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 effect s are most crucial in female organism because of the natural fluctuations o f ovarian hormones due to the estrous cycle. In this study, we have analyze d how estrogen and progesterone (P) affect the anxiety level in ovariectomi zed (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 act ivity and the highest grooming activity, as compared with other experimenta l groups. Time spent on the open arms and locomotor activity of OVX animals treated with estradiol benzoate (EB) did not differ from the vehicle-treat ed animals. In addition, the hormonal treatments modified the PR-immunoreac tivity in many brain areas, such as medial preoptic area of hypothalamus, v entromedial hypothalamus, mammilar body of hypothalamus, septo-hippocampal region, and periaqueductal gray. The injections of EB and P induced sequent ial changes of PR-ir in comparison with vehicle-treated mice, whereas injec tion of vehicle induced the significant decrease of PR-ir in all brain area s examined. Our data suggest that sex steroid hormones play an important ro le in induction of anxiety. Furthermore, this action might be partially med iated through the classical steroid receptors. (C) 2001 Elsevier Science B. V. All rights reserved.