Acute tryptophan depletion (ATD) is a technique used extensively to study the effect of low

serotonin Serotonin (), also known as 5-hydroxytryptamine (5-HT), is a monoamine neurotransmitter with a wide range of functions in both the central nervous system (CNS) and also peripheral tissues. It is involved in mood, cognition, reward, learning, ...

in the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

. This experimental approach reduces the availability of

tryptophan Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α-carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromat ...

, an

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

which serves as the precursor to serotonin. The lack of mood-lowering effects after ATD in healthy subjects seems to contradict a direct causal relationship between acutely decreased serotonin levels and depression. However, mood-lowering effects are observed in certain vulnerable individuals. For example, a meta-analysis show that the effect size for the effects of tryptophan depletion on mood in depressed people not taking antidepressants was large (Hedge's g = −1.9 (95% CIs −3.02 to −0.78) Hence, a more accurate interpretation is that tryptophan depletion studies suggest a role for 5-HT in people vulnerable to depression and in those remitted on SSRI treatment

References

Serotonin {{Neuroscience-stub