Neuroendocrine challenge tests with citalopram and reboxetine: Implications for personality and behavior

Neuroendocrine challenge tests have widely been used to investigate the activity of neurotransmitters systems in patients and healthy volunteers. However, most of the studies are of relatively low sample size and none of them investigated the interaction between different systems (e.g. 5-HT and NE). We therefore conducted different independent studies in healthy male volunteers with Citalopram or Reboxetine as challenge substances. Moreover, a combined challenge study with both substances in a 3-way cross over design has also been done. The results clearly indicate that single oral dosages of Citalopram (20mg) and Reboxetine (2mg) stimulate the HPA-axis resulting in elevated cortisol levels. Moreover, high responses to the drug are accompanied by higher levels in self rated subclinical depression (Reboxetine) or aggression (Citalopram). In addition, high responses to Citalopram were related to indicators of aggression (behaviour) in situations characterized by helplessness. More interestingly the combination between high responses to Citalopram and low ones to Reboxetine were associated with indicators of neuroticism. The results will be discussed with respect to the biological basis of personality on the one and with respect to the need to combine challenge tests across different systems on the other hand.