Tryptophan depletion reverses the therapeutic effect of selective serotonin reuptake inhibitors in social anxiety disorder.

BACKGROUND: Tryptophan depletion studies have suggested that central serotonin (5-hydroxytryptamine, 5-HT) function mediates the therapeutic effect of selective serotonin reuptake inhibitors (SSRIs) in depression and panic disorder. The present study tested the hypothesis that temporary reduction in central 5-HT transmission, through acute tryptophan depletion, could reverse the therapeutic effect of the SSRIs in social anxiety disorder (SAD) patients. METHODS: Fourteen patients with SAD who showed sustained clinical improvement with SSRI treatment underwent tryptophan depletion in a double-blind, placebo-controlled, crossover design, over 2 days 1 week apart. At the peak time of depletion, the participants also underwent three behavioral challenges: autobiographical script, verbal task, and neutral script. Psychological outcome was assessed with the Spielberger State Anxiety Inventory (STAI) Form Y-1 and visual analog scales (VAS) measuring anxiety, depression, and somatic symptoms. RESULTS: Anxiety was significantly increased on the depletion day compared with the control day, both on the STAI Form Y-1 and composite VAS score. Furthermore, there was a significant depletion x time interaction, explained mainly by the anxiogenic effect of the autobiographical script. In contrast, the verbal and the neutral tasks failed to differentiate between depletion and placebo. CONCLUSIONS: Tryptophan depletion induced significant increase of anxiety in treated SAD patients, which was more prominent during the recital of an autobiographical script. This finding supports the notion that SSRIs improve social anxiety by increasing 5-HT availability. The autobiographical script seems to be a more robust challenge test for SAD than the stressful verbal task.

Caffeine and central noradrenaline: effects on mood, cognitive performance, eye movements and cardiovascular function.

There have been numerous studies on the effects of caffeine on behaviour and cardiovascular function. It is now important to clarify the mechanisms that underlie such effects, and the main objective of the present study was to investigate whether changes in central noradrenaline underlie some of the behavioural and cardiovascular effects of caffeine. This was examined using a clonidine challenge paradigm. Twenty-four healthy volunteers were assigned to one of four conditions: (i) clonidine/caffeine; (ii) clonidine/placebo; (iii) placebo/caffeine: (iv) placebo/placebo. Baseline measurements of mood, cognitive performance, saccadic eye movements and cardiovascular function were recorded. Subsequently, volunteers were given either clonidine (200 microg) or placebo and consumed coffee containing caffeine (1.5 mg/kg) or placebo. The test battery was then repeated 30 min, 150 min and 270 min later. A second cup of coffee (with the same amount of caffeine as the first) was consumed 120 min after the first cup. The results showed that clonidine reduced alertness, impaired many aspects of performance and slowed saccadic eye movements; caffeine removed many of these impairments. Both clonidine and caffeine influenced blood pressure (clonidine reduced it, caffeine raised it) but the effects appeared to be independent, suggesting that separate mechanisms were involved. In addition, there were some behavioural effects of caffeine that were independent of the clonidine effect (e.g. effects on speed of encoding of new information) and these may reflect other neurotransmitter systems (e.g cholinergic effects). Overall, the results suggest that caffeine counteracts reductions in the turnover of central noradrenaline. This mechanism may underlie the beneficial effects of caffeine seen in low alertness states.