Preprotachykinin gene expression in the mediobasal hypothalamus of estrogen-treated and ovariectomized control rats.

We have determined the localization of preprotachykinin (PPT) mRNA-containing neurons in the mediobasal hypothalamus of the rat. PPT mRNA-containing neurons are present in the ventromedial nucleus (with a concentration in the ventrolateral aspect (VL-VM], the dorsomedial nucleus, the lateral hypothalamus and the arcuate nucleus. This distribution is consistent with the findings of immunocytochemical studies of substance P-immunoreactive neurons in the hypothalamus. We have also examined whether PPT gene expression is regulated by estrogen in the VL-VM by comparing the levels of PPT mRNA in the VL-VM of ovariectomized rats and ovariectomized, estrogen-replaced rats. Both in situ hybridization and slot blot hybridization analysis revealed no changes in PPT mRNA content in the VL-VM following estrogen treatment. These results suggest that estrogen does not regulate lordosis behavior by affecting PPT gene expression in VL-VM neurons.