Seasonal variability in behavioral despair in female rats.

Separate groups of female Wistar rats were tested every three months over a year to assess the extent of seasonal variability in the behavioral despair model of depression consisting of 2 swim tests separated by 24 h. There was a significant seasonal variability in the duration of immobility in the swim tests; duration of immobility was shorter in August and November than in February and May. These findings suggest reduced immobility and susceptibility to behavioral despair in summer and fall compared to winter and spring.