The incidence of mood disorders and depression is doubled in women during the reproductive years as compared to men. Cyclic changes in ovarian steroids have been closely linked to the depressive affectivity. However, the role that ovarian hormones play in the development of depression has been largely understudied. Most animal models of depression-like behaviors test male subject and only few studies have included females in their experiments. This application is aimed at testing the central hypothesis that ovarian hormones play a significant role in the development of depression-like behaviors in females, using the social isolation model of depression. Normal cycling animals and ovariectomized animals will each be divided in two groups. Half the animals will be pair housed and the other half will be singly housed for 8 consecutive weeks. At the end of the housing periods, rats will be tested using the forced swim test and the sucrose preference tests. These are procedures frequently used to assess depression-like behaviors in rodents. Results of the proposed experiments will behaviorally complement the current studies of the PI that are aimed at elucidating the role of neurotrophic factors and opioid peptides interaction in the hippocampus of female rats. The experiments proposed herein will shed light on the role of ovarian hormones during the development of depressive behaviors in females.