Neural responses of rats in the forced swimming test: [F-18]FDG micro PET study.

The forced swimming test (FST) is a widely used tool in the assessment of behavioral despair and prediction of response to antidepressants. However, the neural mechanisms underlying behavioral changes between pretest and test sessions of the FST remain unclear. In this study, we investigated changes in rat brain activity during the FST using [F-18]Fluorodeoxyglucose micro PET. In both pretest and test sessions, the activity of the cerebellum and striatum increased, whereas significant deactivation was observed in the hippocampus, inferior colliculus, orbital cortex, and insula. The periaqueductal gray (PAG) region activated markedly in the pretest session, but did not activate in the test session. There was a significant increase in immobility and a decrease in climbing during the behavioral analysis test session. These results suggest that the PAG region may play an important role in the modulation of FST coping strategies subsequent to failure of the escape response during the pretest session.