EXPRESSION OF ESTROGEN RECEPTOR-BETA MESSENGER-RIBONUCLEIC-ACID IN OXYTOCIN AND VASOPRESSIN NEURONS OF THE RAT SUPRAOPTIC AND PARAVENTRICULAR NUCLEI

The regulatory actions of estrogen on magnocellular oxytocin (OT) and vasopressin (VP) neurons of the paraventricular (PVN) and supraoptic ( SON) nuclei are well documented. To date it is still debated whether t he effect of estrogens is exerted directly or mediated by estrogen-sen sitive interneurons. Previous immunocytochemical (ICC) and in situ hyb ridization (ISH) studies detected either law levels or absence of the classical estrogen receptor (ER-alpha) in the PVN and the SON of the r at. The present experiments using a combined ICC and ISH method were u ndertaken to examine the expression of the recently cloned beta form o f ER (ER-beta) in OT- and VP-immunoreactive (IR) neuronal systems of t he rat hypothalamus. The results demonstrate that the highest cellular levels of ER-beta messenger RNA (mRNA) in OT-IR neurons can be visual ized in the caudal portion of the PVN and in an area ventro-medial to the central core of TTP-ITC cells. These neurons were previously shown to project caudally to the brain stem and the spinal cord to regulate autonomic functions. in addition, the whole rostro-caudal extent of t he PVN and the SON contained OT-IR neurons that coexpressed variable l evels of ER-beta mRNA. Similarly, the presence of ER-beta mRNA was see n in a large population of VP-IR paraventricular and supraoptic newton s. In the SON, somewhat stronger hybridization signal was detected in VP-IR neurons as compared with OT-IR neurons. Together, these findings provide strong support for the concept that the functions of OT- and VP-IR neurons in the PVN and the SON are regulated directly by estroge n and that the genomic effects of estrogens are mediated by ER-beta.