Unpredictable chronic mild stress not chronic restraint stress induces depressive behaviours in mice.

The chronic stress model was developed on the basis of the stress-diathesis hypothesis of depression. However, these behavioural responses associated with different stress paradigms are quite complex. This study examined the effects of two chronic stress regimens on anxiety-like and depressive behaviours. C57BL/6 mice were subjected to unpredictable chronic mild stress or to chronic restraint stress for 4 weeks. Subsequently, both anxiety-like behaviours (open field, elevated plus maze and novelty suppressed feeding) and depression-like behaviours (tail suspension, forced swim and sucrose preference) were evaluated. Both chronic stress models generated anxiety-like behaviours, whereas only unpredictable chronic mild stress could induce depressive behaviours such as increased immobility and decreased sucrose consumption. These results of the present study provide additional evidence on how chronic stress affects behavioural responses and point to the importance of the validity of animal models of chronic stress in studying depression.