BACKGROUND: Selective serotonin reuptake inhibitors (SSRIs) are first-line 
treatments for posttraumatic stress disorder (PTSD). Serotonergic (5HT) 
attenuation of stress sensitivity is postulated from SSRIs' effects in other 
anxiety disorders, and we studied this in PTSD.
METHODS: Ten patients with PTSD fully recovered on SSRIs (Clinical Global 
Impression Scale-I 1 and 2) were enrolled in the study. Patients were tested on 
two occasions 1 week apart; in each session, they received a drink containing 
large neutral amino acids (LNAAs) either with (sham tryptophan depletion [STD], 
control) or without (acute tryptophan depletion [ATD]) tryptophan. At 5.5 hours 
after the drink, subjects were exposed to a trauma-related exposure challenge. 
Self-reports of PTSD (visual analogue scales [VAS] and the Davidson Trauma Scale 
[DTS]), anxiety (Spielberger State Inventory [STAI] Form Y-1), and mood (Profile 
of Mood States [POMS]) were obtained. Heart rate (HR), systolic (SBP) and 
diastolic (DBP) blood pressure were also measured.
RESULTS: The trauma-related exposure challenge induced anxiety on both days, 
with more marked responses on the ATD day according to VAS, DTS, POMS, and DBP 
(p < .05). A trend of significance (.1 > p > .05) was observed for STAI Form 
Y-1, HR, and SBP.
CONCLUSIONS: These data demonstrate that ATD accentuates responses to 
trauma-related stimuli in SSRI-recovered PTSD. They also suggest that 
SSRI-induced increases in serotonin function restrain PTSD symptoms, especially 
under provocation, supporting a role for serotonin in mediating stress 
resilience.