Acute tryptophan depletion

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Acute tryptophan depletion (ATD) is a technique used extensively to study the effect of low serotonin in the brain. [1] This experimental approach reduces the availability of tryptophan, an amino acid which serves as the precursor to serotonin. [1] [2] 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. [1] 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) [3] 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 [4]

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References

  1. 1 2 3 van Donkelaar EL, Blokland A, Ferrington L, Kelly PA, Steinbusch HW, Prickaerts J (July 2011). "Mechanism of acute tryptophan depletion: is it only serotonin?". Molecular Psychiatry. 16 (7): 695–713. doi: 10.1038/mp.2011.9 . PMID   21339754.
  2. Young SN (September 2013). "Acute tryptophan depletion in humans: a review of theoretical, practical and ethical aspects". Journal of Psychiatry & Neuroscience. 38 (5): 294–305. doi:10.1503/jpn.120209. PMC   3756112 . PMID   23428157.
  3. Ruhé HG, Mason NS, Schene AH (April 2007). "Mood is indirectly related to serotonin, norepinephrine and dopamine levels in humans: a meta-analysis of monoamine depletion studies". Molecular Psychiatry. 12 (4): 331–59. doi:10.1038/sj.mp.4001949.
  4. Jauhar S, Arnone D, Baldwin DS, Bloomfield M, Browning M, Cleare AJ, Corlett P, Deakin JF, Erritzoe D, Fu C, Fusar-Poli P, Goodwin GM, Hayes J, Howard R, Howes OD, Juruena MF, Lam RW, Lawrie SM, McAllister-Williams H, Cowen PJ. "(2023). A leaky umbrella has little value: Evidence clearly indicates the serotonin system is implicated in depression". Molecular Psychiatry. 28 (8): 3149–52. doi:10.1038/s41380-023-02095-y. PMC   10618084 .