Effect of opioid receptors agonists on feeding behaviour using different diets in ad libitum fed neonatal chicken

Despite progress in studying the role of opioids in reward, the effect of opioid receptors on feeding behaviour in ad libitum fed meat-type chicken offered different diet types is still unclear. So in this study, 12 experiments (each included 4 groups) were designed to determine the role of μ, δ, and κ receptors with different diets on feeding responses in ad libitum fed neonatal chicken. In Experiment 1, group A chicken were intracerebroventricularly (ICV) injected with saline, groups B-D chicken were ICV injected with DAMGO (µ-opioid receptor agonist; 125, 250, and 500 pmol), then standard diet without fat was offered. In Experiment 2, group A chicken were ICV injected with saline, groups B-D chicken were ICV injected with DAMGO (125, 250, and 500 pmol) and diet with nutrient energy ratio 20% below standard was provided to the birds. Experiments 3-4 were similar to Experiment 1, except after injection, diets containing nutrient energy ratio 20% above standard and standard diet with fat were provided to the birds, respectively. In Experiment 5, chicken were ICV injected with saline, DPDPE (δ-opioid receptor agonist) at doses of 20, 40, and 80 nmol, and then received standard diet without fat. Experiments 6-8 were similar to Experiment 5 in which diet containing nutrient energy ratio by 20% lower than standard, diet containing nutrient energy ratio by 20% higher than standard, and diet containing fat were provided instead of standard diet without fat to the birds, respectively. In Experiment 9, birds received ICV injection of saline and U-50488H (κ-opioid receptor agonist; 10, 20, and 40 nmol) and were provided standard diet without fat. Experiments 10-12 were similar to Experiment 9 but after ICV injection, birds were fed diet containing by 20% lower nutrient energy ratio, diet containing by 20% higher nutrient energy ratio, and standard diet containing fat, respectively. Then the cumulative food intake was measured until 180 min post injection. According to the results, DAMGO decreased while DPDPE and U-50488H increased the food intake (P < 0.05). These findings suggest endogenous governing food preferences via δ- and κ-opioid receptor in ad libitum fed neonatal chicken.