Colocalization of neurotensin messenger ribonucleic acid (mRNA) and progesterone receptor mRNA in rat arcuate neurons under estrogen-stimulated conditions

In the female rat, estrogen and progesterone directly or indirectly regulate the activity of neurotensin (NT)-synthesizing neurosecretory cells located in the hypothalamic arcuate nucleus (ARC). To determine whether these NT neurons are subject to direct regulation by ovarian steroids, estrogen-inducible messenger RNA (mRNA) encoding nuclear progesterone receptor (PR) was used as a cellular marker for nuclear estrogen receptor (ER) as well as PR, and double label in situ hybridization was employed to determine the extent to which NT/neuromedin N mRNA and PR mRNA are colocalized in ARC neurons under estrogen-stimulated conditions. In estradiol-treated ovariectomized rats, approximately 80% of NT/neuromedin N mRNA- expressing cells in sections through the dorsomedial division of the ARC and approximately 60% of such cells in sections through the ventrolateral division of the ARC were found to contain PR mRNA. Depending on the ARC division and rostrocaudal level, double labeled cells accounted for approximately 20-50% of PR mRNA-containing cells. These results indicate that under estrogen-stimulated conditions the majority of NT neurons in the ARC express both PR and ER, as previous studies of this region indicate that estrogen-inducible PR occurs only in cells that also express ER. In the rat, NT neurons appear to be a major ARC cell type subject to direct regulation by estrogen and progesterone.