeding behaviour in 3-h food-deprived (FD₃) neonatal layer-type chicks. In total 432 chickens were allocated into 9 experiments, each per 4 treatment groups. In Experiment 1, birds were intracerebroventricularly (ICV) injected with D-Ala2-NMe-Phe4-Glyol5-enkephalin (DAMGO), µ-opioid receptor agonist (125, 250, and 500 pmol). In Experiment 2, chickens were ICV treated with D-Pen², D-Pen⁵enkephalin (D-Pen^2,5enkephalin, DPDPE), δ-opioid receptor agonist (20, 40, and 80 pmol). In Experiment 3, the effect of ICV injection of U-50488H, κ-opioid receptor agonist (10, 20, and 30 nmol) was investigated in chicks. In Experiment 4, chickens were injected with para-chlorophenylalanine (PCPA), cerebral serotonin depletive (1.5 µg) + DAMGO (125 pmol). In Experiment 5, birds were treated with PCPA (1.5 µg) + DPDPE (40 pmol). In Experiment 6, birds received 1.5 µg PCPA + U-50488H (30 nmol). In Experiments 7-9, birds were injected like in Experiments 4-6, but with SB242084, 5-HT₂c receptor antagonist (1.5 µg) instead of the PCPA injection. Cumulative food intake was recorded until 3 h post injection. According to the results, the ICV injection of DAMGO significantly decreased whereas that of DPDPE + U-50488H increased food intake (P ≤ 0.05). Co-administration of PCPA + DAMGO significantly decreased hypophagia induced by DAMGO (P ≤ 0.05). PCPA had no effect on DPDPE + U-50488H-induced hyperphagia (P ≥ 0.05). SB242084 significantly attenuated the hypophagic effect of DAMGO (P ≤ 0.05), while SB242084 had no modulatory effect on the food intake induced by DPDPE + U-50488H (P ≥ 0.05). These results suggest that there is an interaction between the opioidergic and 5-HTergic systems mediating the hypophagic effect of µ-opioid receptors via the 5-HT₂c receptor in neonatal layer-type chicks. 9 60