extend the results from a previous report. In a study by Rygula and colleagues (2005),

investigators used a more extensive stress regimen of hour-long daily sessions of social

defeat for five straight weeks to elicit behavioral despair in subsequent Porsolt swim

testing. The daily social defeat stress regimen used in our study effectively increased

immobility in the repeatedly stressed rats as well, with briefer stressful interactions and a

shorter regimen than previously reported.

 Conclusions and Future Directions

 In conclusion, the behavioral, hormonal, and glandular changes produced by

repeated social defeat closely resemble many of the psychopathological symptoms in

patients with major depression. The daily social defeat stress regimen provides an

interesting and effective model for stress-induced psychopathology.

 The effect of repeated social defeat on the overall circadian rhythm was not

evaluated, nor was the persistence of the altered regulation across days, weeks, or

months. Both of these topics may be interesting issues for future studies. Also, potential

adaptations in stress-related molecules (CRH and AVP in the hypothalamus, CRH1 and

Vlb in the pituitary and amygdala, and mineralocorticoid receptor and gluccocorticoid

receptor in the hippocampus) after social defeat should be investigated. These studies

will enhance our growing knowledge of the neurobiological basis for stress-induced

psychopathology (e.g., maj or depression).