title: Tryptophan-free diet: effects on the acoustic startle reflex in rats.
abstract: In Experiment 1, body weights of rats fed a powdered tryptophan-free (TF) diet decreased monotonically during a 13-day period. Control animals fed the same diet supplemented with 0.5% L-tryptophan gained weight. The groups did not differ significantly in acoustic startle amplitude measured at 2, 4, 6, 7, 9, 11, and 13 days despite a 28% decrease in whole-brain serotonin in the TF rats. In Experiment 2, daily intubation of rats with a syrup form of each diet maintained the two groups' body weights at comparable levels. TF diet intubation decreased whole-brain serotonin by 64% and produced significantly elevated startle amplitudes, which returned to control levels when 0.5% L-tryptophan was added to the diet. Changes in whole-brain serotonin level preceded changes in startle amplitude by several days. In Experiment 3, acute injections of 125 mg/kg L-tryptophan significantly reduced the startle amplitude of TF diet intubated rats and significantly raised their brain serotonin levels. The results show that acoustic startle reflex is increased by a TF diet, provided the animals receive adequate nourishment, and suggest that this facilitation may result from depletion of brain serotonin.
mesh_terms: D000161:Acoustic Stimulation; D000818:Animals; D004032:Diet; D006801:Humans; D007441:Intubation, Gastrointestinal; D008297:Male; D051381:Rats; D013216:Reflex, Startle / Q000502:physiology*; D013997:Time Factors; D014364:Tryptophan / Q000008:administration & dosage / Q000172:deficiency*
chemical_list: D014364:Tryptophan