Neural distribution of estrogen receptor immunoreactive cells in the female musk shrew

In this report we describe the neural distribution of estrogen receptor immunoreactivity (ER-IR) in the female musk shrew ( Suncus murinus). The highest concentrations of neurons containing ER-IR were found in the preoptic areas, the lateral septum, the anterior arcuate and ventromedial nuclei of the hypothalamus, the medial nuclei of the amygdala, and the midbrain central grey. Additional preoptic, hypothalamic, limbic and modbrain nuclei also contained ER-IR cells. The distribution of ER-IR was similar to that described in other mammals and birds, with several important differences. In the female musk shrew, there was little differences in ER-IR intensity or distribution when brains from gonadally intact and ovariectomized musk shrews were compared. In addition, long-term treatment with a supraphysiological dose of estradiol was required to detect a decrease in ER-IR intensity. Finally ER-IR was noted in both nuclear and cytoplasmic regions of cells in ovariectomized and gonadally intact musk shrews. The dense ER-IR noted in intact females as well as the presence of cytoplasmic stain may be due to the unusual relationship between estradiol, ovulation and sexual receptivity in this species.