The Phenotype of Cells Expressing Estrogen Receptor Alpha in the Nucleus of the Solitary Tract

Estrogen protects females from hypertension. The nucleus tractus solitarius (NTS) is a hindbrain site involved in the regulation of blood pressure, however little is known about estrogen receptors within the NTS. The purpose of these studies was to determine the phenotype of the cells expressing estrogen alpha receptors in the nucleus tractus solitarius. Four female Sprague-Dawley rats were transcardially perfused with 4% paraformaldehyde and hindbrains harvested. In coronal sections containing the NTS (40μm thick), immunohistochemistry was performed to determine which type of cells were expressed with estrogen receptor alpha (ERα) expressing cells. We used the anti-ERα antibody with an antibody for each protein of interest: anti-tyrosine hydroxylase (TH), anti-glial fibrillary acidic protein (GFAP), anti-NeuN, and anti-Iba-1. Sections were captured using an Olympus BX41 Fluorescence Microscope and analyzed using ImageJ. The NTS was divided into 2 regions: sections caudal to the area postrema (caudal) and sections lying below the area postrema (sub-postrema, SP) and the number of immunoreactive neurons in each region counted and expressed as an average number of labeled neurons per section±SEM. The number of sections analyzed ranged from 5-10 per individual in caudal and 2-4 per individual in SP. At sacrifice, females were in estrus (1), diestrus (2) or proestrus (3). NeuN in SP NTS (n=4) was observed in 151±53 and ERα in 50±21 neurons per section. Colocalization of ERα and NeuN in SP NTS was observed in 11±6 neurons per section (about 7%). NeuN in caudal NTS was observed in 59±7 and ERα 27±3 neurons per section. Colocalization of ERα and NeuN in caudal NTS was observed in 4±1 neurons per section (about 7%). TH in SP NTS (n=6) was observed in 49±8 and ERα in 51±12 neurons per section. Colocalization of ERα and TH in SP NTS was observed in 26±4 neurons per section (about 53%). TH in caudal NTS was observed in 26±6 and ERα 29±7 neurons per section. Colocalization of ERα and TH in caudal NTS was observed in 17±4 neurons per section (about 51%). Due to the quantity and shape of GFAP immunoreactive cells in the NTS (n=4), we were not able to count the number cells. Colocalization of ERα and GFAP expressing cells were not observed in our study. Cells expressing Iba1 were not observed in the later trials of our study (n=4). ERα is expressed on a subset of catecholaminergic NTS neurons, as well as non-catecholaminergic neurons. Since the NTS catecholaminergic neurons contribute to responses to stress (e.g., hypoxia), this finding could provide a substrate for estrogen-mediated cardiovascular protection in females.