L-DOPA induced extracellular dopamine increases in the ventromedial hypothalamus affects food intake by chickens on a lysine-free diet

Previous work from our laboratory suggests that ventromedial hypothalamic (VMH) dopamine levels were associated with decreased in food intake by chicken on a lysine-free diet. Dopamine in the VMH started to decrease from its baseline after presenting a lysine-free diet and subsequently food intake decreased. In the present study, the dopamine levels were manipulated by perfusing L-3-4-dihydroxyphenylalanine (L-DOPA) into the VMH of chicken using the in vivo microdialysis technique and food intake was concomitantly measured when chickens received an experimental lysine-free diet. A microdialysis probe was implanted into the VMH. L-DOPA was then administered locally at 2 μg/ml through the dialysis probe into the VMH of free moving chicken for 15 min and the extracellular levels of dopamine (DA), norepinephrine (NE) and serotonin (5-HT) were measured. Hourly food intake was also measured simultaneously both for control and experimental groups. Microdialysates collected from the VMH were analyzed using high performance liquid chromatography with electrochemical detection. Local administration of L-DOPA in chicken VMH increased extracellular levels of DA, which was observed at 1-2.5h. There were no differences of NE and 5-HT levels from baseline in either group. Food intake was higher in L-DOPA treated chickens than controls at 2h. Chickens received the lysine-free diet ate as much of their diet as the controls in the subsequent 2h when the DA level was kept higher than the baseline. The findings suggest that L-DOPA induced extracellular DA increased in the VMH which was temporarily followed by the restoration of food intake in the lysine-free group.