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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)

Tryptophan depletion does not modify response to CCK-4 challenge in patients with panic disorder after treatment with citalopram.

RATIONALE: Data by [Bell et al. J Psychopharmacol (2002) 16:5-14] suggest that a decrease in 5-HT neurotransmission predisposes to panic attacks and that the antipanic effect of SSRIs depends upon the availability of 5-HT in the brain. OBJECTIVES: Our aim was to assess the effect of acute tryptophan depletion (TD) on cholecystokinin-tetrapeptide (CCK-4)- induced symptoms in patients with panic disorder (PD) who had responded to a 10-week treatment with a selective serotonin (5-HT) reuptake inhibitor (SSRI), citalopram. MATERIALS AND METHODS: A total of 18 patients (6 males and 12 females, mean age 34.5 years) received a tryptophan-free amino acid drink and a control drink, each followed by a CCK-4 challenge (25 mug), 1 week apart in a double-blind crossover design. RESULTS: The results showed no significant differences in response to the CCK-4 challenge between the TD and the control conditions. Panic rate after the CCK-4 challenge was 27.8% after depletion and 33.3% after control drink (chi (2)=0.13, p=0.72). No significant effects of TD were observed in panic intensity scores, subjective anxiety, or cardiovascular indices. CONCLUSIONS: This study demonstrates that an acute lowering of brain 5-HT availability with TD does not affect response to a CCK-4 challenge in PD patients successfully treated with citalopram. Thus, the reduction of CCK-4 sensitivity following SSRI-treatment in patients with PD may be related to mechanisms other than 5-HT availability in the brain, possibly to a reduction in brain cholecystokinin receptor sensitivity.[1]


  1. Tryptophan depletion does not modify response to CCK-4 challenge in patients with panic disorder after treatment with citalopram. Tõru, I., Shlik, J., Maron, E., Vasar, V., Nutt, D.J. Psychopharmacology (Berl.) (2006) [Pubmed]
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