Effects of immobilization stress on emotional behaviors in dopamine D3 receptor knockout mice.

A central problem in understanding the dopamine system in anxiety and depression is to specify functions of different members of the dopamine receptor family. Recent studies have reported that the dopamine D2/D3 receptor agonist pramipexole exerts an antidepressant-like effect in the chronic mild stress model and in the behavioral despair model, suggesting dopamine D3 receptor may be an important target for antidepressant actions. The aim of the present study was to examine the role of dopamine D3 receptor on the anxiety-like and depression-like behaviors induced by immobilization stress. We subjected D3 receptor knockout (D3KO) mice to a series of behavioral paradigms after acute (1 h) or chronic (1 h a day for 14 days) immobilization stress. The results showed that immobilization stress significantly altered the anxiety-like behaviors (open field test and elevated plus maze) and depression-like behaviors (tail suspension test) in both D3KO mice and their wild-type littermates. Moreover, further analysis of the data indicated that the D3KO mice, but not their littermates, failed to show a change in immobility time in the tail suspension test after the acute and chronic stress as compared to intact controls, suggesting an increased resistance to the immobilization stress given before behavioral tests. Although our study did not suggest a significant role of D3 receptor in regulating basal anxiety-like and depression-like behaviors, it demonstrated the mice lacking D3 receptor might be more resistant to stressful procedure than their WT littermates.