Announced rewards counteract the impairment of anticipatory behaviour in socially stressed rats

It is known that stress can influence the sensitivity to rewarding stimuli. Previous observations revealed that socially stressed rats do not display an appetitive behavioural response in anticipation of a reward. A previous study showed that this insensitivity to rewards (anhedonia) could be restored by chronic administration of an antidepressant. Several lines of evidence exist for the role of dopamine in the mechanism of action of antidepressant treatments concerning their therapeutic effect on anhedonia. Therefore, it was hypothesized that regular activation of the reward system, that involves mesolimbic dopaminergic systems, could counteract the effect of social stress on reward-sensitivity. For this, it was investigated whether a treatment of regular reward announcements could prevent the development of anhedonia. This was confirmed by the result that socially stressed rats that received this treatment were able to display anticipatory behaviour which is characterized by increased activity after presentation of a stimulus that was previously associated with a sucrose reward. Surprisingly, a non-treated socially stressed group, that did not show an anticipatory response for sucrose, did display anticipatory behaviour for another type of reward (enriched cage). It seems that, although one might assume the existence of an anhedonic state based upon the absence of anticipatory activity towards a sucrose reward, this assumption cannot be generalised to other types of reward. It will be discussed whether this might be caused by the highly rewarding properties of the enriched cage which probably has a therapeutical efficacy of its own.