Tyrosine and tryptophan influence on tonic immobility in the chicken

The serotonergic and catecholaminergic systems have been shown to affect both tonic immobility and food intake in the domestic fowl. Tryptophan, the amino acid precursor of serotonin, has been demonstrated to influence tonic immobility and food intake when injected intraperitoneally. Tyrosine, amino acid precursor of the catecholamines, is also known to affect food intake when administered orally. In two experiments, tryptophan and tyrosine were intubated intragastrically into male chickens at levels known to affect food intake, and their effect on tonic immobility was measured. Tryptophan and tyrosine delivered intragastrically had no effect on either duration or susceptibility of tonic immobility. These data suggest that changes in appetite observed as a result of orally administered tyrosine and tryptophan were not due to a general inhibition or stimulation of the central nervous system.