Effects of castration and androgen-treatment on the expression of FSH-β and LH-β in the three-spine stickleback, gasterosteus aculeatus—Feedback differences mediating the photoperiodic maturation response?

In many animals, including the three-spine stickleback (Gasterosteus aculeatus), photoperiod strongly influences reproduction. The aim of this study was to investigate if feedback mechanisms on the brain–pituitary–gonadal axis play a role in mediating the photoperiodic response in the stickleback. To that end, stickleback males, exposed to either non-stimulatory short photoperiod (light/dark 8:16) or under stimulatory long photoperiod (LD 16:8), were subjected to either sham-operation, castration, castration combined with treatment with the androgens 11-ketoandrostenedione (11KA) and testosterone (T), and the effects on levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH)-β mRNA were analyzed. During breeding season the kidney of the stickleback male hypertrophies and produces a glue used for building nests. Kidney weight and expression of both LH-β and FSH-β were higher in sham-operated fish kept under long than under short photoperiod. Under both photoperiods, LH-β mRNA levels were lower in castrated males compared to sham-operated males and treatment with 11KA and T increased expression, indicating a positive feedback. A positive feedback was also found on FSH-β expression under long photoperiod, where castration decreased, and androgen replacement restored FSH-β mRNA expression. On the contrary, castration under short photoperiod instead increased FSH-β levels whereas treatment with 11KA and T decreased FSH-β expression, indicating a negative feedback on FSH-β under these conditions. The positive feedback on FSH-β expression under stimulatory photoperiod may accelerate maturation, whereas the negative feedback under inhibitory photoperiod may suppress maturation. This could be part of the mechanisms by which photoperiod controls maturation.