Central dopaminergic, serotoninergic, as well as GABAergic systems mediate NMU-induced hypophagia in newborn chicken

Dopaminergic, serotoninergic, and GABAergic systems influence feeding; however, it is unknown how these chemicals interact with neuromedin U (NMU)-induced feeding in birds. In the current study, ten trials were conducted to determine the links between the above-mentioned systems and NMU.

In the foremost experimentation, chickens were given intracerebroventricularly injections of NMU (0.1, 1, and 10 µg). NMU (10 µg), SCH23390 (5 nmol), a D₁ receptor antagonist, and NMU + SCH23390 were administered in the second experiment. In subsequent experiments, instead of SCH23390, were applied AMI-193 (5 nmol D₂ receptor antagonist), NGB2904 (6.4 nmol D₃ receptor antagonist), L-741,742 (6 nmol D₄ receptor antagonist), 6-OHDA (2.5 nmol dopamine inhibitor), SB242084 (5-HT_2c receptor antagonist, 1.5 μg), 8-OH-DPAT (5-HT_1A receptor agonist, 15.25 nmol), picrotoxin (GABA_A receptor antagonist, 0.5 μg), and CGP54626 (GABA_B receptor antagonist, 20 ng). Then, cumulative intake of food was recorded for 2 h.

According to the results, NMU reduced feeding when compared to the control group (p < 0.05). The NMU-induced hypophagia was reduced with co-injection of NMU and SCH23390 (p < 0.05). Hypophagia was diminished with NMU and AMI-193 (p < 0.05). NMU + NGB2904 and NMU + L-741,742 co-injections had no influence (p > 0.05). 6-OHDA reduced the hypophagia (p < 0.05). NMU and SB242084 decreased the hypophagia (p < 0.05), whereas NMU and 8-OH-DPAT had no effect (p > 0.05). The effects were amplified with picrotoxin (p < 0.05). NMU with CGP54626 had no influence on the hypophagia (p > 0.05).

Thus, NMU-induced hypophagia is probably mediated by D₁/D₂, 5-HT_2c, and GABA_A receptors in neonatal chicks.