Alleviation by Hypericum perforatum of the stress-induced impairment of spatial working memory in rats.

It is recognized that chronic stress is an important risk factor for the development of several cognitive impairments involving working memory. Working memory refers to the memory in which the information to be remembered changes from trial-to-trial and should be assessed in a task able to detect retrieval of that information. In the present study, we tested the hypothesis that preventive administration of Hypericum perforatum (also named St John's wort) may counteract the working memory impairments caused by repeated stress. Specifically, we attempted to characterize the preventive action of long-lasting treatment with St John's wort (350 mg/kg, p.o.) on the spatial working memory impairments caused by chronic restraint stress (2 h daily for 21 days) or durable medication with exogenous corticosterone (5 mg/kg, s.c.) in male Wistar rats. Spatial working memory was tested in Barnes maze (BM) and in the Morris water maze (MWM). We found that H. perforatum prevented the deleterious effects of both chronic restraint stress and prolonged corticosterone on working memory measured in both tests. The herb significantly improved hippocampus dependent spatial working memory in comparison with control (p < 0.01) and alleviated some other negative effects of stress on cognitive functions.