Effects of experimental acute tryptophan depletion on acoustic startle response in females

Previous studies suggest an important role for serotonergic (5-HT) modulation of the acoustic startle reflex (ASR) and prepulse inhibition (PPI). Acute challenge of brain serotonin by means of tryptophan depletion test (TDT) represents an established human challenge tool for temporary reduction of tryptophan (−TRP) levels and central nervous serotonin. Under these experimental conditions, PPI was found attenuated in males, but greater biochemical effects of TDT in the central nervous system of females are known. Therefore, in order to explore influence of 5-HT on various standard startle parameters in females, 16 young healthy females participated in a double-blind, cross-over TDT study. Acoustic stimuli were presented in 15 pulse-alone trials (100 dB, 40 ms) randomly followed by 25 pulse-alone or prepulse (70 dB, 30 ms; 120 ms interval) trials alongside electromyographic eyeblink recordings and mood state assessments. During 81% depletion of free plasma TRP, mean ASR magnitudes were significantly reduced compared to control (+TRP) condition while there were no differences in habituation or PPI nor did startle parameters correlate with mood states. Changes of plasma TRP and mood states correlated in tendency negatively in (−TRP) for depression and positively in (+TRP) for fatigue. In conclusion, this first study of startle parameters after TDT in a homogenous female population demonstrates that depletion of brain 5-HT in women only influences ASR.