Co-expression of estrogen and thyroid hormone receptors in individual hypothalamic neurons

Estrogen receptors (ER) and thyroid hormone receptors (TR) are members of t he nuclear receptor family of transcription factors that induce or repress the expression of target genes. Previous behavioral studies in female roden ts have demonstrated that thyroid hormones can antagonize the effects of es trogen in the central nervous system (CNS), particularly by attenuating est rogen's ability to facilitate reproductive behaviors. Additional molecular studies have suggested a mechanism for this antagonism by showing that liga nd-activated ER alpha and TRs have the potential to interact in their trans criptional controls. Although the expression patterns of ER alpha and TRs i n the rodent brain appear to overlap in behaviorally relevant areas, it rem ained to be determined whether these two classes of proteins coexist in viv o at the level of single neurons. To address this possibility, we employed a highly sensitive double-label in situ hybridization technique using digox igenin and S-35-labeled cRNA probes to analyze, in detail, the expression o f ER alpha mRNA with TR alpha1 and TR alpha2 mRNAs in the same neurons of t he ovariectomized (OVX) adult mouse brain. Our results demonstrate that a l arge majority of the ER alpha -positive neurons also expresses TR alpha1 an d TR alpha2 mRNAs. Quantitative examination of the cellular expression in t he ventromedial and arcuate nuclei of the hypothalamus (VMH and Are) showed that 81.5% and 80.5% of the neurons endowed with ER alpha mRNA also contai n TR alpha1 and TR alpha2 mRNAs, respectively. In the amygdala, more than 6 0.5% and 67% of ER alpha -positive cells also contain TR alpha1 and TR alph a2 mRNAs, respectively. These findings provide the first anatomical evidenc e that ER and TR can be found in the same neurons. including hypothalamic n eurons. This coexpression of ER alpha and TR provides the cellular basis fo r a new level of neuronal integration in a brain region where estrogens con trol female reproductive behaviors. J. Comp. Neurol. 437:286-295, 2001. (C) 2001 Wiley-Liss, Inc.