The effects of tryptophan depletion on impulsivity and mood in healthy men and women

Reduced serotonergic neurotransmission contributes to the pathophysiology of mood disorders, and the majority of modern antidepressants block the serotonin reuptake in the brain. It is also known that people with major depressive disorder are frequently found to have impaired impulse control, and that impulsivity is associated with serotonin. In two separate studies with healthy participants using different designs and a technique called acute tryptophan depletion, which decreases serotonin levels in the brain, men adopted an impulsive response style, but did not experience any mood changes. The second and largest study included both men and women, and the findings regarding men were replicated. However, women reported a worsening of their mood, and they adopted a more cautious response style commonly associated with depression. The lowered mood reported by women in response to tryptophan depletion was also influenced by variation in the promoter region of the triallelic serotonin transporter gene (5-HTTLPR). The possibility of a synergic effect between novel situations and reduced neurotransmission of serotonin is also discussed. These findings confirm the notion that serotonergic neurotransmission is involved in a competition between behavioral suppression and active responding. When the serotonergic neurotransmission was reduced, men would on average increase active responding (impulsive response style), while women would increase behavioral suppression (cautious response style). Serotonin could therefore be one of the mechanisms explaining the sex difference in the prevalence and clinical presentation of mood and impulsivity disorders. This might be relevant in understanding why women show a higher prevalence of mood and anxiety disorders compared to men, while men show a higher prevalence of alcoholism, AD/HD and impulse control disorders. The sex of a given participant or patient should therefore be taken into consideration when conducting research, prescribing treatment or diagnosing conditions associated with serotonin