The application of the
tryptophan depletion test is based on the assumption that the decrease of plasma or serum
tryptophan concentration following the ingestion of a
tryptophan-free
amino acid drink reflects a central nervous effect on
serotonin metabolism. In the present study the impact of
tryptophan depletion on polysomnographically recorded sleep in patients with
primary insomnia was studied. Fifteen patients with
primary insomnia slept for four nights in the sleep laboratory. Prior to the fourth night the
tryptophan depletion test was applied. Sleep EEG variables served as outcome parameters. Patients with
primary insomnia, compared to baseline values showed a highly significant decrease of serum
tryptophan concentrations after the
amino acid drink. Concerning sleep parameters, stage 1 (% sleep period time=SPT) was increased, whereas stage 2 (% SPT) was decreased. Indices of phasic activity of rapid eye movement (REM) sleep (REM density) were increased after the
tryptophan depletion compared to baseline. The results suggest a negative impact of
tryptophan depletion on sleep continuity and a stimulating effect on phasic measures of REM sleep in patients with
primary insomnia.