Aromatase activity in the brain of the three-spined stickleback, Gasterosteus aculeatus. III. Effects of castration under different conditions and of replacement with different androgens.

Non-breeding stickleback males were gonadectomized or sham-operated in winter. They were then exposed to a high temperature and either a short photoperiod which did not induce breeding or to a longer, stimulatory, photoperiod. In the latter experiment empty Silastic capsules or capsules filled with the aromatizable androgen, androstenedione or the non-aromatizable androgen, 11-ketoandrostenedione were implanted intraperitoneally in the operated fish. Furthermore, males that were already in breeding condition were gonadectomized or sham-operated in late spring. Brains were freeze-sectioned and punches from the nucleus preopticus-nucleus anterioris periventricularis region were incubated with [19-3H]-androstenedione. After extraction of steroids with CH2CI2, the tritium activity remaining in the water phase gives a measure of aromatization as tritiated water and formic acid are formed when [19-3H]-androstenedione is aromatized to oestrogens. The aromatase activity was higher in sham-operated than in castrated fish in all three experiments. Both androstenedione and 11-ketoandrostenedione abolished the effect of gonadectomy on aromatization.