Plasma NPY concentrations during tryptophan and sham depletion in medication-free patients with remitted depression

Background: Neuropeptide Y (NPY) and serotonergic systems have been implicated in the pathophysiology of depression but have not yet been linked together. Methods: In a randomized, double-blind crossover study, 28 medication-free patients with remitted depression and 26 healthy control subjects underwent tryptophan depletion (TD) and sham depletion. Plasma NPY concentrations were determined at baseline and at + 5, + 7, and + 24 h during TD and sham depletion, respectively. Hamilton Depression Rating Scale (HDRS, 24-item) scores were assessed at baseline and at + 7 and + 24 h after TD and sham depletion, respectively. Results: There was no difference between healthy subjects and patients with remitted depression in baseline plasma NPY concentrations and in plasma NPY concentrations during TD and sham depletion, respectively. Plasma NPY concentrations did not differ between TD and sham depletion. At no time point there was an association between HDRS scores and plasma NPY concentrations in patients with remitted depression. Limitations: Plasma NPY concentrations in rMDD patients were not obtained during the symptomatic phase of the illness. Only peripheral measurements of NPY were used. Conclusions: Decreased plasma NPY concentrations, as described previously during a spontaneous episode of major depression, appear as state but not as trait marker in depression. No evidence was found for an involvement of plasma NPY in relapse during TD. There appears no direct functional link between serotonergic neurotransmission and plasma NPY concentrations.