Analysis of mouse plus-maze behavior modulated by ovarian steroids

Ovarian hormones, acting through membrane and nuclear receptors, can evoke different changes in psychophysiological status of the subject. Such effects are most crucial in female organism because of the natural fluctuations of ovarian hormones due to the estrous cycle. In this study, we have analyzed how estrogen and progesterone (P) affect the anxiety level in ovariectomized (OVX) mice. Using plus-maze paradigm, we have found that mice receiving injection of progesterone in 6 h revealed the lowest level of open arm activity and the highest grooming activity, as compared with other experimental groups. Time spent on the open arms and locomotor activity of OVX animals treated with estradiol benzoate (EB) did not differ from the vehicle-treated animals. In addition, the hormonal treatments modified the PR-immunoreactivity in many brain areas, such as medial preoptic area of hypothalamus, ventromedial hypothalamus, mammilar body of hypothalamus, septo-hippocampal region, and periaqueductal gray. The injections of EB and P induced sequential changes of PR-ir in comparison with vehicle-treated mice, whereas injection of vehicle induced the significant decrease of PR-ir in all brain areas examined. Our data suggest that sex steroid hormones play an important role in induction of anxiety. Furthermore, this action might be partially mediated through the classical steroid receptors. (C) 2001 Elsevier Science B.V. All rights reserved.