Tyrosine hydroxylase mRNA in the neurons of the tuberoinfundibularregion and zona incerta examinedafter gonadal steroid hormonetreatment

The dopamine-producing neurons of the tuberoinfundibular region are known targets of estrogen and progesterone, and are of considerable neuroendocrine importance. To determine the anatomical distribution, and number of cells that contain tyrosinehydroxylase (TH) mRNA in the tuberoinfundibularregion and other regions of the brain we carried outin situhybridization on sections prepared from ovari-ectomized female rats given either oil vehicle, orestrogen, or estrogen plus progesterone. The intensity of label per cell was assessed to compare therelative amount of mRNA found per cell among TH-mRNA containing cells. [³H]cRNA probes to the ratTH sequence were used. Autoradiograms demonstrated the presence of TH-mRNA in the cytoplasmof cells in the arcuate and periventricular nuclei, zona incerta, substantia nigra, and the adrenal medulla. The number and anatomical distribution ofcells that contained TH-mRNA was identical to thenumber and distribution of cells previously demonstrated by others to contain TH immunoreactivity. Inthe arcuate and periventricular nuclei, compared totreatment with estrogen alone, estrogen plus progesterone did lead to a statistically significant decrease in the number of TH mRNA-containing cellswe could detect. No alteration in the mean numberof grains per cell, among cells detected as containing TH-mRNA was found in any group. In contrast, these same hormone treatments had no effect onthe number TH-mRNA producing cells we could detect in the zona incerta. Most of the cells in the zonaincerta are found within the same tissue sections asarcuate/periventricular cells. Since dopamine ischaracterized primarily as an inhibitory neurotransmitter, our data are consistent with the hypothesisthat less TH-mRNA would be present in the tuberoinfundibular region when the endocrine state of theanimal is likely to result in high serum levels of LHand PRL, and when the female is likely to be sexually active.