It has been proposed that hedonic deficits can also be induced in rodents by chronic stress ( Katz, 1981 Willner et al, 1987 D'Aquila et al, 1997 Harkin et al, 2002). Thus, behavioral correlates of stress-induced anhedonia and of chronic stress alone can be separated in the present model.Īnhedonia, a decreased ability to experience pleasures, is a core symptom of human depression ( Hamilton, 1967 Klein, 1974 Kessler et al, 1994).
On the other hand, increased anxiety, altered locomotor activity, and loss of body weight were consequences of chronic stress, which occurred independently from anhedonia. Using a battery of behavioral tests after termination of the stress procedure, we found that anhedonia, but not chronic stress per se, is associated with key analogues of depressive symptoms, such as increased floating during forced swimming and decreased exploration of novelty. These animals were used as an internal control for stress-induced behavioral features not associated with the anhedonic state, since they were exposed to the same stressors as the anhedonic mice. In contrast, most mice with nonsubmissive behavior did not develop a decrease in sucrose preference and were regarded as nonanhedonic. Interestingly, predisposition for stress-induced anhedonia was indicated by submissive behavior in a resident–intruder test. This protocol resulted in a strong decrease in sucrose preference, a putative indicator of anhedonia in rodents. In order to develop a model for a depression-like syndrome in mice, we subjected male C57BL/6 mice to a 4-week-long chronic stress procedure, consisting of rat exposure, restraint stress, and tail suspension.
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