Investigating the effects of different herbal preparations, 5-hydroxytryptophan and involuntary exercise on affective bias modification in male Lister Hooded rats

Mood disorders are a prevalent global health concern with natural health products, including herbal supplements, an increasingly popular choice as an alternative or complementary therapy. Despite their widespread use, few studies have tested the clinical efficacy of natural health products or explored their underlying mechanisms in animal models. Modification of affective biases has been linked to mood in humans and animal models and may provide insights into potential antidepressant effects. In this study, we used a translational rodent model of affective bias modification to investigate the effects of five commonly used supplements: Hypericum perforatum , that is, St. John's Wort (SJW), Mucuna pruriens , Rhodiola rosea root extract, Valerian root extract and 5-hydroxytryptophan. Exercise is also thought to improve mood disorders, but clinical studies reveal mixed results therefore we also tested the effect of involuntary exercise on affective biases. In separate experiments, male Lister Hooded rats were acutely treated with SJW, Mucuna pruriens , Rhodiola rosea root extract, Valerian root extract and 5-hydroxytryptophan, or underwent an involuntary exercise manipulation. Our results showed a significant positive affective bias following treatment with SJW, whilst the involuntary exercise induced a negative affective bias in rats. No effects were found following the other acute treatments. These data suggest SJW has similar effects in terms of affective bias modification as conventional antidepressants. The negative affective bias observed with involuntary exercise suggests the animals experience a negative affective state and suggests exercise-based therapy may be less effective if the patient perceives this as involuntary.