Feeding a Lysine-free Diet Decreases Food Intake without Changes in Hypothalamic Monoamine Concentrations in Growing Chicks

Abstract

The objective of this study was to determine the relationship between the early reduction in intake of a lysine-free diet and the changes in hypothalamic monoamine concentration in growing chicks. Food intake was hourly measured after presentation of the control and lysine-free diets for 7 hours. At first, third and seventh hours, chicks were decapitated and brains were removed. Monoamines were determined in the hypothalamus using a HPLC-ECD system. Food intakes from 4 to 5 and 5 to 6 hours were significantly less in chicks on the lysine-free diet than in the control chicks. Initial concentrations of monoamines (mean values with SD, ng per mg wet tissue) in the hypothalamic area including the three nuclei were as follows; serotonin (5-hydroxytryptamine, 5-HT) 9.0±1.8, norepinephrine 2.0±0.5, epinephrine 1.51±0.38 and dopamine O.405±0.100. In general, the concentration of hypothalamic monoamines did not significantly vary with the dietary lysine depletion. These results indicated that the early reduction of food intake by feeding the lysine-free diet occurred without the change in the overall concentration of monoamines in the hypothalamus.