Progesterone receptor isoforms expression pattern in the rat brain during the estrous cycle

Progesterone receptor (PR) isoforms expression was determined in the hypoth alamus, the preoptic area, the hippocampus and the frontal cerebral cortex of the rat at 12:00 h on each day of the estrous cycle by using reverse tra nscription coupled to polymerase chain reaction. Rats under a 14:10 h light -dark cycle, with lights on at 06:00 h were used. We found that PR-B isofor m was predominant in the hypothalamus, the preoptic area and the frontal ce rebral cortex. Both PR isoforms were similarly expressed in the hippocampus . The highest PR-B expression was found on proestrus day in the hypothalamu s; on metestrus in the preoptic area; and on diestrus in the frontal cortex . We observed no changes in PR isoforms expression in the hippocampus durin g the estrous cycle. These results indicate that PR isoforms expression is differentially regulated during the estrous cycle in distinct brain regions and that PR-B may be involved in progesterone actions upon the hypothalamu s, the preoptic area and the frontal cortex of the rat.