Effects of estrogen receptor a and b gene deletion on estrogenic induction of progesterone receptors in the locus coeruleus in female mice

Locus coeruleus (LC) is involved in the LHRH regulation by gonadal steroids. We investigated the expression of progesterone and estrogen receptors (PR; ER) in LC neurons of ERa (aERKO) or ERb (bERKO) knockout mice, and their wild-type (aWT and bWT). Immunocytochemical studies showed that LC expresses PR and both ERs, although ERb was more abundant. Estradiol benzoate (EB) decreased ERa-positive cells in WT and bERKO mice, and progesterone caused a further reduction, whereas none of the steroids influenced ERb expression. ERb deletion increased ERa while ERa deletion did not alter ERb expression. In both WT mice, EB increased PR expression, which was diminished by progesterone. These steroid effects were also observed in aERKO animals but to a lesser extent, suggesting that ERa is partially responsible for the estrogenic induction of PR in LC. Steroid effects on PR in bERKO mice were similar to those in the aERKO but to a lesser extent, probably because PR expression was already high in the oil-treated group. This expression seems to be specific of LC neurons, since it was not observed in other areas studied, the preoptic area and ventromedial nucleus of hypothalamus. These findings show that LC in mice expresses aER, bER, and PR, and that a balance between them may be critical for the physiological control of reproductive function.