The effect of intracerebroventricular injection of L-DOPA and 6-hydroxy-dopamine on noradrenaline-induced food intake in layer chickens

Food intake is regulated by a complex system of central and peripheral signals which ‎interact ‎together to modulate appetite. Noradrenaline has an essential role in the central ‎control of food ‎intake in birds. On the other hand, dopamine (DA) is a hypophagic ‎agent in birds. ‎The present ‎study aimed to investigate the effect of L-DOPA and 6-‎hydroxy-dopamine on noradrenaline-induced food intake in neonatal chickens. A total ‎of ninety-six neonatal female laying hens (Hy‎line) were randomly divided into two ‎experimental groups. Immediately after ‎intracerebroventricular (ICV) injection of ‎control diluent (normal saline) or drug solution, ‎cumulative food intake (g) was ‎measured based on the ‎percentage of the body weight (%BW). ‎Control solution (normal ‎saline, group1), L-DOPA (125 nmol, group 2), noradrenaline (300 nmol, ‎group 3), and ‎L-DOPA + noradrenaline (group 4) were injected in the first experiment.‎ In the ‎second ‎experiment, the control solution (group1), 6-hydroxy-dopamine (6-OH-DA, 2.5 nmol, ‎‎group 2), noradrenaline (300 nmol, group 3), and 6-OH-DA + noradrenaline (group 4) ‎were ‎injected. The results showed that ICV injection of noradrenaline decreased food ‎intake (P<0.05). ‎Furthermore, co-injection of L-DOPA and noradrenaline significantly ‎amplified noradrenaline-induced hypophagia in neonatal chicks (P<0.05). In contrast, ‎co-injection of 6-OH-DA and ‎noradrenaline significantly reduced hypophagia induced ‎by noradrenaline in chicks (P<0.05). ‎According to the results, noradrenaline-induced ‎food intake is probably mediated by the ‎dopaminergic system in neonatal chickens.‎