Evidence indicating participation of the serotonergic system in controlling feeding behavior in Coturnix japonica (Galliformes: Aves)

Abstract

We investigated participation of the brain serotonergic system in food intake control by using oral and systemic administration of serotonin precursors in quails (Coturnix japonica). Dietary supplemental tryptophan (0.1-50.0 g/kg) provoked a dose-dependent inhibition of food intake during a 5-h observation period, which persisted up to 24 h for doses of 30.0 and 50.0 g/kg. Normally fed and fasted animals treated with hydroxytryptophan (12.5-50.0 mg/kg) by the intracoelomic route showed an acute inhibition of food intake. Hypophagia in fasted birds was only effective when the precursor was administered immediately before food presentation. A similar response was obtained by administering serotonin (0.125-2.5 mg/kg, sc), with animals showing a hypnogenic response within the first ten minutes after administration, suggesting that, in contrast to mammals, the amine crosses the blood-brain barrier in quails. Administration of hydroxytryptophan at all doses tested induced significant dipsogenic behavior despite the concomitant hypnogenic response. The results suggest the involvement of serotonergic pathways in food intake control in quails and also show, for the first time, hypnogenic action induced by serotonin and a hyperdipsic effect elicited by hydroxytryptophan.