The effects of acute, chronic and withdrawn progesterone in male and female Mongolian gerbils (Meriones unguiculatus) in two tests of anxiety

Progesterone generally produces anxiolytic effects in rats and mice. However, sex differences in response to this neuroactive steroid have not been systematically investigated. Thus, this study investigated the anxiety-modulating actions of acute, chronic and withdrawn progesterone treatment in male and female Mongolian gerbils (Meriones unguiculatus) in the elevated plus-maze (EPM) and black–white box (BWB). Gerbils were tested after receiving vehicle, 0.5, 2.5, 7.5 or 15 mg/kg progesterone administered acutely, chronically (14 days) or after a 24-h withdrawal period following chronic treatment. Data analyses showed that overall the effects of progesterone were similar in males and females. Progesterone produced few behavioural alterations in the EPM following any of the treatment regimes. However, acute and chronic progesterone reduced anxiety in the BWB (as shown by increased exploration, locomotion and entries into the white compartment). In contrast, withdrawal of progesterone produced minimal effects in the EPM and BWB. This study suggests that the BWB maybe the most suitable test for detecting the anxiolytic effects of neuroactive steroids in gerbils. However, further research is needed to clarify the behavioural effects of progesterone in this species.