Failure of tryptophan load-induced increases in brain serotonin to alter food intake in the rat

The effects on food consumption of 50 and 100 mg/kg $\text{1}$-tryptophan injections, versus control saline treatment, were compared in 24-hour food-deprived rats at two time points in the rats' daily light-dark cycle. No effect of the two tryptophan doses, relative to the saline treatment, on food intake was observed, although tryptophan loading significantly raised brain tryptophan, serotonin, and 5-hydroxyindoleacetic acid levels, in a dose-dependent manner, over baseline concentrations. Implications of these data for serotonergic modulation of food intake regulation are considered.