Second form of gonadotropin-releasing hormone in mouse: immunocytochemistry reveals hippocampal and periventricular distribution.

Hypothalamic GnRH (GnRH-I) is known and named for its role in regulating reproductive function in vertebrates by controlling release of gonadotropins from the pituitary. However, another form of GnRH of unknown function (pGlu-His-Trp-Ser-His-Gly-Trp-Tyr-Pro-Gly; GnRH-II) is expressed in the mesencephalon of all vertebrate classes except jawless fish. Here we show with immunocytochemical staining that the GnRH-II peptide is localized to the mouse midbrain as in other vertebrates, as well as in cells surrounding the ventricles and in cells adjacent to the hippocampus. Staining of adjacent sections using GnRH-I antibody revealed that the distribution of GnRH-I does not overlap with that of GnRH-II.