Stimulatory effects of methyltestosterone on pituitary gonadotropic cells and testes leydig cells of the three-spined stickleback, Gasterosteus aculeatus L., in winter.

Male three-spined sticklebacks were kept for a month in short photoperiod at ca. 20 degrees in winter. During this period methyltestosterone (MT), dissolved in the water (35 micrograms/liter), stimulated the appearance of breeding colors and kidney hypertrophy, characters which were both absent in the controls. MT furthermore prevented the onset of spermatogenesis. The gonadotropic cells of the MT-treated fish contained significantly more dilated endoplasmic reticulum and less granules than those of the controls. The nuclei of the testes Leydig cells were enlarged after treatment with MT. These findings suggest the existence of a positive feedback of androgen on the gonadal-pituitary axis of the male stickleback in winter.