Actions of progesterone on depression-like behavior in a model of surgical menopause are mediated by GABAA receptors

Abstract Introduction In rats, long-term ovariectomy results in low concentrations of steroid hormones and reproduces anxiety- and depression-like behavior after surgical menopause in women. Progesterone produces antidepressant-like effects two weeks post-ovariectomy (i.e., early post-ovariectomy) through actions on γ-aminobutyric acid-A (GABAA) receptors, but its antidepressant-like effects and mechanism of action in rats eight weeks post-ovariectomy (i.e., late post-ovariectomy, considered a model of surgical menopause) remain unknown. Objective To explore the antidepressant-like effects of progesterone and the participation of GABAA receptors in rats eight weeks post-ovariectomy. Method Long-term ovariectomized female Wistar rats were treated sub-acutely with vehicle or progesterone (.5, 1, and 2 mg/kg) and subjected to the open field and forced swim tests, and behavior was compared with cycling or fluoxetine-treated rats. The rats were then pretreated with picrotoxin (1 mg/kg) followed by progesterone (1 mg/kg) to explore the role of GABAA receptors in long-term-induced depression-like behavior. Results Long-term ovariectomized rats exhibited depression-like behavior in the forced swim test compared with intact rats, an effect that was not observed in progesterone- and fluoxetine-treated long-term ovariectomized rats. These effects were not attributable to psychomotor alterations. In the open field test, the time spent rearing and grooming was lower in ovariectomized rats compared with intact rats, which was not observed in progesterone- and fluoxetine-treated rats. Picrotoxin blocked the effects of progesterone in both behavioral tests. Discussion and conclusion These results indicated that sub-acute progesterone treatment reduced depression-like behavior through actions on GABAA receptors in a rat model of surgical menopause.