Aromatase activity in the brain of the three-spined stickleback, Gasterosteus aculeatus. I. Distribution and effects of season and photoperiod.

Tritiated androstenedione was in vitro aromatized to estrone and estradiol by the stickleback brain. Highest aromatase activity was found in the diencephalon, particularly in the periventricular hypothalamic region containing the nucleus preopticus (NPO), in the area containing the nucleus lateralis tuberis, and in the pituitary. This localization suggests a role of aromatase in controlling the secretion of gonadotropic hormone. The activity in the area containing the NPO was higher in May than in December. The possible role of seasonal changes in aromatase activity in the control of the yearly reproductive cycle is discussed.