An analysis of the distribution of estrogen receptor (ER) via immunoenzymatic assay in the brain of ovariectomized rats reveals the presence of large amounts of ER-like immunoreactive material in the cytosol of the hippocampus: a brain area described to contain little estrogen-binding activity. The protein detected in the hippocampus by the specific antibody is indistinguishable from the rat ER in its response to hormonal treatments and in its electrophoretic mobility. The presence of elevated amounts of ER in such an important part of the limbic system creates new possibilities for interpreting the role played by this sex hormone in the central nervous system of rat. In mammals, estrogens have a profound influence on the activity of the limbic system as indicated by their control on the release and synthesis of hypothalamic factors, and on the display of sexual and affective behaviors (1). Such a modulatory activity is exerted by the hormone via binding to specific receptors concentrated in most of the areas of the limbic system. Studies conducted (2) have indeed indicated high levels of estrogen-binding activity in hypothalamus, amygdala, and septum and very low levels in hippocampus. In view of the key functional role exerted by the hippocampus in the limbic system we have postulated that the estrogen receptor (ER) is actually synthesized in this brain area but its presence is not visualized by hormone-binding techniques. The availability of monoclonal antibodies (mAb) which can specifically recognize the ER (3) now allows further analysis of the brain regions where this protein is synthesized and stored.
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Maggi et al. (1989) studied this question.