Neuroendocrine control of reproduction in lampreys.

In most vertebrate classes, the hypothalamus and pituitary have well-defined roles in the control of reproduction. Until recently, there was little evidence for neuroendocrine control of reproduction in lampreys, one of the only two living representative groups of the oldest lineage of vertebrates, the Agnathans. The question whether there is hypothalamic control over reproduction has special significance since these fishes, with the hagfishes, are modern descendants of the most primitive vertebrates available for study. This paper summarizes the studies on the structure and function of lamprey GnRH which provide evidence for the regulatory influence of the hypothalamus on the pituitary-gonadal axis. These data imply that evolution of this mechanism most likely antedated the origin of all known vertebrates.