Influence of chronic mild stress on the behavioural effects of acute tryptophan depletion induced by a gelatin-based mixture.

Several types of stress can increase vulnerability to developing depression. This depression may be caused by the effects of stress on the serotonergic system, which may make the system more vulnerable. The aim of this experiment was to evaluate whether chronic mild stress (CMS) resulted in long-lasting vulnerability of the serotonergic system, reflected by stronger behavioural responses to a serotonergic challenge with acute tryptophan depletion (ATD) several weeks after the CMS had ended. Male Wistar rats were exposed to 3 weeks of CMS followed by a 2-week resting period. CMS resulted in blunted weight gain and lower sucrose consumption. After the resting period, rats were repeatedly treated with a gelatin-based protein-carbohydrate mixture, either with or without L-tryptophan, to acutely challenge the serotonergic system and the rats were tested in several tests of anxiety-related and depression-related behaviour and memory. CMS and ATD both influenced behaviour on some tests, but overall this CMS procedure did not result in increased sensitivity to ATD, as there were no CMSxATD interaction effects on behaviour. In conclusion, CMS did not result in long-lasting vulnerability of the serotonergic system, measured by the behavioural response to ATD several weeks after the CMS had ended.