Estrogen target cells in the forebrain of river lamprey, Ichthyomyzon unicuspis

Estrogen-concentrating cells in the brain of river lamprey, Ichthyomyzon unicuspis, are identified and mapped by thaw-mount autoradiography. After injection of 3H-estradiol-17 beta, cells with nuclear concentration of radioactivity are found in the ventral periventricular area of the telencephalon, and in preoptic, central hypothalamic, and thalamic regions of the diencephalon, while in the pallium no such target cells are found. Injection of unlabeled estradiol prior to the administration of 3H-estradiol reduces of eliminates the nuclear concentration of radioactivity. The autoradiographic results demonstrate the presence of estrogen target cells in the brain of descendents of one of the phylogenetically earliest vertebrate lines. The topographical distribution of these target neurons, which are accumulated in certain periventricular structures, is similar to the distribution of estrogen target neurons described previously for other nonmammalian and mammalian vertebrates. Accordingly, estrogen feedback and activation sites are present throughout vertebrate phylogeny.