Estrogen and Androgen Target Cells in the Brain of Fishes, Reptiles and Birds: Phylogeny and Ontogeny

Abstract

The cellular and subcellular distribution of 3H estradiol in the forebrain of goldfish, platyfish, lizard, turtle, and ring dove was studied by thaw-mount autoradiography. The topographic distribution of estrogen target cells in these non-mammalian species corresponds to the general pattern established earlier in our laboratory for mammals. In all non-mammalians studied, accumulations of estrogen target cells exist in preoptic-septal, central hypothalamic and thalamic areas. While allocortical distribution of estrogen target cells is present in the avian and reptilian species, it appears to be absent in the teleosts. Differences in brain evolution probably account for it. This phylogenetically delayed acquisition of telencephalic steroid target sites seems paralleled by an ontogenetic delay, as observed in the chick embryo: early embryonic appearance of estrogen uptake (receptors) in preoptic and central hypothalamic regions and late appearance of estrogen receptors in the amygdala. Androgen distribution in the forebrain of the dove and lizard overlaps with the estrogen distribution with some exceptions.