Differential expression of estrogen receptor alpha and beta in rat dorsal root ganglion neurons

Estrogen receptor alpha (ERalpha) and estrogen receptor beta (ERbeta) mRNAs are both expressed in rat dorsal root ganglion (DRG) neurons, but the distribution of these two mRNAs differs markedly. Radiolabeled probes highly specific to ERalpha or ERbeta mRNAs were used for in situ hybridization studies; two antibodies specific to ERalpha protein were used for immunocytochemistry and specific primers were used for reverse transcription polymerase chain reaction (RT-PCR) studies. These revealed that ERbeta mRNA is widely expressed in the DRG of both male and female rats, with virtually all neurons showing positive signals. In contrast, ERalpha mRNA, as well as nuclear localized ERalpha protein, is more restricted in its localization and is present in many, but not all, of the small-sized (<600 microm(2)) DRG neurons, but is only rarely present in larger neurons. The L6-S1 DRG levels, which contain sensory neurons that innervate reproductive tissues, are relatively enriched in ERalpha compared to L3-L5 DRG levels, which contain sensory neurons that innervate hind limb regions. Long-term estrogen treatment of ovariectomized rats (21-28 days) dramatically reduces immunocytochemically detectable ERalpha protein in the DRG relative to that in ovariectomized controls. RT-PCR studies also showed that long-term estrogen treatment of ovariectomized rats downregulates the levels of ERalpha mRNA, but upregulates the levels of ERbeta mRNA in the DRG. Interestingly, in intact cycling female rats, ERalpha and ERbeta mRNA levels in the DRG were both higher during proestrus compared to metestrus. These findings suggest that the changes in expression of estrogen receptors which occur dynamically during the estrus cycle differ from those induced by long-term estrogen treatment of ovariectomized animals.