How can an anhedonic state be induced in the laboratory rat? In 1981, Katz and collaborators developed a procedure whereby rats were submitted to a variety of chronic, unpredictable stressors such as electric shocks, immersion in cold water, tail pinch, etc. Following a week of such a stress regimen, animals

exhibited behavioral deficits and hormonal Inhibitors,research,lifescience,medical changes that, could be prevented by administration of antidepressants, but. not. by other psychotropic substances. Unlike control animals, the chronically stressed animals did not increase drinking when saccharine or sucrose was added to their drinking water to enhance palatability.9,10 This observation was particularly important, as it. implied that this chronic stress regimen was able Inhibitors,research,lifescience,medical to induce dysfunctioning of the reward systems. This abnormality in the drinking behavior could reflect. the development, of an anhedonic state in animals. Later, Willner adapted this procedure by using less severe stressors which were supposed to provide a better analogy with mild unpredictable stressors encountered in daily life.“ Inhibitors,research,lifescience,medical Rats exposed to such a mild stress procedure progressively develop a reduced

sensitivity to reward as evaluated by reduction in sucrose consumption. This behavioral deficit. could be restored by chronic treatment with antidepressants. Considering that chronic low-grade stressors are an important factor in the etiology of depression, we have adapted Willner’s procedure to our laboratory needs. This stress procedure used in all experiments reported here is described in Table I. 12 Table I. Chronic, mild, unpredictable stress procedure. Reproduced from reference Inhibitors,research,lifescience,medical 12: B-HT2C receptor agonists exhibit antidepressant-like Inhibitors,research,lifescience,medical properties in the anhedonia model of depression in rats. Eur Neuropyschopharrnacol.

1996:6:169-175. Copyright © 1996, … How can an anhedonic state be evaluated in laboratory rats? Different, behavioral paradigms can be used to evaluate sensitivity to reward in animals: sucrose consumption, place conditioning, and self-stimulation behavior. Initially, Willner used sucrose consumption measurement. He showed that, the chronic mild stress procedure induced a substantial else reduction in consumption and/or preference of sucrose solutions.“ This reduction was interpreted as reflecting a decreased sensitivity to reward in stressed animals. However, sucrose consumption can vary from one experiment to another and can be find more influenced by body weight, loss resulting from the stress.13 Papp et al14 have used the place preference paradigm to study the stress effects on reward induced by sweet solutions or amphetamine. In this paradigm, pleasure intensity is monitored by the preference exhibited by the animals for an environment previously associated with appetitive properties of food or amphetamine.