The elevated plus maze is a widely used behavioral assay for rodents and it has been validated to assess the anti-anxiety effects of pharmacological agents and steroid hormones, and to define brain regions and mechanisms underlying anxiety-related behavior. Briefly, rats or mice are placed at the junction of the four arms of the maze, facing an open arm, and entries/duration in each arm are recorded by a video-tracking system and observer simultaneously for 5 min. Other ethological parameters (i.e., rears, head dips and stretched-attend postures) can also be observed. An increase in open arm activity (duration and/or entries) reflects anti-anxiety behavior. In our laboratory, rats or mice are exposed to the plus maze on one occasion; thus, results can be obtained in 5 min per rodent.

Estrogen (E₂) has many effects in the central nervous system, including effects on anxiety and depression behavior. This review will address effects of E₂ on behaviors related to anxiety and depression in women and animal models and include recent findings from our laboratory related to this topic. E₂'s antianxiety and antidepressant-like effects may depend upon many factors, including the regimen of E₂ utilized and interactions with the hypothalamic–pituitary–adrenal axis. Brain targets for E₂'s effects on anxiety and depression include the hippocampus and amygdala. Administration of E₂, compared to vehicle, subcutaneously or to the hippocampus or amygdala of ovariectomized rats decreases anxiety and depressive behavior. Intracellular estrogen receptors (ERs) may be important for E₂'s anxiolytic and antidepressant-like effects. Administration of an ER antagonist to the hippocampus, but not amygdala, increases anxiety and depression behavior of naturally receptive female rats. Studies utilizing ER knockout mice or selective ER modulators suggest that ER-mediated effects of E₂ on anxiety and depressive behavior may require ERβ. In addition, the behavioral effects of E₂ may involve membrane actions and/or changes in cell cycle processes involved in energy expenditure. Elucidating the mechanisms by which E₂ affects anxiety and depression is important in order to enhance its therapeutic potential. It is particularly important to investigate the putative receptor mechanisms and brain targets for E₂ to determine whether mood-enhancing effects of E₂ can occur without deleterious proliferative effects in reproductive tissues.

17β-Estradiol (E₂) may influence anxiety behavior; however, its effects and mechanisms are not well understood. To determine whether E₂'s effects on anxiety behavior may involve actions at intracellular estrogen receptor (ER) α or β isoforms, selective ER modulators (SERMs) were administered (10 μg; s.c.) to ovariectomized rats 48 h before testing for anxiety behavior. Rats received sesame oil vehicle, 17β-E₂, which has a high affinity for ERα and ERβ, or SERMs that vary in their activity at ERα and β. ERα-selective SERMs were propyl pyrazole triol (PPT), which has more selective effects at ERα, than does the other ERα SERM utilized, 17α-E_2, which also binds ERβ. ERβ-selective SERMs were diarylpropionitrile (DPN) and 7,12-dihydrocoumestan (coumestrol). DPN is more selective at ERβ than coumestrol, which also binds ERα. 17β-E₂ and ERβ-selective SERMs (DPN, coumestrol) produced clear antianxiety behavior in the open field, elevated plus maze, emergence, light–dark transition, defensive freezing, and Vogel punished drinking tasks. Anxiety behavior of rats administered ERα-selective SERMs (PPT, 17α-E₂) was not different from vehicle; however, PPT and 17α-E₂ enhanced sexual receptivity in a manner similar to 17β-E_2. Coadministration of tamoxifen (10 mg/kg) blocked the antianxiety behavior produced by 17β-E₂, DPN, or coumestrol. Together, these data suggest that actions at ERβ may underlie some of E₂'s antianxiety effects.