抄録
1. The pars distalis weight of the adenohypophysis of intact birds, Emberiza rustica latifascia, increased significantly after 15 days of exposure to long days;thereafter the weight decreased and returned to an initial level. In gonadectomized birds the weight of the pars distalis increased significantly after 15 days of exposure to long days, and this increase was maintained until the end of the experi ment (48 days after beginning of exposure to long days).
2. The acid phosphatase activity of the pars distalis of intact birds increased after 15 daysof exposure to long days; thereafter it decreased to an initial level. The elevated phosphatase activity of the pars distalis of gonadectomized birds observed after 15 days of exposure to long days was maintained until the end of the experiment (48 days after beginning of exposure to long days).
3. Birds implanted with pellets of testosterone or estradiol exibited no increase in the weight and acid phosphatase activity of the pars distalis after the exposure to long days.
4. Testosterone and estradiol inhibited gonadal development in birds subjected to long days.
5. The acid phosphatase activity of the median eminence increased in intact birds (Experiment 2) and gonadectomized birds subjected to long days, but not in birds implanted with the sex steroid pellets.
6. From these findings it is concluded that a negative gonadal feedback mechanism operates at least through the median eminence, even in the birds which have a long-lasting breeding season. A possibility is discussed that the negative gonadal feedback mechanism is involved in the natural gonadal involution at the end of the breeding season of the bird.
7. Intact birds, whether female Or male, experienced an increase of body weight after 27 days of exposure to long days and the increase was maintained until the end of the experiment (48 days after beginning of exposure to long days). Gonadectomized birds did not show such an increase during the experimental period.
