Relationship between brain gonadotropin-releasing hormone and final reproductive period of the adult male sea lamprey, Petromyzon marinus.

Gonadotropin-releasing hormone (GnRH) concentrations were measured in brains of adult male sea lamprey, Petromyzon marinus, during their final reproductive period. The lampreys were collected during their upstream migration in coastal New Hampshire rivers and sampled at the trap (referred to as Group A) or they were transferred to an artificial spawning channel (referred to as Group B). Plasma estradiol and progesterone were also measured, and histological examination of the gonadal stages was done as well. The concentrations of brain GnRH and plasma estradiol fluctuated significantly through time. There was a rise in brain concentrations of GnRH coincident with an increase in temperature just prior to spawning. In addition, there was a significant progressive correlation between increasing plasma estradiol and temperature in lampreys from Group B during the period studied. These studies provide evidence for progressive seasonal relationships between changes in brain GnRH and gametogenic and steroidogenic activity of the gonads in adult male sea lampreys during their final reproductive period.