Autoradiographic localization of progestin-concentrating cells in the brain of the zebra finch.

The production of song in passerine birds is under the control of steroid hormones, and brain regions involved in song production have been shown to contain androgen and/or estrogen receptors. Studies to date, however, have not considered the possible role of progestins in this behavior. As one approach to this question, the autoradiographic method was used to investigate the distribution of progestin-concentrating cells in the brain of the adult male zebra finch (Poephila guttata) after injection of the radiolabeled synthetic progestin [17 alpha-methyl-3H]-promegestone. In the telencephalon, identifiable groups of progestin-accumulating cells were found in the hyperstriatum dorsale, at the medial edge of the lobus parolfactorius, and in the medial septum. In the diencephalon, labeled groups of cells were found in the preoptic area, through much of the medial hypothalamus--including nucleus periventricularis magnocellularis, nucleus medialis hypothalami posterialis, and area infundibularis--and in the medial spiriform nucleus and dorsomedial thalamus. In the myelencephalon, labeled cells are described at the dorsal edge of the medulla and scattered lateral to nXII. These findings offer no support for the hypothesis that progestin acts on any of the known song regions, but do suggest areas of progestin action in the avian central nervous system outside of the known song system. Not surprisingly, these include many areas of the medial hypothalamus and other midline structures.