Hypericum perforatum subspecies angustifolium shows a protective activity on the consequences of unavoidable stress exposure at lower doses than Hypericum perforatum perforatum.

Clinical studies have demonstrated that the antidepressant efficacy of Hypericum perforatum extract is comparable to that of classic antidepressants, such as imipramine. The role played by its components, particularly hypericin and hyperforin, has been examined in different experimental models of depression. The present study was carried out in order to verify the hypothesis that hyperforin is the main active antidepressant component. For this purpose we evaluated the activity of a dry extract from a subspecies of H. perforatum, H. perforatum spp. angustifolium, which has a higher hyperforin content than H. perforatum perforatum, in a series of experimental models of depression. The models used are based on the development of hyporeactivity to aversive stimuli induced by unavoidable stress exposure in rats. The extract of H. perforatum angustifolium presented an efficacy that was similar to that obtained with a treatment with imipramine or H. perforatum perforatum. Furthermore, in the models used the H. perforatum angustifolium extract was active at doses eight times lower than those necessary to produce a comparable activity with H. perforatum extract.

Acquisition of a palatable-food-sustained appetitive behavior in satiated rats is dependent on the dopaminergic response to this food in limbic areas.

Rats exposed to repeated unavoidable stress show decreased dopamine output in the nucleus accumbens shell (NAcS) and do not acquire vanilla sugar (VS)-sustained appetitive behavior (VAB). Rats treated with lithium for 3 weeks also show decreased NAcS dopamine output, yet they acquire VAB. Feeding a novel palatable food increases extraneuronal dopamine levels in the NAcS and medial prefrontal cortex (mPFC) in rats. In order to investigate the role of food-induced dopamine release in VAB acquisition, we studied by microdialysis the dopaminergic response in the NAcS and mPFC to the presentation and consumption of VS in satiated control rats, and in satiated rats exposed to repeated stress or lithium treatment. The dopaminergic response to VS was also studied in rats familiar with VS, or that had acquired VAB. In control rats, VS feeding was accompanied by increased dopamine output in the NAcS and mPFC, and one-trial habituation to this effect developed in the NAcS. Rats exposed to a 7-day stress showed reduced interest in VS pellets, and when fed VS they did not show a dopaminergic response in the NAcS and mPFC. Lithium-treated rats rapidly ate VS pellets and showed increased dopamine output in the NAcS and mPFC, with no habituation in the NAcS response. Rats familiar with VS and rats that had already learned VAB ate VS pellets. The first group showed a lower dopaminergic response to VS consumption than the control group, but the latter showed no dopaminergic response in the NAcS and mPFC. We propose that the limbic dopaminergic response to a novel palatable food plays a role in associative learning and that it is predictive of the competence to learn an appetitive behavior. Moreover, in our experimental conditions a phasic increase in mesolimbic dopamine no longer signals the VS stimulus once it has become a reinforcer in an appetitive task.