Breakthrough in neuroendocrinology by discovering novel neuropeptides and neurosteroids: 1. Discovery of gonadotropin-inhibitory hormone (GnIH) across vertebrates.

Bargmann-Scharrer's discovery of "neurosecretion" in the first half of the 20th century has since matured into the scientific discipline of neuroendocrinology. Identification of novel neurohormones, such as neuropeptides and neurosteroids, is essential for the progress of neuroendocrinology. Our studies over the past two decades have significantly broadened the horizons of this field of research by identifying novel neuropeptides and neurosteroids in vertebrates that have opened new lines of scientific investigation in neuroendocrinology. Since the discovery of gonadotropin-releasing hormone (GnRH) in mammals at the beginning of 1970s, it was generally believed that GnRH is the only hypothalamic neuropeptide regulating gonadotropin release in vertebrates. In 2000, however, we discovered a novel hypothalamic neuropeptide that actively inhibits gonadotropin release in quail and termed it gonadotropin-inhibitory hormone (GnIH). It now appears that GnIH is highly conserved across vertebrates, including humans, and serves a number of behavioral and physiological functions other than regulation of reproduction, providing enormous opportunity for investigators from a wide array of disciplines to study this neuropeptide. This review summarizes the discovery of GnIH and its contribution to the progress of neuroendocrinology.